提取Launcher中的WorkSapce，可以左右滑動切換屏幕頁面的類
By:Yao.GUET 轉載請註明出處。
http://blog.csdn.net/Yao_GUET
對於Launcher的桌面滑動大家應該都比較熟悉了，最好的體驗應該是可以隨着手指的滑動而顯示不同位置的桌面，
比一般用ViewFlinger+動畫所實現的手勢切換頁面感覺良好多了~~~~
分析了一下Launcher中的WorkSpace，裏面有太多的代碼我們用不上了（拖拽，長按，，，），把裏面的冗餘代碼去掉得到實現滑動切換屏幕所必需的。。。。
新建一個ScrollLayout類，繼承自ViewGroup。
重寫onMeasure和onLayout兩個方法：
其中onMeasure方法中，得到ScrollLayout的佈局方式（一般使用FILL_PARENT），然後再枚舉其中所有的子view，設置它們的佈局（FILL_PARENT），這樣在ScrollLayout之中的每一個子view即爲充滿屏幕可以滑動顯示的其中一頁。
在onLayout方法中，橫向畫出每一個子view，這樣所得到的view的高與屏幕高一致，寬度爲getChildCount()-1個屏幕寬度的view。
添加一個Scroller來平滑過渡各個頁面之間的切換，
重寫onInterceptTouchEvent和onTouchEvent來響應手指按下划動時所需要捕獲的消息，例如划動的速度，划動的距離等。再配合使用scrollBy (int x, int y)方法得到慢速滑動小距離的時候，所需要顯示的內容。最後當手指起來時，根據划動的速度與跨度來判斷是向左滑動一頁還是向右滑動一頁，確保每次用戶操作結束之後顯示的都是整體的一個子view.
ScrollLayout源碼：
package com.yao_guet.test;
import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;
/**
* 仿Launcher中的WorkSapce，可以左右滑動切換屏幕的類
* @author Yao.GUET
* blog: http://blog.csdn.net/Yao_GUET
* date: 2011-05-04
*/
public class ScrollLayout extends ViewGroup {
private static final String TAG = "ScrollLayout";
private Scroller mScroller;
private VelocityTracker mVelocityTracker;
private int mCurScreen;
private int mDefaultScreen = 0;
private static final int TOUCH_STATE_REST = 0;
private static final int TOUCH_STATE_SCROLLING = 1;
private static final int SNAP_VELOCITY = 600;
private int mTouchState = TOUCH_STATE_REST;
private int mTouchSlop;
private float mLastMotionX;
private float mLastMotionY;
public ScrollLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
// TODO Auto-generated constructor stub
}
public ScrollLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// TODO Auto-generated constructor stub
mScroller = new Scroller(context);
mCurScreen = mDefaultScreen;
mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// TODO Auto-generated method stub
if (changed) {
int childLeft = 0;
final int childCount = getChildCount();
for (int i=0; i<childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
final int childWidth = childView.getMeasuredWidth();
childView.layout(childLeft, 0,
childLeft+childWidth, childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
Log.e(TAG, "onMeasure");
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
if (widthMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ScrollLayout only canmCurScreen run at EXACTLY mode!");
}
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
if (heightMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ScrollLayout only can run at EXACTLY mode!");
}
// The children are given the same width and height as the scrollLayout
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
// Log.e(TAG, "moving to screen "+mCurScreen);
scrollTo(mCurScreen * width, 0);
}
/**
* According to the position of current layout
* scroll to the destination page.
*/
public void snapToDestination() {
final int screenWidth = getWidth();
final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;
snapToScreen(destScreen);
}
public void snapToScreen(int whichScreen) {
// get the valid layout page
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));
if (getScrollX() != (whichScreen*getWidth())) {
final int delta = whichScreen*getWidth()-getScrollX();
mScroller.startScroll(getScrollX(), 0,
delta, 0, Math.abs(delta)*2);
mCurScreen = whichScreen;
invalidate(); // Redraw the layout
}
}
public void setToScreen(int whichScreen) {
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));
mCurScreen = whichScreen;
scrollTo(whichScreen*getWidth(), 0);
}
public int getCurScreen() {
return mCurScreen;
}
@Override
public void computeScroll() {
// TODO Auto-generated method stub
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(event);
final int action = event.getAction();
final float x = event.getX();
final float y = event.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "event down!");
if (!mScroller.isFinished()){
mScroller.abortAnimation();
}
mLastMotionX = x;
break;
case MotionEvent.ACTION_MOVE:
int deltaX = (int)(mLastMotionX - x);
mLastMotionX = x;
scrollBy(deltaX, 0);
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "event : up");
// if (mTouchState == TOUCH_STATE_SCROLLING) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000);
int velocityX = (int) velocityTracker.getXVelocity();
Log.e(TAG, "velocityX:"+velocityX);
if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
// Fling enough to move left
Log.e(TAG, "snap left");
snapToScreen(mCurScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurScreen < getChildCount() - 1) {
// Fling enough to move right
Log.e(TAG, "snap right");
snapToScreen(mCurScreen + 1);
} else {
snapToDestination();
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
// }
mTouchState = TOUCH_STATE_REST;
break;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
break;
}
return true;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
// TODO Auto-generated method stub
Log.e(TAG, "onInterceptTouchEvent-slop:"+mTouchSlop);
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE) &&
(mTouchState != TOUCH_STATE_REST)) {
return true;
}
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_MOVE:
final int xDiff = (int)Math.abs(mLastMotionX-x);
if (xDiff>mTouchSlop) {
mTouchState = TOUCH_STATE_SCROLLING;
}
break;
case MotionEvent.ACTION_DOWN:
mLastMotionX = x;
mLastMotionY = y;
mTouchState = mScroller.isFinished()? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mTouchState = TOUCH_STATE_REST;
break;
}
return mTouchState != TOUCH_STATE_REST;
}
}
測試程序佈局：
<?xml version="1.0" encoding="utf-8"?>
<com.yao_guet.test.ScrollLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/ScrollLayoutTest"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
android:background="#FF00"
android:layout_width="fill_parent"
android:layout_height="fill_parent"></LinearLayout>
<FrameLayout
android:background="#F0F0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"></FrameLayout>
<FrameLayout
android:background="#F00F"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
</FrameLayout>
<LinearLayout
android:background="#FF00"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button1" />
</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button2" />
</LinearLayout>
</com.yao_guet.test.ScrollLayout>
提取Launcher中的WorkSapce，可以左右滑動切換屏幕頁面的類
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