use onLayout implements LinearLayout in vertical orientation

矫情吗；* 2023-10-17 17:49 34阅读 0赞

**use onLayout implements LinearLayout in vertical orientation**

import android.content.Context;
    import android.util.AttributeSet;
    import android.view.View;
    import android.view.ViewGroup;
    
    public class MyLayout extends ViewGroup {
        public MyLayout(Context context, AttributeSet attrs) {
            super(context, attrs);
        }
    
        //onMeasure被Android在onLayout之前调用。
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            //所有子View加起来总的高度和宽度。
            int measuredWidth = 0;
            int measuredHeight = 0;
    
            int count = getChildCount();
            for (int i = 0; i < count; i++) {
                View v = this.getChildAt(i);
                if (v.getVisibility() != View.GONE) {
                    this.measureChild(v, widthMeasureSpec, heightMeasureSpec);
    
                    measuredWidth = Math.max(measuredWidth, v.getMeasuredWidth());
                    measuredHeight += v.getMeasuredHeight();
                }
            }
    
            //仔细检查！不要疏忽掉一些padding的值。
            measuredWidth += getPaddingLeft() + getPaddingRight();
            measuredHeight += getPaddingTop() + getPaddingBottom();
    
            this.setMeasuredDimension(measuredWidth, measuredHeight);
        }
    
        // Android系统在onMeasure之后调用onLayout。
        @Override
        protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
            // 在left，top，right，bottom这四个坐标参数“框”出来一个盛放子View的矩形空间，在此空间内一个一个摆放子View。
    
            int count = this.getChildCount();
            for (int i = 0; i < count; i++) {
                View v = getChildAt(i);
                if (v.getVisibility() != View.GONE) {
                    int childHeight = v.getMeasuredHeight();
    
                    //在细分的(left, top, right, top + childHeight)框出来的矩形空间内摆放这一子View。
                    v.layout(left, top, right, top + childHeight);
    
                    //把顶点的锚定位置往下移。
                    top = top + childHeight;
                }
            }
        }
    }