DllImportAttribute.PreserveSig 字段

定义

命名空间:

System.Runtime.InteropServices

程序集:

System.Runtime.InteropServices.dll

Source:

DllImportAttribute.cs

指示是否直接转换具有 HRESULT 返回值的非托管方法，或者是否 HRESULT 自动将返回值转换为异常。

public: bool PreserveSig;

public bool PreserveSig;

val mutable PreserveSig : bool

Public PreserveSig As Boolean 

字段值

Boolean

示例

下面的代码示例使用 DllImportAttribute 在字段设置为 true 的情况下PreserveSig导入非托管SHAutoComplete函数一次，并将 PreserveSig 字段设置为 false。 此代码示例使 SHAutoComplete 函数生成任何错误，其中一次和下一次都会生成异常 HRESULT 。

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;

internal class Win32
{
    // The SHAutoComplete function allows you
    // to add auto-compete functionality to your
    // Windows Forms text boxes. In .NET Framework
    // 1.1 and earlier, you can use SHAutoComplete.
    // Later versions have this ability built in without
    // requiring platform invoke.

    // See the MSDN documentation of the
    // SHAutoComplete function for the
    // complete set of flags.
    public enum SHAutoCompleteFlags
    {
        SHACF_DEFAULT = 0x00000000,
        SHACF_FILESYSTEM = 0x00000001
    }

    // Use the DllImportAttribute to import the SHAutoComplete function.
    // Set the PreserveSig to false to specify exception errors.
    [DllImportAttribute("shlwapi.dll", EntryPoint = "SHAutoComplete", ExactSpelling = true, PreserveSig = false)]
    public static extern void SHAutoComplete(IntPtr hwndEdit, SHAutoCompleteFlags dwFlags);

    // Use the DllImportAttribute to import the SHAutoComplete function.
    // Use the default value of the PreserveSig field to specify HRESULT errors.
    [DllImportAttribute("shlwapi.dll", EntryPoint = "SHAutoComplete", ExactSpelling = true)]
    public static extern int SHAutoCompleteHRESULT(IntPtr hwndEdit, SHAutoCompleteFlags dwFlags);
}

static class Program
{
    static void Main()
    {
        Run();
    }

    static void Run()
    {
        // Create a null (nothing in Visual Basic) IntPtr
        // to pass to the SHAutoComplete method.  Doing so
        // creates a failure and demonstrates the two ways
        // that the PreserveSig property allows you to handle
        // failures.
        // Normally, you would pass a handle to a managed
        // Windows Forms text box.
        IntPtr iPtr = new IntPtr(0);

        // Call the SHAutoComplete function using exceptions.
        try
        {
            Console.WriteLine("Calling the SHAutoComplete method with the PreserveSig field set to false.");

            Win32.SHAutoComplete(iPtr, Win32.SHAutoCompleteFlags.SHACF_DEFAULT);
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception handled: " + e.Message);
        }

        Console.WriteLine("Calling the SHAutoComplete method with the PreserveSig field set to true.");

        // Call the SHAutoComplete function using HRESULTS.
        int HRESULT = Win32.SHAutoCompleteHRESULT(iPtr, Win32.SHAutoCompleteFlags.SHACF_DEFAULT);

        Console.WriteLine("HRESULT handled: " + HRESULT.ToString());
    }
}

Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Runtime.InteropServices



Module Win32
    ' The SHAutoComplete function allows you 
    ' to add auto-compete functionality to your
    ' Windows Forms text boxes. In .NET Framework 
    ' 1.1 and earlier, you can use SHAutoComplete.
    ' Later versions have this ability built in without
    ' requiring platform invoke.
    ' See the MSDN documentation of the 
    ' SHAutoComplete function for the 
    ' complete set of flags.

    Public Enum SHAutoCompleteFlags
        SHACF_DEFAULT = &H1
        SHACF_FILESYSTEM = &H1
    End Enum 


    ' Use the DllImportAttribute to import the SHAutoComplete function. 
    ' Set the PreserveSig to false to specify exception errors.
    <DllImportAttribute("shlwapi.dll", EntryPoint:="SHAutoComplete", ExactSpelling:=True, PreserveSig:=False)> _
    Public Sub SHAutoComplete(ByVal hwndEdit As IntPtr, ByVal dwFlags As SHAutoCompleteFlags)
    End Sub


    ' Use the DllImportAttribute to import the SHAutoComplete function. 
    ' Use the default value of the PreserveSig field to specify HRESULT errors.
    <DllImportAttribute("shlwapi.dll", EntryPoint:="SHAutoComplete", ExactSpelling:=True)> _
    Public Function SHAutoCompleteHRESULT(ByVal hwndEdit As IntPtr, ByVal dwFlags As SHAutoCompleteFlags) As Integer
    End Function
End Module



Module Program

    Sub Main()
        Run()

    End Sub


    Sub Run()
        ' Create a null (nothing in Visual Basic) IntPtr
        ' to pass to the SHAutoComplete method.  Doing so
        ' creates a failure and demonstrates the two ways  
        ' that the PreserveSig property allows you to handle 
        ' failures.  
        ' Normally, you would pass a handle to a managed
        ' Windows Forms text box.
        Dim iPtr As New IntPtr(0)

        ' Call the SHAutoComplete function using exceptions.
        Try
            Console.WriteLine("Calling the SHAutoComplete method with the PreserveSig field set to false.")

            Win32.SHAutoComplete(iPtr,Win32.SHAutoCompleteFlags.SHACF_DEFAULT)
        Catch e As Exception
            Console.WriteLine("Exception handled: " + e.Message)
        End Try

        Console.WriteLine("Calling the SHAutoComplete method with the PreserveSig field set to true.")

        ' Call the SHAutoComplete function using HRESULTS.
        Dim HRESULT As Integer = Win32.SHAutoCompleteHRESULT(iPtr,Win32.SHAutoCompleteFlags.SHACF_DEFAULT)

        Console.WriteLine("HRESULT handled: " + HRESULT.ToString())

    End Sub
End Module

注解

将 PreserveSig 字段设置为 true 以直接转换具有 HRESULT 值的非托管签名;将其设置为 false 以自动将返回值转换为 HRESULT 异常。 默认情况下， PreserveSig 字段为 true。

当 为 时 true，托管方法签名返回包含值的 HRESULT 整数值。 在这种情况下，必须手动检查返回值并在应用程序中做出相应的响应。

将 字段设置为 PreserveSigfalse时，托管方法签名具有 void 返回类型或最后一个非托管 [out， retval] 参数的类型。 当非托管方法生成 时 HRESULT，运行时会自动忽略返回值 S_OK (或 0) ，并且不会引发异常。 对于 HRESULT以外的 S_OK，运行时会自动引发对应于 的 HRESULT异常。

如果异常更适合应用程序的错误报告结构，则可以决定将默认错误报告行为从 更改为 HRESULT异常。

此字段类似于 PreserveSigAttribute;但是，与 字段相反 PreserveSig ，属性的默认值为 false。

在某些情况下, Visual Basic 开发人员会使用DllImportAttribute代替 Declare 语句在托管代码中定义 DLL 函数。 设置 PreserveSig 字段便是这其中的一种情况。

另请参阅

• PreserveSigAttribute