长度自适应 自动换行Flowlayout

import android.annotation.SuppressLint;
import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

/**
 * 根据子View的宽度排列的流式布局
 */
public class FlowLayout extends ViewGroup {
   public FlowLayout(Context context) {
      super(context);
   }

   public FlowLayout(Context context, AttributeSet attrs) {
      super(context, attrs);
   }

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

   /**
    * 父容器生成 子view 的布局LayoutParams;
    * 一句话道出LayoutParams的本质：LayoutParams是Layout提供给其中的Children使用的。
    * 如果要自定义ViewGroup支持子控件的layout_margin参数,
    * 则自定义的ViewGroup类必须重载generateLayoutParams()函数，
    * 并且在该函数中返回一个ViewGroup.MarginLayoutParams派生类对象，这样才能使用margin参数。
    */
   @Override
   protected LayoutParams generateLayoutParams(LayoutParams p) {
      return new MarginLayoutParams(p);
   }

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

   @Override
   protected LayoutParams generateDefaultLayoutParams() {
      return new MarginLayoutParams(LayoutParams.MATCH_PARENT,
            LayoutParams.MATCH_PARENT);
   }

   @SuppressLint("DrawAllocation")
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
      int measureWidth = MeasureSpec.getSize(widthMeasureSpec);
      int measureHeight = MeasureSpec.getSize(heightMeasureSpec);
      int measureWidthMode = MeasureSpec.getMode(widthMeasureSpec);
      int measureHeightMode = MeasureSpec.getMode(heightMeasureSpec);

      int lineWidth = 0;
      int lineHeight = 0;
      int height = 0;
      int width = 0;
      int count = getChildCount();
      for (int i = 0; i < count; i++) {
         View child = getChildAt(i);
         measureChild(child, widthMeasureSpec, heightMeasureSpec);
         // 如果忘记重写generateLayoutParams，则hild.getLayoutParams()将不是MarginLayoutParams的实例
         // 在强制转换时就会出错，此时我们把左右间距设置为0，但由于在计算布局宽高时没有加上间距值，
         // 就是计算出的宽高要比实际小，所以是onLayout时就会出错
         MarginLayoutParams lp = null;
         if (child.getLayoutParams() instanceof MarginLayoutParams) {
            lp = (MarginLayoutParams) child.getLayoutParams();
         } else {
            lp = new MarginLayoutParams(0, 0);
         }
         int childWidth = child.getMeasuredWidth() + lp.leftMargin
               + lp.rightMargin;
         int childHeight = child.getMeasuredHeight() + lp.topMargin
               + lp.bottomMargin;

         if (lineWidth + childWidth > measureWidth) {
            // 需要换行
            width = Math.max(lineWidth, width);
            height += lineHeight;
            // 因为由于盛不下当前控件，而将此控件调到下一行，所以将此控件的高度和宽度初始化给lineHeight、lineWidth
            lineHeight = childHeight;
            lineWidth = childWidth;
         } else {
            // 否则累加值lineWidth,lineHeight取最大高度
            lineHeight = Math.max(lineHeight, childHeight);
            lineWidth += childWidth;
         }

         // 最后一行是不会超出width范围的，所以要单独处理
         if (i == count - 1) {
            height += lineHeight;
            width = Math.max(width, lineWidth);
         }
      }
      /*
       * 当属性是MeasureSpec.EXACTLY时，那么它的高度就是确定的，
       * 只有当是wrap_content时，根据内部控件的大小来确定它的大小时,
       * 大小是不确定的，属性是AT_MOST,此时，就需要我们自己计算它的应当的大小，并设置进去
       */
      setMeasuredDimension(
            (measureWidthMode == MeasureSpec.EXACTLY) ? measureWidth
                  : width,
            (measureHeightMode == MeasureSpec.EXACTLY) ? measureHeight
                  : height);
   }

   @Override
   protected void onLayout(boolean changed, int l, int t, int r, int b) {
      int count = getChildCount();
      int lineWidth = 0;
      int lineHeight = 0;
      int top = 0, left = 0;
      for (int i = 0; i < count; i++) {
         View child = getChildAt(i);
         MarginLayoutParams lp = (MarginLayoutParams) child
               .getLayoutParams();
         int childWidth = child.getMeasuredWidth() + lp.leftMargin
               + lp.rightMargin;
         int childHeight = child.getMeasuredHeight() + lp.topMargin
               + lp.bottomMargin;

         if (childWidth + lineWidth > getMeasuredWidth()) {
            // 如果换行,当前控件将跑到下一行，从最左边开始，所以left就是0，而top则需要加上上一行的行高，才是这个控件的top点;
            top += lineHeight;
            left = 0;
            // 同样，重新初始化lineHeight和lineWidth
            lineHeight = childHeight;
            lineWidth = childWidth;
         } else {
            lineHeight = Math.max(lineHeight, childHeight);
            lineWidth += childWidth;
         }
         // 计算childView的left,top,right,bottom
         int lc = left + lp.leftMargin;
         int tc = top + lp.topMargin;
         int rc = lc + child.getMeasuredWidth();
         int bc = tc + child.getMeasuredHeight();
         child.layout(lc, tc, rc, bc);
         // 将left置为下一子控件的起始点
         left += childWidth;
      }
   }
}