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回答
Android: 仿Launcher Workspace左右滑动控件
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修改Launcher的Workspace,去掉Drag相关的操作,精简为一个支持左右滑动的控件

每屏中可以自由放置layout



主要的问题是对

    @Override
    public boolean dispathTouchEvent(MotionEvent ev) {}

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {}

    @Override
    public boolean onTouchEvent(MotionEvent ev) {}

的理解,不然不好控制touch事件


代码贴上,其实没啥参考价值:

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

    
    <com.mylauncher.Workspace	
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:launcher="http://schemas.android.com/apk/res/com.mylauncher"    
        android:id="@+id/workspace"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="horizontal"
        android:fadeScrollbars="true"
        launcher:defaultScreen="0">
        
        <com.mylauncher.CellLayout	android:background="#ff0000ff"
        	android:id="@+id/cell1"
	        android:layout_width="match_parent"
	        android:layout_height="match_parent"    
	        android:orientation="vertical"    	
        	>
            <TextView	
	        android:layout_width="fill_parent"
	        android:layout_height="wrap_content"
	    	android:textSize="30sp"			    		
	    	android:textStyle="bold"   	        
	        android:text="@string/screen1" />
            <Button		
	        android:layout_width="fill_parent"
	        android:layout_height="wrap_content"
	    	android:textSize="30sp"			    		
	    	android:textStyle="bold"  	        
	        android:text="@string/screen1" /> 	        
	        
        </com.mylauncher.CellLayout>
        
        <com.mylauncher.CellLayout	android:background="#ffff0000"
        	android:id="@+id/cell2"
	        android:layout_width="match_parent"
	        android:layout_height="match_parent"  
	        android:orientation="vertical"      	
        	>
            <TextView	
	        android:layout_width="fill_parent"
	        android:layout_height="wrap_content"
	    	android:textSize="30sp"			    		
	    	android:textStyle="bold"  	        
	        android:text="@string/screen2" />     
            <Button		 
	        android:layout_width="fill_parent"
	        android:layout_height="wrap_content"
	    	android:textSize="30sp"			    		
	    	android:textStyle="bold"  	        
	        android:text="@string/screen2" />  	 	               
        </com.mylauncher.CellLayout>    
        
        <com.mylauncher.CellLayout	android:background="#ff00ff00"
        	android:id="@+id/cell3"
	        android:layout_width="match_parent"
	        android:layout_height="match_parent"   
	        android:orientation="vertical"     	
        	>
            <TextView	
	        android:layout_width="fill_parent"
	        android:layout_height="wrap_content"
	    	android:textSize="30sp"			    		
	    	android:textStyle="bold"  	        
	        android:text="@string/screen3" />      
            <Button		 
	        android:layout_width="fill_parent"
	        android:layout_height="wrap_content"
	    	android:textSize="30sp"			    		
	    	android:textStyle="bold"  	        
	        android:text="@string/screen3" />  	              
        </com.mylauncher.CellLayout>              
        
    </com.mylauncher.Workspace>

package com.mylauncher;

import android.app.WallpaperManager;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.os.IBinder;
import android.os.Parcel;
import android.os.Parcelable;
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.view.ViewParent;
import android.view.animation.Interpolator;
import android.widget.Scroller;

/**
 * The workspace is a wide area with a wallpaper and a finite number of screens. Each
 * screen contains a number of icons, folders or widgets the user can interact with.
 * A workspace is meant to be used with a fixed width only.
 */
public class Workspace extends ViewGroup {
    @SuppressWarnings({"UnusedDeclaration"})
    private static final String TAG = "MyLauncher.Workspace";
    private static final int INVALID_SCREEN = -1;
    
    /**
     * The velocity at which a fling gesture will cause us to snap to the next screen
     */
    private static final int SNAP_VELOCITY = 600;

    private final WallpaperManager mWallpaperManager;
    
    private int mDefaultScreen;

    private boolean mFirstLayout = true;

    private int mCurrentScreen;
    private int mNextScreen = INVALID_SCREEN;
    private Scroller mScroller;
    private VelocityTracker mVelocityTracker;


