自定义一个ContentProvider，重写增、删、改、查的方法

好的，以下是一个简单的自定义ContentProvider，实现了增、删、改、查操作：

public class MyContentProvider extends ContentProvider {

    private static final String AUTHORITY = "com.example.myprovider";
    private static final String TABLE_NAME = "my_table";
    private static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + TABLE_NAME);

    private static final int CODE_ITEM = 1;
    private static final int CODE_DIR = 2;

    private static final UriMatcher URI_MATCHER = new UriMatcher(UriMatcher.NO_MATCH);

    static {
        URI_MATCHER.addURI(AUTHORITY, TABLE_NAME, CODE_DIR);
        URI_MATCHER.addURI(AUTHORITY, TABLE_NAME + "/#", CODE_ITEM);
    }

    private SQLiteDatabase mDb;

    @Override
    public boolean onCreate() {
        mDb = new MyDatabaseHelper(getContext()).getWritableDatabase();
        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection,
                        @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        Cursor cursor;
        switch (URI_MATCHER.match(uri)) {
            case CODE_DIR:
                cursor = mDb.query(TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case CODE_ITEM:
                String id = uri.getLastPathSegment();
                cursor = mDb.query(TABLE_NAME, projection, "_id=?", new String[]{id}, null, null, sortOrder);
                break;
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
        return cursor;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        switch (URI_MATCHER.match(uri)) {
            case CODE_DIR:
                return "vnd.android.cursor.dir/" + AUTHORITY + "." + TABLE_NAME;
            case CODE_ITEM:
                return "vnd.android.cursor.item/" + AUTHORITY + "." + TABLE_NAME;
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        long id = mDb.insert(TABLE_NAME, null, values);
        if (id > 0) {
            return ContentUris.withAppendedId(CONTENT_URI, id);
        }
        throw new SQLException("Failed to insert row into " + uri);
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        int count;
        switch (URI_MATCHER.match(uri)) {
            case CODE_DIR:
                count = mDb.delete(TABLE_NAME, selection, selectionArgs);
                break;
            case CODE_ITEM:
                String id = uri.getLastPathSegment();
                count = mDb.delete(TABLE_NAME, "_id=?", new String[]{id});
                break;
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
        return count;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection,
                      @Nullable String[] selectionArgs) {
        int count;
        switch (URI_MATCHER.match(uri)) {
            case CODE_DIR:
                count = mDb.update(TABLE_NAME, values, selection, selectionArgs);
                break;
            case CODE_ITEM:
                String id = uri.getLastPathSegment();
                count = mDb.update(TABLE_NAME, values, "_id=?", new String[]{id});
                break;
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
        return count;
    }
}

需要注意的是，该ContentProvider的数据库操作都是在UI线程中进行的，不适合于大量数据的操作。如果需要进行大量数据的操作，需要使用异步线程来进行。