DllImportAttribute Class


Indicates that the attributed method is exposed by an unmanaged dynamic-link library (DLL) as a static entry point.

Namespace:   System.Runtime.InteropServices
Assembly:  mscorlib (in mscorlib.dll)


[AttributeUsageAttribute(AttributeTargets.Method, Inherited = false)]
public sealed class DllImportAttribute : Attribute


Initializes a new instance of the DllImportAttribute class with the name of the DLL containing the method to import.


When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)


Gets the name of the DLL file that contains the entry point.


This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)


Returns the hash code for this instance.(Inherited from Attribute.)


Gets the Type of the current instance.(Inherited from Object.)


When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)


When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)


Returns a string that represents the current object.(Inherited from Object.)


Enables or disables best-fit mapping behavior when converting Unicode characters to ANSI characters.


Indicates the calling convention of an entry point.


Indicates how to marshal string parameters to the method and controls name mangling.


Indicates the name or ordinal of the DLL entry point to be called.


Controls whether the DllImportAttribute.CharSet field causes the common language runtime to search an unmanaged DLL for entry-point names other than the one specified.


Indicates whether unmanaged methods that have HRESULT or retval return values are directly translated or whether HRESULT or retval return values are automatically converted to exceptions.


Indicates whether the callee calls the SetLastError Win32 API function before returning from the attributed method.


Enables or disables the throwing of an exception on an unmappable Unicode character that is converted to an ANSI "?" character.

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)


Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from Attribute.)

You can apply this attribute to methods.

The DllImportAttribute attribute provides the information needed to call a function exported from an unmanaged DLL. As a minimum requirement, you must supply the name of the DLL containing the entry point.

You apply this attribute directly to C# and C++ method definitions; however, the Visual Basic compiler emits this attribute when you use the Declare statement. For complex method definitions that include BestFitMapping, CallingConvention, ExactSpelling, PreserveSig, SetLastError, or ThrowOnUnmappableChar fields, you apply this attribute directly to Visual Basic method definitions.

Note   JScript does not support this attribute. You can use C# or Visual Basic wrapper classes to access unmanaged API methods from JScript programs.

For additional information about using the platform invoke service to access functions in unmanaged DLLs, see Consuming Unmanaged DLL Functions.


The DllImportAttribute does not support marshaling of generic types.

The following code example shows how to use the DllImportAttribute attribute to import the Win32 MessageBox function. The code example then calls the imported method.

using System;
using System.Runtime.InteropServices;

class Example
    // Use DllImport to import the Win32 MessageBox function.
    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);

    static void Main()
        // Call the MessageBox function using platform invoke.
        MessageBox(new IntPtr(0), "Hello World!", "Hello Dialog", 0);

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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