1.3 自定义 ViewGroup

//循环子View,并定义他们的位置
for (int i = 0; i count; i++){
View childView = getChildAt(i);
width = childView.getMeasuredWidth();
height = childView.getMeasuredHeight();
params = (MarginLayoutParams) getLayoutParams();

switch (i){
case 0: //第一个组件
l = params.leftMargin;
i1 = getHeight() – height – params.bottomMargin;
break;
case 1: //第二个组件
l = getWidth() – width – params.leftMargin – params.rightMargin;
i1 = getHeight() – height – params.bottomMargin;
break;
}
i2 = l + width;
i3 = height + i1;
//调用子View的layout,就是上篇自定义View说的layout方法
childView.layout(l, i1, i2, i3);
}
}

private int mScreenHeight;
private int mStartY;
private int mEnd;
private Scroller mScroller;
private int mLastY;
private int childCount;
public CustomScrollView(Context context) {
this(context,null);
}

public CustomScrollView(Context context, AttributeSet attrs) {
super(context,attrs);

//初始化一些需要的属性
WindowManager wm= (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
mScreenHeight=wm.getDefaultDisplay().getHeight();
mScroller = new Scroller(getContext());
}

//在onMeasure中测量子view
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int childCount = getChildCount();
for (int i=0;ichildCount;i++){
View childView = getChildAt(i);
measureChild(childView,widthMeasureSpec,heightMeasureSpec);
}
}

//确定子View的位子
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
childCount = getChildCount();
//设置这个ViewGroup的高度
MarginLayoutParams lp = (MarginLayoutParams) getLayoutParams();
lp.height=mScreenHeight * childCount;
setLayoutParams(lp);
//绘制子view的位置
for (int i = 0; ichildCount; i++){
View childView = getChildAt(i);
if(childView.getVisibility()!=View.GONE){
childView.layout(l,i*mScreenHeight,r,(i+1)*mScreenHeight);
}
}

}

//step3：增添我们需要的触摸响应事件
@Override
public boolean onTouchEvent(MotionEvent event) {
//在这个触摸事件中，需要判断两个距离，一个是手指移动的距离一个是view滚动的距离
//这是随着手指的移动会发送改变的量
int y = (int) event.getY();
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
mLastY = y;
mStartY = getScrollY();

break;
case MotionEvent.ACTION_MOVE:
//当我们再次触碰屏幕时，如果之前的滚动动画还没有停止，我们也让他立即停止
if(!mScroller.isFinished()){
mScroller.abortAnimation();
}
int dY= mLastY –y;
//滚动触碰到上边缘时一给个下拉反弹的效果
if(getScrollY()0){
dY/=3;
}
//判断滚动的
if(getScrollY()>mScreenHeight*getChildCount()–mScreenHeight){
dY=0;
}
//让我们的view滚动相应的dy距离
scrollBy(0,dY);
mLastY=y;
break;
case MotionEvent.ACTION_UP:
mEnd = getScrollY();
int dScrollY = mEnd – mStartY;
if(dScrollY>0){//向上滚动的情况
if(getScrollY()0){
mScroller.startScroll(0,getScrollY(),0,-dScrollY);
}else{
if (dScrollYmScreenHeight/3){
mScroller.startScroll(0,getScrollY(),0,-dScrollY);
}else{
mScroller.startScroll(0,getScrollY(),0,mScreenHeight–dScrollY);
}
}
}else{//向下滚动的情况
if(getScrollY()>mScreenHeight*getChildCount()–mScreenHeight){
mScroller.startScroll(0,getScrollY(),0,-dScrollY);
}else{
if(–dScrollYmScreenHeight/3){
mScroller.startScroll(0,getScrollY(),0,-dScrollY);
}else {
mScroller.startScroll(0, getScrollY(), 0, –mScreenHeight – dScrollY);
}
}
}
break;
}
//重绘界面
postInvalidate();
return true;
}

//控制滑屏控制
@Override
public void computeScroll() {
super.computeScroll();
if(mScroller.computeScrollOffset()){
scrollTo(0,mScroller.getCurrY());
postInvalidate();
}
}
}