    
    /**
     * Target drop area calculated during last acceptDrop call.
     */
    private int[] mTargetCell = null;

    private float mLastMotionX;
    private float mLastMotionY;
    
    private final static int TOUCH_STATE_REST = 0;
    private final static int TOUCH_STATE_SCROLLING = 1;

    private int mTouchState = TOUCH_STATE_REST;

    private OnLongClickListener mLongClickListener;


    

    
    private int[] mTempCell = new int[2];
    private int[] mTempEstimate = new int[2];

    private boolean mAllowLongPress = true;

    private int mTouchSlop;
    private int mMaximumVelocity;
    
    private static final int INVALID_POINTER = -1;

    private int mActivePointerId = INVALID_POINTER;
    
    private Drawable mPreviousIndicator;
    private Drawable mNextIndicator;
    
    private static final float NANOTIME_DIV = 1000000000.0f;
    private static final float SMOOTHING_SPEED = 0.75f;
    private static final float SMOOTHING_CONSTANT = (float) (0.016 / Math.log(SMOOTHING_SPEED));
    private float mSmoothingTime;
    private float mTouchX;

    private WorkspaceOvershootInterpolator mScrollInterpolator;

    private static final float BASELINE_FLING_VELOCITY = 2500.f;
    private static final float FLING_VELOCITY_INFLUENCE = 0.4f;
    
    private static class WorkspaceOvershootInterpolator implements Interpolator {
        private static final float DEFAULT_TENSION = 1.3f;
        private float mTension;

        public WorkspaceOvershootInterpolator() {
            mTension = DEFAULT_TENSION;
        }
        
        public void setDistance(int distance) {
            mTension = distance > 0 ? DEFAULT_TENSION / distance : DEFAULT_TENSION;
        }

        public void disableSettle() {
            mTension = 0.f;
        }

        public float getInterpolation(float t) {
            // _o(t) = t * t * ((tension + 1) * t + tension)
            // o(t) = _o(t - 1) + 1
            t -= 1.0f;
            return t * t * ((mTension + 1) * t + mTension) + 1.0f;
        }
    }
    
    /**
     * Used to inflate the Workspace from XML.
     *
     * @param context The application's context.
     * @param attrs The attribtues set containing the Workspace's customization values.
     */
    public Workspace(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    /**
     * Used to inflate the Workspace from XML.
     *
     * @param context The application's context.
     * @param attrs The attribtues set containing the Workspace's customization values.
     * @param defStyle Unused.
     */
    public Workspace(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        mWallpaperManager = WallpaperManager.getInstance(context);
        
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.Workspace, defStyle, 0);
        mDefaultScreen = a.getInt(R.styleable.Workspace_defaultScreen, 1);
        a.recycle();

        setHapticFeedbackEnabled(false);
        initWorkspace();
    }

    /**
     * Initializes various states for this workspace.
     */
    private void initWorkspace() {
        Context context = getContext();
        mScrollInterpolator = new WorkspaceOvershootInterpolator();
        mScroller = new Scroller(context, mScrollInterpolator);
        mCurrentScreen = mDefaultScreen;


        final ViewConfiguration configuration = ViewConfiguration.get(getContext());
        mTouchSlop = configuration.getScaledTouchSlop();
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
    }















    boolean isDefaultScreenShowing() {
        return mCurrentScreen == mDefaultScreen;
    }

    /**
     * Returns the index of the currently displayed screen.
     *
     * @return The index of the currently displayed screen.
     */
    int getCurrentScreen() {
        return mCurrentScreen;
    }

