【Android】Android中的搜索过滤操作实现

我在【Android】搜索框架中转载了一篇文章，这篇文章讲述了如何使用Android平台自带的搜索框架从而实现搜索的原生展现。这篇文章则要叙述如何实现搜索功能。

搜索在很多应用中都非常常见，比如联系人应用，Google Play中，能够有让我们快速找到需要寻找的内容。

在手机端，搜索需要注意搜索结果的展示，我们希望用户可以尽可能看到更多的搜索结果，所以我们一般使用ListView展现搜索结果，信息简单而且有价值。下面以联系人应用、ListView展示搜索结果为例，讲述如何搜索功能。

一、简介

一般来说，我们可以使用以下几种方式实现搜索：

1）暴力搜索——直接使用数据库提供的功能，每次都从数据库中读取搜索的结果，存进一个数据结构用于Adapter显示，调用notifyDataSetChanged()刷新数据；

2）利用filter进行搜索。这块涉及到Filterable接口。推荐文章：Android实现Filterable通过输入文本框实现联系人自动筛选。有两点值得注意：a）Android原生组件AutoCompleteTextview就是使用该方法实现的；b）这个方法本质上还是调用notifyDataSetChanged()方法，并且还是要自己去实现搜索部分，只是整个方法看上去比较优雅，而且不用再去搜索数据库，最重要的一点是这个时候搜索过程被自动移到另外一个线程之中，搜索完毕之后才会刷新UI；

二、CursorAdapter

以上两种方法都比较简单，接下来要讲的方法并非有什么新奇之处，只是利用Android已有的API去实现该功能，避免自己去实现已有的实现。方法没有好坏之分，能实现功能的情况下越简单越好，暴力搜索也很OK。首先，我们认识一下一个类：CursorAdapter（一看就知道是干嘛的了吧），上源码：

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.support.v4.widget;

import android.content.Context;
import android.database.ContentObserver;
import android.database.Cursor;
import android.database.DataSetObserver;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Filter;
import android.widget.FilterQueryProvider;
import android.widget.Filterable;

/**
 * Static library support version of the framework's {@link android.widget.CursorAdapter}.
 * Used to write apps that run on platforms prior to Android 3.0.  When running
 * on Android 3.0 or above, this implementation is still used; it does not try
 * to switch to the framework's implementation.  See the framework SDK
 * documentation for a class overview.
 */
public abstract class CursorAdapter extends BaseAdapter implements Filterable,
        CursorFilter.CursorFilterClient {
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected boolean mDataValid;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected boolean mAutoRequery;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected Cursor mCursor;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected Context mContext;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected int mRowIDColumn;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected ChangeObserver mChangeObserver;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected DataSetObserver mDataSetObserver;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected CursorFilter mCursorFilter;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected FilterQueryProvider mFilterQueryProvider;

    /**
     * If set the adapter will call requery() on the cursor whenever a content change
     * notification is delivered. Implies {@link #FLAG_REGISTER_CONTENT_OBSERVER}.
     *
     * @deprecated This option is discouraged, as it results in Cursor queries
     * being performed on the application's UI thread and thus can cause poor
     * responsiveness or even Application Not Responding errors.  As an alternative,
     * use {@link android.app.LoaderManager} with a {@link android.content.CursorLoader}.
     */
    @Deprecated
    public static final int FLAG_AUTO_REQUERY = 0x01;

    /**
     * If set the adapter will register a content observer on the cursor and will call
     * {@link #onContentChanged()} when a notification comes in.  Be careful when
     * using this flag: you will need to unset the current Cursor from the adapter
     * to avoid leaks due to its registered observers.  This flag is not needed
     * when using a CursorAdapter with a
     * {@link android.content.CursorLoader}.
     */
    public static final int FLAG_REGISTER_CONTENT_OBSERVER = 0x02;

    /**
     * Constructor that always enables auto-requery.
     *
     * @deprecated This option is discouraged, as it results in Cursor queries
     * being performed on the application's UI thread and thus can cause poor
     * responsiveness or even Application Not Responding errors.  As an alternative,
     * use {@link android.app.LoaderManager} with a {@link android.content.CursorLoader}.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     */
    @Deprecated
    public CursorAdapter(Context context, Cursor c) {
        init(context, c, FLAG_AUTO_REQUERY);
    }

