Android OnTouchEvent（）中的错误

我正在尝试在android中实现不同的手势。textView2的文本将根据调用的手势进行更改，但我在OnTouchEvent（）的最后一个方法中遇到错误。请帮助。提前感谢

public class MainActivity extends
AppCompatActivity implements GestureDetector.OnGestureListener ,  
GestureDetector.OnDoubleTapListener {

private TextView t;
private GestureDetectorCompat gd;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    t=(TextView)findViewById(R.id.textView2);
    this.gd=new GestureDetectorCompat(this,this);
    gd.setOnDoubleTapListener(this);
}

@Override
public boolean onDown(MotionEvent e) {
    t.setText("on down");
    return true;
}

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
    t.setText("on Fling");
    return true;
}

@Override
public void onLongPress(MotionEvent e) {
    t.setText("on long press");

}

@Override
public void onShowPress(MotionEvent e) {
    t.setText("on show press");
}

@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
    t.setText("on scroll");
    return true;
}

@Override
public boolean onSingleTapUp(MotionEvent e) {
    t.setText("on single tap");
    return true;
}

@Override
public boolean onDoubleTap(MotionEvent e) {
    t.setText("on double tap");
    return true;
}

@Override
public boolean onDoubleTapEvent(MotionEvent e) {
    t.setText("on double tap event");
    return true;
}

@Override
public boolean onSingleTapConfirmed(MotionEvent e) {
    t.setText("on single tap confirmed");
    return true;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    this.gestureDetector.OnTouchEvent(event);
    return true;
}

---

您遇到了什么错误？无法解析gestureDetector在您的类中没有gestureDetector字段，因此编译失败。我是Android新手，请您详细解释或修复该错误。我将非常感谢您，您遇到了什么错误？无法解决gestureDetector在您的类中没有gestureDetector字段，因此编译失败。我是Android新手，请您详细解释或为我修复该错误。我会感谢你的