    /**
     * Sets the current screen.
     *
     * @param currentScreen
     */
    void setCurrentScreen(int currentScreen) {
        if (!mScroller.isFinished()) mScroller.abortAnimation();
        
        mCurrentScreen = Math.max(0, Math.min(currentScreen, getChildCount() - 1));
        //mPreviousIndicator.setLevel(mCurrentScreen);
        //mNextIndicator.setLevel(mCurrentScreen);
        scrollTo(mCurrentScreen * getWidth(), 0);

        invalidate();
    }




    /**
     * Registers the specified listener on each screen contained in this workspace.
     *
     * @param l The listener used to respond to long clicks.
     */
    @Override
    public void setOnLongClickListener(OnLongClickListener l) {
        mLongClickListener = l;
        final int count = getChildCount();
        for (int i = 0; i < count; i++) {
            getChildAt(i).setOnLongClickListener(l);
        }
    }



    private void updateWallpaperOffset(int scrollRange) {
        IBinder token = getWindowToken();
        if (token != null) {
            mWallpaperManager.setWallpaperOffsetSteps(1.0f / (getChildCount() - 1), 0 );
            mWallpaperManager.setWallpaperOffsets(getWindowToken(),
                    Math.max(0.f, Math.min(mScrollX/(float)scrollRange, 1.f)), 0);
        }
    }
    
    @Override
    public void scrollTo(int x, int y) {
        super.scrollTo(x, y);
        mTouchX = x;
        mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
    }
    
    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            mTouchX = mScrollX = mScroller.getCurrX();
            mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
            mScrollY = mScroller.getCurrY();
            
            postInvalidate();
        } else if (mNextScreen != INVALID_SCREEN) {
            mCurrentScreen = Math.max(0, Math.min(mNextScreen, getChildCount() - 1));
            //mPreviousIndicator.setLevel(mCurrentScreen);
            //mNextIndicator.setLevel(mCurrentScreen);

            mNextScreen = INVALID_SCREEN;
            //clearChildrenCache();
        } else if (mTouchState == TOUCH_STATE_SCROLLING) {
            final float now = System.nanoTime() / NANOTIME_DIV;
            final float e = (float) Math.exp((now - mSmoothingTime) / SMOOTHING_CONSTANT);
            final float dx = mTouchX - mScrollX;
            mScrollX += dx * e;
            mSmoothingTime = now;

            // Keep generating points as long as we're more than 1px away from the target
            if (dx > 1.f || dx < -1.f) {
                
                postInvalidate();
            }
        }
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        boolean restore = false;
        int restoreCount = 0;

        // ViewGroup.dispatchDraw() supports many features we don't need:
        // clip to padding, layout animation, animation listener, disappearing
        // children, etc. The following implementation attempts to fast-track
        // the drawing dispatch by drawing only what we know needs to be drawn.

        boolean fastDraw = mTouchState != TOUCH_STATE_SCROLLING && mNextScreen == INVALID_SCREEN;
        // If we are not scrolling or flinging, draw only the current screen
        if (fastDraw) {
            drawChild(canvas, getChildAt(mCurrentScreen), getDrawingTime());
        } else {
            final long drawingTime = getDrawingTime();
            final float scrollPos = (float) mScrollX / getWidth();
            final int leftScreen = (int) scrollPos;
            final int rightScreen = leftScreen + 1;
            if (leftScreen >= 0) {
                drawChild(canvas, getChildAt(leftScreen), drawingTime);
            }
            if (scrollPos != leftScreen && rightScreen < getChildCount()) {
                drawChild(canvas, getChildAt(rightScreen), drawingTime);
            }
        }

        if (restore) {
            canvas.restoreToCount(restoreCount);
        }
    }

    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        computeScroll();

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        final int width = MeasureSpec.getSize(widthMeasureSpec);
        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        if (widthMode != MeasureSpec.EXACTLY) {
            throw new IllegalStateException("Workspace can only be used in EXACTLY mode.");
        }

        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (heightMode != MeasureSpec.EXACTLY) {
            throw new IllegalStateException("Workspace can only be used in EXACTLY mode.");
        }

