对于大多数需要集合类别的案例，建议的方法是使用。

For most scenarios that require collection classes, the recommended approach is to use the ones provided in the.

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集合类别必须提供方法，根据事件索引键来设定、存取和撷取事件处理常式委派。

The collection class must provide methods for setting, accessing, and retrieving the event handler delegate based on the event key.

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我们还可以为每个集合中的内容添加一个类别提示(如清单4所示)。

You can also add an indication of the categories of content covered by each collection (see Listing 4).

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