Q: 自定义viewGroup 不报错但也不显示

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当自定义的ViewGroup无法显示时，通常需要重写onLayout和onMeasure方法。onLayout用于为子视图分配大小和位置，而onMeasure负责测量视图的内容尺寸。确保这两个方法都正确实现才能使自定义ViewGroup正常工作。

Q: 自定义viewGroup 不报错但也不显示

A: 在viewGroup中override onLayout和onMeasure方法（缺一不可）。代码片段例子：

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
		mainView.getView().layout(0, 0, point.x, point.y);
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		mainView.getView().measure(widthMeasureSpec, heightMeasureSpec);
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	}

原理见API原文：

onLayout:

Called from layout when this view should assign a size and position to each of its children. Derived classes with children should override this method and call layout on each of their children.

Layout:

This is the second phase of the layout mechanism. (The first is measuring). In this phase, each parent calls layout on all of its children to position them.

onMeasure:

Measure the view and its content to determine the measured width and the measured height.

measure:

This is called to find out how big a view should be.

Refer:

http://www.eoeandroid.com/thread-22629-1-1.html