        // The children are given the same width and height as the workspace
        final int count = getChildCount();
        for (int i = 0; i < count; i++) {
            getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
        }


        if (mFirstLayout) {
            setHorizontalScrollBarEnabled(false);
            scrollTo(mCurrentScreen * width, 0);
            setHorizontalScrollBarEnabled(true);
            updateWallpaperOffset(width * (getChildCount() - 1));
            mFirstLayout = false;
        }
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        int childLeft = 0;

        final int count = getChildCount();
        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != View.GONE) {
                final int childWidth = child.getMeasuredWidth();
                child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
                childLeft += childWidth;
            }
        }
    }

    @Override
    public boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate) {
        int screen = indexOfChild(child);
        if (screen != mCurrentScreen || !mScroller.isFinished()) {
            snapToScreen(screen);
            return true;
        }
        return false;
    }




    @Override
    public boolean dispatchUnhandledMove(View focused, int direction) {
        if (direction == View.FOCUS_LEFT) {
            if (getCurrentScreen() > 0) {
                snapToScreen(getCurrentScreen() - 1);
                return true;
            }
        } else if (direction == View.FOCUS_RIGHT) {
            if (getCurrentScreen() < getChildCount() - 1) {
                snapToScreen(getCurrentScreen() + 1);
                return true;
            }
        }
        return super.dispatchUnhandledMove(focused, direction);
    }




    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {


        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onTouchEvent will be called and we do the actual
         * scrolling there.
         */

        /*
         * Shortcut the most recurring case: the user is in the dragging
         * state and he is moving his finger.  We want to intercept this
         * motion.
         */
         
        final int action = ev.getAction();
               
        
        Log.d(TAG, "onInterceptTouchEvent, action: " + action + " mTouchState: " + mTouchState);
        
        if ((action == MotionEvent.ACTION_MOVE) && (mTouchState != TOUCH_STATE_REST)) {
        	Log.d(TAG, "onInterceptTouchEvent, MotionEvent.ACTION_MOVE mTouchState: " + mTouchState);
            return true;
        }

        acquireVelocityTrackerAndAddMovement(ev);
        
        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_MOVE: {
            	Log.d(TAG, "onInterceptTouchEvent.ACTION_MOVE.................");
                /*
                 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                 * whether the user has moved far enough from his original down touch.
                 */

                /*
                 * Locally do absolute value. mLastMotionX is set to the y value
                 * of the down event.
                 */
                final int pointerIndex = ev.findPointerIndex(mActivePointerId);
                final float x = ev.getX(pointerIndex);
                final float y = ev.getY(pointerIndex);
                final int xDiff = (int) Math.abs(x - mLastMotionX);
                final int yDiff = (int) Math.abs(y - mLastMotionY);

                final int touchSlop = mTouchSlop;
                boolean xMoved = xDiff > touchSlop;
                boolean yMoved = yDiff > touchSlop;
                
                if (xMoved || yMoved) {
                    
                    if (xMoved) {
                    	Log.d(TAG, "onInterceptTouchEvent.ACTION_MOVE.TOUCH_STATE_SCROLLING................");
                        // Scroll if the user moved far enough along the X axis
                        mTouchState = TOUCH_STATE_SCROLLING;
                        mLastMotionX = x;
                        mTouchX = getScrollX();
                        mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
                        //enableChildrenCache(mCurrentScreen - 1, mCurrentScreen + 1);
                    }
                    // Either way, cancel any pending longpress
                    if (mAllowLongPress) {
                        mAllowLongPress = false;
                        // Try canceling the long press. It could also have been scheduled
                        // by a distant descendant, so use the mAllowLongPress flag to block
                        // everything
                        final View currentScreen = getChildAt(mCurrentScreen);
                        currentScreen.cancelLongPress();
                    }
                }
                break;
            }

            case MotionEvent.ACTION_DOWN: {
            	Log.d(TAG, "onInterceptTouchEvent.ACTION_DOWN.................");
                final float x = ev.getX();
                final float y = ev.getY();
                // Remember location of down touch
                mLastMotionX = x;
                mLastMotionY = y;
                mActivePointerId = ev.getPointerId(0);
                mAllowLongPress = true;

