Android 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：

01<?xml version="1.0" encoding="utf-8"?>   

02<RelativeLayout

03    android:layout_width="fill_parent"

04    android:layout_height="fill_parent"

05    xmlns:android="http://schemas.android.com/apk/res/android">   

06    <com.genius.scroll.MyScrollLayout   

07      xmlns:android="http://schemas.android.com/apk/res/android"   

08      android:id="@+id/ScrollLayout"   

09      android:layout_width="fill_parent"   

10      android:layout_height="fill_parent">    

11      <FrameLayout   

12        android:background="@drawable/guide01"   

13        android:layout_width="fill_parent"   

14        android:layout_height="fill_parent">

15      </FrameLayout>       

16      <FrameLayout   

17        android:background="@drawable/guide02"   

18        android:layout_width="fill_parent"   

19        android:layout_height="fill_parent">

20      </FrameLayout>           

21      <FrameLayout    

22        android:background="@drawable/guide03"    

23        android:layout_width="fill_parent"   

24        android:layout_height="fill_parent">     

25      </FrameLayout>       

26      <FrameLayout   

27        android:background="@drawable/guide04"   

28        android:layout_width="fill_parent"   

29        android:layout_height="fill_parent">   

30      </FrameLayout>       

31      <FrameLayout   

32        android:background="@drawable/guide05"   

33        android:layout_width="fill_parent"   

34        android:layout_height="fill_parent">   

35      </FrameLayout>         

36    </com.genius.scroll.MyScrollLayout>

37    <LinearLayout

38        android:orientation="horizontal"

39        android:id="@+id/llayout"

40        android:layout_width="wrap_content"

41        android:layout_height="wrap_content"

42        android:layout_marginBottom="24.0dip"

43        android:layout_alignParentBottom="true"

44        android:layout_centerHorizontal="true">     

45        <ImageView android:clickable="true" 

46            android:padding="15.0dip"

47            android:layout_gravity="center_vertical"

48            android:layout_width="wrap_content"

49            android:layout_height="wrap_content"

50            android:src="@drawable/guide_round" />

51        <ImageView android:clickable="true" 

52            android:padding="15.0dip" 

53            android:layout_gravity="center_vertical"

54            android:layout_width="wrap_content"

55            android:layout_height="wrap_content"

56            android:src="@drawable/guide_round" />

57        <ImageView android:clickable="true" 

58            android:padding="15.0dip" 

59            android:layout_gravity="center_vertical"

60            android:layout_width="wrap_content"

61            android:layout_height="wrap_content"

62            android:src="@drawable/guide_round" />

63        <ImageView android:clickable="true" 

64            android:padding="15.0dip" 

65            android:layout_gravity="center_vertical"

66            android:layout_width="wrap_content"

67            android:layout_height="wrap_content"

68            android:src="@drawable/guide_round" />

69        <ImageView android:clickable="true" 

70            android:padding="15.0dip" 

71            android:layout_gravity="center_vertical"

72            android:layout_width="wrap_content"

73            android:layout_height="wrap_content"

74            android:src="@drawable/guide_round" />

75    </LinearLayout>  

76</RelativeLayout>

        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。

001public class MyScrollLayout extends ViewGroup{

002 

003    private static final String TAG = "ScrollLayout";     

004    private VelocityTracker mVelocityTracker;           // 用于判断甩动手势   

005    private static final int SNAP_VELOCITY = 600;       

006    private Scroller  mScroller;                        // 滑动控制器   

007    private int mCurScreen;                            

008    private int mDefaultScreen = 0;                         

009    private float mLastMotionX;      

010     

011    private OnViewChangeListener mOnViewChangeListener; 

012    public MyScrollLayout(Context context) {

013        super(context);

014        init(context);

015    }  

016    public MyScrollLayout(Context context, AttributeSet attrs) {

017        super(context, attrs);

018        init(context);

019    }  

020    public MyScrollLayout(Context context, AttributeSet attrs, int defStyle) {

021        super(context, attrs, defStyle);   

022        init(context);

023    }  

024    private void init(Context context)

025    {

026        mCurScreen = mDefaultScreen;                       

027        mScroller = new Scroller(context);     

028    }

029 

030    @Override

031    protected void onLayout(boolean changed, int l, int t, int r, int b) {

032        // TODO Auto-generated method stub     

033         if (changed) {   

034                int childLeft = 0;   

035                final int childCount = getChildCount();                    

036                for (int i=0; i<childCount; i++) {   

037                    final View childView = getChildAt(i);   

