Android教程：高仿launcher和墨跡左右拖動效果

有這樣的想法，做出一個模仿launcher的效果。自己也曾從網上搜過很多資料，也思考過怎麼實現，最終還是參考了別人的資料實現了此效果，也解決了我這半個多月的冥思苦想，再次感謝，今天把代碼貼出來供大家學習，因為這方面做得比較好的資料缺失比較少（因為本人搜了很多資料都不能達到效果），如果大家覺得還不錯，請頂起。

更多Android相關信息見Android 專題頁面 http://www.linuxidc.com/topicnews.aspx?tid=11

首先自定義一個 ViewGroup：

1. public class MyScrollLayout extends ViewGroup{  
2.   
3.     private VelocityTracker mVelocityTracker;           // 用於判斷甩動手勢      
4.     private static final int SNAP_VELOCITY = 600;          
5.     private Scroller  mScroller;                        // 滑動控制器      
6.     private int mCurScreen;                               
7.     private int mDefaultScreen = 0;                            
8.     private float mLastMotionX;         
9.  //   private int mTouchSlop;                             
10.       
11.    private OnViewChangeListener mOnViewChangeListener;    
12.    
13.     public MyScrollLayout(Context context) {  
14.         super(context);  
15.         // TODO Auto-generated constructor stub  
16.         init(context);  
17.     }     
18.     public MyScrollLayout(Context context, AttributeSet attrs) {  
19.         super(context, attrs);  
20.         // TODO Auto-generated constructor stub  
21.         init(context);  
22.     }  
23.       
24.     public MyScrollLayout(Context context, AttributeSet attrs, int defStyle) {  
25.         super(context, attrs, defStyle);  
26.         // TODO Auto-generated constructor stub       
27.         init(context);  
28.     }  
29.       
30.     private void init(Context context)  
31.     {  
32.         mCurScreen = mDefaultScreen;            
33.      //   mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();                  
34.         mScroller = new Scroller(context);   
35.           
36.     }  
37.   
38.     @Override  
39.     protected void onLayout(boolean changed, int l, int t, int r, int b) {  
40.         // TODO Auto-generated method stub        
41.          if (changed) {      
42.                 int childLeft = 0;      
43.                 final int childCount = getChildCount();                       
44.                 for (int i=0; i<childCount; i++) {      
45.                     final View childView = getChildAt(i);      
46.                     if (childView.getVisibility() != View.GONE) {      
47.                         final int childWidth = childView.getMeasuredWidth();      
48.                         childView.layout(childLeft, 0,       
49.                                 childLeft+childWidth, childView.getMeasuredHeight());      
50.                         childLeft += childWidth;      
51.                     }      
52.                 }      
53.             }      
54.     }  
55.   
56.     @Override  
57.     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
58.         // TODO Auto-generated method stub  
59.         super.onMeasure(widthMeasureSpec, heightMeasureSpec);         
60.         final int width = MeasureSpec.getSize(widthMeasureSpec);         
61.         final int widthMode = MeasureSpec.getMode(widthMeasureSpec);        
62.                   
63.         final int count = getChildCount();         
64.         for (int i = 0; i < count; i++) {         
65.             getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);         
66.         }                  
67.         scrollTo(mCurScreen * width, 0);          
68.     }  
69.   
70.      public void snapToDestination() {      
71.             final int screenWidth = getWidth();      
72.             final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;      
73.             snapToScreen(destScreen);      
74.      }    
75.       
76.      public void snapToScreen(int whichScreen) {          
77.             // get the valid layout page      
78.             whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));      
79.             if (getScrollX() != (whichScreen*getWidth())) {                       
80.                 final int delta = whichScreen*getWidth()-getScrollX();      
81.                         mScroller.startScroll(getScrollX(), 0,       
82.                         delta, 0, Math.abs(delta)*2);  
83.                   
84.                 mCurScreen = whichScreen;      
85.                 invalidate();       // Redraw the layout                      
86.                 if (mOnViewChangeListener != null)  
87.                 {  
88.                     mOnViewChangeListener.OnViewChange(mCurScreen);  
89.                 }  
90.             }      
91.         }      
92.   
93.     @Override  
94.     public void computeScroll() {  
95.         // TODO Auto-generated method stub  
96.         if (mScroller.computeScrollOffset()) {      
97.             scrollTo(mScroller.getCurrX(), mScroller.getCurrY());    
98.             postInvalidate();      
99.         }     
100.     }  
101.   
102.     @Override  
103.     public boolean onTouchEvent(MotionEvent event) {  
104.         // TODO Auto-generated method stub                            
105.             final int action = event.getAction();      
106.             final float x = event.getX();      
107.             final float y = event.getY();      
108.                   
109.             switch (action) {      
110.             case MotionEvent.ACTION_DOWN:                 
111.                   Log.i("", "onTouchEvent  ACTION_DOWN");                   
112.                 if (mVelocityTracker == null) {      
113.                         mVelocityTracker = VelocityTracker.obtain();      
114.                         mVelocityTracker.addMovement(event);   
115.                 }              
116.                 if (!mScroller.isFinished()){      
117.                     mScroller.abortAnimation();      
118.                 }                  
119.                 mLastMotionX = x;                
120.                 break;      
121.                       
122.             case MotionEvent.ACTION_MOVE:    
123.                int deltaX = (int)(mLastMotionX - x);                 
124.                if (IsCanMove(deltaX))  
125.                {  
126.                  if (mVelocityTracker != null)  
127.                  {  
128.                         mVelocityTracker.addMovement(event);   
129.                  }     
130.                 mLastMotionX = x;       
131.                 scrollBy(deltaX, 0);      
132.                }  
133.            
134.                break;                         
135.             case MotionEvent.ACTION_UP:                       
136.                 int velocityX = 0;  
137.                 if (mVelocityTracker != null)  
138.                 {  
139.                     mVelocityTracker.addMovement(event);   
140.                     mVelocityTracker.computeCurrentVelocity(1000);    
141.                     velocityX = (int) mVelocityTracker.getXVelocity();  
142.                 }                                     
143.                 if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {         
144.                     // Fling enough to move left            
145.                     snapToScreen(mCurScreen - 1);         
146.                 } else if (velocityX < -SNAP_VELOCITY         
147.                         && mCurScreen < getChildCount() - 1) {         
148.                     // Fling enough to move right            
149.                     snapToScreen(mCurScreen + 1);         
150.                 } else {         
151.                     snapToDestination();         
152.                 }        
153.                                   
154.                 if (mVelocityTracker != null) {         
155.                     mVelocityTracker.recycle();         
156.                     mVelocityTracker = null;         
157.                 }         
158.           //      mTouchState = TOUCH_STATE_REST;  
159.                 break;        
160.             }                     
161.             return true;      
162.     }  
163.   
164.     private boolean IsCanMove(int deltaX)  
165.     {  
166.         if (getScrollX() <= 0 && deltaX < 0 ){  
167.             return false;  
168.         }     
169.         if  (getScrollX() >=  (getChildCount() - 1) * getWidth() && deltaX > 0){  
170.             return false;  
171.         }         
172.         return true;  
173.     }  
174.       
175.     public void SetOnViewChangeListener(OnViewChangeListener listener)  
176.     {  
177.         mOnViewChangeListener = listener;  
178.     }  
179. }