Inherit from a 'Form' which has parameters

Question

I have a Form named ScanFolder, and I need another Form, that needs to be very similar to ScanFolder, so I decided to use form inheritance. But there seems to be some misunderstanding with the constructor.

ScanFolder looks like:

public partial class ScanFolder : Form
{
    public ScanFolder(MainForm parent, bool[] autoModes, GlobalMethods GMethodsClass)
    {
        //Doing something with parameters
    }
}

I tried to inherit Form like this:

public partial class Arch2 : ScanFolder
{
}

But I get warning Constructor on type 'mhmm.ScanFolder' not found, and also there is an error on Arch2 Form edit mode, where I see a call stack error.

So I tried something like this:

public partial class Arch2 : ScanFolder
{
    public Arch2(MainForm parent, bool[] autoModes, GlobalMethods GMethodsClass)
        : base(parent, autoModes, GMethodsClass)
    {
    }
}

But it is still the same.

As you can see, I clearly don't have any idea what I'm doing. What I'm trying to achieve is getting Arch2 to look the same as ScanFolder, so I can see it in designer view and also override some methods or event handlers.

Even if you get this working, you can't display a form in the Designer if it does not have a default constructor (meaning one that does not accept any parameters). — Cody Gray - on strike, Apr 20 '11 at 10:45
So if I get rid of all parameters and find any other way to use them in Form, I will be able to see my inherited form in design view? — andree, Apr 20 '11 at 10:46
you can add another method in ScanFolder to init the params InitParams(MainForm parent, bool[] autoModes, GlobalMethods GMethodsClass) and leave the constructor empty to handle the GUI only — Gabriel, Apr 20 '11 at 10:52
Related: *['UserControl' constructor with parameters in C#](http://stackoverflow.com/questions/1784303)* — Peter Mortensen, Feb 17 '14 at 14:43

vgru · Accepted Answer · 2017-02-09T16:42:43.833

To use the Forms designer, you will need to have a parameterless constructor:

public partial class ScanFolder : Form
{
    public ScanFolder()
    {
         InitializeComponent(); // added by VS
    }

    public ScanFolder(MainForm parent, bool[] autoModes, GlobalMethods gm)
       : this() // <-- important
    {
         // don't forget to call the parameterless ctor in each
         // of your ctor overloads
    }
}

Or, if you really need to have some init params, you can do it the other way around:

public partial class ScanFolder : Form
{
    public ScanFolder()
        : this(null, new bool[0], new GlobalMethods())
    {

    }

    public ScanFolder(MainForm parent, bool[] autoModes, GlobalMethods gm)
    {
        InitializeComponent(); // added by VS
        // other stuff
    }
}

I recommend the first approach, otherwise you need to pass some reasonable default parameters (I don't recommend passing a null parameter).

It seems that in some cases you will also have to restart Visual Studio after changing the class.

Sorry, but what do you mean by "call parameterless constructor"? Do i need to use ScanFolder() in each over overrided constructors in ScanFolder class? And what about inherited class? Should it look like my example in above post? — andree, Apr 20 '11 at 11:03
+1. This worked. However, I had to ***restart Visual Studio*** in order for the designer to work (coming from a state where I didn't have a parameterless constructor) - rebuilding the solution, etc. was not enough. Perhaps this information could be added to the answer. — Peter Mortensen, Feb 17 '14 at 08:54

score 1 · Answer 2 · edited Jul 10 '12 at 12:21

You can use this code in parent form:

public partial class ScanFolder : Form
{
 public ScanFolder(MainForm parent, bool[] autoModes, GlobalMethods GMethodsClass)
  {
    //doing something with parameters
  }
}

and then in child form as:

public partial class ScanFolder : Form
{
  public ScanFolder(MainForm parent, bool[] autoModes, GlobalMethods GMethodsClass)
     : base(parent,autoModes,GMethodsClass)
  {
    //doing something with parameters
  }
}

Inherit from a 'Form' which has parameters

2 Answers2

Linked