Android开发之ContentProvider的简单使用

ContentProvider，内容提供者

官网结构图：

作为四大组件之一的ContentProvider，主要是用于应用间数据共享使用的。

ContentProvider把应用的数据封装起来，然后提供一个对外访问的ContentResolver接口。

假如只是本应用使用的数据，直接通过SQLiteDatabase操作数据库。

主要原理：一个Uri对象通过ContentResolver请求该应用的数据，ContentProvider解析该Uri并返回给需要的数据。

实现自定义的ContentProvider，需要继承抽象类android.content.ContentProvider，并实现5个方法：

onCreate()    初始化provider，返回一个布尔值，创建成功返回一个true

query(Uri,String[],String,String[],String)   从ContentProvider中查询数据  返回一个Cursor

insert(Uri,ContentValues)  通过ContentProvider插入新的数据   返回一个Uri

update(Uri,ContentValues,String,String[])   通过ContentProvider更新数据   返回一个int

delete(Uri,String,String[])   通过ContentProvider删除数据       返回一个int

getType(Uri)   根据传入的Uri,返回相应的MIME类型。  返回一个String

Uri类：

一个Uri有三部分组成：Scheme+Authority+Path

1.scheme, contentprovider为content://

2.Authority,一般使用应用的包名，如com.example.appone或者也可以这样com.example.appone.provider

3.Path,即提供对外访问的table，如访问表table,写成/table

上面的Uri可以写成这样：content://com.example.appone.provider/table

一个字符串通过Uri类中的parse()方法可以转换为Uri对象,如下：

Uri uri=Uri.parse("content://com.example.appone.provider/table");

UriMatcher类，ContentUris类和contentResolver类

UriMather类用于匹配uri，用法如下：

    private static final int PEOPLE = 1;
    private static final int PEOPLE_ID = 2;
    private static final int PEOPLE_PHONES = 3;
    private static final int PEOPLE_PHONES_ID = 4;
    private static final int PEOPLE_CONTACTMETHODS = 7;
    private static final int PEOPLE_CONTACTMETHODS_ID = 8;

    private static final int DELETED_PEOPLE = 20;

    private static final int PHONES = 9;
    private static final int PHONES_ID = 10;
    private static final int PHONES_FILTER = 14;

    private static final int CONTACTMETHODS = 18;
    private static final int CONTACTMETHODS_ID = 19;

    private static final int CALLS = 11;
    private static final int CALLS_ID = 12;
    private static final int CALLS_FILTER = 15;

    private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH); //常量UriMatcher.NO_MATCH表示不匹配任何路径的返回码(-1)

    static
    {
        sURIMatcher.addURI("contacts", "people", PEOPLE); //如果match()方法匹配，返回匹配码为1
        sURIMatcher.addURI("contacts", "people/#", PEOPLE_ID);    //如果match（）方法匹配，返回匹配码为2
        sURIMatcher.addURI("contacts", "people/#/phones", PEOPLE_PHONES);
        sURIMatcher.addURI("contacts", "people/#/phones/#", PEOPLE_PHONES_ID);
        sURIMatcher.addURI("contacts", "people/#/contact_methods", PEOPLE_CONTACTMETHODS);
        sURIMatcher.addURI("contacts", "people/#/contact_methods/#", PEOPLE_CONTACTMETHODS_ID);
        sURIMatcher.addURI("contacts", "deleted_people", DELETED_PEOPLE);
        sURIMatcher.addURI("contacts", "phones", PHONES);
        sURIMatcher.addURI("contacts", "phones/filter/*", PHONES_FILTER);
        sURIMatcher.addURI("contacts", "phones/#", PHONES_ID);
        sURIMatcher.addURI("contacts", "contact_methods", CONTACTMETHODS);
        sURIMatcher.addURI("contacts", "contact_methods/#", CONTACTMETHODS_ID);
        sURIMatcher.addURI("call_log", "calls", CALLS);
        sURIMatcher.addURI("call_log", "calls/filter/*", CALLS_FILTER);
        sURIMatcher.addURI("call_log", "calls/#", CALLS_ID);
    }

