Android ContentProvider

• ContentProvider，Android四大组件之一。可以实现进程间数据共享。

有3个辅助类

• ContentUris类，用来在Uri后追加id、获取id。
• UriMatcher类 ，用来注册ContentProvider的Uri，根据提供的Uri匹配ContentProvider中对应的表。
• ContentObserver，内容观察者，指定Uri的ContentProvider的内容发送改变，并通知注册了观察者。

操作类

ContentResolver抽象类，用来管理所有的ContentProvider。通过Uri来确定ContentProvider。有增删改查的方法。

示例
数据源SQLite数据库

public class DBOpenHelper extends SQLiteOpenHelper {
    /**
     * 数据库的名字
     */
    private static final String DB_NAME = "customer.db";
    /**
     * 版本号
     */
    private static int sDBVersion = 1;

    /**
     * 表名
     */

    public static final String TABLE_MAN_NAME = "man";
    public static final String TABLE_DOG_NAME = "dog";


    public DBOpenHelper(Context context) {
        super(context, DB_NAME, null, sDBVersion);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL("create table if not exists " + TABLE_MAN_NAME + "(_id integer primary key autoincrement,name text)");
        db.execSQL("create table if not exists " + TABLE_DOG_NAME + "(_id integer primary key autoincrement,name text)");
    }

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

    }
}

自定义ContentProvider

public class MyContentProvider extends ContentProvider {

    private DBOpenHelper dbOpenHelper = null;
    private SQLiteDatabase db = null;
    public static final String AUTOHORITY = "com.example.study.contentprovider";
    public static final int CODE_MAN = 1;
    public static final int CODE_DOG = 2;
    static UriMatcher sUriMatcher = null;

    static {
        sUriMatcher = new UriMatcher(NO_MATCH);
        //权限
        //路径，可以是任何值
        //匹配的时候会返回的code
        sUriMatcher.addURI(AUTOHORITY, "man", CODE_MAN);
        sUriMatcher.addURI(AUTOHORITY, "dog", CODE_DOG);
    }


    @Override
    public boolean onCreate() {
        dbOpenHelper = new DBOpenHelper(getContext());
        db = dbOpenHelper.getWritableDatabase();
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        String tableName = getTableName(uri);
        Cursor query = db.query(tableName, null, null, null, null, null, null);
        query.moveToFirst();
        return query;
    }

    @Override
    public String getType(Uri uri) {
        return null;
    }


    @Override
    public Uri insert(Uri uri, ContentValues values) {
        String tableName = getTableName(uri);
        db.insert(tableName, null, values);
        Log.i("name",Thread.currentThread().getName());
        getContext().getContentResolver().notifyChange(uri,null);
        return uri;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        String tableName = getTableName(uri);
        db.delete(tableName, selection, selectionArgs);
        return 0;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        String tableName = getTableName(uri);
        db.update(tableName, values, selection, selectionArgs);
        return 0;
    }

    /**
     * 根据URI匹配 URI_CODE，从而匹配ContentProvider中相应的表名
     */
    private String getTableName(Uri uri) {
        String tableName = null;
        switch (sUriMatcher.match(uri)) {
            case CODE_MAN:
                tableName = DBOpenHelper.TABLE_MAN_NAME;
                break;
            case CODE_DOG:
                tableName = DBOpenHelper.TABLE_DOG_NAME;
                break;
            default:
                tableName=DBOpenHelper.TABLE_MAN_NAME;
        }
        return tableName;
    }
}

Activity中

 	private ContentResolver contentResolver;
    private Uri uri;
    private Cursor query;
    private ContentValues values;
    private ContentObserver contentObserver;
   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_content_provider);
        ButterKnife.bind(this);
        contentResolver = getContentResolver();
        contentObserver = new ContentObserver(new Handler()) {
            @Override
            public boolean deliverSelfNotifications() {
                Log.i("cp", "deliverSelfNotifications");
                return true;
            }

            @Override
            public void onChange(boolean selfChange) {
                super.onChange(selfChange);
                Log.i("cp", "onChange---  selfChange:"+selfChange);
            }

            @Override
            public void onChange(boolean selfChange, Uri uri) {
                super.onChange(selfChange, uri);
                Log.i("cp", "onChange---  selfChange:"+selfChange+"   uri:"+uri.toString());
            }
        };
        uri = Uri.parse("content://com.example.study.contentprovider/man");
        //注册内容观察者
        contentResolver.registerContentObserver(uri, false,contentObserver );
    }

	...
			//点击
			case R.id.add_man:
                uri = Uri.parse("content://com.example.study.contentprovider/man");
                insert(uri, new ContentValues(), "小明");
                break;
            case R.id.query_man:
                uri = Uri.parse("content://com.example.study.contentprovider/man");
                query = contentResolver.query(uri, null, null, null, null, null);
                while (query.moveToNext()) {
                    int id = query.getInt(0);
                    String name = query.getString(1);
                    String s = " id:" + id + "   name:" + name;
                    buffer.append(s + "\n");
                    Log.i("cp", s);
                }

                break;
            case R.id.delete_man:
                uri = Uri.parse("content://com.example.study.contentprovider/man");
                contentResolver.delete(uri, null, null);
                break;
            case R.id.add_dog:
                uri = Uri.parse("content://com.example.study.contentprovider/dog");
                insert(uri, new ContentValues(), "秋田");
                break;
            case R.id.query_dog:
                uri = Uri.parse("content://com.example.study.contentprovider/dog");
                query = contentResolver.query(uri, null, null, null, null, null);
                while (query.moveToNext()) {
                    int id = query.getInt(0);
                    String name = query.getString(1);
                    String s = " id:" + id + "   name:" + name;
                    buffer.append(s + "\n");
                    Log.i("cp", s);
                }
                break;
            case R.id.delete_dog:
                uri = Uri.parse("content://com.example.study.contentprovider/dog");
                contentResolver.delete(uri, null, null);
                break;
           ....

		...
		if (null != query) {
            query.close();
            query=null;
        }

上面的点击进行了添加，查询，删除的操作。

总结
四大组件之一。
夸进程通信。数据共享。
原理是Binder机制
线程池处理任务，需要考虑线程安全。