Android 自定义ViewGroup布局控件，垂直滚动引导

1、Scroller类：滚动辅助类，功能很吊，可以跟踪当前View的滚动情况。设置mScroller滚动的位置时，并不会导致View的滚

动，通常是用mScroller记录/计算View滚动的位置，再重写View的computeScroll()，完成实际的滚动。

初始化方法：mScroller = new Scroller(context); http://www.cnblogs.com/xbx2015/p/4683681.html

2、View自身带有很多滚动的特性，厉害

    public void setScrollX(int value) {         throw new RuntimeException("Stub!");     }

    public void setScrollY(int value) {         throw new RuntimeException("Stub!");     }

    public final int getScrollX() {         throw new RuntimeException("Stub!");     }

    public final int getScrollY() {         throw new RuntimeException("Stub!");     }

    public void scrollTo(int x, int y) {         throw new RuntimeException("Stub!");     }

    public void scrollBy(int x, int y) {         throw new RuntimeException("Stub!");     }

    public void computeScroll() {         throw new RuntimeException("Stub!");     }

import android.content.Context;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Scroller;

public class VerticalLinearLayout extends ViewGroup
{
    /**
     * 屏幕的高度
     */
    private int mScreenHeight;
    /**
     * 手指按下时的getScrollY
     */
    private int mScrollStart;
    /**
     * 手指抬起时的getScrollY
     */
    private int mScrollEnd;
    /**
     * 记录移动时的Y
     */
    private int mLastY;
    /**
     * 滚动的辅助类
     */
    private Scroller mScroller;
    /**
     * 是否正在滚动
     */
    private boolean isScrolling;
    /**
     * 加速度检测
     */
    private VelocityTracker mVelocityTracker;
    /**
     * 记录当前页
     */
    private int currentPage = 0;

    private OnPageChangeListener mOnPageChangeListener;

    public VerticalLinearLayout(Context context, AttributeSet attrs)
    {
        super(context, attrs);

        /**
         * 获得屏幕的高度
         */
        WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        DisplayMetrics outMetrics = new DisplayMetrics();
        wm.getDefaultDisplay().getMetrics(outMetrics);
        mScreenHeight = outMetrics.heightPixels;
        // 初始化
        mScroller = new Scroller(context);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int count = getChildCount();
        for (int i = 0; i < count; ++i)
        {
            View childView = getChildAt(i);
            measureChild(childView, widthMeasureSpec, heightMeasureSpec);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b)
    {
        if (changed)
        {
            int childCount = getChildCount();
            // 设置主布局的高度
            MarginLayoutParams lp = (MarginLayoutParams) getLayoutParams();
            lp.height = mScreenHeight * childCount;
            setLayoutParams(lp);

            for (int i = 0; i < childCount; i++)
            {
                View child = getChildAt(i);
                if (child.getVisibility() != View.GONE)
                {
                    child.layout(l, i * mScreenHeight, r, (i + 1) * mScreenHeight);// 调用每个自布局的layout
                }
            }

        }

    }

    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        // 如果当前正在滚动，调用父类的onTouchEvent
        if (isScrolling)
            return super.onTouchEvent(event);

        int action = event.getAction();
        int y = (int) event.getY();

        obtainVelocity(event);
        switch (action)
        {
        case MotionEvent.ACTION_DOWN:

            mScrollStart = getScrollY();
            mLastY = y;
            break;
        case MotionEvent.ACTION_MOVE:

            if (!mScroller.isFinished())
            {
                mScroller.abortAnimation();
            }

            int dy = mLastY - y;
            // 边界值检查
            int scrollY = getScrollY();
            // 已经到达顶端，下拉多少，就往上滚动多少
            if (dy < 0 && scrollY + dy < 0)
            {
                dy = -scrollY;
            }
            // 已经到达底部，上拉多少，就往下滚动多少
            if (dy > 0 && scrollY + dy > getHeight() - mScreenHeight)
            {
                dy = getHeight() - mScreenHeight - scrollY;
            }

            scrollBy(0, dy);
            mLastY = y;
            break;
        case MotionEvent.ACTION_UP:

            mScrollEnd = getScrollY();

            int dScrollY = mScrollEnd - mScrollStart;

            if (wantScrollToNext())// 往上滑动
            {
                if (shouldScrollToNext())
                {
                    mScroller.startScroll(0, getScrollY(), 0, mScreenHeight - dScrollY);

                } else
                {
                    mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
                }

            }

            if (wantScrollToPre())// 往下滑动
            {
                if (shouldScrollToPre())
                {
                    mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - dScrollY);

                } else
                {
                    mScroller.startScroll(0, getScrollY(), 0, -dScrollY);
                }
            }
            isScrolling = true;
            postInvalidate();
            recycleVelocity();
            break;
        }

        return true;
    }

    /**
     * 根据滚动距离判断是否能够滚动到下一页
     * 
     * @return
     */
    private boolean shouldScrollToNext()
    {
        return mScrollEnd - mScrollStart > mScreenHeight / 2 || Math.abs(getVelocity()) > 600;
    }

    /**
     * 根据用户滑动，判断用户的意图是否是滚动到下一页
     * 
     * @return
     */
    private boolean wantScrollToNext()
    {
        return mScrollEnd > mScrollStart;
    }

    /**
     * 根据滚动距离判断是否能够滚动到上一页
     * 
     * @return
     */
    private boolean shouldScrollToPre()
    {
        return -mScrollEnd + mScrollStart > mScreenHeight / 2 || Math.abs(getVelocity()) > 600;
    }

    /**
     * 根据用户滑动，判断用户的意图是否是滚动到上一页
     * 
     * @return
     */
    private boolean wantScrollToPre()
    {
        return mScrollEnd < mScrollStart;
    }

    @Override
    public void computeScroll()
    {
        super.computeScroll();
        if (mScroller.computeScrollOffset())
        {
            scrollTo(0, mScroller.getCurrY());
            postInvalidate();
        } else
        {

            int position = getScrollY() / mScreenHeight;

            Log.e("xxx", position + "," + currentPage);
            if (position != currentPage)
            {
                if (mOnPageChangeListener != null)
                {
                    currentPage = position;
                    mOnPageChangeListener.onPageChange(currentPage);
                }
            }

            isScrolling = false;
        }

    }

    /**
     * 获取y方向的加速度
     * 
     * @return
     */
    private int getVelocity()
    {
        mVelocityTracker.computeCurrentVelocity(1000);
        return (int) mVelocityTracker.getYVelocity();
    }

    /**
     * 释放资源
     */
    private void recycleVelocity()
    {
        if (mVelocityTracker != null)
        {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    /**
     * 初始化加速度检测器
     * 
     * @param event
     */
    private void obtainVelocity(MotionEvent event)
    {
        if (mVelocityTracker == null)
        {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(event);
    }

    /**
     * 设置回调接口
     * 
     * @param onPageChangeListener
     */
    public void setOnPageChangeListener(OnPageChangeListener onPageChangeListener)
    {
        mOnPageChangeListener = onPageChangeListener;
    }

    /**
     * 回调接口
     * 
     * @author zhy
     * 
     */
    public interface OnPageChangeListener
    {
        void onPageChange(int currentPage);
    }
}