    /**
     * Constructor that allows control over auto-requery.  It is recommended
     * you not use this, but instead {@link #CursorAdapter(Context, Cursor, int)}.
     * When using this constructor, {@link #FLAG_REGISTER_CONTENT_OBSERVER}
     * will always be set.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     * @param autoRequery If true the adapter will call requery() on the
     *                    cursor whenever it changes so the most recent
     *                    data is always displayed.  Using true here is discouraged.
     */
    public CursorAdapter(Context context, Cursor c, boolean autoRequery) {
        init(context, c, autoRequery ? FLAG_AUTO_REQUERY : FLAG_REGISTER_CONTENT_OBSERVER);
    }

    /**
     * Recommended constructor.
     *
     * @param c The cursor from which to get the data.
     * @param context The context
     * @param flags Flags used to determine the behavior of the adapter; may
     * be any combination of {@link #FLAG_AUTO_REQUERY} and
     * {@link #FLAG_REGISTER_CONTENT_OBSERVER}.
     */
    public CursorAdapter(Context context, Cursor c, int flags) {
        init(context, c, flags);
    }

    /**
     * @deprecated Don't use this, use the normal constructor.  This will
     * be removed in the future.
     */
    @Deprecated
    protected void init(Context context, Cursor c, boolean autoRequery) {
        init(context, c, autoRequery ? FLAG_AUTO_REQUERY : FLAG_REGISTER_CONTENT_OBSERVER);
    }

    void init(Context context, Cursor c, int flags) {
        if ((flags & FLAG_AUTO_REQUERY) == FLAG_AUTO_REQUERY) {
            flags |= FLAG_REGISTER_CONTENT_OBSERVER;
            mAutoRequery = true;
        } else {
            mAutoRequery = false;
        }
        boolean cursorPresent = c != null;
        mCursor = c;
        mDataValid = cursorPresent;
        mContext = context;
        mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;
        if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) {
            mChangeObserver = new ChangeObserver();
            mDataSetObserver = new MyDataSetObserver();
        } else {
            mChangeObserver = null;
            mDataSetObserver = null;
        }

        if (cursorPresent) {
            if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);
        }
    }

    /**
     * Returns the cursor.
     * @return the cursor.
     */
    public Cursor getCursor() {
        return mCursor;
    }

    /**
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        if (mDataValid && mCursor != null) {
            return mCursor.getCount();
        } else {
            return 0;
        }
    }
    
    /**
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        if (mDataValid && mCursor != null) {
            mCursor.moveToPosition(position);
            return mCursor;
        } else {
            return null;
        }
    }

    /**
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        if (mDataValid && mCursor != null) {
            if (mCursor.moveToPosition(position)) {
                return mCursor.getLong(mRowIDColumn);
            } else {
                return 0;
            }
        } else {
            return 0;
        }
    }
    
    @Override
    public boolean hasStableIds() {
        return true;
    }

    /**
     * @see android.widget.ListAdapter#getView(int, View, ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(position)) {
            throw new IllegalStateException("couldn't move cursor to position " + position);
        }
        View v;
        if (convertView == null) {
            v = newView(mContext, mCursor, parent);
        } else {
            v = convertView;
        }
        bindView(v, mContext, mCursor);
        return v;
    }

    @Override
    public View getDropDownView(int position, View convertView, ViewGroup parent) {
        if (mDataValid) {
            mCursor.moveToPosition(position);
            View v;
            if (convertView == null) {
                v = newDropDownView(mContext, mCursor, parent);
            } else {
                v = convertView;
            }
            bindView(v, mContext, mCursor);
            return v;
        } else {
            return null;
        }
    }
    
    /**
     * Makes a new view to hold the data pointed to by cursor.
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     * @param parent The parent to which the new view is attached to
     * @return the newly created view.
     */
    public abstract View newView(Context context, Cursor cursor, ViewGroup parent);

    /**
     * Makes a new drop down view to hold the data pointed to by cursor.
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     * @param parent The parent to which the new view is attached to
     * @return the newly created view.
     */
    public View newDropDownView(Context context, Cursor cursor, ViewGroup parent) {
        return newView(context, cursor, parent);
    }

