RecyclerView显示相同的项目

Question

我正在尝试实现RecyclerView，以显示JSONArray中的数据。 解析工作完美，但是RecyclerView在每个项目中显示必须仅在最后一个项目中的信息。 有屏幕截图可以清楚地说明。

这是我的代码：

MainActivity.java

public class MainActivity extends AppCompatActivity {
RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;

protected void onCreate(Bundle savedInstanceState) {
    setTheme(R.style.AppTheme);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_layout);
    new parseTask().execute();
}

private class parseTask extends AsyncTask<Void, Void, String> {

    HttpURLConnection urlConnection = null;
    BufferedReader reader = null;
    String resultJson = "";
    ProgressDialog pdLoading = new ProgressDialog(MainActivity.this, R.style.MyDialogStyle);

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pdLoading.setMessage("\tLoading...");
        pdLoading.setCancelable(false);
        pdLoading.show();
    }

    @Override
    protected String doInBackground(Void... params) {
        try {
            URL url = new URL("http://songo.eu.pn/db_GetFromSongs.php");
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();
            InputStream inputStream = urlConnection.getInputStream();
            StringBuffer buffer = new StringBuffer();
            reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }

            resultJson = buffer.toString();

        } catch (Exception e) {
            e.printStackTrace();
        }
        return resultJson;
    }

    @Override
    protected void onPostExecute(String strJson) {
        super.onPostExecute(strJson);
        List<DataSongs> data = new ArrayList<>();
        JSONObject dataJsonObj = null;

        try {
            dataJsonObj = new JSONObject(strJson);
            JSONArray songs = dataJsonObj.getJSONArray("Songs");
            DataSongs songData = new DataSongs();
            for (int i = 0; i < songs.length(); i++) {
                JSONObject song = songs.getJSONObject(i);
                songData.songName = song.getString("song");
                songData.songGenreID = song.getString("GenreID");
                songData.songUserID = song.getString("UserID");
                data.add(songData);
                Log.e("songo", "SongName: " + data.get(i).songName);
            }

            mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
            mAdapter = new RecyclerAdapter(MainActivity.this, data, mRecyclerView);
            mRecyclerView.setHasFixedSize(true);
            mLayoutManager = new LinearLayoutManager(MainActivity.this);
            mRecyclerView.setAdapter(mAdapter);
            mRecyclerView.setLayoutManager(mLayoutManager);

        } catch (JSONException e) {
            e.printStackTrace();
        }

        pdLoading.dismiss();
    }
}

RecyclerAdapter.java

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {

private Context context;
private LayoutInflater inflater;
List<DataSongs> data = Collections.emptyList();

public RecyclerAdapter(Context context, List<DataSongs> data, RecyclerView recyclerView) {
    this.context = context;
    inflater = LayoutInflater.from(context);
    this.data = data;
    this.recyclerView = recyclerView;
}

class ViewHolder extends RecyclerView.ViewHolder{

    TextView tv_songName;
    TextView tv_songGenreID;
    TextView tv_songUserID;

    public ViewHolder(View itemView) {
        super(itemView);
        tv_songName = (TextView) itemView.findViewById(R.id.tv_songName);
        tv_songGenreID = (TextView) itemView.findViewById(R.id.tv_songGenreID);
        tv_songUserID = (TextView) itemView.findViewById(R.id.tv_songUserID);
    }
}

// Создает новые views (вызывается layout manager-ом)
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View v=inflater.inflate(R.layout.recycler_item, parent,false);
    return new ViewHolder(v);
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    DataSongs current = data.get(position);
    holder.tv_songName.setText(current.songName);
    holder.tv_songGenreID.setText(current.songGenreID);
    holder.tv_songUserID.setText(current.songUserID);
    Log.e("songo", "SongName: " + data.get(position).songName);        
}

@Override
public int getItemCount() {
    return data.size();
}

来自MainActivity的日志按原样显示信息（无相等的行）。

RecyclerAdapter的日志显示每个songName都相同。

Answer 1

您每次迭代都覆盖相同的DataSongs实例。

        DataSongs songData = new DataSongs();
        for (int i = 0; i < songs.length(); i++) {
            JSONObject song = songs.getJSONObject(i);
            songData.songName = song.getString("song");
            songData.songGenreID = song.getString("GenreID");
            songData.songUserID = song.getString("UserID");
            data.add(songData);
            Log.e("songo", "SongName: " + data.get(i).songName);
        }

请注意， new关键字仅被调用一次。
产生的列表将多次包含相同的对象，并且其属性设置为列表中的最后一首歌曲。

只需在循环内移动songData的创建

        for (int i = 0; i < songs.length(); i++) {
            JSONObject song = songs.getJSONObject(i);

            DataSongs songData = new DataSongs();
            songData.songName = song.getString("song");
            songData.songGenreID = song.getString("GenreID");
            songData.songUserID = song.getString("UserID");
            data.add(songData);
            Log.e("songo", "SongName: " + data.get(i).songName);
        }

