安卓:如何选择RotateAnimation的旋转方向？

Question

我目前正在开发一个应用程序，在该应用程序中，我想用箭头指示路径(它的工作方式类似于指南针)。

为了将箭头移动到正确的方向，我使用了RotateAnimation类。它工作得很好，但当初始度数位置远离最终度数位置时，旋转不会选择更快的方式。

在此视频中，您可以看到行为：https://youtu.be/vypZni

下面是用户单击按钮"02“时执行的代码：

RotateAnimation rotateAnimation = new RotateAnimation(355f, 8f, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
rotateAnimation.setInterpolator(new LinearInterpolator());
rotateAnimation.setDuration(3000);
rotateAnimation.setFillAfter(true);
test.startAnimation(rotateAnimation);

下面是当用户点击按钮"03“时执行的代码：

RotateAnimation rotateAnimation = new RotateAnimation(8f, 350f, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
rotateAnimation.setInterpolator(new LinearInterpolator());
rotateAnimation.setDuration(3000);
rotateAnimation.setFillAfter(true);
test.startAnimation(rotateAnimation);

正如您在视频中看到的，旋转并不选择更快的方式。在第一个动画中，更快的方法是顺时针旋转(但系统选择逆时针旋转)，在第二个动画中，更快的方法是逆时针旋转(但系统选择顺时针旋转)。

是否有解决方案或技巧来迫使系统选择更快的方式，以便从点A旋转到点B？

Answer 1

如果参数toDegrees大于参数fromDegrees，则RotationAnimation对象将顺时针旋转。实际上，你不想从355f转到8f，而是从355f转到368f ( 360度加8度)。

因此，在这里，您将更改您的两段代码，如下所示：

RotateAnimation rotateAnimation = new RotateAnimation(355f, 368f, 
Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
rotateAnimation.setInterpolator(new LinearInterpolator());
rotateAnimation.setDuration(3000);
rotateAnimation.setFillAfter(true);
test.startAnimation(rotateAnimation);

和

RotateAnimation rotateAnimation = new RotateAnimation(368f, 350f, 
Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
rotateAnimation.setInterpolator(new LinearInterpolator());
rotateAnimation.setDuration(3000);
rotateAnimation.setFillAfter(true);
test.startAnimation(rotateAnimation);

但我建议您，如果您愿意使用14+接口创建一个应用程序来使用View的animate()方法，如下所示：

test.animate()
  .rotationBy(13f)
  .setDuration(3000)
  .setInterpolator(new LinearInterpolator())
  .start();

rotationBy(offset)方法将使用中心枢轴将视图旋转offset度，如果偏移为正数，则顺时针旋转，否则为逆时针旋转。

Answer 2

+1 @MaximeClaude的答案可以大大缩短：

//declarations
private static final int HALF_CIRCLE = 180;
private static final int WHOLE_CIRCLE = 360;
private float currentAzimuth = 0f;

public void rotate(float rotationDegrees, View... views) {
    float from = currentAzimuth;
    float to = rotationDegrees;
    float min = Math.min(from, to);
    if (Maths.abs(to - from) > HALF_CIRCLE) {
        if (min == from) {
            from += WHOLE_CIRCLE;
        } else {
            to += WHOLE_CIRCLE;
        }
    }
    currentAzimuth = rotationDegrees;

    Animation anim = new RotateAnimation(from, to, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
    anim.setFillAfter(true); //make the arrow stay at its destination (after rotation)
    anim.setDuration(200);
    for (View view : views) {
        view.startAnimation(anim);
    }
}

并使用android.view.OrientationEventListener设置视图方向：

mOrientationEventListener = new OrientationEventListener(context) {
    @Override
    public void onOrientationChanged(int orientation) {
        rotate(orientation, arrowView);
    }
};

Answer 3

对于后来询问的人，这是一个普遍的案例，灵感来自@David Fournier的答案：

//declarations
    private static final int HALF_CIRCLE = 180;
    private static final int WHOLE_CIRCLE = 360;
    private float azimuth = 0f;
    private float currenttAzimuth = 0f;

    /**
     * "will set rotation from " + currentAzimuth + " to " + azimuth
     */
    public void rotate(Double bearing){
        if(bearing != null) {
            azimuth  = (float)bearing.doubleValue();
            float min = Math.min(azimuth,currenttAzimuth);

            float tempAzimuth = 0.0f;
            float tempCurrentAzimuth = 0.0f;

            Animation rotateAnim = null;
            if(Math.abs(azimuth - currenttAzimuth) > HALF_CIRCLE) {
                if(min == currenttAzimuth) {
                    tempCurrentAzimuth = currenttAzimuth + WHOLE_CIRCLE;
                    tempAzimuth = azimuth;
                }
                else {
                    tempCurrentAzimuth = currenttAzimuth ;
                    tempAzimuth = azimuth + WHOLE_CIRCLE;
                }
                rotateAnim = new RotateAnimation(tempCurrentAzimuth, tempAzimuth,
                    Animation.RELATIVE_TO_SELF, 0.5f,
                    Animation.RELATIVE_TO_SELF, 0.5f);
            }
            else {
                rotateAnim = new RotateAnimation(currenttAzimuth, azimuth,
                    Animation.RELATIVE_TO_SELF, 0.5f,
                    Animation.RELATIVE_TO_SELF, 0.5f);
            }
            currenttAzimuth = azimuth;
            rotateAnim.setFillAfter(true); //make the arrow stay at its destination (after rotation)
            rotateAnim.setDuration(500);
            arrowView.startAnimation(rotateAnim);
        }
    }