1.重新测量、布局
继承ViewGroup重写onMeasure和onLayout方法
1)在onMeasure中计算childVIew的测量值及模式，并设置自己的宽高
测量子View：
方法1:调用 measureChildren(widthMeasureSpec, heightMeasureSpec);
方法2:遍历childVIew调用
measureChild(childVIew, widthMeasureSpec, heightMeasureSpec);
设置自身ViewGro宽高：
设置自定义的控件MyViewGroup的大小，如果是MeasureSpec.EXACTLY则直接使用父ViewGroup传入的宽和高，否则设置为自己计算的宽和高
setMeasuredDimension(widthMode == MeasureSpec.EXACTLY ? widthSize : width, heightMode == MeasureSpec.EXACTLY ? heightSize : height);
2)在onLayout中为每个子View设置布局，可以获取每个子View并分别得到子View坐标，调用child.layout(left, top,right , bottom)为子View设置布局位置。
2.滑动事件处理
3)重写onInterceptTouchEvent，在MotionEvent.ACTION_MOVE事件中通过水平、竖直方向位移大小判断，并对水平方向事件进行拦截（返回true为拦截，由自己处理）
if (Math.abs(deltaX) > Math.abs(deltaY)) {return true;}
4)重写onTouchEvent，在MotionEvent.ACTION_MOVE调用scrollBy(-deltaX, 0)实现左右滑动；在MotionEvent.ACTION_UP用scroller.startScroll(getScrollX(), 0, dx, 0, 500)限定ViewGroup左右边界
下面贴上代码，结合代码看便于理解:
public class ZhanfHorizontalScrollview extends ViewGroup {
private int childCount;//子View数量
private int childIndex;//子View索引
private int measuredHeight;//子View的高度
private int measuredWidth;//子View的宽度
private Scroller scroller;//弹性滑动对象，用于实现View的弹性滑动
private VelocityTracker velocityTracker;//速度追踪，
public ZhanfHorizontalScrollview(Context context) {
this(context, null);
}
public ZhanfHorizontalScrollview(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public ZhanfHorizontalScrollview(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
scroller = new Scroller(getContext());
velocityTracker = VelocityTracker.obtain();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// 获得它的父容器为它设置的测量模式和大小
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
// 1.计算自定义的ViewGroup中所有子控件的大小
// measureChildren(widthMeasureSpec, heightMeasureSpec);
int height = 0;
int width = 0;
if (childCount > 0) {
for (int i = 0; i < childCount; i++) {
View child = getChildAt(i);
if (child != null && child.getVisibility() != GONE) {
// 2.计算自定义的ViewGroup中所有子控件的大小
measureChild(child, widthMeasureSpec, heightMeasureSpec);
measuredHeight = child.getMeasuredHeight();
measuredWidth = child.getMeasuredWidth();
height = Math.max(height, measuredHeight);
width += measuredWidth;
}
}
}
// 设置自定义的控件MyViewGroup的大小，如果是MeasureSpec.EXACTLY则直接使用父ViewGroup传入的宽和高，否则设置为自己计算的宽和高
setMeasuredDimension(widthMode == MeasureSpec.EXACTLY ? widthSize : width, heightMode == MeasureSpec.EXACTLY ? heightSize : height);
}
@Override
protected void onLayout(boolean b, int i, int i1, int i2, int i3) {
childCount = getChildCount();
int height = 0;
int width = 0;
if (childCount > 0) {
for (int index = 0; index < childCount; index++) {
View child = getChildAt(index);
if (child.getVisibility() != GONE && child != null) {
measuredHeight = getMeasuredHeight();
measuredWidth = getMeasuredWidth();
height = Math.max(height, measuredHeight);
child.layout(width, 0, width + measuredWidth, height);
}
width += measuredWidth;
}
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
velocityTracker.addMovement(event);
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
//如果动画还没有结束，再次点击时结束上次动画，即开启这次新的ACTION_DOWN的动画
if (!scroller.isFinished()) {
scroller.abortAnimation();
}
break;
case MotionEvent.ACTION_MOVE:
int deltaX = x - mLastX;
scrollBy(-deltaX, 0);
break;
case MotionEvent.ACTION_UP:
int scrollX = getScrollX();//View的左边缘 - View内容的左边缘 位置的像素点
// int scrollToChildIndex = scrollX / measuredWidth;
velocityTracker.computeCurrentVelocity(1000);
float xVelocity = velocityTracker.getXVelocity();//获取X方向手指滑动的速度，之前必须调用computeCurrentVelocity（）方法
if (Math.abs(xVelocity) > 200) {//当滑动速度>200Px/S时
childIndex = xVelocity > 0 ? childIndex - 1 : childIndex + 1;
} else {
childIndex = (scrollX + measuredWidth / 2) / measuredWidth;
}
childIndex = Math.max(0, Math.min(childIndex, childCount - 1));//限定childIndex在0到childCount之间
int dx = childIndex * measuredWidth - scrollX;
scroller.startScroll(getScrollX(), 0, dx, 0, 500);//up 时自动滚动到
invalidate();
break;
}
mLastX = x;
mLastY = y;
return true;
}
@Override
public void computeScroll() {
if (scroller.computeScrollOffset()) {
scrollTo(scroller.getCurrX(), scroller.getCurrY());
postInvalidate();
}
}
//分别记录上次滑动的坐标
private int mLastX = 0;
private int mLastY = 0;
//分别记录上次滑动的坐标（onINterceptTouchEvent）
private int mLastXIntercept = 0;
private int mLastYIntercept = 0;
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int x = (int) ev.getX();
int y = (int) ev.getY();
switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
if (!scroller.isFinished()) {
scroller.abortAnimation();
}
break;
case MotionEvent.ACTION_MOVE:
int deltaX = x - mLastXIntercept;
int deltaY = y - mLastYIntercept;
if (Math.abs(deltaX) > Math.abs(deltaY)) {
return true;
}
break;
case MotionEvent.ACTION_UP:
break;
}
mLastX = x;
mLastY = y;
mLastXIntercept = x;
mLastYIntercept = y;
return super.onInterceptTouchEvent(ev);
}
}
好了，有关水平滑动的实现就到这里。记住，自定义ViewGroup无非就是对子VIew进行逐个measure、layout，再进行相应情况的事件拦截、处理的过程，细细做下来也没那么难
参考：
《Android开发艺术探索》——3.5View的滑动冲突
Android 手把手教您自定义ViewGroup（一）
