Using the MarshalAsAttribute Attribute

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

You can use the MarshalAsAttribute attribute to customize marshaling behavior. For example, you can perform the following tasks:

• Marshal arrays and strings in a structure.

• Provide needed flexibility to support common COM interop scenarios.

• Provide consistency in marshaling types through the platform invoke and vtable marshaler as compared to the IDispatch marshaler.

If using the MarshalAsAttribute for the unmanaged type fails, a NotSupportedException or a native exception may occur. If it fails, either use a known supported type, or remove the attribute and specify an IntPtr as the type. The Interop log reports information about marshaling errors.

The following table describes marshaling support for the values from the UnmanagedType enumeration.

Unmanaged Type	Types valid on	Supported in structures	Notes
BStr, TBStr	String
LPWStr, LPTStr	String	Yes	ANSI strings must be marshaled using an IntPtr and passed as an array of bytes.
LPStr	N/A		ANSI strings must be marshaled using an IntPtr and passed as an array of bytes.
IUnknown	Object	Yes
IDispatch	Object	Yes
ByValTStr	String	Yes	Supported in structures only.
ByValArray	Any array	Yes
SafeArray	Any array	Yes
VBByRefStr	String
Bool	Boolean, integer types
I1, I2, I4	Integer types of appropriate length
U1, U2, U4	Unsigned integer types of appropriate length
I8	N/A
U8	N/A
R4	4-byte real numbers
R8	8-byte real numbers
Struct	Object
Interface	Object
SysInt, SysUInt	Integer types of appropriate sign and length
AnsiBStr	N/A		ANSI strings must be marshaled using an IntPtr and passed as an array of bytes.
VariantBool	Boolean
FunctionPtr	N/A
AsAny	N/A
LPArray	N/A
LPStruct	N/A
Error	4 byte integers
Currency	Decimal

See Also

Tasks

How to: Create Log Files

Concepts

Marshaling Structures in the .NET Compact Framework

Other Resources

Marshaling Support in the .NET Compact Framework