Question

问题：：我试图将我的mediaplayer方法（位于适配器内部）合并到我的片段（我想在其中放置我的mediaplayer对象）。
为什么？-因为我希望适配器不包含任何方法/逻辑。它应该仅膨胀视图，而不能增加其他任何内容。

我试图将我的MediaPlayer方法（位于适配器内部）移到片段中，但是当我尝试在片段（应该播放并停止播放歌曲）中找到playB和stopB时，它给了我nullException。我查看了我的XML文件（我的playB + stopB ID所在的位置），一切正常。

我的适配器：

public class ListViewAdapter extends BaseAdapter {

//Create variables
MediaPlayer mediaPlayer;
Song currentSong;
int layout;
ArrayList<Song> arrayList;
Context context;

//Constructor
public ListViewAdapter(int layout, ArrayList<Song> arrayList, Context context) {
    this.layout = layout;
    this.arrayList = arrayList;
    this.context = context;
}

//ViewHolder class holding my views
private class Viewholder {
    TextView artistTxt, songNameTxt;
    ImageView playB, stopB;
    CircleImageView artistImg;
}

@Override
public int getCount() {
    return arrayList.size();
}

@Override
public Object getItem(int position) {
    return null;
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public View getView(int position, View view, ViewGroup parent) {

    //Create viewholder variable
    final Viewholder viewholder;

    //Check if view is null
    if (view == null) {

        //Create new ViewHolder object
        viewholder = new Viewholder();

        //Inflate my view
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = layoutInflater.inflate(R.layout.listview_customlayout, null);

        //Find my view id's
        viewholder.artistImg = view.findViewById(R.id.artistImgBackgroundDetail);
        viewholder.artistTxt = view.findViewById(R.id.artistTxt);
        viewholder.songNameTxt = view.findViewById(R.id.songNameTxt);
        viewholder.playB = view.findViewById(R.id.playB);
        viewholder.stopB = view.findViewById(R.id.stopB);

        //Set my view to viewholder
        view.setTag(viewholder);
    } else {
        viewholder = (Viewholder) view.getTag();
    }

    //Assign song to my arraylist
    final Song song = arrayList.get(position);

    //Set my views to their resources
    viewholder.artistImg.setImageResource(song.getArtistImg());
    viewholder.artistTxt.setText(song.getArtist());
    viewholder.songNameTxt.setText(song.getSongName());

    return view;

如您所见-非常简单的适配器，我可以在其中修改自定义列表视图。

这是我的片段类，我无法找到视图ID：**

MediaPlayer mediaPlayer;
Song currentSong;
int position;
ImageView playB, stopB;

@Nullable
@Override
public View onCreateView(@NonNull final LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_main, container, false);

    //Actionbar
    ((AppCompatActivity) getActivity()).getSupportActionBar().setTitle("Song list");

    //Find my listview
    songListView = view.findViewById(R.id.songListView);
    playB = getActivity().findViewById(R.id.playB);
    stopB = getActivity().findViewById(R.id.stopB);

    //create a new arraylist object
    arrayList = new ArrayList<>();


    adapter = new ListViewAdapter(R.layout.listview_customlayout, arrayList, getActivity());

    //Set my listview to my custom adapter
    songListView.setAdapter(adapter);

    //Click on a specific song from my list
    songListView.setOnItemClickListener(new ListViewClickListener());


    final Song song = arrayList.get(position);


    //get all songs
    mediaPlayer = MediaPlayer.create(getActivity(), song.getSong());

    //Play button click performed
    playB.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {


            //Checks if my current song is null and creates a new song
            if (currentSong == null) {
                mediaPlayer = MediaPlayer.create(getActivity(), song.getSong());
            }

            //if mediaplayer is not null and my current song is not equal to the new song i clicked on
            if (mediaPlayer != null && currentSong != song) {

                //resets the mediaplayer and creates a new song from the position in the list
                mediaPlayer.reset();

                mediaPlayer = MediaPlayer.create(getActivity(), song.getSong());
                playB.setImageResource(R.drawable.play_orange);

                mediaPlayer.start();
                playB.setImageResource(R.drawable.pause_orange);
            } else {
                mediaPlayer.pause();
                playB.setImageResource(R.drawable.play_orange);
            }

            //check if current song is null or the newly clicked song is equal to my current song
            //if true then assign the newly clicked song as my CURRENT one
            //--so it doesnt play the same song for every single one
            if (currentSong == null || song != currentSong) {
                currentSong = song;
            }
        }
    });

    //Stop song when click performed
    stopB.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //stops my current song and make it null
            if (currentSong != null) {
                mediaPlayer.stop();
                mediaPlayer.release();

                currentSong = null;
                playB.setImageResource(R.drawable.play_orange);
            }
        }
    });


    //return my view
    return view;

我想让我的ListViewAdapter只能使视图膨胀，这意味着我不得包含功能。

任何建议都会被我视为要尽力而为：）

如果您需要其他信息，请告诉我。我会很乐意尽力弄清楚。

谢谢。

Answer 1

只需尝试一下建立界面

ClickUpdate.java

public interface ClickUpdate {
    void getClicks();
}

内部

ListViewAdapter.java

public static ClickUpdate clickupadte;
public static void setonConnectionListener(ClickUpdate clicklisten) {
            ListViewAdapter.clickupadte = clicklisten
        }

也可以在listviewadapter中单击stopB

viewholder.stopB.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                clickupadte.getClicks();
            }
        });

然后在里面

片段类内部oncreateview初始化

ListViewAdapter.setonConnectionListener(this);

还实现了ClickUpdate，然后在片段类内部生成了一个名为getClicks的覆盖方法，我认为在该方法中给出

 if (currentSong != null) {
            mediaPlayer.stop();
            mediaPlayer.release();

            currentSong = null;
            //playB.setImageResource(R.drawable.play_orange);//this will  cause null point error,if occured to avoid the error pass viewholder.playB inside clickupadte.getClicks(); function
        }

Answer 2

在MVVM模式中，应该将适配器与视图而不是视图模型关联。因此，您可能要做的是使适配器成为片段类的内部类。如果您具有mediaPlayer全局变量，则可以在适配器和片段中使用它的相同实例（如果要查找的话）。

希望这会有所帮助！

将逻辑从适配器移动到片段-错误：找不到视图ID

2 个答案: