java.lang.NullPointerException-应用程序不断崩溃

我试图从另一个类访问自定义arraylist的内容，以便在版面上显示文本和图像。没有生成错误，但是当我尝试从列表中打开布局时，我的应用程序崩溃。我只能通过Android studio中的日志猫访问错误

我的活动

public class PlayingActivity extends AppCompatActivity {

    private Song songs;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_playing);

        // Find the image view in the activity_playing.xml layout with the ID playing_album_art_img_view.
        ImageView imageView = findViewById(R.id.playing_album_art_img_view);
        // Get the Album art from the currentSong object and set this text on
        // the song ImageView
        imageView.setImageResource(songs.getAlbumArt());

        // Find the TextView in the activity_playing.xml layout with the ID playing_artiste_text_view.
        TextView pArtisteTextView = findViewById(R.id.playing_artiste_text_view);
        // Get the Artiste from the currentSong object and set this text on
        // the Artiste TextView.
        pArtisteTextView.setText(songs.getArtiste());

        // Find the TextView in the activity_playing.xml layout with the ID playing_song_text_view.
        TextView pSongTitleTextView = findViewById(R.id.playing_song_text_view);
        // Get the song title from the currentSong object and set this text on
        // the song title TextView.
        pSongTitleTextView.setText(songs.getSongTitle());

    }

` 我的歌曲课

public class Song extends ArrayList<Song> {

/** Song title */
private String mSongTitle;

/** Artiste's name */
private String mArtiste;

和我的listView的SongAdapter

  public SongAdapter(Context context, ArrayList<Song> songs) {
    super(context, 0, songs);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // Check if an existing view is being reused, otherwise inflate the view
    View listItemView = convertView;
    if (listItemView == null) {
        listItemView = LayoutInflater.from(getContext()).inflate(
                R.layout.song_item, parent, false);
    }

    // Get the {@link Song} object located at this position in the list
    Song currentSong = getItem(position);

    // Find the TextView in the song_item.xml layout with the ID artiste_text_view.
    TextView artisteTextView = listItemView.findViewById(R.id.artiste_text_view);
    // Get the Artiste from the currentSong object and set this text on
    // the Artiste TextView.
    artisteTextView.setText(currentSong.getArtiste());

    // Find the TextView in the song_item.xml layout with the ID song_title_text_view.
    TextView songTitleTextView = listItemView.findViewById(R.id.song_title_text_view);
    // Get the song title from the currentSong object and set this text on
    // the song title TextView.
    songTitleTextView.setText(currentSong.getSongTitle());

    // Find the ImageView in the song_item.xml layout with the ID playing_album_art_img_view.
    ImageView songAlbumArtImageView = listItemView.findViewById(R.id.playing_album_art_img_view);
    // Get the song album art from the currentSong object and set this text on
    // the song album art ImageView.
    songAlbumArtImageView.setImageResource(currentSong.getAlbumArt());

    // Return the whole list item layout (containing 2 TextViews) so that it can be shown in
    // the ListView.
    return listItemView;
}

---

您的这条线路有故障：

ImageView songAlbumArtImageView = listItemView.findViewById(R.id.playing_album_art_img_view); // May be id is wrong.

songAlbumArtImageView.setImageResource(currentSong.getAlbumArt()); // So it's crashing here.

---

对于代码中的所有注释，我会给你+1：DAdd你的

song_项目

code..song_项目使用Arrayadapter填充列表视图谢谢你的回复。。即使在我删除了与ImageView相关的所有内容之后，我也会收到与TextView相同的错误，如下所示：您可以发布您的

R.layout.song\u项目

xml文件吗？有两种可能是您正在获取的ID错误，否则您的

currentSong

对象为空。我已添加了我的song\u项目布局文件，但我认为这与我的currentSong有关。通过删除我的问题的ImageView实现，我避开了NPE，但是对于其他遇到类似问题的人。。更好的方法是在我的word类中添加一个新的构造函数，该构造函数将处理带有图像的视图，以避免没有图像的视图导致错误

<LinearLayout 
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="16dp">

     <TextView
        android:id="@+id/song_title_text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        tools:text="Ada" />

    <TextView
        android:id="@+id/artiste_text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        tools:text="Flavour" />

Process: com.example.android.musicalstructureapp, PID: 30680
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
    at com.example.android.musicalstructureapp.SongAdapter.getView(SongAdapter.java:58)
    at android.widget.AbsListView.obtainView(AbsListView.java:2491)

ImageView songAlbumArtImageView = listItemView.findViewById(R.id.playing_album_art_img_view); // May be id is wrong.

songAlbumArtImageView.setImageResource(currentSong.getAlbumArt()); // So it's crashing here.