038                    if (childView.getVisibility() != View.GONE) {   

039                        final int childWidth = childView.getMeasuredWidth();   

040                        childView.layout(childLeft, 0,    

041                                childLeft+childWidth, childView.getMeasuredHeight());   

042                        childLeft += childWidth;   

043                    }   

044                }   

045            }   

046    }

047 

048    @Override

049    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

050        // TODO Auto-generated method stub

051        super.onMeasure(widthMeasureSpec, heightMeasureSpec);      

052        final int width = MeasureSpec.getSize(widthMeasureSpec);      

053        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);                   

054        final int count = getChildCount();      

055        for (int i = 0; i < count; i++) {      

056            getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);      

057        }               

058        scrollTo(mCurScreen * width, 0);       

059    }

060 

061     public void snapToDestination() {   

062            final int screenWidth = getWidth();   

063            final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;   

064            snapToScreen(destScreen);   

065     } 

066     

067     public void snapToScreen(int whichScreen) {       

068            // get the valid layout page   

069            whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));   

070            if (getScrollX() != (whichScreen*getWidth())) {                    

071                final int delta = whichScreen*getWidth()-getScrollX();   

072                        mScroller.startScroll(getScrollX(), 0,    

073                        delta, 0, Math.abs(delta)*2);              

074                mCurScreen = whichScreen;   

075                invalidate();       // Redraw the layout                   

076                if (mOnViewChangeListener != null)

077                {

078                    mOnViewChangeListener.OnViewChange(mCurScreen);

079                }

080            }   

081        }   

082 

083    @Override

084    public void computeScroll() {

085        // TODO Auto-generated method stub

086        if (mScroller.computeScrollOffset()) {   

087            scrollTo(mScroller.getCurrX(), mScroller.getCurrY()); 

088            postInvalidate();   

089        }  

090    }

091 

092    @Override

093    public boolean onTouchEvent(MotionEvent event) {

094        // TODO Auto-generated method stub                         

095            final int action = event.getAction();   

096            final float x = event.getX();   

097            final float y = event.getY();                  

098            switch (action) {   

099            case MotionEvent.ACTION_DOWN:              

100                  Log.i("", "onTouchEvent  ACTION_DOWN");                

101                if (mVelocityTracker == null) {   

102                        mVelocityTracker = VelocityTracker.obtain();   

103                        mVelocityTracker.addMovement(event);

104                }           

105                if (!mScroller.isFinished()){   

106                    mScroller.abortAnimation();   

107                }               

108                mLastMotionX = x;             

109                break;                     

110            case MotionEvent.ACTION_MOVE: 

111               int deltaX = (int)(mLastMotionX - x);              

112               if (IsCanMove(deltaX)){

113                 if (mVelocityTracker != null){

114                        mVelocityTracker.addMovement(event);

115                 }  

116                mLastMotionX = x;    

117                scrollBy(deltaX, 0);   

118               }      

119               break;                      

120            case MotionEvent.ACTION_UP:                    

121                int velocityX = 0;

122                if (mVelocityTracker != null){

123                    mVelocityTracker.addMovement(event);

124                    mVelocityTracker.computeCurrentVelocity(1000); 

125                    velocityX = (int) mVelocityTracker.getXVelocity();

126                }                                  

127                if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {            

128                    Log.e(TAG, "snap left");   

129                    snapToScreen(mCurScreen - 1);      

130                } else if (velocityX < -SNAP_VELOCITY      

131                        && mCurScreen < getChildCount() - 1) {          

132                    Log.e(TAG, "snap right");   

133                    snapToScreen(mCurScreen + 1);      

134                } else {      

135                    snapToDestination();      

136                }                                  

137                if (mVelocityTracker != null) {      

138                    mVelocityTracker.recycle();      

139                    mVelocityTracker = null;      

140                }      

141                break;     

142            }                  

143            return true;   

144    }

145 

146    private boolean IsCanMove(int deltaX)

147    {

148        if (getScrollX() <= 0 && deltaX < 0 ){

149            return false;

150        }  

151        if  (getScrollX() >=  (getChildCount() - 1) * getWidth() && deltaX > 0){

152            return false;

153        }      

154        return true;

155    }

156     

157    public void SetOnViewChangeListener(OnViewChangeListener listener)

158    {

159        mOnViewChangeListener = listener;

160    }

161}

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：

1public interface OnViewChangeListener {

2    public void OnViewChange(int view);

