页面滑动切换（类Launcher滑动屏幕实现）

          下面的这个例子也是从网上找来的，不是自己写的，一直想学习下，但是一直没有写，以前也研究研究的是launcher的页面跳转，launcher修改--左右滑动屏幕切换源码追踪说实话，那个代码有点复杂，所以理解的也不是很透彻。看到这个例子，比较简单些，再这里学习下：

       首先，看下效果图吧：虽然很花哨，都是背景图片。

       看下他的布局文件：

        底部的LinearLayout是放了5个按钮，上面使用到了一个自定义的控件：MyScrollLayout下面再看下这个自定义控件：里面使用frameLayout放了5张图片。

public class MyScrollLayout extends ViewGroup{

    private static final String TAG = "ScrollLayout";      
    private VelocityTracker mVelocityTracker;  			// 用于判断甩动手势    
    private static final int SNAP_VELOCITY = 600;        
    private Scroller  mScroller;						// 滑动控制器	
    private int mCurScreen;    						    
	private int mDefaultScreen = 0;    						 
    private float mLastMotionX;       
    
    private OnViewChangeListener mOnViewChangeListener;	 
	public MyScrollLayout(Context context) {
		super(context);
		init(context);
	}	
	public MyScrollLayout(Context context, AttributeSet attrs) {
		super(context, attrs);
		init(context);
	}	
	public MyScrollLayout(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);	
		init(context);
	}	
	private void init(Context context)
	{
		mCurScreen = mDefaultScreen;    	    	        
	    mScroller = new Scroller(context); 	    
	}

	@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 SNAP_VELOCITY && mCurScreen > 0) {             
	                Log.e(TAG, "snap left");    
	                snapToScreen(mCurScreen - 1);       
	            } else if (velocityX < -SNAP_VELOCITY       
	                    && mCurScreen < getChildCount() - 1) {           
	                Log.e(TAG, "snap right");    
	                snapToScreen(mCurScreen + 1);       
	            } else {       
	                snapToDestination();       
	            }      	            	            
	            if (mVelocityTracker != null) {       
	                mVelocityTracker.recycle();       
	                mVelocityTracker = null;       
	            }       
	            break;      
	        }    	            
	        return true;    
	}

	private boolean IsCanMove(int deltaX)
	{
		if (getScrollX() <= 0 && deltaX < 0 ){
			return false;
		}	
		if  (getScrollX() >=  (getChildCount() - 1) * getWidth() && deltaX > 0){
			return false;
		}		
		return true;
	}
	
	public void SetOnViewChangeListener(OnViewChangeListener listener)
	{
		mOnViewChangeListener = listener;
	}
}

首先注意，他继承了ViewGroup类，在这里面主要重写了onMeasure()、onTouchEvent()等方法，在这里使用了一个自定义的接口private OnViewChangeListener mOnViewChangeListener。看下它的定义：

public interface OnViewChangeListener {
	public void OnViewChange(int view);
}

      这个接口里之定义了一个回调方法：OnViewChange()这个方法的具体实现，是在主Activity中：

public class SwitchViewDemoActivity extends Activity implements OnViewChangeListener, OnClickListener{
    /** Called when the activity is first created. */

	private MyScrollLayout mScrollLayout;	
	private ImageView[] mImageViews;	
	private int mViewCount;	
	private int mCurSel;
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);        
        init();
    }
    
    private void init()
    {
    	mScrollLayout = (MyScrollLayout) findViewById(R.id.ScrollLayout); 	
    	LinearLayout linearLayout = (LinearLayout) findViewById(R.id.llayout);   	
    	mViewCount = mScrollLayout.getChildCount();
    	mImageViews = new ImageView[mViewCount];   	
    	for(int i = 0; i < mViewCount; i++)    	{
    		mImageViews[i] = (ImageView) linearLayout.getChildAt(i);
    		mImageViews[i].setEnabled(true);
    		mImageViews[i].setOnClickListener(this);
    		mImageViews[i].setTag(i);
    	}    	
    	mCurSel = 0;
    	mImageViews[mCurSel].setEnabled(false);    	
    	mScrollLayout.SetOnViewChangeListener(this);
    }

    private void setCurPoint(int index)
    {
    	if (index < 0 || index > mViewCount - 1 || mCurSel == index)    	{
    		return ;
    	}    	
    	mImageViews[mCurSel].setEnabled(true);
    	mImageViews[index].setEnabled(false);    	
    	mCurSel = index;
    }

    @Override
	public void OnViewChange(int view) {
		// TODO Auto-generated method stub
		setCurPoint(view);
	}

	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		int pos = (Integer)(v.getTag());
		setCurPoint(pos);
		mScrollLayout.snapToScreen(pos);
	}
}

        这个OnViewChange()方法，主要调用了setCurPoint()方法，就是完成界面的跳转。在MyScrollLayout中的snapToScreen()方法中就是典型的回调方法：

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    	            
	            if (mOnViewChangeListener != null)
	            {
	            	mOnViewChangeListener.OnViewChange(mCurScreen);
	            }
	        }    
	    } 

mOnViewChangeListener.OnViewChange(mCurScreen);

         这句代码就是典型的回调。

在MyScrollLayout的onTouchEvent()的方法里面是对触屏事件做出的响应：

final int action = event.getAction();    
	        final float x = event.getX();    
	        final float y = event.getY();    	            
	        switch (action) {    
	        case MotionEvent.ACTION_DOWN: 	        	
	        	  Log.i("", "onTouchEvent  ACTION_DOWN");	        	  
	        	if (mVelocityTracker == null) {    
			            mVelocityTracker = VelocityTracker.obtain();    
			            mVelocityTracker.addMovement(event); 
			    }        	 
	            if (!mScroller.isFinished()){    
	                mScroller.abortAnimation();    
	            }                
	            mLastMotionX = x;	           
	            break;    	                
	        case MotionEvent.ACTION_MOVE:  
	           int deltaX = (int)(mLastMotionX - x);	           
        	   if (IsCanMove(deltaX)){
        		 if (mVelocityTracker != null){
  		            	mVelocityTracker.addMovement(event); 
  		         }   
  	            mLastMotionX = x;     
  	            scrollBy(deltaX, 0);	
        	   }       
	           break;    	                
	        case MotionEvent.ACTION_UP:       	        	
	        	int velocityX = 0;
	            if (mVelocityTracker != null){
	            	mVelocityTracker.addMovement(event); 
	            	mVelocityTracker.computeCurrentVelocity(1000);  
	            	velocityX = (int) mVelocityTracker.getXVelocity();
	            }	               	                
	            if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {             
	                Log.e(TAG, "snap left");    
	                snapToScreen(mCurScreen - 1);       
	            } else if (velocityX < -SNAP_VELOCITY       
	                    && mCurScreen < getChildCount() - 1) {           
	                Log.e(TAG, "snap right");    
	                snapToScreen(mCurScreen + 1);       
	            } else {       
	                snapToDestination();       
	            }      	            	            
	            if (mVelocityTracker != null) {       
	                mVelocityTracker.recycle();       
	                mVelocityTracker = null;       
	            }       
	            break;      
	        }    	       

通过判断移动距离和移动方向做出不同的响应。

其他的代码都比较好懂了，有什么问题欢迎大家讨论，下面是代码的下载地址：

http://download.csdn.net/detail/aomandeshangxiao/4017928