Android中如何通过自定义ViewGroup实现一个弹性滑动效果

本篇内容主要讲解"Android中如何通过自定义ViewGroup实现一个弹性滑动效果"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"Android中如何通过自定义ViewGroup实现一个弹性滑动效果"吧!

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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