Android自定义ViewGroup实现弹性滑动效果

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

代码语言：javascript复制

 @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

代码语言：javascript复制

@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

代码语言：javascript复制

 @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

代码语言：javascript复制

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

代码语言：javascript复制

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();
}
}
}

以上就是本文的全部内容，希望对大家的学习有所帮助。

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