How to Use the Marshal Class in VB.NET

Encoder QR Code 2d barcode in VB.NET How to Use the Marshal Class

How to Use the Marshal Class
QR Code Generation In VB.NET
Using Barcode creator for VS .NET Control to generate, create QR Code 2d barcode image in .NET framework applications.
www.OnBarcode.com
QR Code ISO/IEC18004 Scanner In Visual Basic .NET
Using Barcode reader for VS .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
The Marshal class provides a set of static methods that are useful for interoperability. Perhaps most useful is the Marshal.GetLastWin32Error method, which returns an integer
Painting Bar Code In VB.NET
Using Barcode maker for VS .NET Control to generate, create barcode image in .NET framework applications.
www.OnBarcode.com
Barcode Scanner In VB.NET
Using Barcode decoder for .NET framework Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
Lesson 1: Using COM Components from the .NET Framework
Draw QR Code In Visual C#.NET
Using Barcode generation for VS .NET Control to generate, create QR-Code image in .NET framework applications.
www.OnBarcode.com
Paint QR Code JIS X 0510 In .NET
Using Barcode printer for ASP.NET Control to generate, create QR Code JIS X 0510 image in ASP.NET applications.
www.OnBarcode.com
representing the last error that occurred. Typically, if an error occurs, Win32 functions return a Boolean value of false to indicate that an error occurred you must then call Marshal.GetLastWin32Error to retrieve the error code. The following code sample demonstrates this:
Generating QR Code JIS X 0510 In Visual Studio .NET
Using Barcode generator for VS .NET Control to generate, create Denso QR Bar Code image in .NET framework applications.
www.OnBarcode.com
Bar Code Creator In VB.NET
Using Barcode encoder for .NET Control to generate, create barcode image in .NET applications.
www.OnBarcode.com
' VB Dim f As Boolean = Win32Call() If Not f Then Console.WriteLine("Error: {0}", Marshal.GetLastWin32Error()) End If // C# Boolean f = Win32Call(); if (!f) { Console.WriteLine("Error: {0}", Marshal.GetLastWin32Error()); }
Printing Barcode In VB.NET
Using Barcode encoder for Visual Studio .NET Control to generate, create barcode image in Visual Studio .NET applications.
www.OnBarcode.com
European Article Number 13 Generator In VB.NET
Using Barcode creation for .NET framework Control to generate, create EAN 13 image in Visual Studio .NET applications.
www.OnBarcode.com
Another useful method is Marshal.SizeOf, which returns the number of bytes required for a class or object after it is marshaled to an unmanaged class. The following code sample demonstrates how to check the size both of a class and of an object. In this example, the size is 8 bytes for each because the class and the object are the same type:
Data Matrix ECC200 Encoder In Visual Basic .NET
Using Barcode creator for .NET framework Control to generate, create DataMatrix image in .NET applications.
www.OnBarcode.com
GTIN - 12 Creator In Visual Basic .NET
Using Barcode creation for .NET framework Control to generate, create UPC-E image in VS .NET applications.
www.OnBarcode.com
' VB Console.WriteLine(Marshal.SizeOf(GetType(Point))) Dim p As New Point() Console.WriteLine(Marshal.SizeOf(p)) // C# Console.WriteLine(Marshal.SizeOf(typeof(Point))); Point p = new Point(); Console.WriteLine(Marshal.SizeOf(p));
Data Matrix Drawer In None
Using Barcode drawer for Excel Control to generate, create Data Matrix image in Microsoft Excel applications.
www.OnBarcode.com
Making Matrix 2D Barcode In Visual Studio .NET
Using Barcode drawer for .NET framework Control to generate, create Matrix Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Other useful methods include the following:
EAN-13 Supplement 5 Generator In None
Using Barcode creator for Online Control to generate, create GTIN - 13 image in Online applications.
www.OnBarcode.com
Bar Code Recognizer In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Copy
UPC Symbol Generation In None
Using Barcode creator for Font Control to generate, create UPCA image in Font applications.
www.OnBarcode.com
Universal Product Code Version A Printer In None
Using Barcode drawer for Online Control to generate, create GS1 - 12 image in Online applications.