    /**
     * Bind an existing view to the data pointed to by cursor
     * @param view Existing view, returned earlier by newView
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     */
    public abstract void bindView(View view, Context context, Cursor cursor);
    
    /**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     * 
     * @param cursor The new cursor to be used
     */
    public void changeCursor(Cursor cursor) {
        Cursor old = swapCursor(cursor);
        if (old != null) {
            old.close();
        }
    }

    /**
     * Swap in a new Cursor, returning the old Cursor.  Unlike
     * {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>
     * closed.
     *
     * @param newCursor The new cursor to be used.
     * @return Returns the previously set Cursor, or null if there wasa not one.
     * If the given new Cursor is the same instance is the previously set
     * Cursor, null is also returned.
     */
    public Cursor swapCursor(Cursor newCursor) {
        if (newCursor == mCursor) {
            return null;
        }
        Cursor oldCursor = mCursor;
        if (oldCursor != null) {
            if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver);
            if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver);
        }
        mCursor = newCursor;
        if (newCursor != null) {
            if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver);
            mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
            mDataValid = true;
            // notify the observers about the new cursor
            notifyDataSetChanged();
        } else {
            mRowIDColumn = -1;
            mDataValid = false;
            // notify the observers about the lack of a data set
            notifyDataSetInvalidated();
        }
        return oldCursor;
    }

    /**
     * <p>Converts the cursor into a CharSequence. Subclasses should override this
     * method to convert their results. The default implementation returns an
     * empty String for null values or the default String representation of
     * the value.</p>
     *
     * @param cursor the cursor to convert to a CharSequence
     * @return a CharSequence representing the value
     */
    public CharSequence convertToString(Cursor cursor) {
        return cursor == null ? "" : cursor.toString();
    }

    /**
     * Runs a query with the specified constraint. This query is requested
     * by the filter attached to this adapter.
     *
     * The query is provided by a
     * {@link android.widget.FilterQueryProvider}.
     * If no provider is specified, the current cursor is not filtered and returned.
     *
     * After this method returns the resulting cursor is passed to {@link #changeCursor(Cursor)}
     * and the previous cursor is closed.
     *
     * This method is always executed on a background thread, not on the
     * application's main thread (or UI thread.)
     * 
     * Contract: when constraint is null or empty, the original results,
     * prior to any filtering, must be returned.
     *
     * @param constraint the constraint with which the query must be filtered
     *
     * @return a Cursor representing the results of the new query
     *
     * @see #getFilter()
     * @see #getFilterQueryProvider()
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     */
    public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
        if (mFilterQueryProvider != null) {
            return mFilterQueryProvider.runQuery(constraint);
        }

        return mCursor;
    }

    public Filter getFilter() {
        if (mCursorFilter == null) {
            mCursorFilter = new CursorFilter(this);
        }
        return mCursorFilter;
    }

    /**
     * Returns the query filter provider used for filtering. When the
     * provider is null, no filtering occurs.
     *
     * @return the current filter query provider or null if it does not exist
     *
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public FilterQueryProvider getFilterQueryProvider() {
        return mFilterQueryProvider;
    }

    /**
     * Sets the query filter provider used to filter the current Cursor.
     * The provider's
     * {@link android.widget.FilterQueryProvider#runQuery(CharSequence)}
     * method is invoked when filtering is requested by a client of
     * this adapter.
     *
     * @param filterQueryProvider the filter query provider or null to remove it
     *
     * @see #getFilterQueryProvider()
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public void setFilterQueryProvider(FilterQueryProvider filterQueryProvider) {
        mFilterQueryProvider = filterQueryProvider;
    }

    /**
     * Called when the {@link ContentObserver} on the cursor receives a change notification.
     * The default implementation provides the auto-requery logic, but may be overridden by
     * sub classes.
     * 
     * @see ContentObserver#onChange(boolean)
     */
    protected void onContentChanged() {
        if (mAutoRequery && mCursor != null && !mCursor.isClosed()) {
            if (false) Log.v("Cursor", "Auto requerying " + mCursor + " due to update");
            mDataValid = mCursor.requery();
        }
    }

    private class ChangeObserver extends ContentObserver {
        public ChangeObserver() {
            super(new Handler());
        }

        @Override
        public boolean deliverSelfNotifications() {
            return true;
        }