                /*
                 * If being flinged and user touches the screen, initiate drag;
                 * otherwise don't.  mScroller.isFinished should be false when
                 * being flinged.
                 */
                Log.d(TAG, "mScroller.isFinished()................." + mScroller.isFinished());
                mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
                break;
            }

            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                Log.d(TAG, "onInterceptTouchEvent.ACTION_UP.................");

                
                // Release the drag
                //clearChildrenCache();
                mTouchState = TOUCH_STATE_REST;
                mActivePointerId = INVALID_POINTER;
                mAllowLongPress = false;
                releaseVelocityTracker();
                break;
                
            case MotionEvent.ACTION_POINTER_UP:
				Log.d(TAG, "onInterceptTouchEvent.ACTION_POINTER_UP.................");
                onSecondaryPointerUp(ev);
                break;
        }

        /*
         * The only time we want to intercept motion events is if we are in the
         * drag mode.
         */
        Log.d(TAG, "onInterceptTouchEvent.mTouchState != TOUCH_STATE_REST................." + (mTouchState != TOUCH_STATE_REST));  
        return mTouchState != TOUCH_STATE_REST;
    }
    
    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
                MotionEvent.ACTION_POINTER_INDEX_SHIFT;
        final int pointerId = ev.getPointerId(pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose a new
            // active pointer and adjust accordingly.
            // TODO: Make this decision more intelligent.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mLastMotionX = ev.getX(newPointerIndex);
            mLastMotionY = ev.getY(newPointerIndex);
            mActivePointerId = ev.getPointerId(newPointerIndex);
            if (mVelocityTracker != null) {
                mVelocityTracker.clear();
            }
        }
    }

    /**
     * If one of our descendant views decides that it could be focused now, only
     * pass that along if it's on the current screen.
     *
     * This happens when live folders requery, and if they're off screen, they
     * end up calling requestFocus, which pulls it on screen.
     */
    @Override
    public void focusableViewAvailable(View focused) {
        View current = getChildAt(mCurrentScreen);
        View v = focused;
        while (true) {
            if (v == current) {
                super.focusableViewAvailable(focused);
                return;
            }
            if (v == this) {
                return;
            }
            ViewParent parent = v.getParent();
            if (parent instanceof View) {
                v = (View)v.getParent();
            } else {
                return;
            }
        }
    }




    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        


        acquireVelocityTrackerAndAddMovement(ev);

        final int action = ev.getAction();

        switch (action & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
        	Log.d(TAG, "onTouchEvent.ACTION_DOWN.................");
            /*
             * If being flinged and user touches, stop the fling. isFinished
             * will be false if being flinged.
             */
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
            }

            // Remember where the motion event started
            mLastMotionX = ev.getX();
            mActivePointerId = ev.getPointerId(0);
            if (mTouchState == TOUCH_STATE_SCROLLING) {
                //enableChildrenCache(mCurrentScreen - 1, mCurrentScreen + 1);
            }
            break;
        case MotionEvent.ACTION_MOVE:
        	Log.d(TAG, "onTouchEvent.ACTION_MOVE.................");
            if (mTouchState == TOUCH_STATE_SCROLLING) {
            	Log.d(TAG, "onTouchEvent.ACTION_MOVE.TOUCH_STATE_SCROLLING................");
                // Scroll to follow the motion event
                final int pointerIndex = ev.findPointerIndex(mActivePointerId);
                final float x = ev.getX(pointerIndex);
                final float deltaX = mLastMotionX - x;
                mLastMotionX = x;

