安卓学习笔记之自定义ViewGroup

涉及的知识点

- ViewGroup的测量与布局- View的测量与布局- 滑动冲突的处理- VelocityTracker滑动速率跟踪- Scroller实现弹性滑动- 屏幕宽高的获取等


实现步骤

1. 创建MyScrollView继承ViewGroup&＃xff0c;实现构造与方法2. 在onMeasure方法中对子View进行测量&＃xff0c;同时计算出ViewGroup的宽高&＃xff0c;并通过setMeasuredDimension设置3. 在onLayout方法中进行布局4. 在onInterceptTouchEvent方法中进行滑动冲突的处理5. 在onTouchEvent方法中进行滑动事件的处理6. 实现弹性滑动


具体实现

继承ViewGroup

public class MyScrollView extends ViewGroup {/*** 可视为点击事件的距离&＃xff0c;视为滑动的临界值*/private int touchSlop;private Scroller mScroller;/*** 屏幕宽度*/private int screenHeight;/*** 滑动速度跟踪类*/private VelocityTracker velocityTracker;/*** 滑动的起始坐标*/private int startX, startY;/*** getScrollY的起始与结束值*/private int startScrollY, endScrollY;public MyScrollView(Context context) {this(context, null);}public MyScrollView(Context context, AttributeSet attrs) {this(context, attrs, 0);}public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);touchSlop &＃61; ViewConfiguration.get(context).getScaledTouchSlop();mScroller &＃61; new Scroller(context, new OvershootInterpolator()); // 添加InterpolatorscreenHeight &＃61; getScreenHeight(context);}


/*** 获取屏幕高*/private int getScreenHeight(Context context) {Display d &＃61; ((Activity) context).getWindowManager().getDefaultDisplay();Point outSize &＃61; new Point();d.getSize(outSize); // outSize保存着屏幕的宽高return outSize.y;}

onMeasure中进行测量

&＃64;Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);final int measureHeight &＃61; measureHeight(heightMeasureSpec); // 通过模式测量的高度final int measureWidth &＃61; measureWidth(widthMeasureSpec); // 通过模式测量的宽度int totalHeight &＃61; 0; // 实际的总高度int maxWidth &＃61; 0; // 实际的最大宽度measureChildren(widthMeasureSpec, heightMeasureSpec); //测量子viewint childCount &＃61; getChildCount(); //子view数量for (int i &＃61; 0; i int height &＃61; child.getMeasuredHeight();int width &＃61; child.getMeasuredWidth();totalHeight &＃43;&＃61; height;maxWidth &＃61; Math.max(maxWidth, child.getMeasuredWidth() &＃43; child.getPaddingLeft() &＃43; child.getPaddingRight());}//比较出最大宽度与最大高度&＃xff0c;并设置给MyScrollViewsetMeasuredDimension(Math.max(measureWidth, maxWidth), Math.max(measureHeight, totalHeight));}/*** 通过widthMeasureSpec得到的宽度** &＃64;param widthMeasureSpec* &＃64;return*/private int measureWidth(int widthMeasureSpec) {int mode &＃61; MeasureSpec.getMode(widthMeasureSpec);int specSize &＃61; MeasureSpec.getSize(widthMeasureSpec);int finalSize &＃61; 200; //给定默认值switch (mode) {case MeasureSpec.EXACTLY:finalSize &＃61; specSize;break;case MeasureSpec.AT_MOST:finalSize &＃61; Math.min(finalSize, specSize);break;}return finalSize;}/*** 通过heightMeasureSpec得到的高度** &＃64;param heightMeasureSpec* &＃64;return*/private int measureHeight(int heightMeasureSpec) {int mode &＃61; MeasureSpec.getMode(heightMeasureSpec);int specSize &＃61; MeasureSpec.getSize(heightMeasureSpec);int finalSize &＃61; 200;switch (mode) {case MeasureSpec.EXACTLY:finalSize &＃61; specSize;break;case MeasureSpec.AT_MOST:finalSize &＃61; Math.min(finalSize, specSize);break;}return finalSize;}

onLayout方法中进行布局

&＃64;Overrideprotected void onLayout(boolean changed, int l, int t, int r, int b) {int childCount &＃61; getChildCount();
// int paddingTop &＃61; 0;
// for (int i &＃61; 0; i
// View child &＃61; getChildAt(i);
// int height &＃61; child.getMeasuredHeight();
// int childLeft &＃61; l &＃43; child.getPaddingLeft();
// child.layout(childLeft, paddingTop, childLeft &＃43; child.getMeasuredWidth(), paddingTop &＃43; child.getMeasuredHeight());
// paddingTop &＃43;&＃61; height;
// lastChildY &＃61; paddingTop;
// }for (int i &＃61; 0; i // 这里让每一个child都填充了屏幕child.layout(l, screenHeight * i, r, screenHeight * (i &＃43; 1));}}

