如何围绕圆圈为视图设置动画？

Question

我想将一个无限移动动画围绕一个圆圈设置为View，如下图所示。我该如何实现？

此视图可能是TextView 或任何简单或复杂的视图。

我知道我可以将视图放在ViewGroup 中并设置旋转动画，但我不想旋转视图，因为视图的方向很重要。

Answer 1

我不知道有什么本机可以做到这一点，所以我认为你最好的方法是确定你的动画路径（xy 坐标）并创建一个Handler 到重复postDelayed。您的处理程序触发的每次迭代都只会translate 视图到路径中的下一个点。

编辑：我已经创建了一个解决方案，并通过左右移动和绕圈移动对其进行了测试。

ViewPathAnimator.java：

import android.graphics.Path;
import android.graphics.PathMeasure;
import android.os.Handler;
import android.util.Pair;
import android.view.View;

import java.lang.ref.WeakReference;
import java.util.HashMap;

public class ViewPathAnimator
{
    public static final int DEFAULT_DELAY     = 1000 / 10;
    public static final int DEFAULT_FRAMESKIP = 3;

    private static Handler                        handler;
    private static HashMap<Integer, PathRunnable> animatedViews;

    public static void animate(View view, Path path)
    {
        animate(view, path, DEFAULT_DELAY, DEFAULT_FRAMESKIP);
    }

    public static void animate(View view, Path path, int delay)
    {
        animate(view, path, delay, DEFAULT_FRAMESKIP);
    }

    public static void animate(View view, Path path, int delay, int frameSkip)
    {
        if (animatedViews == null)
        {
            animatedViews = new HashMap<>();
        }

        if (handler == null)
        {
            handler = new Handler();
        }

        if (animatedViews.containsKey(view.hashCode()))
        {
            cancel(view);
        }

        PathRunnable runnable = new PathRunnable(view, path, delay, frameSkip);
        animatedViews.put(view.hashCode(), runnable);
        handler.postDelayed(runnable, delay);
    }

    public static void cancel(View view)
    {
        if (animatedViews != null && handler != null)
        {
            PathRunnable task = animatedViews.get(view.hashCode());
            if (task != null)
            {
                handler.removeCallbacks(task);
                animatedViews.remove(view.hashCode());
            }
        }
    }

    private static class PathRunnable implements Runnable
    {
        private WeakReference<View> view;
        Pair<Float, Float>[] points;
        private int delay;
        private int frameSkip;
        private int frame;

        PathRunnable(View view, Path path, int delay, int frameSkip)
        {
            this.view = new WeakReference<>(view);
            this.points = getPoints(path);
            this.delay = delay;
            this.frameSkip = Math.max(frameSkip, 0);
            this.frame = 0;
        }

        @Override
        public void run()
        {
            frame = (frame + frameSkip + 1) % points.length;
            Pair<Float, Float> pair = points[frame];

            View v = view.get();
            if (v != null)
            {
                v.setTranslationX(pair.first);
                v.setTranslationY(pair.second);

                handler.postDelayed(this, delay);
            }
        }

        // https://stackoverflow.com/questions/7972780/how-do-i-find-all-the-points-in-a-path-in-android
        private Pair<Float, Float>[] getPoints(Path path)
        {
            PathMeasure pathMeasure = new PathMeasure(path, true);
            int         frames      = (int) pathMeasure.getLength();

            Pair<Float, Float>[] pointArray   = new Pair[frames];
            float                length       = pathMeasure.getLength();
            float                distance     = 0f;
            float                speed        = length / pointArray.length;
            int                  counter      = 0;
            float[]              aCoordinates = new float[2];

            while ((distance < length) && (counter < pointArray.length))
            {
                // get point from the path
                pathMeasure.getPosTan(distance, aCoordinates, null);
                pointArray[counter] = new Pair<>(aCoordinates[0], aCoordinates[1]);
                counter++;
                distance = distance + speed;
            }

            return pointArray;
        }
    }
}

现在可以给它一个 Graphics 路径来制作动画，就像这样

View view = findViewById(R.id.text);
Path path = new Path();
path.addCircle(0, 0, 100, Path.Direction.CW);

ViewPathAnimator.animate(view, path, 1000/ 30, 2);

Answer 2

我提出的这个解决方案解决了这个问题，顺时针旋转视图容器，逆时针旋转TextView :)

布局：

<RelativeLayout
    android:id="@+id/cont"
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="150dp"
    android:animateLayoutChanges="true"
    android:clipChildren="false">

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:text="M"
        android:textSize="60sp"/>
</RelativeLayout>

动画：

    View v = findViewById(R.id.cont);
    View text = findViewById(R.id.text);

    int durationMillis = 10000;

    RotateAnimation r = new RotateAnimation(0, 360,
            Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
    r.setDuration(durationMillis);
    r.setInterpolator(new LinearInterpolator());
    r.setRepeatMode(Animation.RESTART);
    r.setRepeatCount(Animation.INFINITE);
    text.startAnimation(r);

    RotateAnimation rC = new RotateAnimation(360, 0,
            Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
    rC.setDuration(durationMillis);
    rC.setInterpolator(new LinearInterpolator());
    rC.setRepeatMode(Animation.RESTART);
    rC.setRepeatCount(Animation.INFINITE);
    v.startAnimation(rC);

但是如果您想在其他路径中移动对象并寻找通用解决方案，请查看@Kevin 的解决方案（感谢他）。

Answer 3

可能是ValueAnimator可以帮忙吗？根据它动画的进度，你可以计算你的路径坐标并将它设置到你的视图吗？