Unable to start activity ComponentInfo……加载含有自定义View类的xml文件出错

自定义了ShowWindow类，继承自View类，加载含有自定义View类的xml文件出错

最后看api发现构建custom view步骤如下：

Subclass a View
Define Custom Attributes
Apply Custom Attributes to a View
Add Properties and Events
Design For Accessibility

其中第第一条说明如下

All of the view classes defined in the Android framework extend 

View

.
Your custom view can also extend 

View

 directly,
or you can save time by extending one of the existing view subclasses, such as

Button

.

To allow the Android Developer Tools to interact with your
view, at a minimum you must provide a constructor that takes a 

Context

 and
an 

AttributeSet

 object as parameters.
This constructor allows the layout editor to create and edit an instance of your view.

自定义的view类至少要有含有偶context和attributeset的构造函数