Question

I have created a WindowsFormControlLibrary porject. It works fine, I can drop it on the forms,call its methods,etc …
but now as a property of it, I am passing the name of a Label to it. and I want this custom control to be able to use that label name and for example change its font to bold .
so the question is that if I have a WinForm and I have a Label on that form and my custom control on that form, then how can I tell my custom control to do something with that label which I am passing its name to it?

Answer 1

First, if you wish to access a Control from your UserControl, you will need to use the FindForm() method.

Second, you will be required to expose your TextBox control, for example, through a property of your form.

Then, you would need to know the type of this Form returned by this FindForm() method.

Once you know it, you need to type-cast this result to the correct type.

So, here a sample untested pseudo-code to give you the idea:

public partial class MyMainForm {
    private TextBox textBox1;

    public MyMainForm() {
        textBox1 = new Textbox();
        textBox1.Name = @"textBox1";
        textBox1.Location = new Point(10, 10);
        textBox1.Size = new Size(150, 23);
        this.Controls.Add(textBox1);
    }

    public Font MyTextBoxFont {
        get {
            return textBox1.Font;
        } set {
            if (value == null) return;
            textbox1.Font = value;
        }
    }
}

Then, assuming you have dropped your control on your form, your UserControl could have a property like so:

public partial class MyUserControl {
    private Form GetContainerForm {
        get {
            return this.FindForm();
        }
    }

    // And later on, where you need to set your TextBox's font:
    private void SetContainerInputFieldFont(Font f) {
        if (GetContainerForm == null) return; // Or throw, depending on what you need to do.

        ((MyMainForm)GetContainerForm).MyTextBoxFont = f
    }
}