MarshalAsAttribute.SizeParamIndex 字段

定义

命名空间:

System.Runtime.InteropServices

程序集:

System.Runtime.InteropServices.dll

Source:

MarshalAsAttribute.cs

指示从零开始的参数，该参数包含数组元素的计数，与 COM 中的 size_is 类似。

public: short SizeParamIndex;

public short SizeParamIndex;

val mutable SizeParamIndex : int16

Public SizeParamIndex As Short 

字段值

Int16

示例

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

// Force the layout of your fields to the C-style struct layout.
// Without this, the .NET Framework will reorder your fields.

[StructLayoutAttribute(LayoutKind::Sequential)]
value struct Vertex
{
public:
   float x;
   float y;
   float z;
};


// Add [In] or [In, Out] attributes as appropriate.
// Marshal as a C-style array of Vertex, where the second (SizeParamIndex is zero-based)
// parameter (size) contains the count of array elements.

[DllImport("SomeDLL.dll")]
extern void SomeUnsafeMethod( [MarshalAs(UnmanagedType::LPArray,SizeParamIndex=1)]array<Vertex>^data, long size );
int main()
{
   array<Vertex>^verts = gcnew array<Vertex>(3);
   SomeUnsafeMethod( verts, verts->Length );
}

using System.Runtime.InteropServices;
using SomeNamespace;

namespace SomeNamespace
{
    // Force the layout of your fields to the C style struct layout.
    // Without this, the .NET Framework will reorder your fields.
    [StructLayout(LayoutKind.Sequential)]
    public struct Vertex
    {
        float	x;
    float	y;
        float	z;
    }

    class SomeClass
    {
        // Add [In] or [In, Out] attributes as approppriate.
        // Marshal as a C style array of Vertex, where the second (SizeParamIndex is zero-based)
        //  parameter (size) contains the count of array elements.
        [DllImport ("SomeDll.dll")]
        public static extern void SomeUnsafeMethod(
                                      [MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)] Vertex[] data,
                                      long size );

        public void SomeMethod()
        {
            Vertex[] verts = new Vertex[3];
            SomeUnsafeMethod( verts, verts.Length );
        }
    }
}

class Test
{
    public static void Main()
    {
        SomeClass AClass = new SomeClass();

        AClass.SomeMethod();
    }
}

Option Strict Off

Imports System.Runtime.InteropServices
Imports SomeNamespace

Namespace SomeNamespace
    ' Force the layout of your fields to the C style struct layout.
    ' Without this, the .NET Framework will reorder your fields.
    
    <StructLayout(LayoutKind.Sequential)> _
    Structure Vertex
        Dim x As Decimal
        Dim y As Decimal
        Dim z As Decimal
    End Structure

    Class SomeClass
        ' Add [In] or [In, Out] attributes as approppriate.
        ' Marshal as a C style array of Vertex, where the second (SizeParamIndex is zero-based)
        '  parameter (size) contains the count of array elements.

        Declare Auto Sub SomeUnsafeMethod Lib "somelib.dll" ( _
                                      <MarshalAs(UnmanagedType.LPArray, SizeParamIndex:=1)> data() As Vertex, _
                                      size As Long ) 

        Public Sub SomeMethod()
            Dim verts(3) As Vertex
            SomeUnsafeMethod( verts, verts.Length )
        End Sub

    End Class

End Namespace

Module Test
    Sub Main
        Dim AClass As New SomeClass

        AClass.SomeMethod
        End Sub
End Module

注解

字段 SizeParamIndex 支持托管到非托管和非托管到托管的调用。 它对调用 COM 对象的托管代码没有任何影响。

根据托管类型和应用的属性，可以将数组作为安全数组或 C 样式数组传递。

当数组作为 C 样式数组传递时，封送处理程序无法确定数组的大小。 因此，若要将托管数组传递给非托管函数或方法，必须提供两个参数：

• 数组，由引用或值定义。

• 数组大小，由引用或值定义。

数组大小参数的从零开始的索引是使用 SizeParamIndex 字段定义的。

如果使用字段同时 SizeParamIndex 指定 和 MarshalAsAttribute.SizeConstUnmanagedType.LPArray ，则字段值的总和将产生大小总计。

有关详细信息，请参阅 数组的默认封送处理。

另请参阅

• SizeConst
• LPArray