InAttribute 类

定义

public ref class InAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)]
public sealed class InAttribute : Attribute

[System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)]
[System.Runtime.InteropServices.ComVisible(true)]
public sealed class InAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)>]
type InAttribute = class
    inherit Attribute

[<System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type InAttribute = class
    inherit Attribute

Public NotInheritable Class InAttribute
Inherits Attribute

继承

Object

Attribute

InAttribute

属性

AttributeUsageAttribute ComVisibleAttribute

示例

以下示例演示如何将 和 OutAttribute 应用于InAttribute将数组作为参数传递的平台调用原型。 方向属性的组合允许调用方查看被调用方所做的更改。

using namespace System;
using namespace System::Runtime::InteropServices;

// Declare a class member for each structure element.

[StructLayout(LayoutKind::Sequential, CharSet = CharSet::Unicode)]
public ref class OpenFileName
{
public:
    int structSize;
    String^ filter;
    String^ file;
    // ...
};

private ref class NativeMethods
{
public:

    // Declare a managed prototype for the unmanaged function.

    [DllImport("Comdlg32.dll", CharSet = CharSet::Unicode)]
    static bool GetOpenFileName([In, Out]OpenFileName^ ofn);
};

void main() {}

using System.Runtime.InteropServices;
using System;

// Declare a class member for each structure element.
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public class OpenFileName
{
    public int structSize = 0;
    public string filter = null;
    public string file = null;
    // ...
}

internal static class NativeMethods
{
    // Declare a managed prototype for the unmanaged function.
    [DllImport("Comdlg32.dll", CharSet = CharSet.Unicode)]
    internal static extern bool GetOpenFileName([In, Out] OpenFileName ofn);
}

public class MainMethod
{
    static void Main()
    { }
}

Imports System.Runtime.InteropServices

' Declare a class member for each structure element.
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)>
Public Class OpenFileName

    Public structSize As Integer = 0
    Public filter As String = Nothing
    Public file As String = Nothing
    ' ...

End Class

Friend Class NativeMethods
    ' Declare managed prototype for the unmanaged function.
    Friend Declare Unicode Function GetOpenFileName Lib "Comdlg32.dll" (
       <[In](), Out()> ByVal ofn As OpenFileName) As Boolean
End Class

Public Class App
    Public Shared Sub Main()

    End Sub
End Class

注解

可以将此属性应用于参数。

InAttribute是可选的。 仅 COM 互操作和平台调用支持 属性。 在没有显式设置的情况下，互操作封送处理器会基于参数类型、参数是按引用传递还是按值传递，以及类型是 blittable 还是非 blittable。 例如， StringBuilder 类始终假定为 In/Out，值传递的字符串数组假定为 In。

不能将 应用于 InAttribute 使用 C#样式 out 关键字修改的参数。 若要避免将 Visual Basic 中的关键字与 InAttribute减去 属性混淆In，请使用<[In]>带有属性括号的窗体。

将 InAttribute 和 OutAttribute 组合在应用于数组和格式化的非 blittable 类型时特别有用。 调用方仅在应用这两个属性时，才会看到被调用方对这些类型所做的更改。 由于这些类型需要在封送处理期间复制，因此可以使用 InAttribute 和 OutAttribute 来减少不必要的副本。

有关封送处理行为的影响的详细信息 InAttribute ，请参阅 方向属性。

另请参阅

• OutAttribute
• StringBuilder
• 可直接复制到本机结构中的类型和非直接复制到本机结构中的类型