从API:18开始，路径可以用一个斜线开始。 例如：

sURIMatcher.addURI("contacts", "/people", PEOPLE);

注册完需要匹配的Uri后，在getType()方法中可以使用sURIMatcher.match(uri)方法对输入的Uri进行匹配，如果匹配成功就返回匹配码，匹配码是调用addURI()方法传入的第三个参数。

    public String getType(Uri url)
    {
        int match = sURIMatcher.match(url);
        switch (match)
        {
            case PEOPLE:
                return "vnd.android.cursor.dir/person";
            case PEOPLE_ID:
                return "vnd.android.cursor.item/person";
... snip ...
                return "vnd.android.cursor.dir/snail-mail";
            case PEOPLE_ADDRESS_ID:
                return "vnd.android.cursor.item/snail-mail";
            default:
                return null;
        }
    }

ContentUris类，用于获取Uri路径后面的ID部分，它有两个比较实用的方法：

    withAppendedId(uri, id)用于为路径加上ID部分

Uri uri = Uri.parse("content://com.ljq.provider.personprovider/person")
Uri resultUri = ContentUris.withAppendedId(uri, 10); 
//生成后的Uri为：content://com.ljq.provider.personprovider/person/10

    parseId(uri)方法用于从路径中获取ID部分

Uri uri = Uri.parse("content://com.ljq.provider.personprovider/person/10")
long personid = ContentUris.parseId(uri);//获取的结果为:10

ContentResolver类，当外部应用需要对ContentProvider的数据库进行CRUD时，可以使用ContentResolver类来完成。获取ContentResolver对象，可以通过Content的getContentResolver()方法获取到。ContentResolver使用insert()、delete()、update()、query()方法，来操作数据。

实现了一个Demo，代码如下：

1.工具类：Xin类

package com.example.appone;

public class Xin {

    public static final String DBNAME = "xinonlinedb";
    public static final String TNAME = "xinonline";
    public static final int VERSION = 3;

    public static String TID = "tid";
    public static final String EMAIL = "email";
    public static final String USERNAME = "username";
    public static final String DATE = "date";
    public static final String SEX = "sex";

    public static final String AUTOHORITY = "com.example.appone.provider";
    public static final int ITEM = 1;
    public static final int ITEM_ID = 2;

    public static final String CONTENT_TYPE = "vnd.android.cursor.dir";
    public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item";

}

2.创建数据库：DBlite类

package com.example.appone;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DBlite extends SQLiteOpenHelper {

    public DBlite(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE " + Xin.TNAME + "(" + Xin.TID
                + " integer primary key autoincrement not null," + Xin.EMAIL
                + " text not null, " + Xin.USERNAME + " text not null,"
                + Xin.DATE + " text not null, " + Xin.SEX + " text not null);");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

}

3.创建自定义的ContentProvider，对数据库进行包装：MyProvider类

package com.example.appone;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;

public class MyProvider extends ContentProvider {

    private DBlite dBlite;
    private SQLiteDatabase db;
    private Cursor cursor;

    private static final UriMatcher sMatcher;
    static {
        sMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        sMatcher.addURI(Xin.AUTOHORITY, Xin.TNAME, Xin.ITEM);
        sMatcher.addURI(Xin.AUTOHORITY, Xin.TNAME + "/#", Xin.ITEM_ID);

    }

    @Override
    public boolean onCreate() {
        dBlite = new DBlite(getContext(), Xin.DBNAME, null, Xin.VERSION);
        return true;

    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        db = dBlite.getWritableDatabase();
        switch (sMatcher.match(uri)) {
        case Xin.ITEM:
            cursor = db.query(Xin.TNAME, projection, selection, selectionArgs,
                    null, null, sortOrder);
            break;
        case Xin.ITEM_ID:
            String id = uri.getPathSegments().get(1);
            cursor = db.query(Xin.TNAME, projection, "tid=?",
                    new String[] { id }, null, null, sortOrder);
            break;

        default:
            break;
        }
        return cursor;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        db = dBlite.getWritableDatabase();
        long returnId = db.insert(Xin.TNAME, null, values);
        Uri uriReturn = Uri.parse("content://" + Xin.AUTOHORITY + "/"
                + Xin.TNAME + "/" + returnId);

