Android自定义ViewGroup实现受边界限制的滚动操作（3）

package com.example.libingyuan.horizontallistview.ScrollViewGroup;import android.content.Context;import android.util.AttributeSet;import android.util.DisplayMetrics;import android.view.MotionEvent;import android.view.View;import android.view.ViewGroup;import android.view.WindowManager;import android.widget.Scroller;/** * 自定义ViewGroup * 在滚动的基础上，增加了边界限制 */public class ScrollViewGroup extends ViewGroup { //滚动计算辅助类 private Scroller mScroller; //手指落点的X坐标 private float mLastMotionX = 0; //屏幕宽度 private int screenWidth; /**  * 使用new关键字创建对象的时候调用  * @param context 上下文  */ public ScrollViewGroup(Context context) {  this(context, null); } /**  * 在XML文件中使用的时候调用  * @param context 上下文  * @param attrs 属性：如 android:layout_width="wrap_content"  */ public ScrollViewGroup(Context context, AttributeSet attrs) {  this(context, attrs, 0); } /**  * 在xml文件中调用，并且使用了自定义属性的时候调用  * @param context 上下文  * @param attrs 属性：如 android:layout_width="wrap_content"  * @param defStyleAttr 自定义属性的id  */ public ScrollViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {  super(context, attrs, defStyleAttr);  init(context); } /**  * 初始化方法  * 初始化滚动辅助类Scroller以及计算出屏幕宽度  * @param context  */ private void init(Context context) {  mScroller = new Scroller(context);  WindowManager manager = (WindowManager) context    .getSystemService(Context.WINDOW_SERVICE);  DisplayMetrics outMetrics = new DisplayMetrics();  manager.getDefaultDisplay().getMetrics(outMetrics);  screenWidth = outMetrics.widthPixels; } /**  * 滚动时需要重写的方法，用于控制滚动  */ @Override public void computeScroll() {  //判断滚动时候停止  if (mScroller.computeScrollOffset()) {   //滚动到指定的位置   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());   //这句话必须写，否则不能实时刷新   postInvalidate();  } } /**  * 手指触屏事件监听  * @param event  * @return  */ @Override public boolean onTouchEvent(MotionEvent event) {  // TODO Auto-generated method stub  int action = event.getAction();  float x = event.getX();  switch (action) {   case MotionEvent.ACTION_DOWN:    if (!mScroller.isFinished()) {     mScroller.abortAnimation();    }    mLastMotionX = event.getX();    break;   case MotionEvent.ACTION_MOVE:    float delt = mLastMotionX - x;    mLastMotionX = x;    scrollBy((int) delt, 0);    break;   case MotionEvent.ACTION_UP:    View lastChild=getChildAt(getChildCount()-1);    int finalyChild= (int) (lastChild.getX()+lastChild.getWidth()-screenWidth);    if (getScrollX()<0){     scrollTo(0,0);    }    if (getScrollX()>=finalyChild)     scrollTo(finalyChild,0);    invalidate();    break;   default:    break;  }  return true; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  //重新设置宽高  this.setMeasuredDimension(measureWidth(widthMeasureSpec, heightMeasureSpec), measureHeight(widthMeasureSpec, heightMeasureSpec)); }  /**  * 测量宽度  */ private int measureWidth(int widthMeasureSpec, int heightMeasureSpec) {  // 宽度  int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);  int modeWidth = MeasureSpec.getMode(widthMeasureSpec);  //父控件的宽（wrap_content）  int width = 0;  int childCount = getChildCount();  //重新测量子view的宽度，以及最大高度  for (int i = 0; i < childCount; i++) {   View child = getChildAt(i);   measureChild(child, widthMeasureSpec, heightMeasureSpec);   MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();   int childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;   width += childWidth;  }  return modeWidth == MeasureSpec.EXACTLY ? sizeWidth : width; } /**  * 测量高度  */ private int measureHeight(int widthMeasureSpec, int heightMeasureSpec) {  //高度  int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);  int modeHeight = MeasureSpec.getMode(heightMeasureSpec);  //父控件的高（wrap_content）  int height = 0;  int childCount = getChildCount();  //重新测量子view的宽度，以及最大高度  for (int i = 0; i < childCount; i++) {   View child = getChildAt(i);   measureChild(child, widthMeasureSpec, heightMeasureSpec);   MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();   int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;   height += childHeight;  }  height = height / childCount;  return modeHeight == MeasureSpec.EXACTLY ? sizeHeight : height; } /**  * 给子布局设定位置  */ @Override protected void onLayout(boolean changed, int l, int t, int r, int b) {  int childLeft = 0;//子View左边的间距  int childWidth;//子View的宽度  int height = getHeight();//屏幕的宽度  int childCount = getChildCount();//子View的数量  for (int i = 0; i < childCount; i++) {   View child = getChildAt(i);   MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();   childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;   child.layout(childLeft, 0, childLeft + childWidth, height);   childLeft += childWidth;  } } @Override public LayoutParams generateLayoutParams(AttributeSet attrs) {  return new MarginLayoutParams(getContext(), attrs); }}