Calling a DLL Function 之二 Callback Functions

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原文链接：http://www.cnblogs.com/MayGarden/archive/2010/01/09/1642836.html

本文介绍了在托管应用程序中如何实现和使用回调函数。回调函数通常用于完成由非托管DLL函数发起的任务，例如枚举操作。文章详细说明了创建和调用此类函数的过程，并提供了一个示例。

Callback Functions

A callback function is code within a managed application that helps an unmanaged DLL function complete a task. Calls to a callback function pass indirectly from a managed application, through a DLL function, and back to the managed implementation. Some of the many DLL functions called with platform invoke require a callback function in managed code to run properly.

To call most DLL functions from managed code, you create a managed definition of the function and then call it. The process is straightforward.

Using a DLL function that requires a callback function has some additional steps. First, you must determine whether the function requires a callback by looking at the documentation for the function. Next, you have to create the callback function in your managed application. Finally, you call the DLL function, passing a pointer to the callback function as an argument. The following illustration summarizes these steps.

Callback function and implementation

Callback functions are ideal for use in situations in which a task is performed repeatedly. Another common usage is with enumeration functions, such as EnumFontFamilies, EnumPrinters, and EnumWindows in the Win32 API. The EnumWindows function enumerates through all existing windows on your computer, calling the callback function to perform a task on each window. For instructions and an example, see How to: Implement Callback Functions.

转载于:https://www.cnblogs.com/MayGarden/archive/2010/01/09/1642836.html