从类访问 Main活动到变量从其他类

Question

在Mainactive类中，我无法访问gamePanel变量或对象。在程序中稍后的其他类中，它运行良好。我遇到了以下错误：

java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=100, result=-1, data=Intent { act=inline-data (has extras) }} to activity {com.example.camerademo3/com.example.camerademo3.MainActivity}:
Attempt to read from field 'java.util.ArrayList com.example.camerademo3.GamePanel.images2' on a null object reference

类主要活动：

public class MainActivity extends Activity {
    GamePanel gamePanel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        //some code
        setContentView(new GamePanel(this));

        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        startActivityForResult(intent, 100);

        //some code
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        //some code

        if (requestCode == 100) {
            Bitmap captureImage = (Bitmap) data.getExtras().get("data");
            gamePanel.images.add(captureImage);  // no access here
        }

        //some code
    }
}

类游戏面板：

public class GamePanel extends SurfaceView implements SurfaceHolder.Callback {
    //some code

    protected ArrayList<Bitmap> images;

    public GamePanel(Context context) {
        super(context);
        images = new ArrayList<>();
    }

    //some code
}

Answer 1

你没有把你的游戏面板存放在任何地方。我想你想这样做

gamePanel = new GamePanel(this)
setContentView(gamePanel)

否则，当你引用gamePanel时，它将为空，因为你从未设置它。