        @Override
        public void onChange(boolean selfChange) {
            onContentChanged();
        }
    }

    private class MyDataSetObserver extends DataSetObserver {
        @Override
        public void onChanged() {
            mDataValid = true;
            notifyDataSetChanged();
        }

        @Override
        public void onInvalidated() {
            mDataValid = false;
            notifyDataSetInvalidated();
        }
    }

}

这边有几点比较有意思，值得注意：

1）这个类实现了Filterable接口和CursorFilter.CursorFilterClient接口，第一个接口已经有所认识，第二个接口暂时不提，后面论述；

2）下面这个方法：

/**
     * @see android.widget.ListAdapter#getView(int, View, ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(position)) {
            throw new IllegalStateException("couldn't move cursor to position " + position);
        }
        View v;
        if (convertView == null) {
            v = newView(mContext, mCursor, parent);
        } else {
            v = convertView;
        }
        bindView(v, mContext, mCursor);
        return v;
    }

我们知道ListView，GridView之类的ViewGroup子类都自带组件复用机制，View可以重复显示在界面上而不需要重新去实例化它，而通常这个都是需要我们在getView()方法里面自己实现，而实现机制就非常类似上面这段代码，这里，CursorAdapter已经帮我们实现了，如果View为空则执行newView操作，最后执行bindView()方法，最后返回v。而在CurosrAdapter类里面，bindView和newView方法都是抽象方法，需要开发者自己实现的，而根据这边的源码，我们很容易知道这两个方法应该如何实现：1）newView中应该重新生成一个View；2）bindView中应该重新对View中的组件进行“赋值”操作；完全不需要去考虑复用组件。

下面回到第1）点，第1）点中还有半点不明白的地方：CursorFilter.CursorFilterClient。首先了解一下CursorFilter这个类，上源码：

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.support.v4.widget;

import android.database.Cursor;
import android.widget.Filter;

/**
 * <p>The CursorFilter delegates most of the work to the CursorAdapter.
 * Subclasses should override these delegate methods to run the queries
 * and convert the results into String that can be used by auto-completion
 * widgets.</p>
 */
class CursorFilter extends Filter {
    
    CursorFilterClient mClient;
    
    interface CursorFilterClient {
        CharSequence convertToString(Cursor cursor);
        Cursor runQueryOnBackgroundThread(CharSequence constraint);
        Cursor getCursor();
        void changeCursor(Cursor cursor);
    }

    CursorFilter(CursorFilterClient client) {
        mClient = client;
    }
    
    @Override
    public CharSequence convertResultToString(Object resultValue) {
        return mClient.convertToString((Cursor) resultValue);
    }

    @Override
    protected FilterResults performFiltering(CharSequence constraint) {
        Cursor cursor = mClient.runQueryOnBackgroundThread(constraint);

        FilterResults results = new FilterResults();
        if (cursor != null) {
            results.count = cursor.getCount();
            results.values = cursor;
        } else {
            results.count = 0;
            results.values = null;
        }
        return results;
    }

    @Override
    protected void publishResults(CharSequence constraint, FilterResults results) {
        Cursor oldCursor = mClient.getCursor();
        
        if (results.values != null && results.values != oldCursor) {
            mClient.changeCursor((Cursor) results.values);
        }
    }
}

这个类继承了Filter，如果你仔细看过前面推荐了解Filterable的那篇文章（Android实现Filterable通过输入文本框实现联系人自动筛选），对这个一定看上去非常眼熟，OK，这边几乎没什么不同，唯一的不同就是将查询操作交给了一个叫做CursorFilterClient的接口对象，这货长的是这副样子的：

interface CursorFilterClient {
        CharSequence convertToString(Cursor cursor);
        Cursor runQueryOnBackgroundThread(CharSequence constraint);
        Cursor getCursor();
        void changeCursor(Cursor cursor);
    }

