这构造器用来通过一个目标对象和一个函数指针形成一个委托。

The constructor is used to form a delegate over a target object and a function pointer.

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注意该处理器函数必须具备由委托定义的签名。

Note that the handler function must have the signature defined by the delegate.

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在一个元数据中，一旦我们有了一个委托类型和一个我们想要调用的目标函数，我们必须从目标形成一个实例。

Once we have a delegate type in the metadata and a target function we'd like to call, we must form an instance of the delegate over a target.

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