打造安卓流式布局

public class FlowLayout extends ViewGroup {

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

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

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);
        int modeWidth = MeasureSpec.getMode(widthMeasureSpec);

        int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);
        int modeHeight = MeasureSpec.getMode(heightMeasureSpec);

        int width = 0;
        int height = 0;
        // 记录每一行的宽度和高度
        int lineWidth = 0;
        int lineHeight = 0;
        //得到内部元素的个数
        int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            //测量子View的宽和高
            measureChild(child,widthMeasureSpec,heightMeasureSpec);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
            //子View占据的宽度
            int childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
            // 子View占据的高度
            int childHeight = child.getMeasuredHeight() + lp.bottomMargin + lp.topMargin;
            // 换行
            if (lineWidth + childWidth > sizeWidth - getPaddingLeft() - getPaddingRight()){
                width = Math.max(width,lineWidth);
                // 重置lineWidth
                lineWidth = childWidth;
                // 记录行高
                height += lineHeight;
                lineHeight = childHeight;
            }else {
                lineWidth += childWidth;
                // 得到当前行最大高度
                lineHeight = Math.max(lineHeight,childHeight);
            }
            // 最后一个控件(无论是否换行都要执行这个语句)
            if ( i == childCount - 1){
                width = Math.max(lineWidth,width);
                height += lineHeight;
            }

        }
        Log.d("TAG", "sizeHeight" + sizeHeight);
        Log.d("TAG", "sizeWidth" + sizeWidth);
      setMeasuredDimension(
              modeWidth == MeasureSpec.EXACTLY  ? sizeWidth:width + getPaddingRight() + getPaddingLeft(),
              modeHeight == MeasureSpec.EXACTLY ? sizeHeight:height + getPaddingTop() + getPaddingBottom()
      );
    }

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

    /*
    * 存储所有的View
    * */
    private List<List<View>> allViews = new ArrayList<>();
    private List<Integer> mLineHeight = new ArrayList<>();
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        allViews.clear();
        mLineHeight.clear();
        // 当前ViewGroup的宽度
        int width = getWidth();

        int lineWidth = 0;
        int lineHeight = 0;
        List<View> lineViews = new ArrayList<>();
        int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
            int childWidth = child.getMeasuredWidth();
            int childHeight = child.getMeasuredHeight();
            // 换行
            if (lineWidth + childWidth + lp.leftMargin + lp.rightMargin > width - getPaddingLeft() - getPaddingRight()){
                mLineHeight.add(lineHeight);
                allViews.add(lineViews);
                lineWidth = 0;
                lineHeight = childHeight + lp.topMargin + lp.bottomMargin;
                lineViews = new ArrayList<>();
            }
            lineWidth += childWidth + lp.leftMargin + lp.rightMargin;
            lineHeight = Math.max(lineHeight,childHeight + lp.topMargin + lp.bottomMargin);

            lineViews.add(child);
        }
        // 处理最后一行
        mLineHeight.add(lineHeight);
        allViews.add(lineViews);

        // 设置子View的位置
        int left = getPaddingLeft();
        int top = getPaddingTop();

        // 行数
        int lineNum = allViews.size();
        for (int i = 0; i < lineNum; i++) {
            // 当前行的所有View
            lineViews = allViews.get(i);
            lineHeight = mLineHeight.get(i);
            for (int j = 0;j < lineViews.size();j++){
                View child = lineViews.get(j);
                //判断child的状态
                if (child.getVisibility() == View.GONE){
                    continue;
                }
                MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

                int lc = left + lp.leftMargin;
                int tc = top + lp.topMargin;
                int rc = lc + child.getMeasuredWidth();
                int bc = tc + child.getMeasuredHeight();
                // 为子View进行布局
                child.layout(lc,tc,rc,bc);
                left += child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
            }
            left = getPaddingLeft();
            top += lineHeight;
        }
    }

}