OKOK，CursorAdapter是实现了这个接口的，我们来看看最重要的两个接口具体在这里面是怎么实现的吧：

/**
     * Runs a query with the specified constraint. This query is requested
     * by the filter attached to this adapter.
     *
     * The query is provided by a
     * {@link android.widget.FilterQueryProvider}.
     * If no provider is specified, the current cursor is not filtered and returned.
     *
     * After this method returns the resulting cursor is passed to {@link #changeCursor(Cursor)}
     * and the previous cursor is closed.
     *
     * This method is always executed on a background thread, not on the
     * application's main thread (or UI thread.)
     * 
     * Contract: when constraint is null or empty, the original results,
     * prior to any filtering, must be returned.
     *
     * @param constraint the constraint with which the query must be filtered
     *
     * @return a Cursor representing the results of the new query
     *
     * @see #getFilter()
     * @see #getFilterQueryProvider()
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     */
    public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
        if (mFilterQueryProvider != null) {
            return mFilterQueryProvider.runQuery(constraint);
        }

        return mCursor;
    }

查询操作又交给了另外一个对象：FilterQueryProvider。

/**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     * 
     * @param cursor The new cursor to be used
     */
    public void changeCursor(Cursor cursor) {
        Cursor old = swapCursor(cursor);
        if (old != null) {
            old.close();
        }
    }

    /**
     * Swap in a new Cursor, returning the old Cursor.  Unlike
     * {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>
     * closed.
     *
     * @param newCursor The new cursor to be used.
     * @return Returns the previously set Cursor, or null if there wasa not one.
     * If the given new Cursor is the same instance is the previously set
     * Cursor, null is also returned.
     */
    public Cursor swapCursor(Cursor newCursor) {
        if (newCursor == mCursor) {
            return null;
        }
        Cursor oldCursor = mCursor;
        if (oldCursor != null) {
            if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver);
            if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver);
        }
        mCursor = newCursor;
        if (newCursor != null) {
            if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver);
            mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
            mDataValid = true;
            // notify the observers about the new cursor
            notifyDataSetChanged();
        } else {
            mRowIDColumn = -1;
            mDataValid = false;
            // notify the observers about the lack of a data set
            notifyDataSetInvalidated();
        }
        return oldCursor;
    }

更新完毕以后调用该方法刷新列表。

现在假设你要去使用这样CursorAdapter，我们来看看如何进行：

第一步，首先根据上面的说明去实现bindView和newView两个方法，然后传递一个Cursor进来实例化CursorAdapter，这样子首先实现了一个基本的Adapter的功能；

第二步，我们要实现搜索过滤功能。我们在使用Filterable接口的时候，调用方法如下：

adapter.getFilter().filter(et_filter.getText().toString());  

在这里一样的。这里CursorAdapter的getFileter()方法实现如下：

public Filter getFilter() {
        if (mCursorFilter == null) {
            mCursorFilter = new CursorFilter(this);
        }
        return mCursorFilter;
    }

它返回的是一个CursorFilter，实例化的时候需要一个CursorFilter.CursorFilterClient参数，这里正好CursorAdapter就实现了这个接口。所以直接用this即可，这里还缺一点，我们缺少一个最最核心的对象：FilterQueryProvider，最后的查询操作就交给了它。它很简单：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;

import android.database.Cursor;

/**
 * This class can be used by external clients of CursorAdapter and
 * CursorTreeAdapter to define how the content of the adapter should be
 * filtered.
 * 
 * @see #runQuery(CharSequence)
 */
public interface FilterQueryProvider {
    /**
     * Runs a query with the specified constraint. This query is requested
     * by the filter attached to this adapter.
     *
     * Contract: when constraint is null or empty, the original results,
     * prior to any filtering, must be returned.
     *
     * @param constraint the constraint with which the query must
     *        be filtered
     *
     * @return a Cursor representing the results of the new query
     */
    Cursor runQuery(CharSequence constraint);
}

就一个接口，所以我们需要在外面继承这个接口实现它，然后通过CursorAdapter的

/**
     * Sets the query filter provider used to filter the current Cursor.
     * The provider's
     * {@link android.widget.FilterQueryProvider#runQuery(CharSequence)}
     * method is invoked when filtering is requested by a client of
     * this adapter.
     *
     * @param filterQueryProvider the filter query provider or null to remove it
     *
     * @see #getFilterQueryProvider()
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public void setFilterQueryProvider(FilterQueryProvider filterQueryProvider) {
        mFilterQueryProvider = filterQueryProvider;
    }

方法设置，之后整个机制完全串联起来，在外调用adapter.getFilter().filter(et_filter.getText().toString());  即可启动整个过滤机制。