Answer 2

        dataJsonObj = new JSONObject(strJson);
        JSONArray songs = dataJsonObj.getJSONArray("Songs");
        DataSongs songData = new DataSongs();
        for (int i = 0; i < songs.length(); i++) {
            JSONObject song = songs.getJSONObject(i);
            songData.songName = song.getString("song");
            songData.songGenreID = song.getString("GenreID");
            songData.songUserID = song.getString("UserID");
            data.add(songData);
            Log.e("songo", "SongName: " + data.get(i).songName);
        }

问题不在于RecyclerView相关，而在于创建对象.DataSongs对象仅创建一次，每次从JSON数组接收数据时都必须创建它。因此，在for循环内部创建它：

        dataJsonObj = new JSONObject(strJson);
        JSONArray songs = dataJsonObj.getJSONArray("Songs");

        for (int i = 0; i < songs.length(); i++) {
            JSONObject song = songs.getJSONObject(i);
            DataSongs songData = new DataSongs();
            songData.songName = song.getString("song");
            songData.songGenreID = song.getString("GenreID");
            songData.songUserID = song.getString("UserID");
            data.add(songData);
            Log.e("songo", "SongName: " + data.get(i).songName);
        }

Answer 3

DataSongs songData = new DataSongs(); 

for循环中的这一行代码每次都需要创建一个新的json对象来解决此问题

Answer 4

尝试这个

 try {
        dataJsonObj = new JSONObject(strJson);
        JSONArray songs = dataJsonObj.getJSONArray("Songs");
        DataSongs songData = null;
        for (int i = 0; i < songs.length(); i++) {
            songData = new DataSongs();
            JSONObject song = songs.getJSONObject(i);
            songData.songName = song.getString("song");
            songData.songGenreID = song.getString("GenreID");
            songData.songUserID = song.getString("UserID");
            data.add(songData);
            Log.e("songo", "SongName: " + data.get(i).songName);
        }

        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
        mAdapter = new RecyclerAdapter(MainActivity.this, data, mRecyclerView);
        mRecyclerView.setHasFixedSize(true);
        mLayoutManager = new LinearLayoutManager(MainActivity.this);
        mRecyclerView.setAdapter(mAdapter);
        mRecyclerView.setLayoutManager(mLayoutManager);

    } catch (JSONException e) {
        e.printStackTrace();
    }

Answer 5

您正在循环外创建对象，因此，仅创建了一个对象

public class MainActivity extends AppCompatActivity {
        RecyclerView mRecyclerView;
        private RecyclerView.Adapter mAdapter;
        private RecyclerView.LayoutManager mLayoutManager;

        protected void onCreate(Bundle savedInstanceState) {
            setTheme(R.style.AppTheme);
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main_layout);
            new parseTask().execute();
        }

        private class parseTask extends AsyncTask<Void, Void, String> {

            HttpURLConnection urlConnection = null;
            BufferedReader reader = null;
            String resultJson = "";
            ProgressDialog pdLoading = new ProgressDialog(MainActivity.this, R.style.MyDialogStyle);

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                pdLoading.setMessage("\tLoading...");
                pdLoading.setCancelable(false);
                pdLoading.show();
            }

            @Override
            protected String doInBackground(Void... params) {
                try {
                    URL url = new URL("http://songo.eu.pn/db_GetFromSongs.php");
                    urlConnection = (HttpURLConnection) url.openConnection();
                    urlConnection.setRequestMethod("GET");
                    urlConnection.connect();
                    InputStream inputStream = urlConnection.getInputStream();
                    StringBuffer buffer = new StringBuffer();
                    reader = new BufferedReader(new InputStreamReader(inputStream));

                    String line;
                    while ((line = reader.readLine()) != null) {
                        buffer.append(line);
                    }

                    resultJson = buffer.toString();

                } catch (Exception e) {
                    e.printStackTrace();
                }
                return resultJson;
            }

            @Override
            protected void onPostExecute(String strJson) {
                super.onPostExecute(strJson);
                List<DataSongs> data = new ArrayList<>();
                JSONObject dataJsonObj = null;

                try {
                    dataJsonObj = new JSONObject(strJson);
                    JSONArray songs = dataJsonObj.getJSONArray("Songs");

                    for (int i = 0; i < songs.length(); i++) {
                        JSONObject song = songs.getJSONObject(i);
                        /**
                         * you were wrong here
                         */
                        DataSongs songData = new DataSongs();

                        songData.songName = song.getString("song");
                        songData.songGenreID = song.getString("GenreID");
                        songData.songUserID = song.getString("UserID");
                        data.add(songData);
                        Log.e("songo", "SongName: " + data.get(i).songName);
                    }

                    mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
                    mAdapter = new RecyclerAdapter(MainActivity.this, data, mRecyclerView);
                    mRecyclerView.setHasFixedSize(true);
                    mLayoutManager = new LinearLayoutManager(MainActivity.this);
                    mRecyclerView.setAdapter(mAdapter);
                    mRecyclerView.setLayoutManager(mLayoutManager);

                } catch (JSONException e) {
                    e.printStackTrace();
                }

                pdLoading.dismiss();
            }
        }