设计一个旋转thumb

 效果：

<SeekBar
       android:id="@+id/seekbar"
       android:layout_width="200dp"
       android:layout_height="30dp"
       android:thumb="@drawable/thumb"
       android:progressDrawable="@drawable/seekbar"
       app:layout_constraintBottom_toBottomOf="parent"
       app:layout_constraintTop_toTopOf="parent"
       app:layout_constraintStart_toStartOf="parent"
       android:max="100"
       android:progress="50"/>

public class MainActivity extends AppCompatActivity {
    SeekBar seekBar;
    private RotateDrawable mRotateThumbDrawable;
    ObjectAnimator  thumbAnimator;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRotateThumbDrawable = (RotateDrawable) AppCompatResources.getDrawable(getApplicationContext(), R.drawable.rotationanimation);
        seekBar = findViewById(R.id.seekbar);
        startRotation();
    }

    public void startRotation() {
        seekBar.setThumb(mRotateThumbDrawable);
        thumbAnimator = ObjectAnimator.ofInt(mRotateThumbDrawable,"level", 0, 10000);

        // 设置动画时长
        thumbAnimator.setDuration(400);
        // 设置重复次数和行为
        thumbAnimator.setRepeatCount(ValueAnimator.INFINITE);
        thumbAnimator.setInterpolator(new LinearInterpolator());
        // 启动动画
        thumbAnimator.start();
    }

    public void stopRotation() {
        if (thumbAnimator != null) {
            thumbAnimator.cancel();
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        stopRotation();
    }
}

//rotationanimation.xml
<?xml version="1.0" encoding="utf-8"?>
<rotate xmlns:android="http://schemas.android.com/apk/res/android"
    android:zAdjustment = "normal"
    android:duration="5000"
    android:drawable="@drawable/thumb"
    android:repeatMode="reverse"
    android:repeatCount="infinite"
    android:fromDegrees="0"
    android:toDegrees="360" />

动画应该在子线程做比较好，这里只为了实现效果，偷个懒~