Keywords: scope resolution, passing classes between parent and child
forms, parameter constructor method, normal constructor, default
constructor, forward reference, sharing classes between forms.
Here is a newbie mistake that I found myself doing (as a newbie), and
that even a master programmer, the guru of this forum, Jon Skeet,
missed! (He knows this I'm sure, but just didn't think this was my
problem; LOL, I am needling him)
If you want to pass information between two forms comprised of
classes, whether or not they are parent/child, modal or modeless,
dialog or non-dialog you have to use the non-normal/ non-default or
parametricized or parameter constructor, not a default (no parameter)
normal constructor. Explanation below.
Let's say you have a button on your form that you click to bring up
another form, and the button has an Events handler called
"clikMeButton2B ringUpANew_Chil d_Form_to_The_M ainForm_Click".
Let's say in Designer mode you've already built a nice new (child or
second or dependent or non-main) form called "Form2" (I think you can
also programmically 'build' a new form, but I like using the Designer
mode, drag-and-drop and let the Wizard figure out how to initialize
the form, but I digress).
Let's say you have a class, called Class1, that you declared in your
first form, during instantiation of that form, having an instance
"myClass1", and now you want that same class instantiation to be
passed to the Form2. How to do that? If you use the wrong
constructor it won't be 'seen' by the new form. Hence you must do
this:
private void
clikMeButton2Br ingUpANew_Child _Form_to_The_Ma inForm_Click(ob ject
sender, EventArgs e)
{
// Form2 frm2 = new Form2(); //Do not do this--it won't
work! You cannot see myClass1 in frm2
Form2 frm2 = new Form2(myClass1) ; // this will work;
myClass1 will be seen in Form2
// of course, we assume you do have a parameter constructor in Form2
that accepts class1 as a parameter, ie., you have a constructor with
this signature in Form2 (Class1 C1) {};//see further below at (#1)
frm2.Show(); //shows the form, etc
}
That's it. Done. You can also pass more than one class of course,
with the proper signature.
(#1) And just to make the point clearer, Form2 must have as a
constructor something besides the normal (default) non parameter
constructor, along these lines:
public Form2(Class1 passClass1_from _Form1)
{
myClass2_that_e xists_in_Form2 = passClass1_from _Form1; //
names are arbitrary of course
InitializeCompo nent();
// other stuff here if you want
}
Done.
One more thing as an aside, and it has nothing to do with the above:
you need, in Form 1, to be careful where you put class1; it has to be
sort of like C++, and placed as a 'forward reference' before Form1 is
constructed, along these lines:
public partial class Form1 : Form
{
Class1 myClass1; //Note where this is located! outside the
default constructor for Form1
// this is called a 'forward reference' in C++, and you need to do
this for C# as well
public Form1()
{
InitializeCompo nent(); //mandatory for all forms, stuff
that the Wizard fills and I don't fool with
myClass1 = new Class1();
//or, if your Class1 takes parameters int i, string s, myclass1=new
Class (10, "hi");
//other stuff here, like, for example, this.AutoValida te =
AutoValidate.En ableAllowFocusC hange; //etc
}
/// other stuff here
}
The point being: you need a forward reference if the Class1 is not
'nested' in the Form1 {}, that is, if Class1 is part of a separate
translation unit or module, even if Class1 is in the same namespace as
Form1.
RL
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