Question

这个函数没有看到activity_listing_music.xml中的id我只想对我的音乐播放器做一个简单的列表视图活动但是java代码看不到来自xml的id 所以我希望有人可以帮忙 AAA 一个一个一个一个一个一个一个一个一个一个一个一个

这是代码：

package musync.demo_app;

<import is here>

public class ListingMusic extends AppCompatActivity {

    <useless code>
    public void doStuff() {
        listView = findViewById(R.id.list);
        arrayList = new ArrayList<>();
        getMusic();
        adapter = new ArrayAdapter<String>(this, android.R.simple_List_item_1, arrayList);
        listView.setAdapter(adapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                //music plater here
            }
        });
    }

    public void getMusic() {
        ContentResolver contentResolver = getContentResolver();
        Uri songUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        Cursor songCursor = contentResolver.query(songUri, null, null, null, null);

        if(songCursor != null && songCursor.moveToFirst()) {
            int songTitle = songCursor.getColumnIndex(MediaStore.Audio.Media.TITLE);
            int songArtist = songCursor.getColumnIndex(MediaStore.Audio.Media.ARTIST);

            do {
                String currentTitle = songCursor.getString(songTitle);
                String currentArtist = songCursor.getString(songArtist);
                arrayList.add(currentTitle + '\n' + currentArtist);
            } while(songCursor.moveToNext());
        }
    }


}

，这是xml：

    <?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="0dp"
    android:paddingTop="0dp"
    android:paddingRight="0dp"
    android:paddingLeft="0dp"
    tools:context="musync.demo_app.ListingMusic">

    <ListView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:dividerHeight="1dp"
        />
</android.support.constraint.ConstraintLayout>

Answer 1

你错过了你的onCreate（）？在java文件中添加onCreate函数，并在调用R.id.listview函数后输入setContentView()。

Answer 2

改变这个：

ListView listView = findViewById(R.id.list);

要：

ListView listView = (ListView) findViewById(R.id.list);

R.id.findViewById（）没有看到id

2 个答案: