android 1.6 launcher研究之launcher的左右滑动

参考： http://blog.csdn.net/assassin4824/archive/2011/05/30/6454923.aspx
http://blog.sina.com.cn/s/blog_4d142b550100s1sx.html
http://blog.csdn.net/xiaoxiaobian3310903/archive/2011/05/24/6443250.aspx
http://www.ibm.com/developerworks/cn/opensource/os-cn-android-anmt2/

ScrollLayout.java

package com.lp;
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，可以左右滑动切换屏幕的类
 */
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);
        //默认显示第一屏
        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;
                    //很明显 0 - 320 | 320 - 640 | 640 - 960 ...（假设屏幕宽320）
                }
            }
        }
    }
    @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);
        //x坐标 y坐标
        //移动到第几屏
        scrollTo(mCurScreen * width, 0);
    }

    /**
     * According to the position of current layout
     * scroll to the destination page.
     * 判断滑动的位置
     * 如果大于当前屏中间的位置 则换屏
     * 否则 仍然是这个屏
     * getScrollX x方向的偏移量
     */

    public void snapToDestination() {
        final int screenWidth = getWidth();
        //判断
        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();
            //开始滚动
            //x，y，x方向移动量，y方向移动量，滚动持续时间，负数往左滚
            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;
    }
    //只有当前LAYOUT中的某个CHILD导致SCROLL发生滚动，才会致使自己的COMPUTESCROLL被调用
    @Override
    public void computeScroll() {
        // TODO Auto-generated method stub
        Log.e(TAG,"computeScroll");
        //如果返回true，表示动画还没有结束
        //因为前面startScroll，所以只有在startScroll完成时 才会为false
        if (mScroller.computeScrollOffset()) {
            Log.e(TAG, mScroller.getCurrX()+"======"+mScroller.getCurrY());
            //产生了动画效果 每次滚动一点
           scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
           postInvalidate();
        }
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        Log.e(TAG,"onTouchEvent start");
        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! "+mScroller.isFinished());
            //如果屏幕的滚动动画没有结束 你就按下了 就结束动画
            if (!mScroller.isFinished()){
                mScroller.abortAnimation();
            }
            mLastMotionX = x;
            break;

        case MotionEvent.ACTION_MOVE:
            Log.e(TAG, "event move!");
            //取得偏移量
            int deltaX = (int)(mLastMotionX - x);
            Log.e(TAG,"detaX: "+deltaX);
            mLastMotionX = x;
            //x方向的偏移量 y方向的偏移量
            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 {
                //一般都掉用这个
                snapToDestination();
            }
            if (mVelocityTracker != null) {
                mVelocityTracker.recycle();
                mVelocityTracker = null;
            }
            // }
            mTouchState = TOUCH_STATE_REST;
            break;
        case MotionEvent.ACTION_CANCEL:
            mTouchState = TOUCH_STATE_REST;
            break;
        }

        return true;
    }
    //这个感觉没什么作用 不管true还是false 都是会执行onTouchEvent的 因为子view里面onTouchEvent返回false了
    @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:
            Log.e(TAG,"onInterceptTouchEvent move");
            final int xDiff = (int)Math.abs(mLastMotionX-x);
            if (xDiff>mTouchSlop) {
                mTouchState = TOUCH_STATE_SCROLLING;

            }
            break;

        case MotionEvent.ACTION_DOWN:
            Log.e(TAG,"onInterceptTouchEvent down");
            mLastMotionX = x;
            mLastMotionY = y;
            Log.e(TAG,mScroller.isFinished()+"");
            mTouchState = mScroller.isFinished()? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
            break;

        case MotionEvent.ACTION_CANCEL:
        case MotionEvent.ACTION_UP:
            Log.e(TAG,"onInterceptTouchEvent up or cancel");
            mTouchState = TOUCH_STATE_REST;
            break;
        }
        Log.e(TAG,mTouchState+"===="+TOUCH_STATE_REST);
        return mTouchState != TOUCH_STATE_REST;
    }

