Android：如何用一根手指旋转视图

Question

我需要旋转一个有一些按钮的视图。随着手指的移动，视图也应该相应地随着它的子视图旋转。

到目前为止，我已经实现了这一点：

private RelativeLayout mCircle;
private double mCurrAngle = 0;
private double mPrevAngle = 0;
int i = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mCircle = (RelativeLayout) findViewById(R.id.circle);
    mCircle.setOnTouchListener(this); // Your activity should implement
                                        // OnTouchListener
}

@Override
public boolean onTouch(View v, MotionEvent event) {
    final float xc = mCircle.getWidth() / 2;
    final float yc = mCircle.getHeight() / 2;

    final float x = event.getX();
    final float y = event.getY();

    switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN: {
        mCircle.clearAnimation();
        mCurrAngle = Math.toDegrees(Math.atan2(x - xc, yc - y));
        break;
    }
    case MotionEvent.ACTION_MOVE: {
        mPrevAngle = mCurrAngle;
        mCurrAngle = Math.toDegrees(Math.atan2(x - xc, yc - y));
        mCircle.setRotation((float) (mPrevAngle - mCurrAngle));         

        animate(mPrevAngle, mCurrAngle, 0);
        break;
    }
    case MotionEvent.ACTION_UP: {
        mPrevAngle = mCurrAngle = 0;
        break;
    }
    }

    return true;
}

private void animate(double fromDegrees, double toDegrees,
        long durationMillis) {
    final RotateAnimation rotate = new RotateAnimation((float) fromDegrees,
            (float) toDegrees, RotateAnimation.RELATIVE_TO_SELF, 0.5f,
            RotateAnimation.RELATIVE_TO_SELF, 0.5f);
    rotate.setDuration(durationMillis);
    rotate.setFillEnabled(true);
    rotate.setFillAfter(true);
    mCircle.startAnimation(rotate);
}

但它并不顺利，因此无法实施。

谢谢。

Answer 1

首先，不要使用动画，因为您想在手指移动时直接改变视图。

然后，对于计算，将 OnTouchListener 附加到要旋转的视图的父视图要容易得多，这样触摸事件的坐标就不会被旋转本身修改。

如果您有一个 ID 为“@+id/root”的父视图，则代码如下：

private RelativeLayout mRoot;
private RelativeLayout mCircle;
int i = 0;
float viewRotation;
double fingerRotation;
double newFingerRotation;

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

    mRoot = (RelativeLayout)findViewById(R.id.root);
     mCircle = (RelativeLayout) findViewById(R.id.circle);
     mRoot.setOnTouchListener(this);
}

@Override
public boolean onTouch(View v, MotionEvent event) {

    final float x = event.getX();
    final float y = event.getY();

    final float xc = mRoot.getWidth()/2;
    final float yc = mRoot.getHeight()/2;

    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            viewRotation = mCircle.getRotation();
            fingerRotation = Math.toDegrees(Math.atan2(x - xc, yc - y));
            break;
        case MotionEvent.ACTION_MOVE:
            newFingerRotation = Math.toDegrees(Math.atan2(x - xc, yc - y));
            mCircle.setRotation((float)(viewRotation + newFingerRotation - fingerRotation));
            break;
        case MotionEvent.ACTION_UP:
            fingerRotation = newFingerRotation = 0.0f;
            break;
    }

    return true;
}