自定义UI——流布局

    流布局的实现是熟悉自定义控件流程一个比较好的例子，在代码中详细注释：

代码：

public class MyFlowLayout extends ViewGroup {

    //每一行行高集合
    List<Integer> heights = new ArrayList<>();
    //每一行子view的集合
    List<List<View>> views = new ArrayList<>();

    public MyFlowLayout(Context context) {
        super(context);
    }

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

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

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //从运行机制来讲，在7.0之前布局加载流程调用scheduleTraversals（）
        // 会依次调用onMeasure-->onLayout，
        // 但是在7.0之后我门会发现运行机制发生了改变，
        // 如果是第一次的onMeasure那么他不会去调用onLayout，
        // 所以这里变成了两次onMeasure一次onLayout 此处清空第一次测量的结果
        heights.clear();
        views.clear();
        //获取父布局的宽高以及自己的测量模式
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        //当前View的宽高
        int measureWidth = 0;
        int measureHeight = 0;
        //记录当前行宽 高
        int curLineWidth = 0;
        int curLineHeight = 0;
        //根据测量模式测量当前控件的尺寸
        if (widthMode == MeasureSpec.EXACTLY && heightMode == MeasureSpec.EXACTLY) {//全部match
            measureHeight = heightSize;
            measureWidth = widthSize;
        } else {
            //获取所有的child数量
            int childCount = getChildCount();
            //记录每一行的view
            List<View> childViews = new ArrayList<>();
            if (childCount > 0) {
                for (int i = 0; i < childCount; i++) {
                    View child = getChildAt(i);
                    measureChild(child, widthMeasureSpec, heightMeasureSpec);//测量子view
                    //获取子view的layoutparam 此处使用MarginLayoutParams可以获取其margin值  保证类型强转 需要重写generateLayoutParams方法
                    MarginLayoutParams childLayoutParam = (MarginLayoutParams) child.getLayoutParams();
                    //获取子view需要的尺寸
                    int iChildWidth = childLayoutParam.leftMargin + childLayoutParam.rightMargin + child.getMeasuredWidth();
                    int iChildHeight = childLayoutParam.topMargin + childLayoutParam.bottomMargin + child.getMeasuredHeight();
                    //是否需要换行
                    if (curLineWidth + iChildWidth > widthSize) {
                        //测量的当前View的宽高
                        measureWidth = Math.max(measureWidth, curLineWidth);
                        measureHeight += curLineHeight;
                        //记录这一行的子view
                        views.add(childViews);
                        //要换行了  记录这一行的行高
                        heights.add(curLineHeight);
                        //换行了 新的一行的行宽为当前子view的测量宽
                        curLineWidth = iChildWidth;
                        curLineHeight = iChildHeight;
                        //新的一行的view集合重新创建
                        childViews = new ArrayList<>();
                        childViews.add(child);
                    } else {//不换行 宽叠加 高取最大
                        childViews.add(child);
                        curLineWidth += iChildWidth;
                        curLineHeight = Math.max(iChildHeight, curLineHeight);
                    }
                    //最后一行的处理  刚好最后一行
                    if (i == childCount - 1) {
                        measureWidth = Math.max(measureWidth, curLineWidth);
                        measureHeight += curLineHeight;

                        views.add(childViews);
                        heights.add(curLineHeight);
                    }
                }
            }
        }
        setMeasuredDimension(measureWidth, measureHeight);//设置宽高
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        //定义左上右下
        int left, top, right, bottom;
        //定义当前的左和上 作为下一个view的左或者下一行的上
        int curLeft = 0;
        int curTop = 0;
        //获取行数
        int lineSize = views.size();
        for (int i = 0; i < lineSize; i++) {
            //获取每一行的view数量
            List<View> childs = this.views.get(i);
            int childCount = childs.size();
            for (int j = 0; j < childCount; j++) {
                View child = childs.get(j);
                MarginLayoutParams params = (MarginLayoutParams) child.getLayoutParams();
                left = curLeft + params.leftMargin;
                top = curTop + params.topMargin;
                right = left + child.getMeasuredWidth();
                bottom = top + child.getMeasuredHeight();
                child.layout(left, top, right, bottom);
                //记录当前的left top
                curLeft += child.getMeasuredWidth() + params.leftMargin + params.rightMargin;
            }
            //一行结束了  左归位  上叠加
            curLeft = 0;
            curTop += heights.get(i);
        }
        //全部布局完成
        heights.clear();
        views.clear();
    }
}

主要运用的自定义控件的测量和布局两个方法。