自定义View-3-重写onLayout

前言：本文主要仿照鸿洋大神的Android 手把手教您自定义ViewGroup

效果图

布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent">
    <TextView  android:layout_width="match_parent" android:layout_height="100dp" android:background="#003839" android:gravity="center" android:visibility="visible" android:text="SECOND"/>

    <com.pengkv.apple.weight.SecondView  android:id="@+id/view_first" android:layout_width="200dp" android:visibility="visible" android:background="#888787" android:layout_height="200dp">

        <TextView  android:layout_width="50dp" android:layout_height="50dp" android:background="#FF4444" android:gravity="center" android:text="0" android:textColor="#FFFFFF" android:textSize="22sp" android:textStyle="bold" />

        <TextView  android:layout_width="50dp" android:layout_height="50dp" android:background="#00ff00" android:gravity="center" android:text="1" android:textColor="#FFFFFF" android:textSize="22sp" android:textStyle="bold" />

        <TextView  android:layout_width="50dp" android:layout_height="50dp" android:background="#ff0000" android:gravity="center" android:text="2" android:textColor="#FFFFFF" android:textSize="22sp" android:textStyle="bold" />

        <TextView  android:layout_width="50dp" android:layout_height="50dp" android:background="#0000ff" android:gravity="center" android:text="3" android:textColor="#FFFFFF" android:textSize="22sp" android:textStyle="bold" />
    </com.pengkv.apple.weight.SecondView>

</LinearLayout>

View代码

public class SecondView extends LinearLayout {

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

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

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// super.onMeasure(widthMeasureSpec,heightMeasureSpec);

        //父容器的宽、高
        int widthMode=MeasureSpec.getMode(widthMeasureSpec);
        int heightMode=MeasureSpec.getMode(heightMeasureSpec);
        int widthSize=MeasureSpec.getSize(widthMeasureSpec);
        int heightSize=MeasureSpec.getSize(heightMeasureSpec);

        //计算出所有childView的宽、高
        measureChildren(widthMeasureSpec,heightMeasureSpec);

        //用于记录子view所占的总宽、高
        int width=0;
        int height=0;
        int childCount=getChildCount();

        //用于记录单个子view的宽、高
        int childWidth=0;
        int childHeight=0;

        //用于记录单个子view的外边距
        MarginLayoutParams childParams=null;

        int leftHeight=0;//左边子view占据的高度
        int rightHeight=0;//右边子view占据的高度
        int topWidth=0;//上边子view占据的宽度
        int bottomWidth=0;//下边子view占据的宽度

        for (int i=0;i<childCount;i++){

            //获取单个子view的宽高
            View childView=getChildAt(i);
            childWidth=childView.getMeasuredWidth();
            childHeight=childView.getMeasuredHeight();
            childParams=(MarginLayoutParams)childView.getLayoutParams();

            if (i == 0 || i == 1)
            {
                topWidth += childWidth + childParams.leftMargin + childParams.rightMargin;
            }

            if (i == 2 || i == 3)
            {
                bottomWidth += childWidth + childParams.leftMargin + childParams.rightMargin;
            }

            if (i == 0 || i == 2)
            {
                leftHeight += childHeight + childParams.topMargin + childParams.bottomMargin;
            }

            if (i == 1 || i == 3)
            {
                rightHeight += childHeight + childParams.topMargin + childParams.bottomMargin;
            }

            //取出子view所占据的最长宽高
            width=Math.max(topWidth,bottomWidth);
            height=Math.max(leftHeight,rightHeight);

            //如果是wrap_content设置为我们计算的值，否则：直接设置为父容器计算的值
            setMeasuredDimension((widthMode==MeasureSpec.EXACTLY)?widthSize:width,(heightMode==MeasureSpec.EXACTLY)?heightSize:height);

        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {

        int childCount=getChildCount();
        int childWidth=0;
        int childHeight=0;
        MarginLayoutParams childParams=null;

        for (int i=0;i<childCount;i++){
            View childView=getChildAt(i);
            childWidth=childView.getMeasuredWidth();
            childHeight=childView.getMeasuredHeight();
            childParams=(MarginLayoutParams)childView.getLayoutParams();

            int childLeft=0,childTop=0,childRight=0,childBottom=0;

            switch (i){
                case 0:
                    childLeft=childParams.leftMargin;
                    childTop=childParams.topMargin;
                    break;
                case 1:
                    childLeft=getWidth()-childWidth-childParams.leftMargin-childParams.rightMargin;
                    childTop=childParams.topMargin;
                    break;
                case 2:
                    childLeft=childParams.leftMargin;
                    childTop=getHeight()-childHeight-childParams.bottomMargin;
                    break;
                case 3:
                    childLeft=getWidth()-childWidth-childParams.leftMargin-childParams.rightMargin;
                    childTop=getHeight()-childHeight-childParams.bottomMargin;
                    break;
            }
            childRight=childLeft+childWidth;
            childBottom=childTop+childHeight;

            childView.layout(childLeft,childTop,childRight,childBottom);//放置view的位置

        }
    }

}