自定义ViewGroup

传承者（Inheritors）打造共同进步生态圈！！！
转载：http://blog.youkuaiyun.com/lmj623565791/article/details/38339817

三段论：

public class CustomViewGroup extends ViewGroup {
    public CustomViewGroup(Context context) {
        super(context);
    }

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

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

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int cCount = getChildCount();
        int cWidth = 0, cHeight = 0;

        MarginLayoutParams cParams = null;

        /**
         * 遍历所有的childView根据其宽和高，以及margin进行布局
         */
        for (int i = 0; i < cCount; i++) {

            View childView = getChildAt(i);
            cWidth = childView.getMeasuredWidth();
            cHeight = childView.getMeasuredHeight();
            cParams = (MarginLayoutParams) childView.getLayoutParams();

            //布局子View的上下左右距离，
            int cl = 0, ct = 0, cr = 0, cb = 0;
            switch (i) {
                case 0:
                    cl = cParams.leftMargin;
                    ct = cParams.topMargin;
                    break;
                case 1:
                    cl = getWidth()-cWidth - cParams.leftMargin-cParams.rightMargin;
                    ct = cParams.topMargin;
                    break;
                case 2:
                    cl = cParams.leftMargin;
                    ct = getHeight()-cHeight-cParams.bottomMargin;
                    break;
                case 3:
                    cl = getWidth() -cWidth - cParams.leftMargin - cParams.rightMargin;
                  ct = getHeight() - cHeight - cParams.bottomMargin;
                    break;


            }

            cr = cl+ cWidth;
            cb = ct +cHeight;

            childView.layout(cl,ct,cr,cb);

        }
    }

    /**
     * Returns a new set of layout parameters based on the supplied attributes set.
     *
     * @param attrs
     * @return
     */

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

    /**
     * 计算所有ChildView的宽度和高度，然后根据ChildView的计算结果，设置自己的宽和高
     *
     * @param widthMeasureSpec
     * @param heightMeasureSpec
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        /**
         * 获得此ViewGroup的上级容器为其推荐的高和宽，以及计算的模式
         */
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);

        //计算出所有的ChildView的宽和高
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        //记录如果是wrap_content设置的宽和高
        int width = 0;
        int height = 0;
        int cCount = getChildCount();
        int cWidth = 0;
        int cHeight = 0;

        MarginLayoutParams cParams = null;

        //用于计算左边和右边的两个childView高度，最终高度取二者最大值
        int lHeight = 0, rHeight = 0;
        //计算于上边和下边的两个childView的宽度，最终宽度取二者最大值
        int tWidth = 0, bWidth = 0;
        //根据ChildView计算出的宽度和高度，以及设置的margin计算容器的宽和高度，主要用于容器是wrap_content时
        for (int i = 0; i < cCount; i++) {
            View childView = getChildAt(i);
            cWidth = childView.getMeasuredWidth();
            cHeight = childView.getMeasuredHeight();
            cParams = (MarginLayoutParams) childView.getLayoutParams();


            //上面两个childView
            if (i == 0 || i == 1) {
                tWidth += cWidth + cParams.leftMargin + cParams.rightMargin;
            }
            if (i == 2 || i == 3) {
                bWidth += cWidth + cParams.leftMargin + cParams.rightMargin;
            }

            if (i == 0 || i == 2) {
                lHeight += cHeight + cParams.topMargin + cParams.bottomMargin;
            }

            if (i == 1 || i == 3) {
                rHeight += cHeight + cParams.topMargin + cParams.bottomMargin;
            }


        }
        width = Math.max(tWidth, bWidth);
        height = Math.max(lHeight, rHeight);

        /**
         * 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);
    }
}

调用

<?xml version="1.0" encoding="utf-8"?>
<com.example.administrator.testapplication.CustomViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:background="#aa333333"
    android:orientation="vertical">
    <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.example.administrator.testapplication.CustomViewGroup>

效果如下

部分方法解释：

 @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return super.generateLayoutParams(attrs);
    }

  /**
     * Returns a new set of layout parameters based on the supplied attributes set.
     */



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


 /**
         * Creates a new set of layout parameters. The values are extracted from
         * the supplied attributes set and context. The XML attributes mapped
         * to this set of layout parameters are:
         */


  public LayoutParams(Context c, AttributeSet attrs) {
            TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.ViewGroup_Layout);
            setBaseAttributes(a,
                    R.styleable.ViewGroup_Layout_layout_width,
                    R.styleable.ViewGroup_Layout_layout_height);
            a.recycle();
        }

  /**
     * Ask all of the children of this view to measure themselves, taking into
     * account both the MeasureSpec requirements for this view and its padding.
     * We skip children that are in the GONE state The heavy lifting is done in
     * getChildMeasureSpec.
     *
     * @param widthMeasureSpec The width requirements for this view
     * @param heightMeasureSpec The height requirements for this view
     */
    protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) {
        final int size = mChildrenCount;
        final View[] children = mChildren;
        for (int i = 0; i < size; ++i) {
            final View child = children[i];
            if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {
                measureChild(child, widthMeasureSpec, heightMeasureSpec);
            }
        }
    }