其实上面说的和第2）种方法差不多，只不过，假如你已经决定使用CursorAdapter了，建议你使用以上方法实现更新，因为，它已经被实现好了，浑然天成。

三、AsyncQueryHandler

从单词表义来看，就是异步查询处理器。在Android中，异步线程似乎是天生的，基本上所有写Android的都会碰到Handler这个类，它就是异步的，用来通知主线程做事情。这个类和AsyncTask很像，都封装了一个操作的几个部分，操作完成之后，只不过，它局限于对ContentProvider进行操作。仔细研究一下这个类，上源码：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.content;

import android.database.Cursor;
import android.net.Uri;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.util.Log;

import java.lang.ref.WeakReference;

/**
 * A helper class to help make handling asynchronous {@link ContentResolver}
 * queries easier.
 */
public abstract class AsyncQueryHandler extends Handler {
    private static final String TAG = "AsyncQuery";
    private static final boolean localLOGV = false;

    private static final int EVENT_ARG_QUERY = 1;
    private static final int EVENT_ARG_INSERT = 2;
    private static final int EVENT_ARG_UPDATE = 3;
    private static final int EVENT_ARG_DELETE = 4;

    /* package */ final WeakReference<ContentResolver> mResolver;

    private static Looper sLooper = null;

    private Handler mWorkerThreadHandler;

    protected static final class WorkerArgs {
        public Uri uri;
        public Handler handler;
        public String[] projection;
        public String selection;
        public String[] selectionArgs;
        public String orderBy;
        public Object result;
        public Object cookie;
        public ContentValues values;
    }

    protected class WorkerHandler extends Handler {
        public WorkerHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            final ContentResolver resolver = mResolver.get();
            if (resolver == null) return;

            WorkerArgs args = (WorkerArgs) msg.obj;

            int token = msg.what;
            int event = msg.arg1;

            switch (event) {
                case EVENT_ARG_QUERY:
                    Cursor cursor;
                    try {
                        cursor = resolver.query(args.uri, args.projection,
                                args.selection, args.selectionArgs,
                                args.orderBy);
                        // Calling getCount() causes the cursor window to be filled,
                        // which will make the first access on the main thread a lot faster.
                        if (cursor != null) {
                            cursor.getCount();
                        }
                    } catch (Exception e) {
                        Log.w(TAG, e.toString());
                        cursor = null;
                    }

                    args.result = cursor;
                    break;

                case EVENT_ARG_INSERT:
                    args.result = resolver.insert(args.uri, args.values);
                    break;

                case EVENT_ARG_UPDATE:
                    args.result = resolver.update(args.uri, args.values, args.selection,
                            args.selectionArgs);
                    break;

                case EVENT_ARG_DELETE:
                    args.result = resolver.delete(args.uri, args.selection, args.selectionArgs);
                    break;
            }

            // passing the original token value back to the caller
            // on top of the event values in arg1.
            Message reply = args.handler.obtainMessage(token);
            reply.obj = args;
            reply.arg1 = msg.arg1;

            if (localLOGV) {
                Log.d(TAG, "WorkerHandler.handleMsg: msg.arg1=" + msg.arg1
                        + ", reply.what=" + reply.what);
            }

            reply.sendToTarget();
        }
    }

    public AsyncQueryHandler(ContentResolver cr) {
        super();
        mResolver = new WeakReference<ContentResolver>(cr);
        synchronized (AsyncQueryHandler.class) {
            if (sLooper == null) {
                HandlerThread thread = new HandlerThread("AsyncQueryWorker");
                thread.start();

                sLooper = thread.getLooper();
            }
        }
        mWorkerThreadHandler = createHandler(sLooper);
    }

    protected Handler createHandler(Looper looper) {
        return new WorkerHandler(looper);
    }