www.OnBarcode.com
Copies data between a managed array and an unmanaged memory pointer
Drawing UPC-A Supplement 2 In .NET Framework
Using Barcode encoder for Visual Studio .NET Control to generate, create UCC - 12 image in .NET applications.
www.OnBarcode.com
Creating USS Code 39 In None
Using Barcode generator for Office Excel Control to generate, create Code 3 of 9 image in Microsoft Excel applications.
www.OnBarcode.com
GenerateGuidForType
Returns the globally unique identifier (GUID) for the specified type or generates a new GUID Returns the programmatic identifier (ProgID) for the Converts an HRESULT error code to a specified type
GenerateProgIdForType
GetExceptionForHR and GetHRForException
corresponding Exception, or vice versa
ReadByte, ReadInt16, ReadInt32, ReadInt64, and ReadIntPtr Reads values from
unmanaged memory
13
Interoperating with COM
WriteByte, WriteInt16, WriteInt32, WriteInt64, and WriteIntPtr
Writes values to
unmanaged memory
ThrowExceptionForHR
Throws an exception with the specified HRESULT value
In addition, Marshal provides two useful read-only properties:
SystemDefaultCharSize The default character size on the system; the default is 2 for Unicode systems and 1 for ANSI systems. SystemMaxDBCSCharSize
The maximum size of a double byte character set
(DBCS), in bytes.
How to Pass Structures
Unmanaged functions often accept structures as parameters. Passing a structure to an unmanaged function might require you to specify the layout of the structure. You can specify the layout of a structure by using the StructLayout and FieldOffset attributes. For example, consider the PtInRect function in User32.dll. The function has the following signature:
BOOL PtInRect(const RECT *lprc, POINT pt);
Notice that the first parameter must be passed by reference (as indicated by the asterisk preceding the parameter name). The following example demonstrates how to specify the layouts of the structures that are required to call the function:
' VB Imports System.Runtime.InteropServices <StructLayout(LayoutKind.Sequential)> Public Structure Point Public x As Integer Public y As Integer End Structure <StructLayout(LayoutKind.Explicit)> Public Structure Rect <FieldOffset(0)> Public left As Integer <FieldOffset(4)> Public top As Integer <FieldOffset(8)> Public right As Integer <FieldOffset(12)> Public bottom As Integer End Structure Class Win32API Declare Auto Function PtInRect Lib "user32.dll" _ (ByRef r As Rect, p As Point) As Boolean End Class
Lesson 1: Using COM Components from the .NET Framework
// C# using System.Runtime.InteropServices; [StructLayout(LayoutKind.Sequential)] public struct Point { public int x; public int y; } [StructLayout(LayoutKind.Explicit)] public struct Rect { [FieldOffset(0)] public int left; [FieldOffset(4)] public int top; [FieldOffset(8)] public int right; [FieldOffset(12)] public int bottom; } class Win32API { [DllImport("User32.dll")] public static extern bool PtInRect(ref Rect r, Point p); }
Notice the use of the LayoutKind enumeration with the StructLayout attribute. LayoutKind.Auto gives full control to the CLR over the layout, including the sequence of the fields. LayoutKind.Sequential allows the CLR to define the layout of the structure using the sequence you specify. LayoutKind.Explicit requires you, the developer, to specify the number of bytes for every field in the structure (using the FieldOffset attribute).
How to Implement Callback Functions
Similar to handling events in a .NET Framework application, some COM functions will want to call into a method that you provide in order to return results. This is often indicated by arguments that begin with the lp- (long pointer) prefix and end with the -Func (function) suffix. For example, the EnumWindows function in User32.dll requires a callback for the first argument, as indicated by its signature:
BOOL EnumWindows(WNDENUMPROC lpEnumFunc, LPARAM lParam)
To call a function that requires a callback, follow these steps: 1. Create a method to handle the callback. 2. Create a delegate for the method. 3. Create a prototype for the function, specifying the delegate for the callback argument. 4. Call the function.
Copyright © OnBarcode.com . All rights reserved.