android 继承ViewGroup实现自定义布局

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Scroller;

/**
* @author :huangxianfeng on 2016/10/13.
* 继承ViewGroup实现自定义布局
*/
public class HorizontalScrollViewEx extends ViewGroup{

private static final String TAG = "HorizontalScrollViewEx";

private int mChildrenSize;
private int mChildWidth;
private int mChildIndex;

//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;

private Scroller mScroller;
private VelocityTracker mVelocityTracker;

public HorizontalScrollViewEx(Context context) {
super(context);
init();
}

public HorizontalScrollViewEx(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}

public HorizontalScrollViewEx(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}

private void init() {
if (mScroller==null){
mScroller = new Scroller(getContext());
mVelocityTracker = VelocityTracker.obtain();
}
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
boolean intercepted = false;
int x = (int)ev.getX();
int y = (int)ev.getY();

switch (ev.getAction()){
case MotionEvent.ACTION_DOWN:
intercepted = false;
if (!mScroller.isFinished()){
mScroller.abortAnimation();
intercepted = true;
}
break;
case MotionEvent.ACTION_MOVE:
int detlaX = x-mLastXIntercept;
int detlaY = y-mLastYIntercept;
if (Math.abs(detlaX) > Math.abs(detlaY)){
intercepted = true;
}else{
intercepted = false;
}
break;
case MotionEvent.ACTION_UP:
intercepted = false;
break;
default:
break;
}
Log.d(TAG,"intercepted = "+intercepted);
mLastX = x;
mLastY = y;
mLastXIntercept = x;
mLastYIntercept = y;

return intercepted;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
mVelocityTracker.addMovement(event);
int x = (int)getX();
int y = (int)getY();

switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
if (!mScroller.isFinished()){
mScroller.abortAnimation();
}
break;
case MotionEvent.ACTION_MOVE:
int detalX = x-mLastX;
int detalY = y-mLastY;
scrollBy(-detalX,0);
break;
case MotionEvent.ACTION_UP:
int scrollX = getScrollX();
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
if (Math.abs(xVelocity) >= 50){
mChildIndex = xVelocity > 0 ? mChildIndex -1 : mChildIndex + 1;
}else{
mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
}

mChildIndex = Math.max(0,Math.min(mChildIndex,mChildrenSize -1 ));
int dx = mChildIndex * mChildWidth - scrollX;
smoothScrollBy(dx, 0);
mVelocityTracker.clear();
break;

default:
break;
}
mLastX = x;
mLastY = y;

return true;
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int measuredWidth = 0;
int measuredHeight = 0;
//拿到自己含有子元素的个数
final int childCount = getChildCount();
measureChildren(widthMeasureSpec,heightMeasureSpec);

int widthSpaceSize = MeasureSpec.getSize(widthMeasureSpec);
int widthSpaceMode = MeasureSpec.getMode(widthMeasureSpec);
int heightSpaceSize  = MeasureSpec.getSize(heightMeasureSpec);
int heightSpaceMode = MeasureSpec.getMode(heightMeasureSpec);
/**
* 1.判断是否含有子元素,如果没有直接把自己的高度和宽度设置为0
* 2.判断子元素的宽度和高度是否采用的warp_content，如果采用了则把所有的子元素的宽度之和给自己并且把
*   第一个子元素的高度给自己。
* 3.再进行分别判断高度和宽度那个用了warp_content，就对其分别设置不一样的值。
*/
if (childCount == 0){
setMeasuredDimension(0,0);
}else if (widthSpaceMode == MeasureSpec.AT_MOST && heightSpaceMode == MeasureSpec.AT_MOST){
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(measuredWidth,measuredHeight);
}else if (heightSpaceMode == MeasureSpec.AT_MOST){
final View childView = getChildAt(0);
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(widthSpaceSize,childView.getMeasuredHeight());
}else if (widthSpaceMode == MeasureSpec.AT_MOST){
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
setMeasuredDimension(measuredWidth,heightSpaceSize);
}
/**
* 以上代码有两个不规范的地方：
* 1.如果没有子元素的时候，不应该直接把宽度/高度直接设置为0，而是要根据LayoutParams中的高度/宽度来做相应的处理
* 2.在测量的时候要考虑到自己和子元素的padding和margin值，这样测出来的才是最标准的
*/
}

/**
* 完成子元素的定位：
* 1.遍历所有的子元素是否处于GONE的状态，不是则放置在合适的位置
* 放置的过程也是由左向右
* 缺点：也是没有考虑到自己个子元素的padding和maigin的值
* @param changed
* @param l
* @param t
* @param r
* @param b
*/
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childLeft = 0;
final int childCount = getChildCount();
mChildrenSize = childCount;

for (int i = 0; i < childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE){
final int childWidth = childView.getMeasuredWidth();
mChildWidth = childWidth;
childView.layout(childLeft,0,childLeft + childWidth,childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}

private void smoothScrollBy(int dx,int dy){
//1000ms内滑向目标位置，效果是谩慢滑动
mScroller.startScroll(getScrollX(),0,dx,0,500);
invalidate();
}

@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()){
scrollTo(mScroller.getCurrX(),mScroller.getCurrY());
postInvalidate();
}
}

@Override
protected void onDetachedFromWindow() {
mVelocityTracker.recycle();
super.onDetachedFromWindow();
}
}