ScrollLayout.java

package com.itap.voiceemoticon.widget;

import com.itap.voiceemoticon.VEApplication;

import android.content.Context;
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;

/**
 * 
 * <br>==========================
 * <br> author：Zenip
 * <br> email：lxyczh@gmail.com
 * <br> create：2013-1-26下午3:49:43
 * <br>==========================
 */
public class ScrollLayout extends ViewGroup {

    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;

    private PageListener pageListener;

    public ScrollLayout(Context context) {
        this(context, null, 0);
    }


    public ScrollLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ScrollLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mScroller = new Scroller(context);
        mCurScreen = mDefaultScreen;
        mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        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;
            }
        }
    }

    @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("ScrollLayout only canmCurScreen run at EXACTLY mode!");
        //        }

        /**
         * wrap_content 传进去的是AT_MOST 固定数值或fill_parent 传入的模式是EXACTLY
         */
        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);
        }
        scrollTo(mCurScreen * width, 0);
    }

    /**
     * According to the position of current layout scroll to the destination
     * page.
     */
    public void snapToDestination() {
        final int screenWidth = getWidth();
        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();
            mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta));
            mCurScreen = whichScreen;
            this.postDelayed(new Runnable() {
                @Override
                public void run() {
                    firePageEvent(mCurScreen);
                }
            }, Math.abs(delta));
            invalidate(); // Redraw the layout
        }
    }

    public void setToScreen(int whichScreen) {
        whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
        mCurScreen = whichScreen;
        firePageEvent(mCurScreen);
        scrollTo(whichScreen * getWidth(), 0);
    }

    /**
     * 获得当前页码
     */
    public int getCurScreen() {
        return mCurScreen;
    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            postInvalidate();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d(VEApplication.TAG, "onTouchEvent  action = " + event.getAction() + ", mTouchState = " + mTouchState);
        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:
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
            }
            mLastMotionX = x;
            break;
        case MotionEvent.ACTION_MOVE:
            int deltaX = (int) (mLastMotionX - x);
            mLastMotionX = x;
            scrollBy(deltaX, 0);
            break;
        case MotionEvent.ACTION_UP:
            final VelocityTracker velocityTracker = mVelocityTracker;
            velocityTracker.computeCurrentVelocity(1000);
            int velocityX = (int) velocityTracker.getXVelocity();

            if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
                // Fling enough to move left
                snapToScreen(mCurScreen - 1);

            } else if (velocityX < -SNAP_VELOCITY && mCurScreen < getChildCount() - 1) {
                // Fling enough to move right
                snapToScreen(mCurScreen + 1);
            } else {
                snapToDestination();
            }
            if (mVelocityTracker != null) {
                mVelocityTracker.recycle();
                mVelocityTracker = null;
            }
            mTouchState = TOUCH_STATE_REST;
            break;
        case MotionEvent.ACTION_CANCEL:
            mTouchState = TOUCH_STATE_REST;
            break;
        }
        return true;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        final int action = ev.getAction();
        Log.d(VEApplication.TAG, "onInterceptTouchEvent  action = " + ev.getAction() + ", mTouchState = " + mTouchState);
        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:
            final int xDiff = (int) Math.abs(mLastMotionX - x);
            if (Math.abs(xDiff) > mTouchSlop) {
                mTouchState = TOUCH_STATE_SCROLLING;
            }
            break;
        case MotionEvent.ACTION_DOWN:
            mLastMotionX = x;
            //	mLastMotionY = y;
            mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
            break;

        case MotionEvent.ACTION_CANCEL:
        case MotionEvent.ACTION_UP:
            mTouchState = TOUCH_STATE_REST;
            break;
        }
        return mTouchState != TOUCH_STATE_REST;
    }

    public void setPageListener(PageListener pageListener) {
        this.pageListener = pageListener;
    }

    public void firePageEvent(int page) {
        if (pageListener != null) {
            pageListener.page(page);
        }
    }

    public interface PageListener {
        void page(int page);
    }
}