protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	int width = getMeasuredWidth();
	int height = getMeasuredHeight();
	int size = Math.min(width, height);
	setMeasuredDimension(size, size);
}

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	int width = (int) ((PADDING + RADIUS) * 2);
	int height = (int) ((PADDING + RADIUS) * 2)
	setMeasuredDimension(resolveSizeAndState(width, widthMeasureSpec,0),
	resolveSizeAndState(height, heightMeasureSpec, 0));
}

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
for (int i = 0; i < getChildCount(); i++) {
	View child = getChildAt(i);
	Rect childBounds = childrenBounds[i];
	// 测量⼦ View
	measureChildWithMargins(child, widthMeasureSpec,
	widthUsed,
	heightMeasureSpec, heightUsed);
	// 保存⼦ View 的位置和尺⼨
	childBounds.set(childlLeft, childTop, childLeft
	+ child.getMeasuredWidth(), chiltTop
	+ child.getMeasuredHeight());
	......
}
// 计算⾃⼰的尺⼨，并保存
int width = ...;
int height = ...;
	setMeasuredDimension(resolveSizeAndState(width,widthMeasureSpec, 0),resolveSizeAndState(height, heightMeasureSpec,0));
}

protected void measureChildWithMargins(View child,  
 int parentWidthMeasureSpec, int widthUsed,  
 int parentHeightMeasureSpec, int heightUsed) {  
 final MarginLayoutParams lp \= (MarginLayoutParams) child.getLayoutParams();  
 final int childWidthMeasureSpec \= getChildMeasureSpec(parentWidthMeasureSpec,  
 mPaddingLeft \+ mPaddingRight \+ lp.leftMargin \+ lp.rightMargin  
                    \+ widthUsed, lp.width);  
 final int childHeightMeasureSpec \= getChildMeasureSpec(parentHeightMeasureSpec,  
 mPaddingTop \+ mPaddingBottom \+ lp.topMargin \+ lp.bottomMargin  
                    \+ heightUsed, lp.height);  
 child.measure(childWidthMeasureSpec, childHeightMeasureSpec);  
}

    public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
        int specMode = MeasureSpec.getMode(spec);
        int specSize = MeasureSpec.getSize(spec);
        int size = Math.max(0, specSize - padding);
        int resultSize = 0;
        int resultMode = 0;
        switch (specMode) {
        // Parent has imposed an exact size on us
        case MeasureSpec.EXACTLY:
            if (childDimension >= 0) {
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // Child wants to be our size. So be it.
                resultSize = size;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size. It can't be
                // bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;
        // Parent has imposed a maximum size on us
        case MeasureSpec.AT_MOST:
            if (childDimension >= 0) {
                // Child wants a specific size... so be it
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // Child wants to be our size, but our size is not fixed.
                // Constrain child to not be bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size. It can't be
                // bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;
        // Parent asked to see how big we want to be
        case MeasureSpec.UNSPECIFIED:
            if (childDimension >= 0) {
                // Child wants a specific size... let him have it
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                // Child wants to be our size... find out how big it should
                // be
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size.... find out how
                // big it should be
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            }
            break;
        }
        //noinspection ResourceType
        return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
    }

protected void onLayout(boolean changed, int l, int t, int r, int b) {
	for (int i = 0; i < getChildCount(); i++) {
		View child = getChildAt(i);
		Rect childBounds = childrenBounds[i];
		// 将每个⼦ View 的位置和尺⼨传递给它
		child.layout(childBounds.left, childBounds.top,
		childBounds.right, childBounds.bottom);
	 }
}