    /**
     * This method begins an asynchronous query. When the query is done
     * {@link #onQueryComplete} is called.
     *
     * @param token A token passed into {@link #onQueryComplete} to identify
     *  the query.
     * @param cookie An object that gets passed into {@link #onQueryComplete}
     * @param uri The URI, using the content:// scheme, for the content to
     *         retrieve.
     * @param projection A list of which columns to return. Passing null will
     *         return all columns, which is discouraged to prevent reading data
     *         from storage that isn't going to be used.
     * @param selection A filter declaring which rows to return, formatted as an
     *         SQL WHERE clause (excluding the WHERE itself). Passing null will
     *         return all rows for the given URI.
     * @param selectionArgs You may include ?s in selection, which will be
     *         replaced by the values from selectionArgs, in the order that they
     *         appear in the selection. The values will be bound as Strings.
     * @param orderBy How to order the rows, formatted as an SQL ORDER BY
     *         clause (excluding the ORDER BY itself). Passing null will use the
     *         default sort order, which may be unordered.
     */
    public void startQuery(int token, Object cookie, Uri uri,
            String[] projection, String selection, String[] selectionArgs,
            String orderBy) {
        // Use the token as what so cancelOperations works properly
        Message msg = mWorkerThreadHandler.obtainMessage(token);
        msg.arg1 = EVENT_ARG_QUERY;

        WorkerArgs args = new WorkerArgs();
        args.handler = this;
        args.uri = uri;
        args.projection = projection;
        args.selection = selection;
        args.selectionArgs = selectionArgs;
        args.orderBy = orderBy;
        args.cookie = cookie;
        msg.obj = args;

        mWorkerThreadHandler.sendMessage(msg);
    }

    /**
     * Attempts to cancel operation that has not already started. Note that
     * there is no guarantee that the operation will be canceled. They still may
     * result in a call to on[Query/Insert/Update/Delete]Complete after this
     * call has completed.
     *
     * @param token The token representing the operation to be canceled.
     *  If multiple operations have the same token they will all be canceled.
     */
    public final void cancelOperation(int token) {
        mWorkerThreadHandler.removeMessages(token);
    }

    /**
     * This method begins an asynchronous insert. When the insert operation is
     * done {@link #onInsertComplete} is called.
     *
     * @param token A token passed into {@link #onInsertComplete} to identify
     *  the insert operation.
     * @param cookie An object that gets passed into {@link #onInsertComplete}
     * @param uri the Uri passed to the insert operation.
     * @param initialValues the ContentValues parameter passed to the insert operation.
     */
    public final void startInsert(int token, Object cookie, Uri uri,
            ContentValues initialValues) {
        // Use the token as what so cancelOperations works properly
        Message msg = mWorkerThreadHandler.obtainMessage(token);
        msg.arg1 = EVENT_ARG_INSERT;

        WorkerArgs args = new WorkerArgs();
        args.handler = this;
        args.uri = uri;
        args.cookie = cookie;
        args.values = initialValues;
        msg.obj = args;

        mWorkerThreadHandler.sendMessage(msg);
    }

    /**
     * This method begins an asynchronous update. When the update operation is
     * done {@link #onUpdateComplete} is called.
     *
     * @param token A token passed into {@link #onUpdateComplete} to identify
     *  the update operation.
     * @param cookie An object that gets passed into {@link #onUpdateComplete}
     * @param uri the Uri passed to the update operation.
     * @param values the ContentValues parameter passed to the update operation.
     */
    public final void startUpdate(int token, Object cookie, Uri uri,
            ContentValues values, String selection, String[] selectionArgs) {
        // Use the token as what so cancelOperations works properly
        Message msg = mWorkerThreadHandler.obtainMessage(token);
        msg.arg1 = EVENT_ARG_UPDATE;

        WorkerArgs args = new WorkerArgs();
        args.handler = this;
        args.uri = uri;
        args.cookie = cookie;
        args.values = values;
        args.selection = selection;
        args.selectionArgs = selectionArgs;
        msg.obj = args;

        mWorkerThreadHandler.sendMessage(msg);
    }

    /**
     * This method begins an asynchronous delete. When the delete operation is
     * done {@link #onDeleteComplete} is called.
     *
     * @param token A token passed into {@link #onDeleteComplete} to identify
     *  the delete operation.
     * @param cookie An object that gets passed into {@link #onDeleteComplete}
     * @param uri the Uri passed to the delete operation.
     * @param selection the where clause.
     */
    public final void startDelete(int token, Object cookie, Uri uri,
            String selection, String[] selectionArgs) {
        // Use the token as what so cancelOperations works properly
        Message msg = mWorkerThreadHandler.obtainMessage(token);
        msg.arg1 = EVENT_ARG_DELETE;

