假设写一个android桌面滑动切换屏幕的控件(一)
首先这个控件应该是继承ViewGroup:
初始化:
public class MyGroup extends ViewGroup{
private Scroller mScroller;
private float mOriMotionX;
private float mLastMotionX;
private VelocityTracker mVelocityTracker;
private int mTouchState = TOUCH_STATE_REST;
private static final int TOUCH_STATE_REST = 0;
private int mTouchSlop;
private int mMaximumVelocity;
private static final int TOUCH_STATE_SCROLLING = 1;
private float mLastDownX;
private static final int DEFAULT_VALUE = 1000;
private int mNextScreen = -1;
private boolean mFlagLimitUp = false;
private static final int SNAP_VELOCITY = 700;
private int mCurrentScreen;
public MyGroup(Context context, AttributeSet attrs) {
super(context, attrs);
initWorkspace();
}
private void initWorkspace() {
mScroller = new Scroller(getContext());
setCurrentScreen(0);
final ViewConfiguration configuration = ViewConfiguration
.get(getContext());
mTouchSlop = configuration.getScaledTouchSlop();//这个是定义控件在scroll的最小像素距离
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity(); //速率。fling的一个以每秒滑动多少像素的值
}先重写onmeasure:
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
}onLayout:
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
int paddingleft = 0;
int paddingTop = 0;
int childLeft = paddingleft;
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
final int childHeight = child.getMeasuredHeight() ;
child.layout(childLeft, paddingTop, childLeft + childWidth,
childHeight + paddingTop);
<strong>childLeft += child.getMeasuredWidth(); //下个child的左边距和第一个child的左边距之间的距离正好是第一个child的width</strong>
}
}
}然后写View的touch事件:
onInterceptTouchEvent仅仅有返回false事件才会传递给控件里的view。就是view的ontouch事件才干够捕捉 View里的onTouchEvent返回为true，才干运行多次touch事件。事件才干得了传递
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
final int action = ev.getAction();
//假设为move事件,mTouchState为TOUCH_STATE_REST为精巧状态，这个是防止子控件在滑动时又用手指去滑，这样的情况下不响应这个事件
if ((action == MotionEvent.ACTION_MOVE)
&& (mTouchState != TOUCH_STATE_REST)) {
return true;
}
final float x = ev.getX();
switch (action) {
case MotionEvent.ACTION_MOVE:
final int xDiff = (int) Math.abs(x - mLastMotionX);
final int touchSlop = mTouchSlop;
boolean xMoved = xDiff > touchSlop;
//假设xMoved为true表示手指在滑动
if (xMoved) {
mTouchState = TOUCH_STATE_SCROLLING;
}
break;
case MotionEvent.ACTION_DOWN:
mLastMotionX = x;
//mScroller.isFinished() 为true表示滑动结束了，这时候我们把状态置为TOUCH_STATE_REST
mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST
: TOUCH_STATE_SCROLLING;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mTouchState = TOUCH_STATE_REST;
break;
default:
break;
}
//假设不是在精巧状态。都返回true,这样事件就不会传递给onTouchEvent了
return mTouchState != TOUCH_STATE_REST;
}
在滑动的时候返回true的原因是这时候不须要响应里面控件的ontouch事件
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
int mScrollX = this.getScrollX(); //mScrollX表示X轴上的距离，往左滑动为正。这个时候屏幕向右移动
final int action = ev.getAction();
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
mOriMotionX = x;
mLastMotionX = x;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
mOriMotionX = x;
mLastMotionX = x;
mLastDownX = x;
return true;
case MotionEvent.ACTION_MOVE:
System.out.println("====action move mScrollX="+mScrollX);
final int buffer = getWidth() / 2; //这个表示在第一页或是最后一页还能够滑动半个屏幕
//假设是往后滑动。屏幕向前，那么mLastMotionX是比x大的。deltaX是正的
int deltaX = (int) (mLastMotionX - x);
mLastMotionX = x;
System.out.println("=====deltaX="+deltaX);
//deltaX<0表示往前滑动
if (deltaX < 0) {
//这个是往右滑动，屏幕向左移动
scrollBy(Math.max(-mScrollX - buffer, deltaX), 0);
}else{
int availableToScroll = 0;
if (getChildCount() > 0) { //此时Workspace上可能未加不论什么item，count == 0
System.out.println("====rihgt="+(getChildAt(
getChildCount() - 1).getRight())+"avail="+(getChildAt(
getChildCount() - 1).getRight()- mScrollX - getWidth()
));
//getChildAt(getChildCount() - 1).getRight()为全部的view加一起的宽度，这里加了3个view,一个view为1080,则这个值为3240
availableToScroll = getChildAt(
getChildCount() - 1).getRight()
- mScrollX - getWidth();
//availableToScroll + buffer能够滑动的最大距离,deltax为滑动的距离
scrollBy(Math.min(availableToScroll + buffer, deltaX), 0);
}
}
return true;
case MotionEvent.ACTION_UP:
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(DEFAULT_VALUE,
mMaximumVelocity);
int velocityX = (int) velocityTracker.getXVelocity();
//velocityX为手指滑动的速率。我们会跟给定值SNAP_VELOCITY做比較
if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {
// 这个时候是手指往前滑动，屏幕是向后移动
snapToScreen(mCurrentScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurrentScreen < getChildCount() - 1) {
// move right
snapToScreen(mCurrentScreen + 1);
} else {
snapToDestination(mLastMotionX < mOriMotionX);
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
mTouchState = TOUCH_STATE_REST;
if (Math.abs(mLastDownX - x) > 10) {
return true;
}
return false;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
return false;
default:
break;
}
return true;
}/**滑动的距离。离屏宽几分之中的一个时，就開始运行换屏动作。*/
/**
* snapToDestination.
* mLastMotionX < mOriMotionX (mLastMotion < mOriMotionX)表示这个是手向后滑动，但屏幕是往前的，反之是向前
* forward为true为往前划动,这时将scrollX加上三分之二的屏幕的宽度
* scrollX / screenWidth 来决定当前在哪个屏幕
* @param forward 是前进还是后退.
*/
public void snapToDestination(boolean forward) {
final int screenWidth = getWidth();
int scrollX = getScrollX();
if (forward) {
scrollX += screenWidth - screenWidth / 3;
} else {
scrollX += screenWidth / 3;
}
System.out.println("======screenWidth="+screenWidth+"scrollX / screenWidth="+(scrollX / screenWidth));
snapToScreen(scrollX / screenWidth);
}
/**
* 假设计算要滑动的距离:(whichScreen * getWidth())为滑动后的X坐标,this.getScrollX()为当前的坐标，两者相减为滑动的距离
* Math.abs(delta) * 2为滑动的持续时间
*/
public void snapToScreen(int whichScreen) {
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
boolean changingScreens = whichScreen != mCurrentScreen;
mNextScreen = whichScreen;
int mScrollX = this.getScrollX();
final int newX = whichScreen * getWidth();
final int delta = newX - mScrollX;
System.out.println("====snapToScreen delta="+delta);
mScroller.startScroll(mScrollX, 0, delta, 0, Math.abs(delta) * 2);
//invalidate很重要，不然你移动一点页面不能回复原状
invalidate();
}代码:http://download.csdn.net/detail/baidu_nod/7731631
