C# "SendMessage" code error

Question

I needed to convert the following code from VB.NET to C#:

Public Class Form1
    Declare Auto Function SendMessage Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer
    Enum ProgressBarColor
        Green = &H1
        Red = &H2
        Yellow = &H3
    End Enum
    Private Shared Sub ChangeProgBarColor(ByVal ProgressBar_Name As Windows.Forms.ProgressBar, ByVal ProgressBar_Color As ProgressBarColor)
        SendMessage(ProgressBar_Name.Handle, &H410, ProgressBar_Color, 0)
    End Sub
End Class

VB.NET code source: Ultimate Programming Tutorials

I used developerFusion's online code converter to convert the code, and this is the C# code that it produced:

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Runtime.InteropServices;
public class Form1
{
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern int SendMessage(IntPtr hWnd, int msg, int wParam, int lParam);
    public enum ProgressBarColor
    {
        Green = 0x1,
        Red = 0x2,
        Yellow = 0x3
    }
    private static void ChangeProgBarColor(System.Windows.Forms.ProgressBar ProgressBar_Name, ProgressBarColor ProgressBar_Color)
    {
        SendMessage(ProgressBar_Name.Handle, 0x410, ProgressBar_Color, 0);
    }
}

EDIT: Removed "ExactSpelling = true" from the DllImport, as it causes an error.

However, that auto-converted code fails to compile due to the following line:

SendMessage(ProgressBar_Name.Handle, 0x410, ProgressBar_Color, 0);

The error that is displayed by the C# compiler is:

Error: The best overloaded method for 'Jyrka98_Modpack_CS.Form1.SendMessage(System.IntPtr, int, int, int)' has some invalid arguments.

It also shows this error:

Argument 3: cannot convert from 'Jyrka98_Modpack_CS.Form1.ProgressBarColor' to 'int'

I don't understand what it means by those error messages. How can I fix that line in C#?

Answer 1

ProgressBarColor is an Enum, which cannot be implicitly evaluated as an int. You will need to cast the value as an int.

Try doing the following:

SendMessage(ProgressBar_Name.Handle, 0x410, (int)ProgressBar_Color, 0); 

Answer 2

Since you don't show how ProgressBarColor is declared, it's a bit of a guess, but since VB is able to automatically convert it to an Integer, I'd assume that it's an enumeration. The VB.NET compiler automatically converts enumeration values to Integer, but the C# compiler does not. In C#, you'll need to explicitly cast the value to an int, like this:

SendMessage(ProgressBar_Name.Handle, 0x410, (int)ProgressBar_Color, 0);

For what it's worth, the proper declaration for the SendMessage API call, according to PINVOKE.NET, is:

[DllImport("user32.dll", CharSet = CharSet.Auto)]
static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

I would recommend using those argument types rather than int, like the code converter used.