Android自定义ViewGroup实现弹性滑动效果

时间：2022-06-25 23:07:19 编辑：袖梨来源：一聚教程网

自定义View实现一个弹性滑动的效果，供大家参考，具体内容如下

实现原理

onMeasure()中测量所有子View

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // 测量所有子View
  int count = getChildCount();
  for (int i = 0; i < count; i++) {
   View childView = getChildAt(i);
   measureChild(childView, widthMeasureSpec, heightMeasureSpec);
  }
  setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
 }

onLayout()中,将所有的子View按照位置依次往下排列

@Override
 protected void onLayout(boolean changed, int l, int t, int r, int b) {
  // 设置ViewGroup的高度,对所有子View进行排列
  int childCount = getChildCount();
  MarginLayoutParams params = (MarginLayoutParams) getLayoutParams();
  params.height = mScreenHeight * childCount;
  for (int i = 0; i < childCount; i++) {
   View childView = getChildAt(i);
   if (childView.getVisibility() != View.GONE) {
    // 给每个ChildView放置在指定位置
    childView.layout(l, i * mScreenHeight, r, (i + 1) * mScreenHeight);
   }
  }
 }

onTouchEvent()中处理滑动

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  switch (event.getAction()) {
   case MotionEvent.ACTION_DOWN:
    mLastY = (int) event.getY();
    mStart = getScrollY();
    return true;
   case MotionEvent.ACTION_MOVE:
    if (!mScroller.isFinished()) {
     // 终止滑动
     mScroller.abortAnimation();
    }
    int offsetY = (int) (mLastY - event.getY());
    Log.d(TAG, "onTouchEvent: getScrollY: " + getScrollY());
    Log.d(TAG, "onTouchEvent: offsetY " + offsetY);
    // 到达顶部,使用offset判断方向
    if (getScrollY() + offsetY < 0) { // 当前已经滑动的 Y 位置
     offsetY = 0;
    }
    // 到达底部
    if (getScrollY() > getHeight() - mScreenHeight && offsetY > 0) {
     offsetY = 0;
    }
    scrollBy(0, offsetY);
    // 滑动完成后,重新设置LastY位置
    mLastY = (int) event.getY();
    break;
   case MotionEvent.ACTION_UP:
    mEnd = getScrollY();
    int distance = mEnd - mStart;
    if (distance > 0) { // 向上滑动
     if (distance < mScreenHeight / 3) {
      Log.d(TAG, "onTouchEvent: distance < screen/3");
      // 回到原来位置
      mScroller.startScroll(0, getScrollY(), 0, -distance);
     } else {
      // 滚到屏幕的剩余位置
      mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - distance);
     }
    } else {    // 向下滑动
     if (-distance < mScreenHeight / 3) {
      mScroller.startScroll(0, getScrollY(), 0, -distance);
     } else {
      mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - distance);
     }
    }
    postInvalidate();
  }
  return super.onTouchEvent(event);
 }

其中ACTION_UP这段代码是处理弹性滑动的

case MotionEvent.ACTION_UP:
    mEnd = getScrollY();
    int distance = mEnd - mStart;
    if (distance > 0) { // 向上滑动
     if (distance < mScreenHeight / 3) {
      Log.d(TAG, "onTouchEvent: distance < screen/3");
      // 回到原来位置
      mScroller.startScroll(0, getScrollY(), 0, -distance);
     } else {
      // 滚到屏幕的剩余位置
      mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - distance);
     }
    } else {    // 向下滑动
     if (-distance < mScreenHeight / 3) {
      mScroller.startScroll(0, getScrollY(), 0, -distance);
     } else {
      mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - distance);
     }
    }
    postInvalidate();

完整代码

public class ScrollViewGroup extends ViewGroup {

 private static final String TAG = "ScrollView";

 private Scroller mScroller;
 private int mScreenHeight; // 窗口高度
 private int mLastY;
 private int mStart;
 private int mEnd;

 public ScrollViewGroup(Context context) {
  this(context, null);
 }

 public ScrollViewGroup(Context context, AttributeSet attrs) {
  this(context, attrs, 0);
 }

 public ScrollViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  mScroller = new Scroller(context);
  // 获取屏幕高度
  WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
  DisplayMetrics metrics = new DisplayMetrics();
  windowManager.getDefaultDisplay().getMetrics(metrics);
  mScreenHeight = metrics.heightPixels;
  Log.d(TAG, "ScrollViewGroup: ScreenHeight " + mScreenHeight);
 }


 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // 测量所有子View
  int count = getChildCount();
  for (int i = 0; i < count; i++) {
   View childView = getChildAt(i);
   measureChild(childView, widthMeasureSpec, heightMeasureSpec);
  }
  setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
 }

 @Override
 protected void onLayout(boolean changed, int l, int t, int r, int b) {
  // 设置ViewGroup的高度,对所有子View进行排列
  int childCount = getChildCount();
  MarginLayoutParams params = (MarginLayoutParams) getLayoutParams();
  params.height = mScreenHeight * childCount;
  for (int i = 0; i < childCount; i++) {
   View childView = getChildAt(i);
   if (childView.getVisibility() != View.GONE) {
    // 给每个ChildView放置在指定位置
    childView.layout(l, i * mScreenHeight, r, (i + 1) * mScreenHeight);
   }
  }
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  switch (event.getAction()) {
   case MotionEvent.ACTION_DOWN:
    mLastY = (int) event.getY();
    mStart = getScrollY();
    return true;
   case MotionEvent.ACTION_MOVE:
    if (!mScroller.isFinished()) {
     // 终止滑动
     mScroller.abortAnimation();
    }
    int offsetY = (int) (mLastY - event.getY());
    Log.d(TAG, "onTouchEvent: getScrollY: " + getScrollY());
    Log.d(TAG, "onTouchEvent: offsetY " + offsetY);
    // 到达顶部,使用offset判断方向
    if (getScrollY() + offsetY < 0) { // 当前已经滑动的 Y 位置
     offsetY = 0;
    }
    // 到达底部
    if (getScrollY() > getHeight() - mScreenHeight && offsetY > 0) {
     offsetY = 0;
    }
    scrollBy(0, offsetY);
    // 滑动完成后,重新设置LastY位置
    mLastY = (int) event.getY();
    break;
   case MotionEvent.ACTION_UP:
    mEnd = getScrollY();
    int distance = mEnd - mStart;
    if (distance > 0) { // 向上滑动
     if (distance < mScreenHeight / 3) {
      Log.d(TAG, "onTouchEvent: distance < screen/3");
      // 回到原来位置
      mScroller.startScroll(0, getScrollY(), 0, -distance);
     } else {
      // 滚到屏幕的剩余位置
      mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - distance);
     }
    } else {    // 向下滑动
     if (-distance < mScreenHeight / 3) {
      mScroller.startScroll(0, getScrollY(), 0, -distance);
     } else {
      mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - distance);
     }
    }
    postInvalidate();
  }
  return super.onTouchEvent(event);
 }


 @Override
 public void computeScroll() {
  if (mScroller.computeScrollOffset()) {
   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
   postInvalidate();
  }
 }
}

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