                if (deltaX < 0) {
                    if (mTouchX > 0) {
                        mTouchX += Math.max(-mTouchX, deltaX);
                        mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
                        invalidate();
                    }
                } else if (deltaX > 0) {
                    final float availableToScroll = getChildAt(getChildCount() - 1).getRight() -
                            mTouchX - getWidth();
                    if (availableToScroll > 0) {
                        mTouchX += Math.min(availableToScroll, deltaX);
                        mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
                        invalidate();
                    }
                } else {
                    awakenScrollBars();
                }
            }
            break;
        case MotionEvent.ACTION_UP:
        	Log.d(TAG, "onTouchEvent.ACTION_UP.................");
            if (mTouchState == TOUCH_STATE_SCROLLING) {
                final VelocityTracker velocityTracker = mVelocityTracker;
                velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                final int velocityX = (int) velocityTracker.getXVelocity(mActivePointerId);
                
                final int screenWidth = getWidth();
                final int whichScreen = (getScrollX() + (screenWidth / 2)) / screenWidth;
                final float scrolledPos = (float) getScrollX() / screenWidth;
                
                if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {
                    // Fling hard enough to move left.
                    // Don't fling across more than one screen at a time.
                    final int bound = scrolledPos < whichScreen ?
                            mCurrentScreen - 1 : mCurrentScreen;
                    snapToScreen(Math.min(whichScreen, bound), velocityX, true);
                } else if (velocityX < -SNAP_VELOCITY && mCurrentScreen < getChildCount() - 1) {
                    // Fling hard enough to move right
                    // Don't fling across more than one screen at a time.
                    final int bound = scrolledPos > whichScreen ?
                            mCurrentScreen + 1 : mCurrentScreen;
                    snapToScreen(Math.max(whichScreen, bound), velocityX, true);
                } else {
                    snapToScreen(whichScreen, 0, true);
                }
            }
            mTouchState = TOUCH_STATE_REST;
            mActivePointerId = INVALID_POINTER;
            releaseVelocityTracker();
            break;
        case MotionEvent.ACTION_CANCEL:
            if (mTouchState == TOUCH_STATE_SCROLLING) {
                final int screenWidth = getWidth();
                final int whichScreen = (getScrollX() + (screenWidth / 2)) / screenWidth;
                snapToScreen(whichScreen, 0, true);
            }
            mTouchState = TOUCH_STATE_REST;
            mActivePointerId = INVALID_POINTER;
            releaseVelocityTracker();
            break;
        case MotionEvent.ACTION_POINTER_UP:
        	Log.d(TAG, "onTouchEvent.ACTION_POINTER_UP.................");
            onSecondaryPointerUp(ev);
            break;
        }

        return true;
    }
    
    private void acquireVelocityTrackerAndAddMovement(MotionEvent ev) {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(ev);
    }

    private void releaseVelocityTracker() {
        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    void snapToScreen(int whichScreen) {
        snapToScreen(whichScreen, 0, false);
    }

    private void snapToScreen(int whichScreen, int velocity, boolean settle) {
        //if (!mScroller.isFinished()) return;

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

        //enableChildrenCache(mCurrentScreen, whichScreen);

        mNextScreen = whichScreen;

        //mPreviousIndicator.setLevel(mNextScreen);
        //mNextIndicator.setLevel(mNextScreen);

        View focusedChild = getFocusedChild();
        if (focusedChild != null && whichScreen != mCurrentScreen &&
                focusedChild == getChildAt(mCurrentScreen)) {
            focusedChild.clearFocus();
        }
        
        final int screenDelta = Math.max(1, Math.abs(whichScreen - mCurrentScreen));
        final int newX = whichScreen * getWidth();
        final int delta = newX - mScrollX;
        int duration = (screenDelta + 1) * 100;

        if (!mScroller.isFinished()) {
            mScroller.abortAnimation();
        }
        
        if (settle) {
            mScrollInterpolator.setDistance(screenDelta);
        } else {
            mScrollInterpolator.disableSettle();
        }
        
        velocity = Math.abs(velocity);
        if (velocity > 0) {
            duration += (duration / (velocity / BASELINE_FLING_VELOCITY))
                    * FLING_VELOCITY_INFLUENCE;
        } else {
            duration += 100;
        }

        awakenScrollBars(duration);
        mScroller.startScroll(mScrollX, 0, delta, 0, duration);
        invalidate();
    }



