如何删除 SQLiteDatabase 中的一行 - Android Content Provider

Question

我正在努力编写一个从 SQLiteDatabase 中删除一行的方法。我在 gridview 中有一个歌曲列表，当用户单击列表中的一个项目时，应用程序会将它们带到我的 SongDetailFragment activity，其中包含有关歌曲的更多信息和一个星形按钮，如果歌曲在在数据库中，星号按钮“打开”，相反，如果该项目不在数据库中，星号按钮“关闭”

当用户单击星号按钮时，我可以在数据库中成功添加一首歌曲，并且我的星号按钮已“打开”。现在我想再次按下同一个按钮并调用 deleteFromDB() 来删除添加到数据库中的歌曲。所以我的 onClick 中有以下代码：

 public void onClick(View v)
            {

                if  (mIsFavourite) {

                   deleteFromDB();

                }

                else {
                    insertData();
                    mIsFavourite = true;
                }

问题是 deleteFromDB() 方法无法正常工作，因为我可以看到歌曲没有从数据库中删除。我不确定修复它的正确语法是什么。

这是我的方法：

   private void deleteFromDB() {

        ContentValues songValues = new ContentValues();


        getActivity().getContentResolver().delete(SongContract.SongEntry.CONTENT_URI,
                SongContract.SongEntry.COLUMN_TITLE + " = ?",
                new String[]{songValues.getAsString(song.getTitle())});

      //switch off button
        imgViewFavButton.setImageResource(android.R.drawable.btn_star_big_off);
    }

这是我的 ContentProvider class 中的删除方法片段：

  @Override
    public int delete(Uri uri, String selection, String[] selectionArgs){
        final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        final int match = sUriMatcher.match(uri);
        int numDeleted;
        switch(match){
            case SONG:
                numDeleted = db.delete(
                        SongContract.SongEntry.TABLE_NAME, selection, selectionArgs);
                // reset _ID
                db.execSQL("DELETE FROM SQLITE_SEQUENCE WHERE NAME = '" +
                        SongContract.SongEntry.TABLE_NAME + "'");
                break;
            case SONG_WITH_ID:
                numDeleted = db.delete(SongContract.SongEntry.TABLE_NAME,
                        SongContract.SongEntry._ID + " = ?",
                        new String[]{String.valueOf(ContentUris.parseId(uri))});
                // reset _ID
                db.execSQL("DELETE FROM SQLITE_SEQUENCE WHERE NAME = '" +
                        SongContract.SongEntry.TABLE_NAME + "'");

                break;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }

        return numDeleted;
    }

这是我的 SongDetailFragment：

public  class SongDetailFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor>{
    private  Song song;
    private static final int CURSOR_LOADER_ID = 0;
    ImageButton imgViewFavButton;
    Boolean mIsFavourite = false;

   // private final Context mContext;

    public SongDetailFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.song_fragment_detail, container, false);


        Intent intent = getActivity().getIntent();
        if (intent != null && intent.hasExtra("song")) {


            song = intent.getParcelableExtra("song");
            //display title
            ((TextView) rootView.findViewById(R.id.detail_title_textview))
                    .setText(song.getTitle());

            ((TextView)rootView.findViewById(R.id.detail_description_textview))
                    .setText(song.getDescription());


            ((TextView)rootView.findViewById(R.id.song_releasedate_textview))
                    .setText(song.getReleaseDate());

            double dRating = song.getVoteAverage();
            String sRating = String.valueOf(dRating);

            ((TextView)rootView.findViewById(R.id.song_rating_textview))
                    .setText(sRating + "/10 ");

            //show song poster


            ImageView imageView = (ImageView) rootView.findViewById(R.id.song_detail_poster_imageview);
            Picasso.with(getActivity()).load(song.getPoster()).into(imageView);
        }

        imgViewFavButton = (ImageButton) rootView.findViewById(R.id.imgFavBtn);

        checkFavourites();

        imgViewFavButton.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {

                if  (mIsFavourite) {

                   deleteFromDB();

                }

                else {
                    insertData();
                    mIsFavourite = true;
                }


            }
        });

        return rootView;
    }

    // insert data into database

    public void insertData(){
        ContentValues songValues = new ContentValues();
        songValues.put(SongContract.SongEntry.COLUMN_ID, song.getsong_id());
        songValues.put(SongContract.SongEntry.COLUMN_IMAGE, song.getPoster());
        songValues.put(SongContract.SongEntry.COLUMN_TITLE, song.getTitle());
        songValues.put(SongContract.SongEntry.COLUMN_OVERVIEW, song.getDescription());
        songValues.put(SongContract.SongEntry.COLUMN_RELEASEDATE, song.getReleaseDate());
        songValues.put(SongContract.SongEntry.COLUMN_RATING, song.getVoteAverage().toString());

           //Insert our ContentValues
        getActivity().getContentResolver().insert(SongContract.SongEntry.CONTENT_URI,
                songValues);

         imgViewFavButton.setImageResource(android.R.drawable.btn_star_big_on);

    }

    private void deleteFromDB() {

        ContentValues songValues = new ContentValues();


        getActivity().getContentResolver().delete(SongContract.SongEntry.CONTENT_URI,
                SongContract.SongEntry.COLUMN_TITLE + " = ?",
                new String[]{songValues.getAsString(song.getTitle())});


        imgViewFavButton.setImageResource(android.R.drawable.btn_star_big_off);
    }



    private void checkFavourites() {
        Cursor c =
                getActivity().getContentResolver().query(SongContract.SongEntry.CONTENT_URI,
                        null,
                        SongContract.SongEntry.COLUMN_ID + " = ?",
                        new String[]{song.getsong_id()},
                        null);

        if (c != null) {
            c.moveToFirst();
            int index = c.getColumnIndex(SongContract.SongEntry.COLUMN_ID);

            if (c.getCount() > 0 && c.getString(index).equals(song.getsong_id())) {
                mIsFavourite = true;
                imgViewFavButton.setImageResource(android.R.drawable.btn_star_big_on);
            }

            else{
                imgViewFavButton.setImageResource(android.R.drawable.btn_star_big_off);
            }

            c.close();

        }



    }


    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args){
        return new CursorLoader(getActivity(),
                SongContract.songEntry.CONTENT_URI,
                null,
                null,
                null,
                null);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState){
        super.onViewCreated(view, savedInstanceState);
    }


    // Set the cursor in our CursorAdapter once the Cursor is loaded
    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {




    }

    // reset CursorAdapter on Loader Reset
    @Override
    public void onLoaderReset(Loader<Cursor> loader){

    }

}

Answer 1

注意这里的这一行：

 ContentValues songValues = new ContentValues();
 getActivity().getContentResolver().delete(SongContract.songEntry.CONTENT_URI,
            SongContract.songEntry.COLUMN_TITLE + " = ?",
            new String[]{songValues.getAsString(song.getTitle())});

您将 songValues 设置为空的 ContentValues object，然后调用 getAsString()，这将 return 为空，因为它不包含 song.getTitle() 的任何键。

只需更改您的数组以包含歌曲标题，此处不需要 ContentValues：

new String[]{song.getTitle()});

如何删除 SQLiteDatabase 中的一行 - Android Content Provider

How to delete a row in SQLiteDatabase - Android Content Provider

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