Android ScrollView的顶部下拉和底部上拉回弹效果

/**
 * A Simple Rebound ScrollView
 * @author Denluoyia
 */
public class ReboundScrollView extends ScrollView{

  private boolean mEnableTopRebound = true;
  private boolean mEnableBottomRebound = true;
  private OnReboundEndListener mOnReboundEndListener;
  private View mContentView;
  private Rect mRect = new Rect();

  public ReboundScrollView(Context context) {
    super(context);
  }

  public ReboundScrollView(Context context, AttributeSet attrs) {
    super(context, attrs);
  }

  public ReboundScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
  }

  /** after inflating view, we can get the width and height of view */
  @Override
  protected void onFinishInflate() {
    super.onFinishInflate();
    mContentView = getChildAt(0);
  }

  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    super.onLayout(changed, l, t, r, b);
    if (mContentView == null) return;
    // to remember the location of mContentView
    mRect.set(mContentView.getLeft(), mContentView.getTop(), mContentView.getRight(), mContentView.getBottom());
  }

  public ReboundScrollView setOnReboundEndListener(OnReboundEndListener onReboundEndListener){
    this.mOnReboundEndListener = onReboundEndListener;
    return this;

  }

  public ReboundScrollView setEnableTopRebound(boolean enableTopRebound){
    this.mEnableTopRebound = enableTopRebound;
    return this;
  }

  public ReboundScrollView setEnableBottomRebound(boolean mEnableBottomRebound){
    this.mEnableBottomRebound = mEnableBottomRebound;
    return this;
  }

  private int lastY;
  private boolean rebound = false;
  private int reboundDirection = 0; //<0 表示下部回弹 >0 表示上部回弹 0表示不回弹

  @Override
  public boolean dispatchTouchEvent(MotionEvent ev) {
    if (mContentView == null){
      return super.dispatchTouchEvent(ev);
    }
    switch (ev.getAction()){
      case MotionEvent.ACTION_DOWN:
        lastY = (int) ev.getY();
        break;

      case MotionEvent.ACTION_MOVE:
        if (!isScrollToTop() && !isScrollToBottom()){
          lastY = (int) ev.getY();
          break;
        }
        //处于顶部或者底部
        int deltaY = (int) (ev.getY() - lastY);
        //deltaY > 0 下拉 deltaY < 0 上拉


        //disable top or bottom rebound
        if ((!mEnableTopRebound && deltaY > 0) || (!mEnableBottomRebound && deltaY < 0)){
          break;
        }

        int offset = (int) (deltaY * 0.48);
        mContentView.layout(mRect.left, mRect.top + offset, mRect.right, mRect.bottom + offset);
        rebound = true;
        break;

      case MotionEvent.ACTION_UP:
        if (!rebound) break;
        reboundDirection = mContentView.getTop() - mRect.top;
        TranslateAnimation animation = new TranslateAnimation(0, 0, mContentView.getTop(), mRect.top);
        animation.setDuration(300);
        animation.setAnimationListener(new Animation.AnimationListener() {
          @Override
          public void onAnimationStart(Animation animation) {

          }

          @Override
          public void onAnimationEnd(Animation animation) {
            if (mOnReboundEndListener != null){
              if (reboundDirection > 0){
                mOnReboundEndListener.onReboundTopComplete();
              }
              if (reboundDirection < 0){
                mOnReboundEndListener.onReboundBottomComplete();
              }
              reboundDirection = 0;
            }
          }

          @Override
          public void onAnimationRepeat(Animation animation) {

          }
        });
        mContentView.startAnimation(animation);
        mContentView.layout(mRect.left, mRect.top, mRect.right, mRect.bottom);
        rebound = false;
        break;
    }
    return super.dispatchTouchEvent(ev);
  }

  @Override
  public void setFillViewport(boolean fillViewport) {
    super.setFillViewport(true); //默认是填充ScrollView 或者再XML布局文件中设置fillViewport属性
  }

  /**
   * 判断当前ScrollView是否处于顶部
   */
  private boolean isScrollToTop(){
    return getScrollY() == 0;
  }

  /**
   * 判断当前ScrollView是否已滑到底部
   */
  private boolean isScrollToBottom(){
    return mContentView.getHeight() <= getHeight() + getScrollY();
  }

  /**
   * listener for top and bottom rebound
   * do your implement in the following methods
   */
  public interface OnReboundEndListener{

    void onReboundTopComplete();

    void onReboundBottomComplete();
  }
}

 public class TestActivity extends AppCompatActivity {

  private ReboundScrollView reboundScrollView;

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

    reboundScrollView = findViewById(R.id.reboundScrollView);
    //reboundScrollView.setEnableTopRebound(false);
    //reboundScrollView.setEnableBottomRebound(false);
    reboundScrollView.setOnReboundEndListener(new ReboundScrollView.OnReboundEndListener() {
      @Override
      public void onReboundTopComplete() {
        Toast.makeText(TestActivity.this, "顶部回弹", Toast.LENGTH_SHORT).show();
      }

      @Override
      public void onReboundBottomComplete() {
        Toast.makeText(TestActivity.this, "底部回弹", Toast.LENGTH_SHORT).show();
      }
    });
  }
}