Android 数据过滤器：Filter

类图：

通常可以将SearchView和ListView结合，实现数据的搜索和过滤。

1.监听SearchView，SearchView.setOnQueryTextListener(OnQueryTextListener listener)；

2.开启ListView的过滤功能，listView.setTextFilterEnabled(true)。必须开启，否则不会过滤；

3..当SearchView接收到输入事件后，调用ListView.setFilterText(filterText)方法，该方法会通过Adapter得到Filter，然后调用Filter.filter(filterText)：

public void setFilterText(String filterText) {
        // TODO: Should we check for acceptFilter()?
        if (mTextFilterEnabled && !TextUtils.isEmpty(filterText)) {
            createTextFilter(false);
            // This is going to call our listener onTextChanged, but we might not
            // be ready to bring up a window yet
            mTextFilter.setText(filterText);
            mTextFilter.setSelection(filterText.length());
            if (mAdapter instanceof Filterable) {
                // if mPopup is non-null, then onTextChanged will do the filtering
                if (mPopup == null) {
                    Filter f = ((Filterable) mAdapter).getFilter();
                    f.filter(filterText);
                }
                // Set filtered to true so we will display the filter window when our main
                // window is ready
                mFiltered = true;
                mDataSetObserver.clearSavedState();
            }
        }
    }

4.Filter.filter(filterText)方法最终会调用Filter.performFiltering(filterText)和Filter.publishResults(CharSequence filterText, FilterResults results)。performFiltering(filterText)方法完成过滤处理并且返回结果FilterResults，而publishResults(CharSequence filterText, FilterResults results)则根据返回的结果进行相应的处理。

5.Filter.publishResults(CharSequence filterText, FilterResults results)调用了BaseAdapter.notifyDataSetChanged()方法，该方法用于当Adapter的数据发生变化时，通知UI主线程根据新的数据绘制界面：

@Override
       protected void publishResults(CharSequence constraint, FilterResults results) {
           //noinspection unchecked
           mObjects = (List<T>) results.values;
           if (results.count > 0) {
               notifyDataSetChanged();
           } else {
               notifyDataSetInvalidated();
           }
       }

数据过滤就这样完成了。

下面给出例子。

布局文件filter_activity.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <SearchView
        android:id="@+id/searchView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >
    </SearchView>

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </ListView>

</LinearLayout>

类文件MainActivity.java：

package com.zzj.ui.filterdemo;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.SearchView.OnQueryTextListener;

import com.zzj.ui.R;

public class MainActivity extends Activity implements OnQueryTextListener {
    private ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.filter_activity);

        SearchView searchView = (SearchView) findViewById(R.id.searchView1);
        searchView.setOnQueryTextListener(this);
        searchView.setSubmitButtonEnabled(false);
        searchView.setIconifiedByDefault(false);

        listView = (ListView) findViewById(R.id.listView1);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, new String[] { "Bei jing",
                        "Shang hai", "Chang sha", "Chang chun", "Nan jing",
                        "Dong jing", "Ji nan", "Qing dao", "Xiang tan",
                        "Zhu zhou", "Heng yang" });
        listView.setAdapter(adapter);
        // 开启过滤功能
        listView.setTextFilterEnabled(true);
    }

    @Override
    public boolean onQueryTextSubmit(String query) {
        return false;
    }

    @Override
    public boolean onQueryTextChange(String newText) {
        if (newText == null || newText.length() == 0) {
            listView.clearTextFilter();
        } else {
            listView.setFilterText(newText);
        }
        return true;
    }
}

效果图：

如图所示，弹出了一个浮动框，这是listView.setFilterText(filterText)弹出来的。如果不想要这个浮动框，可以先获取Filter，然后调用Filter.filter(filterText)。

修改SearchView的监听函数如下：

@Override
    public boolean onQueryTextChange(String newText) {
        ListAdapter adapter = listView.getAdapter();
        if (adapter instanceof Filterable) {
            Filter filter = ((Filterable) adapter).getFilter();
            if (newText == null || newText.length() == 0) {
                filter.filter(null);
            } else {
                filter.filter(newText);
            }
        }
        return true;
    }

使用这种方法不需要开启ListView的过滤功能。效果如下：

上面使用的是ArrayAdapter的过滤功能，我们也可以继承BaseAdapter，然后实现Filterable接口，定义自己的过滤器。