1.实现跨程序数据共享

 在拥有SQLite数据库的程序上，通过提供自定义ContentProvider，从而向其他程序提供访问原程序数据的接口。
 自定义ContenProvider一定要在AndroidManifest.xml文件中注册才可以使用。
 在调用程序中，通过正确的内容URI和getContentResolver()方法获取ContentResolver后，就可以调用原程序中的数据。

 <provider
            android:name=".MyContentProvider"
            android:authorities="com.futuring.app.sharedata"
            android:enabled="true"
            android:exported="true"></provider>

public class MyContentProvider extends ContentProvider {
    //与UriMatcher匹配的自定义代码
    public static final int BOOK_DIR = 0;
    public static final int BOOK_ITEM = 1;
    public static final int CATEGORY_DIR = 2;
    public static final int CATEGORY_ITEM = 3;

    public static final String AUTHORITY = "com.futuring.app.sharedata";

    private static UriMatcher sMatcher;
    //数据库
    private MyDatabaseHelper dbHelper;

    //利用UriMatcher将内容URI与自定义代码匹配
    static {
        sMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        sMatcher.addURI(AUTHORITY, "book", BOOK_DIR);
        sMatcher.addURI(AUTHORITY, "book/#", BOOK_ITEM);
        sMatcher.addURI(AUTHORITY, "category", CATEGORY_DIR);
        sMatcher.addURI(AUTHORITY, "category/#", CATEGORY_ITEM);
    }

    public MyContentProvider() {


    }



   @Override
    public boolean onCreate() {
        // TODO: Implement this to initialize your content provider on startup.
        dbHelper = new MyDatabaseHelper(getContext(), "BookStore.db", null, 2);
        return true;
    }



    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // Implement this to handle requests to delete one or more rows.
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int deletedRows = 0;
        switch (sMatcher.match(uri)) {
            case BOOK_DIR:
                deletedRows = db.delete("Book", selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                deletedRows = db.delete("Book", "id = ?", new String[]{bookId});
                break;
            case CATEGORY_DIR:
                deletedRows = db.delete("Category", selection, selectionArgs);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                deletedRows = db.delete("Category", "id = ?", new String[]{categoryId});
                break;
            default:
                throw new UnsupportedOperationException("Not yet implemented");

        }
        //返回被删除的行数
        return deletedRows;
    }

    @Override
    public String getType(Uri uri) {
        // TODO: Implement this to handle requests for the MIME type of the data
        // at the given URI.
        switch (sMatcher.match(uri)) {
            case BOOK_DIR:
                return "vnd.android.cursor.dir/vnd.com.futuring.app.sharedata.book";
            case BOOK_ITEM:
                return "vnd.android.cursor.item/vnd.com.futuring.app.sharedata.book";
            case CATEGORY_DIR:
                return "vnd.android.cursor.dir/vnd.com.futuring.app.sharedata.category";
            case CATEGORY_ITEM:
                return "vnd.android.cursor.item/vnd.com.futuring.app.sharedata.category";
        }
        throw new UnsupportedOperationException("Not yet implemented");
    }


    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO: Implement this to handle requests to insert a new row.
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Uri uriReturn = null;
        switch (sMatcher.match(uri)) {
            case BOOK_DIR:
            case BOOK_ITEM:
                //db.insert返回新插入数据的id
                long newBookId = db.insert("Book", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newBookId);
                break;
            case CATEGORY_DIR:
            case CATEGORY_ITEM:
                //db.insert返回新插入数据的id
                long newCategoryId = db.insert("Category", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newCategoryId);
                break;
            default:
                throw new UnsupportedOperationException("Not yet implemented");
        }
        //返回新插入数据的Uri
        return uriReturn;

    }


    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        // TODO: Implement this to handle query requests from clients.
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        Cursor cursor = null;
        switch (sMatcher.match(uri)) {
            case BOOK_DIR:
                cursor = db.query("Book", projection, selection,
                        selectionArgs,null, null, sortOrder);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                cursor = db.query("Book", projection, "id = ?",
                        new String[]{bookId}, null, null, sortOrder);
                break;
            case CATEGORY_DIR:
                cursor = db.query("Category", projection, selection, selectionArgs,
                        null, null, sortOrder);
                break;
            case CATEGORY_ITEM:
                //获取以id为结尾的内容URI "..../#"  #代表的变量
                String categoryId = uri.getPathSegments().get(1);
                cursor = db.query("Categroy", projection, "id = ?",
                        new String[]{categoryId}, null, null, sortOrder);
                break;
            default:
                throw new UnsupportedOperationException("Not yet implemented");
        }

        return cursor;

    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        // TODO: Implement this to handle requests to update one or more rows.
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int updateRows = 0;
        switch (sMatcher.match(uri)) {
            case BOOK_DIR:
                updateRows = db.update("Book", values, selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                updateRows = db.update("Book", values, "id = ?",
                        new String[]{bookId});
                break;
            case CATEGORY_DIR:
                updateRows = db.update("Category", values, selection, selectionArgs);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                updateRows = db.update("Category", values, "id = ?",
                        new String[]{categoryId});
                break;
             default:
                 throw new UnsupportedOperationException("Not yet implemented");

        }
        //返回被更新数据的行数
        return updateRows;
    }
}