Android自定义ViewGroup实现可滚动的横向布局（2）

package com.example.libingyuan.horizontallistview.ScrollViewGroup;

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

/**
 * 自定义ViewGroup
 * 在横向布局的基础上，增加啦滚动效果，但是没有边界限制
 */
public class ScrollViewGroup extends ViewGroup {
  private Scroller mScroller;
  private float mLastMotionX = 0;

  public ScrollViewGroup(Context context) {
    this(context, null);
  }

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

  public ScrollViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context);
  }

  private void init(Context context) {
    mScroller = new Scroller(context);
  }

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


  @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:
        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;
  }

  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    int childLeft = 0;
    int childWidth;
    int height = getHeight();
    int childCount = getChildCount();
    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);
  }
}