增益集的主检视为抽象基底类别或介面，会描述主机和增益集使用的方法，如合约中所指定。
The host view of the add-in is the abstract base class or interface that describes the methods used by the host and the add-in, as specified in the contract.
告知设计主应用程式，由提供的矩形表示的区域需要在设计介面上重新绘制。
Notifies the design host that the area represented by the provided rectangle needs to be repainted on the design surface.
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