        return uriReturn;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        db = dBlite.getWritableDatabase();
        int deleteId = 0;
        switch (sMatcher.match(uri)) {
        case Xin.ITEM:
            deleteId = db.delete(Xin.TNAME, selection, selectionArgs);

            break;
        case Xin.ITEM_ID:
            String id = uri.getPathSegments().get(1);
            deleteId = db.delete(Xin.TNAME, "tid=?", new String[] { id });

        default:
            break;
        }
        return deleteId;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        db = dBlite.getWritableDatabase();
        int updateId = 0;
        switch (sMatcher.match(uri)) {
        case Xin.ITEM:
            updateId = db.update(Xin.TNAME, values, selection, selectionArgs);
            break;
        case Xin.ITEM_ID:
            String id = uri.getPathSegments().get(1);
            updateId = db.update(Xin.TNAME, values, "tid= ?",
                    new String[] { id });
            break;

        default:
            break;
        }
        return updateId;
    }

    @Override
    public String getType(Uri uri) {
        switch (sMatcher.match(uri)) {
        case Xin.ITEM:
            return Xin.CONTENT_TYPE + "/vnd." + Xin.AUTOHORITY + Xin.TNAME;
        case Xin.ITEM_ID:
            return Xin.CONTENT_ITEM_TYPE + "/vnd." + Xin.AUTOHORITY + Xin.TNAME;

        }
        return null;
    }

}

4.在manifest文件中对MyProvider进行注册

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.appone"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="21" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <provider
            android:name="com.example.appone.MyProvider"
            android:authorities="com.example.appone.provider"
            android:exported="true" >
        </provider>
    </application>

</manifest>

5.在MainActivity中使用ContentProvider进行CRUD

package com.example.appone;

import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;

public class MainActivity extends Activity implements OnClickListener {

    private String newid;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_contentprovider);

        findViewById(R.id.contentProvider_query).setOnClickListener(this);
        findViewById(R.id.contentProvider_insert).setOnClickListener(this);
        findViewById(R.id.contentProvider_update).setOnClickListener(this);
        findViewById(R.id.contentProvider_delete).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        Uri uriItem = Uri.parse("content://"+Xin.AUTOHORITY+"/"+Xin.TNAME);
        Uri uriId = Uri.parse("content://"+Xin.AUTOHORITY+"/"+Xin.TNAME+"/"+newid);
        switch (v.getId()) {
        case R.id.contentProvider_query:
            Cursor cursor=this.getContentResolver().query(uriItem, null, null, null, null);
            if (cursor!=null) {
                while (cursor.moveToNext()) {
                    String userName=cursor.getString(cursor.getColumnIndex(Xin.USERNAME));
                    String sex = cursor.getString(cursor.getColumnIndex(Xin.SEX));
                    String email = cursor.getString(cursor.getColumnIndex(Xin.EMAIL));
                    String date = cursor.getString(cursor.getColumnIndex(Xin.DATE));
                    Log.e("appone", "获取到的信息为："+userName+email+date+sex);
                }
                cursor.close();
            }
            break;
            
        case R.id.contentProvider_insert:
            ContentValues values = new ContentValues();
            values.put(Xin.EMAIL, "1234@12.com");
            values.put(Xin.USERNAME, "张三");
            values.put(Xin.DATE, "2015");
            values.put(Xin.SEX, "男");
            Uri newUri = this.getContentResolver().insert(uriItem,values);
            newid = newUri.getPathSegments().get(1);
            break;
            
        case R.id.contentProvider_update:
            ContentValues values2= new ContentValues();
            values2.put(Xin.USERNAME, "王五");
            values2.put(Xin.EMAIL, "xxx@ddd.com");
            values2.put(Xin.SEX, "女");
            this.getContentResolver().update(uriId, values2, null, null);
            break;
            
        case R.id.contentProvider_delete:
            this.getContentResolver().delete(uriId, null, null);
            break;

        default:
            break;
        }
    }

}

注意：

首先需要插入消息，然后再查询或者更新或者删除，否则newId的值为空。