A toast is a view containing a quick little message for the user. The toast class helps you create and show those. When the view is shown to the user, appears as a floating view over the application. It will never receive focus. The user will probably be in the middle of typing something else. The idea is to be as unobtrusive as possible, while still showing the user the information you want them to see. Two examples are the volume control, and the brief message saying that your settings have been saved.
Toast 最基本的用法很简单，不用说大家都会（这里切记要调用 show() 去显示）