onInterceptTouchEvent滑动冲突处理

/*** 滑动冲突处理&＃xff0c;* 当Y方向滑动大于X方向滑动距离&＃xff0c;并且Y方向滑动距离大于touchSlop时&＃xff0c;拦截事件* 其他情况不拦截** &＃64;param ev* &＃64;return*/&＃64;Overridepublic boolean onInterceptTouchEvent(MotionEvent ev) {boolean result &＃61; false;switch (ev.getAction()) {case MotionEvent.ACTION_DOWN:startX &＃61; (int) ev.getX();startY &＃61; (int) ev.getY();break;case MotionEvent.ACTION_MOVE:int dX &＃61; (int) (ev.getX() - startX);int dY &＃61; (int) (ev.getY() - startY);if (Math.abs(dY) > Math.abs(dX) && Math.abs(dY) > touchSlop) { //y方向大于x方法距离&＃xff0c;且y方向滑动大于touchSlopresult &＃61; true;} else {result &＃61; false;}break;}return result;}

onTouchEvent滑动事件的处理

&＃64;Overridepublic boolean onTouchEvent(MotionEvent ev) {switch (ev.getAction()) {case MotionEvent.ACTION_DOWN:if (velocityTracker &＃61;&＃61; null) {velocityTracker &＃61; VelocityTracker.obtain();} else {velocityTracker.clear(); // 重置到初始状态}velocityTracker.addMovement(ev); // You should call this for the initial ACTION_DOWNif (!mScroller.isFinished())mScroller.abortAnimation();startX &＃61; (int) ev.getX();startY &＃61; (int) ev.getY();startScrollY &＃61; getScrollY();break;case MotionEvent.ACTION_MOVE:velocityTracker.addMovement(ev); // Add a user&＃39;s movement to the tracker.velocityTracker.computeCurrentVelocity(50); // 计算当前速率&＃xff0c;按每50毫秒int dX &＃61; (int) (ev.getX() - startX);int dY &＃61; (int) (ev.getY() - startY);if (Math.abs(getScrollY()) > screenHeight * (getChildCount() - 1) && dY <0) { // 滑动边界限制return false;}scrollBy(0, -dY);break;case MotionEvent.ACTION_UP:endScrollY &＃61; getScrollY();int deltaScrollY &＃61; endScrollY - startScrollY;int page &＃61; Math.abs(endScrollY / screenHeight); // 当前页if (Math.abs(velocityTracker.getYVelocity()) > 100 && page !&＃61; getChildCount() - 1) { //滑动速率大于100if (velocityTracker.getYVelocity() > 100) { //下滑smoothScroll(0, getScrollY(), 0, -getScrollY() &＃43; page * screenHeight, 500); // 上一页} else if (-velocityTracker.getYVelocity() > 100) { // 上滑smoothScroll(0, getScrollY(), 0, -getScrollY() &＃43; (page &＃43; 1) * screenHeight, 500); // 下一页}} else {if (deltaScrollY <0) { // 下拉if (Math.abs(deltaScrollY) 3) { //小于屏幕1/3时&＃xff0c;回滚smoothScroll(0, getScrollY(), 0, -deltaScrollY, deltaScrollY * 2);} else { // 自动滑动到下一页smoothScroll(0, getScrollY(), 0, -getScrollY() &＃43; page * screenHeight, deltaScrollY * 2);}} else { //上拉if (deltaScrollY > screenHeight / 3) { //大于屏幕1/3时&＃xff0c;自动滑动到下一页smoothScroll(0, getScrollY(), 0, -getScrollY() &＃43; (page &＃43; 1) * screenHeight, deltaScrollY * 2);} else { //回滚smoothScroll(0, getScrollY(), 0, -deltaScrollY, deltaScrollY * 2);}}}break;}startX &＃61; (int) ev.getX();startY &＃61; (int) ev.getY();return true;}

弹性滑动的实现

/*** 弹性滑动* &＃64;param startX* &＃64;param startY* &＃64;param dX* &＃64;param dY* &＃64;param duration*/private void smoothScroll(int startX, int startY, int dX, int dY, int duration) {if (Math.abs(duration) > 800) duration &＃61; 800;mScroller.startScroll(startX, startY, dX, dY, Math.abs(duration));invalidate();}&＃64;Overridepublic void computeScroll() {super.computeScroll();if (mScroller.computeScrollOffset()) {scrollTo(mScroller.getCurrX(), mScroller.getCurrY());invalidate();}}

源码&＃xff1a; http://download.csdn.net/detail/qq_28261343/9600431