3}

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：

01public class SwitchViewDemoActivity extends Activity implements OnViewChangeListener, OnClickListener{

02    /** Called when the activity is first created. */

03 

04    private MyScrollLayout mScrollLayout;  

05    private ImageView[] mImageViews;   

06    private int mViewCount;

07    private int mCurSel;

08     

09    @Override

10    public void onCreate(Bundle savedInstanceState) {

11        super.onCreate(savedInstanceState);

12        setContentView(R.layout.main);       

13        init();

14    }

15     

16    private void init()

17    {

18        mScrollLayout = (MyScrollLayout) findViewById(R.id.ScrollLayout);  

19        LinearLayout linearLayout = (LinearLayout) findViewById(R.id.llayout);     

20        mViewCount = mScrollLayout.getChildCount();

21        mImageViews = new ImageView[mViewCount];   

22        for(int i = 0; i < mViewCount; i++)      {

23            mImageViews[i] = (ImageView) linearLayout.getChildAt(i);

24            mImageViews[i].setEnabled(true);

25            mImageViews[i].setOnClickListener(this);

26            mImageViews[i].setTag(i);

27        }      

28        mCurSel = 0;

29        mImageViews[mCurSel].setEnabled(false);    

30        mScrollLayout.SetOnViewChangeListener(this);

31    }

32 

33    private void setCurPoint(int index)

34    {

35        if (index < 0 || index > mViewCount - 1 || mCurSel == index)      {

36            return ;

37        }      

38        mImageViews[mCurSel].setEnabled(true);

39        mImageViews[index].setEnabled(false);      

40        mCurSel = index;

41    }

42 

43    @Override

44    public void OnViewChange(int view) {

45        // TODO Auto-generated method stub

46        setCurPoint(view);

47    }

48 

49    @Override

50    public void onClick(View v) {

51        // TODO Auto-generated method stub

52        int pos = (Integer)(v.getTag());

53        setCurPoint(pos);

54        mScrollLayout.snapToScreen(pos);

55    }

56}

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：

01public void snapToScreen(int whichScreen) {    

02            // get the valid layout page   

03            whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));   

04            if (getScrollX() != (whichScreen*getWidth())) {                    

05                final int delta = whichScreen*getWidth()-getScrollX();   

06                        mScroller.startScroll(getScrollX(), 0,    

07                        delta, 0, Math.abs(delta)*2);              

08                mCurScreen = whichScreen;   

09                invalidate();       // Redraw the layout                   

10                if (mOnViewChangeListener != null)

11                {

12                    mOnViewChangeListener.OnViewChange(mCurScreen);

13                }

14            }   

15        }

1mOnViewChangeListener.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：

01final int action = event.getAction();   

02            final float x = event.getX();   

03            final float y = event.getY();                  

04            switch (action) {   

05            case MotionEvent.ACTION_DOWN:              

06                  Log.i("", "onTouchEvent  ACTION_DOWN");                

07                if (mVelocityTracker == null) {   

08                        mVelocityTracker = VelocityTracker.obtain();   

09                        mVelocityTracker.addMovement(event);

10                }           

11                if (!mScroller.isFinished()){   

12                    mScroller.abortAnimation();   

13                }               

14                mLastMotionX = x;             

15                break;                     

16            case MotionEvent.ACTION_MOVE: 

17               int deltaX = (int)(mLastMotionX - x);              

18               if (IsCanMove(deltaX)){

19                 if (mVelocityTracker != null){

20                        mVelocityTracker.addMovement(event);

21                 }  

22                mLastMotionX = x;    

23                scrollBy(deltaX, 0);   

24               }      

25               break;                      

26            case MotionEvent.ACTION_UP:                    

27                int velocityX = 0;

28                if (mVelocityTracker != null){

29                    mVelocityTracker.addMovement(event);

30                    mVelocityTracker.computeCurrentVelocity(1000); 

31                    velocityX = (int) mVelocityTracker.getXVelocity();

32                }                                  

33                if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {            

34                    Log.e(TAG, "snap left");   

35                    snapToScreen(mCurScreen - 1);      

36                } else if (velocityX < -SNAP_VELOCITY      

37                        && mCurScreen < getChildCount() - 1) {          

38                    Log.e(TAG, "snap right");   

39                    snapToScreen(mCurScreen + 1);      

40                } else {      

41                    snapToDestination();      

42                }                                  

43                if (mVelocityTracker != null) {      

44                    mVelocityTracker.recycle();      

45                    mVelocityTracker = null;      

46                }      

47                break;     

48            }      

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