Android简单实现一个流式布局

class FlowLayout extends ViewGroup {  
    //item行高  
    private float itemHeight;  
    //item横向间隔  
    private float itemSpace;  
    //列间隔  
    private float dividerHeight;  
  
  
  
    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 );  
    }  
  
    @Override  
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
        measureChildren( widthMeasureSpec,heightMeasureSpec );  
        int widthSize = MeasureSpec.getSize( widthMeasureSpec ); //包含padding  
        int heightSize = MeasureSpec.getSize( heightMeasureSpec );  
        int modeWidth = MeasureSpec.getMode( widthMeasureSpec );  
        int modeHeight = MeasureSpec.getMode( heightMeasureSpec );  

        int resultWidth=0;  
        int resultHeight=0;  

        Map<String,Integer> computeResult = compute(widthSize-getPaddingRight());  

        //如果是精确模式采用父布局指定的尺寸  
        if(modeWidth == MeasureSpec.EXACTLY){  
            resultWidth = widthSize;  
        }else{ //wrap_content AT_MOST  
            resultWidth = computeResult.get( "allChildWidth" );  
        }  
        if(modeHeight == MeasureSpec.EXACTLY){  
            resultHeight = heightSize;  
        }else{  
            resultHeight = computeResult.get( "allChildHeight" );  
        }  

        setMeasuredDimension( resultWidth,resultHeight );  

    }  

    @Override  
    protected void onLayout(boolean changed, int l, int t, int r, int b) {  
        int count = getChildCount();  
        for(int i= 0;i<count;i++){  
            View child=getChildAt( i );  
            Rect rect = (Rect) child.getTag();  
            child.layout( rect.left,rect.top,rect.right,rect.bottom );  
        }  
    }  


    //测量过程  
    //@param flowWidth 该view的宽度  
    //*@return 返回子元素总所占宽度和高度（用于计算Flowlayout的AT_MOST模式设置宽高）  
    private Map<String,Integer> compute(int flowWidth){  
        boolean aRow = true; //是否是单行 ??  
        MarginLayoutParams params;  
        int lineWidth = getPaddingLeft(); //当前行已占宽度  
        int lineHeight = getPaddingTop();  
        int rowMaxHeight = 0; //当前行所有元素的最大高度  

        int count =getChildCount();  

        for(int i=0;i<count;i++){  
        View child = getChildAt( i );  

        params =(MarginLayoutParams) child.getLayoutParams();  
        int childWidth = child.getMeasuredWidth() + params.rightMargin + params.leftMargin;  
        int childHeight = child.getMeasuredHeight() + params.topMargin + params.bottomMargin;  

        rowMaxHeight = Math.max(rowMaxHeight,childHeight);  

        if(lineWidth + childWidth > flowWidth ){ //换行  
            lineHeight += rowMaxHeight;  
            rowMaxHeight = childHeight;  
            aRow = false;  

            //重置行宽度 ？？  
            lineWidth = getPaddingLeft();  
        }  
        lineWidth += childWidth;  
        child.setTag( new Rect( lineWidth - childWidth + params.leftMargin,lineHeight +  
        params.topMargin,lineWidth - params.rightMargin,lineHeight + childHeight - params.bottomMargin ) );  
        }  

        Map<String,Integer> flowMap = new HashMap<>( );  
        if (aRow) {  
            flowMap.put( "allChildWidth",lineWidth + getPaddingRight() );  
        } else {  
            flowMap.put( "allChildWidth",flowWidth + getPaddingRight() );  
        }  
        flowMap.put( "allChildHeight",lineHeight + rowMaxHeight+getPaddingBottom() );  
        return flowMap;  
    }  
}