1. Tool Property Sheets:
是用来更改context属性的编辑框，类似于attribute editor。（property和attribute本质上是一个意思）作用于activated context。 The tool property sheet for the activated context is displayed by double-clicking on the tool’s icon.
应该是这个东东：
（1）弄出这个东东需要写两个MEL文件。（PS：我想应该和obj的file translators一个意思，可以在initializeplugin（）函数中调用MGlobal::sourceFile()来先启动这两个MEL文件）
（2）分别为：<yourContextName>Properties.mel and <yourContextName>Values.mel
(3)The <>Properties.mel file defines the layout of the editor and the actions to be taken by widgets in the editor.
(4)The <>Values.mel file is used to retrieve values from the context with the editor is initialized.
To effectively implement a tool property sheet for your context, you must implement sufficient edit and query options in your context command as well as sufficient access methods in your MPxContext class for setting and retrieving its internal properties.
2. MPxToolCommand
MPxToolCommand是创建命令用于操作context类对象的基类。 他的actions是从MPxContext类中得到的。他是MPxCommand类的子类。
一个Context只能有一个tool command连接到它。
