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Delphi2005学习笔记2——Using Platform Invoke with Delphi 2005

来源：互联网 作者：西部数码 时间：2008-04-09

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Using Platform Invoke with Delphi 2005 This topic describes the basic techniques of using unmanaged APIs from Delphi 2005. Some of the common mistakes and pitfalls are pointed out, and a quick reference for translating Delphi data types is provided. This topic does not attempt to explain the basics of platform invoke or marshaling data. Please refer to the links at the end of this topic for more information on platform invoke and marshaling. Understanding attributes and how they are used is also highly recommended before reading this document. The Win32 API is used for several examples. For further details on the API functions mentioned, please see the Windows Platform SDK documentation. The following topics are discussed in this section:

Calling unmanaged functions
Structures
Callback functions
Passing Object References
Using COM Interfaces

Calling Unmanaged Functions When calling unmanaged functions, a managed declaration of the function must be created that represents the unmanaged types. In many cases functions take pointers to data that can be of variable types. One example of such a function is the Win32 API function SystemParametersInfo that is declared as follows:

BOOL SystemParametersInfo(
  UINT uiAction,  // system parameter to retrieve or set
  UINT uiParam,   // depends on action to be taken
  PVOID pvParam,  // depends on action to be taken
  UINT fWinIni    // user profile update option
);

Depending on the value of uiAction, pvParam can be one of dozens of different structures or simple data types. Since there is no way to represent this with one single managed declaration, multiple overloaded versions of the function must be declared (see Borland.Vcl.Windows.pas), where each overload covers one specific case. The parameter pvParam can also be given the generic declaration IntPtr . This places the burden of marshaling on the caller, rather than the built in marshaler. Note that the data types used in a managed declaration of an unmanaged function must be types that the default marshaler supports. Otherwise, the caller must declare the parameter as IntPtr and be responsible for marshaling the data. Data Types Most data types do not need to be changed, except for pointer and string types. The following table shows commonly used data types, and how to translate them for managed code: Unmanaged Data Type Managed Data Type Input Parameter Output Parameter Pointer to string (PChar) String StringBuilder Untyped parameter/buffer TBytes TBytes Pointer to structure (PRect) const TRect var TRect Pointer to simple type (PByte) const Byte var Byte Pointer to array (PInteger) array of Integer array of Integer Pointer to pointer type (^PInteger) IntPtr

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