        WorkerArgs args = new WorkerArgs();
        args.handler = this;
        args.uri = uri;
        args.cookie = cookie;
        args.selection = selection;
        args.selectionArgs = selectionArgs;
        msg.obj = args;

        mWorkerThreadHandler.sendMessage(msg);
    }

    /**
     * Called when an asynchronous query is completed.
     *
     * @param token the token to identify the query, passed in from
     *            {@link #startQuery}.
     * @param cookie the cookie object passed in from {@link #startQuery}.
     * @param cursor The cursor holding the results from the query.
     */
    protected void onQueryComplete(int token, Object cookie, Cursor cursor) {
        // Empty
    }

    /**
     * Called when an asynchronous insert is completed.
     *
     * @param token the token to identify the query, passed in from
     *        {@link #startInsert}.
     * @param cookie the cookie object that's passed in from
     *        {@link #startInsert}.
     * @param uri the uri returned from the insert operation.
     */
    protected void onInsertComplete(int token, Object cookie, Uri uri) {
        // Empty
    }

    /**
     * Called when an asynchronous update is completed.
     *
     * @param token the token to identify the query, passed in from
     *        {@link #startUpdate}.
     * @param cookie the cookie object that's passed in from
     *        {@link #startUpdate}.
     * @param result the result returned from the update operation
     */
    protected void onUpdateComplete(int token, Object cookie, int result) {
        // Empty
    }

    /**
     * Called when an asynchronous delete is completed.
     *
     * @param token the token to identify the query, passed in from
     *        {@link #startDelete}.
     * @param cookie the cookie object that's passed in from
     *        {@link #startDelete}.
     * @param result the result returned from the delete operation
     */
    protected void onDeleteComplete(int token, Object cookie, int result) {
        // Empty
    }

    @Override
    public void handleMessage(Message msg) {
        WorkerArgs args = (WorkerArgs) msg.obj;

        if (localLOGV) {
            Log.d(TAG, "AsyncQueryHandler.handleMessage: msg.what=" + msg.what
                    + ", msg.arg1=" + msg.arg1);
        }

        int token = msg.what;
        int event = msg.arg1;

        // pass token back to caller on each callback.
        switch (event) {
            case EVENT_ARG_QUERY:
                onQueryComplete(token, args.cookie, (Cursor) args.result);
                break;

            case EVENT_ARG_INSERT:
                onInsertComplete(token, args.cookie, (Uri) args.result);
                break;

            case EVENT_ARG_UPDATE:
                onUpdateComplete(token, args.cookie, (Integer) args.result);
                break;

            case EVENT_ARG_DELETE:
                onDeleteComplete(token, args.cookie, (Integer) args.result);
                break;
        }
    }
}

这里面实际上整个对ContentProvider的增删改查都是交给Handler来实现的，你只需要实现四个接口，告诉AsyncQueryHandler操作完毕之后需要干什么，然后调用相关的接口即可。所以查询的时候也可以通过它实现。

注意：根据项目经验，如果用户向搜索框中输入文字进行搜索，假设连续快速输入sz两个字母，那么你会先搜索s，然后搜索sz，我们假设一种极端情况：因为含有s的搜索结果很大概率上比sz多，假设搜索s的时间为10s，而搜索sz的时间只需要3s，你去更新界面，其实是3s后搜索sz的结果出现，再过7s搜索s的结果出现，而此时搜索框中的输入内容是sz，出现不正常的情况。所以我们在搜索sz之前要做的就是取消搜索s的任务，AsyncQueryHandler提供了该接口：

/**
     * Attempts to cancel operation that has not already started. Note that
     * there is no guarantee that the operation will be canceled. They still may
     * result in a call to on[Query/Insert/Update/Delete]Complete after this
     * call has completed.
     *
     * @param token The token representing the operation to be canceled.
     *  If multiple operations have the same token they will all be canceled.
     */
    public final void cancelOperation(int token) {
        mWorkerThreadHandler.removeMessages(token);
    }

来实现该功能，每一个操作都由一个Token进行标记，取消的时候也需要用这个标记进行。

四、总结

总体来说，除了暴力搜索方法，其余的方法大同小异，不论设计的多么复杂，无非是将搜索的过程放置在异步线程里面，搜索完毕之后更新界面，我们只要记住这一点即可。之所以写文章介绍后面几种方法，是因为既然Android已经帮我们设计好了使用异步线程查询的代码架构，我们直接用即可，肯定更加健壮，也省去重复造轮子的力气。