Moving entry point to DLL in a WinForm app

Question

I am trying to figure out a way to pre-process few things before my WinForm app loads. I tried putting static void Main() in a form within a class library project and commented it out from Program.cs. Which generated a compile time error: "...does not contain a static 'Main' method suitable for an entry point". It makes sense since the program is not loaded, the DLL is not loaded either.

So the question is, is there a way to do this at all? I want the form in the DLL to be able to determine which form to launch the application with:

[STAThread]
static void Main()
{
   Application.EnableVisualStyles();
   Application.SetCompatibleTextRenderingDefault(false);

   if(condition1)
   {
      Application.Run(new Form1());
   }
   else if(condition2)
   {
      Application.Run(new Form2());
   }
}

This logic will be used in more than one app so it makes sense to put it in a common component.

Answer 1

The "static void Main" method has to be within the "EXE" assembly, but you could have this method make a call to your shared assembly's version of "Main". You just can't do it directly.

Answer 2

Keep you Main method in Program.cs. Let it call a method in dll which instantiates a Form based on the condition and return it to Main.

Answer 3

Can you just add a static method in your DLL that your application calls instead of doing the processing in main?

// In DLL
public static class ApplicationStarter
{
     public static void Main()
     {
          // Add logic here.
     }
}

// In program:
{
     [STAThread]
     public static void Main()
     {
          ApplicationStarter.Main();
     }
}

Answer 4

static void Main() doesn't make sense in a class library, however your snippet of code should do exactly what you want if placed in Program.cs.

Also, do you need a catch-all 'else' clause, just in case condition1 and condition2 aren't met? May not be required, but in most cases I would expect some form of feedback rather than the application silently exiting - depends on what you are doing of course.

Edit: This might do what you want, if you simply need to separate the logic into a library

// Program.cs
[STAThread]
static void Main()
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    if(MyLib.Condition1)
    {
        Application.Run(new Form1());
    }
    else if(MyLib.Condition2)
    {
        Application.Run(new Form2());
   }
}


// MyLib.cs
...
public static bool Condition1
{
    get
    {
         return resultOfLogicForCondition1;
    }
}
public static bool Condition2
{
    get
    {
         return resultOfLogicForCondition2;
    }
}

Answer 5

Essentially you are trying to create a custom factory for the form to use for the application. Something like the following:

In the EXE:

static void Main()
{
    Application.Run(new Factory.CreateForm());
}

and in your library:

public static class Factory 
{
    public static Form CreateForm()
    {
        if( condition ) return new Form1();
        else return new Form2();
    }
}