自定义viewgroup（3）--可滚动，但是超过边界会回弹

上一篇文章《自定义viewgroup（2）》地址：http://blog.csdn.net/qq_18148011/article/details/53761551

代码

package com.example.libingyuan.horizontallistview.ScrollViewGroup;

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

/**
 * 自定义ViewGroup
 * 在滚动的基础上，增加了边界限制
 */
public class ScrollViewGroup extends ViewGroup {
    //滚动计算辅助类
    private Scroller mScroller;
    //手指落点的X坐标
    private float mLastMotionX = 0;
    //屏幕宽度
    private int screenWidth;

    /**
     * 使用new关键字创建对象的时候调用
     * @param context 上下文
     */
    public ScrollViewGroup(Context context) {
        this(context, null);
    }
    /**
     * 在XML文件中使用的时候调用
     * @param context 上下文
     * @param attrs 属性：如 android:layout_width="wrap_content"
     */
    public ScrollViewGroup(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    /**
     * 在xml文件中调用，并且使用了自定义属性的时候调用
     * @param context 上下文
     * @param attrs 属性：如 android:layout_width="wrap_content"
     * @param defStyleAttr 自定义属性的id
     */
    public ScrollViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    /**
     * 初始化方法
     * 初始化滚动辅助类Scroller以及计算出屏幕宽度
     * @param context
     */
    private void init(Context context) {
        mScroller = new Scroller(context);
        WindowManager manager = (WindowManager) context
                .getSystemService(Context.WINDOW_SERVICE);
        DisplayMetrics outMetrics = new DisplayMetrics();
        manager.getDefaultDisplay().getMetrics(outMetrics);
        screenWidth = outMetrics.widthPixels;
    }

    /**
     * 滚动时需要重写的方法，用于控制滚动
     */
    @Override
    public void computeScroll() {
        //判断滚动时候停止
        if (mScroller.computeScrollOffset()) {
            //滚动到指定的位置
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            //这句话必须写，否则不能实时刷新
            postInvalidate();
        }
    }

    /**
     * 手指触屏事件监听
     * @param event
     * @return
     */
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        int action = event.getAction();
        float x = event.getX();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                }
                mLastMotionX = event.getX();
                break;
            case MotionEvent.ACTION_MOVE:
                float delt = mLastMotionX - x;
                mLastMotionX = x;
                scrollBy((int) delt, 0);
                break;
            case MotionEvent.ACTION_UP:
                View lastChild=getChildAt(getChildCount()-1);
                int finalyChild= (int) (lastChild.getX()+lastChild.getWidth()-screenWidth);
                if (getScrollX()<0){
                    scrollTo(0,0);
                }
                if (getScrollX()>=finalyChild)
                    scrollTo(finalyChild,0);
                invalidate();
                break;

            default:
                break;
        }

        return true;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        //重新设置宽高
        this.setMeasuredDimension(measureWidth(widthMeasureSpec, heightMeasureSpec), measureHeight(widthMeasureSpec, heightMeasureSpec));
    }

     /**
     * 测量宽度
     */
    private int measureWidth(int widthMeasureSpec, int heightMeasureSpec) {
        // 宽度
        int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);
        int modeWidth = MeasureSpec.getMode(widthMeasureSpec);
        //父控件的宽（wrap_content）
        int width = 0;
        int childCount = getChildCount();

        //重新测量子view的宽度，以及最大高度
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            measureChild(child, widthMeasureSpec, heightMeasureSpec);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
            int childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
            width += childWidth;
        }
        return modeWidth == MeasureSpec.EXACTLY ? sizeWidth : width;
    }

    /**
     * 测量高度
     */
    private int measureHeight(int widthMeasureSpec, int heightMeasureSpec) {
        //高度
        int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);
        int modeHeight = MeasureSpec.getMode(heightMeasureSpec);
        //父控件的高（wrap_content）
        int height = 0;
        int childCount = getChildCount();

        //重新测量子view的宽度，以及最大高度
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            measureChild(child, widthMeasureSpec, heightMeasureSpec);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
            int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
            height += childHeight;
        }
        height = height / childCount;
        return modeHeight == MeasureSpec.EXACTLY ? sizeHeight : height;
    }

    /**
     * 给子布局设定位置
     */
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int childLeft = 0;//子View左边的间距
        int childWidth;//子View的宽度
        int height = getHeight();//屏幕的宽度
        int childCount = getChildCount();//子View的数量
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
            childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
            child.layout(childLeft, 0, childLeft + childWidth, height);
            childLeft += childWidth;
        }
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }
}