}

package com.lp;  
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，可以左右滑动切换屏幕的类 
 */  
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);  
        //默认显示第一屏
        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;  
                    //很明显 0 - 320 | 320 - 640 | 640 - 960 ...（假设屏幕宽320）
                }  
            }  
        }  
    }  
    @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);    
        //x坐标 y坐标
        //移动到第几屏
        scrollTo(mCurScreen * width, 0);           
    }    
      
    /** 
     * According to the position of current layout 
     * scroll to the destination page.
     * 判断滑动的位置 
     * 如果大于当前屏中间的位置 则换屏
     * 否则 仍然是这个屏 
     * getScrollX x方向的偏移量
     */ 
    
    public void snapToDestination() {  
        final int screenWidth = getWidth();  
        //判断
        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(); 
            //开始滚动
            //x，y，x方向移动量，y方向移动量，滚动持续时间，负数往左滚
            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;  
    }  
    //只有当前LAYOUT中的某个CHILD导致SCROLL发生滚动，才会致使自己的COMPUTESCROLL被调用
    @Override  
    public void computeScroll() {  
        // TODO Auto-generated method stub  
        Log.e(TAG,"computeScroll");
        //如果返回true，表示动画还没有结束
        //因为前面startScroll，所以只有在startScroll完成时 才会为false
        if (mScroller.computeScrollOffset()) {  
            Log.e(TAG, mScroller.getCurrX()+"======"+mScroller.getCurrY());
            //产生了动画效果 每次滚动一点 
           scrollTo(mScroller.getCurrX(), mScroller.getCurrY());  
           postInvalidate();  
        }  
    }  
    @Override  
    public boolean onTouchEvent(MotionEvent event) {  
        // TODO Auto-generated method stub  
        Log.e(TAG,"onTouchEvent start");
        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! "+mScroller.isFinished());  
            //如果屏幕的滚动动画没有结束 你就按下了 就结束动画
            if (!mScroller.isFinished()){  
                mScroller.abortAnimation();  
            }  
            mLastMotionX = x;  
            break;  
              
        case MotionEvent.ACTION_MOVE:  
            Log.e(TAG, "event move!"); 
            //取得偏移量
            int deltaX = (int)(mLastMotionX - x); 
            Log.e(TAG,"detaX: "+deltaX);
            mLastMotionX = x;  
            //x方向的偏移量 y方向的偏移量
            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 {     
                //一般都掉用这个
                snapToDestination();     
            }     
            if (mVelocityTracker != null) {     
                mVelocityTracker.recycle();     
                mVelocityTracker = null;     
            }     
            // }     
            mTouchState = TOUCH_STATE_REST;     
            break;  
        case MotionEvent.ACTION_CANCEL:  
            mTouchState = TOUCH_STATE_REST;  
            break;  
        }  
          
        return true;  
    }  
    //这个感觉没什么作用 不管true还是false 都是会执行onTouchEvent的 因为子view里面onTouchEvent返回false了
    @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:  
            Log.e(TAG,"onInterceptTouchEvent move");
            final int xDiff = (int)Math.abs(mLastMotionX-x);  
            if (xDiff>mTouchSlop) {  
                mTouchState = TOUCH_STATE_SCROLLING;  
                  
            }  
            break;  
              
        case MotionEvent.ACTION_DOWN:  
            Log.e(TAG,"onInterceptTouchEvent down");
            mLastMotionX = x;  
            mLastMotionY = y;  
            Log.e(TAG,mScroller.isFinished()+"");
            mTouchState = mScroller.isFinished()? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;  
            break;  
              
        case MotionEvent.ACTION_CANCEL:  
        case MotionEvent.ACTION_UP:  
            Log.e(TAG,"onInterceptTouchEvent up or cancel");
            mTouchState = TOUCH_STATE_REST;  
            break;  
        }  
        Log.e(TAG,mTouchState+"===="+TOUCH_STATE_REST);
        return mTouchState != TOUCH_STATE_REST;  
    }  
      
}  

main.xml

<?xml version="1.0" encoding="utf-8"?>
<com.lp.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.lp.ScrollLayout>