    @Override
    protected Parcelable onSaveInstanceState() {
        final SavedState state = new SavedState(super.onSaveInstanceState());
        state.currentScreen = mCurrentScreen;
        return state;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        SavedState savedState = (SavedState) state;
        super.onRestoreInstanceState(savedState.getSuperState());
        if (savedState.currentScreen != -1) {
            mCurrentScreen = savedState.currentScreen;

        }
    }


    public void scrollLeft() {
    	Log.d(TAG, "scrollLeft.................");
       
        if (mScroller.isFinished()) {
            if (mCurrentScreen > 0) snapToScreen(mCurrentScreen - 1);
        } else {
            if (mNextScreen > 0) snapToScreen(mNextScreen - 1);            
        }
    }

    public void scrollRight() {
    	Log.d(TAG, "scrollRight.................");

        if (mScroller.isFinished()) {
            if (mCurrentScreen < getChildCount() -1) snapToScreen(mCurrentScreen + 1);
        } else {
            if (mNextScreen < getChildCount() -1) snapToScreen(mNextScreen + 1);            
        }
    }

    public int getScreenForView(View v) {
        int result = -1;
        if (v != null) {
            ViewParent vp = v.getParent();
            int count = getChildCount();
            for (int i = 0; i < count; i++) {
                if (vp == getChildAt(i)) {
                    return i;
                }
            }
        }
        return result;
    }


    /**
     * @return True is long presses are still allowed for the current touch
     */
    public boolean allowLongPress() {
        return mAllowLongPress;
    }
    
    /**
     * Set true to allow long-press events to be triggered, usually checked by
     * {@link Launcher} to accept or block dpad-initiated long-presses.
     */
    public void setAllowLongPress(boolean allowLongPress) {
        mAllowLongPress = allowLongPress;
    }

   

    void moveToDefaultScreen(boolean animate) {
        if (animate) {
            snapToScreen(mDefaultScreen);
        } else {
            setCurrentScreen(mDefaultScreen);
        }
        getChildAt(mDefaultScreen).requestFocus();
    }

//    void setIndicators(Drawable previous, Drawable next) {
//        mPreviousIndicator = previous;
//        mNextIndicator = next;
//        previous.setLevel(mCurrentScreen);
//        next.setLevel(mCurrentScreen);
//    }

    public static class SavedState extends BaseSavedState {
        int currentScreen = -1;

        SavedState(Parcelable superState) {
            super(superState);
        }

        private SavedState(Parcel in) {
            super(in);
            currentScreen = in.readInt();
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeInt(currentScreen);
        }

        public static final Parcelable.Creator<SavedState> CREATOR =
                new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }
}
package com.mylauncher;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.LinearLayout;
import android.view.MotionEvent;
import android.util.Log;

public class CellLayout extends LinearLayout {
	private static final String TAG = "MyLauncher.CellLayout";
    public CellLayout(Context context, AttributeSet attrs) {
		super(context, attrs);
		// TODO Auto-generated constructor stub
	}

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
    	Log.d(TAG, "onInterceptTouchEvent, action=" + ev.getAction());
    	return true;
    }
    
    @Override
    public boolean onTouchEvent(MotionEvent ev) {
    	Log.d(TAG, "onTouchEvent, action=" + ev.getAction());
    	return true;
    }    
    
}






原文链接:http://blog.csdn.net/zmyde2010/article/details/6911650
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