流动布局

public class FlowLayout extends ViewGroup {    
    private final int mHorizontalSpacing = dp2px(16); //每个item横向间距    
    private final int mVerticalSpacing = dp2px(8); //每个item横向间距    
    private List<List<View>> allViews = new ArrayList<>(); // 记录所有行，用来layout    
    private List<Integer> lineHeights = new ArrayList<>(); // 记录每行的高度，用来layout    
    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);    
    }    
    public FlowLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {        
        super(context, attrs, defStyleAttr, defStyleRes);    
    }    
    private void clearMeasureParams() {        
        allViews.clear();        
        lineHeights.clear();    
    }    
    
    @Override    
    protected void onLayout(boolean changed, int l, int t, int r, int b) {       
        int lineCount = allViews.size();       
        int paddingLeft =  getPaddingLeft();       
        int paddingTop = getPaddingTop();       
        for (int i = 0; i < lineCount; i++) {            
            List<View> lineViews = allViews.get(i);            
            int lineHeight = lineHeights.get(i);            
            for (int j = 0; j < lineViews.size(); j++) {                
                View view = lineViews.get(j);                
                int left = paddingLeft;                
                int top = paddingTop;                
                int right = left + view.getMeasuredWidth();                
                int bottom = top + view.getMeasuredHeight();                
                view.layout(left, top, right, bottom);                
                paddingLeft = right + mHorizontalSpacing;            
            }            
            paddingTop = paddingTop + lineHeight + mVerticalSpacing;           
            paddingLeft = getPaddingLeft();        
        }    
    }    
    @Override    
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        
        clearMeasureParams();        
        // 先测量子View        
        int childCount = getChildCount();        
        // 获取子View的左 padding        
        int paddingLeft = getPaddingLeft();        
        // 获取子View的右 padding        
        int paddingRight = getPaddingRight();        
        // 获取子View的上 padding        
        int paddingTop = getPaddingTop();        
        // 获取子View的下 padding        
        int paddingBottom = getPaddingBottom();        
        int selfWidth = MeasureSpec.getSize(widthMeasureSpec); // ViewGroup解析父容器传递过来的宽度        
        int selfHeight = MeasureSpec.getSize(heightMeasureSpec); // ViewGroup解析父容器传递过来的高度        
        List<View> lineViews = new ArrayList<>(); // 记录每行显示的所有View        
        int lineWidthUsed = 0; // 记录当前行已经使用的宽度        
        int lineHeightUsed = 0; // 记录当前行已经使用的高度        
        int parentNeedWidth = 0; // measure过程中，子View要求的父ViewGroup的宽        
        int parentNeedHeight = 0; // measure过程中，子View要求的父ViewGroup的高        
        for (int i = 0; i < childCount; i++) {            
            View child = getChildAt(i);            
            LayoutParams layoutParams = child.getLayoutParams();            
            if(child.getVisibility() != View.GONE) {                
                int childWidthMeasureSpec =                        
                    getChildMeasureSpec(widthMeasureSpec, paddingLeft + paddingRight, layoutParams.width);                
                int childHeightMeasureSpec =                        
                    getChildMeasureSpec(heightMeasureSpec, paddingTop + paddingBottom, layoutParams.height);                
                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);                
                // 获取测量的子View的宽度                
                int measuredWidth = child.getMeasuredWidth();                
                // 获取测量的子View的高度                
                int measuredHeight = child.getMeasuredHeight();                
                // 判断是否需要换行                
                if (measuredWidth + lineWidthUsed + mHorizontalSpacing > selfWidth ) {                    
                    allViews.add(lineViews);                    
                    lineHeights.add(lineHeightUsed);                    
                    // 换行，数据清除                    
                    parentNeedWidth = Math.max(parentNeedWidth, lineWidthUsed + mHorizontalSpacing);                    
                    parentNeedHeight = parentNeedHeight + lineHeightUsed + mVerticalSpacing;                    
                    lineViews = new ArrayList<>();                    
                    lineWidthUsed = 0;                    
                    lineHeightUsed = 0;                
                }                
                lineViews.add(child);                
                lineWidthUsed = lineWidthUsed + measuredWidth + mHorizontalSpacing;                
                lineHeightUsed = Math.max(lineHeightUsed, measuredHeight);                
                // 判断是否是最后一行                
                if (i == childCount - 1) {                    
                    allViews.add(lineViews);                    
                    lineHeights.add(lineHeightUsed);                    
                    parentNeedWidth = Math.max(parentNeedWidth, lineWidthUsed + mHorizontalSpacing);                    
                    parentNeedHeight = parentNeedHeight + lineHeightUsed + mVerticalSpacing;                
                }            
            }        
        }        
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);        
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);        
        int realWidth = (widthMode == MeasureSpec.EXACTLY) ? selfWidth : parentNeedWidth;        
        int realHeight = (heightMode == MeasureSpec.EXACTLY) ? selfHeight : parentNeedHeight;        
        // 再测量自己的高度        
        setMeasuredDimension(realWidth, realHeight);    
    }    
    public static int dp2px(int dp) {        
        return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, Resources.getSystem().getDisplayMetrics());    
    }
}