form that returns a value

  • Thread starter Thread starter John
  • Start date Start date
J

John

what is the best way to call a form from another and then return some value
to the original form?
 
Create the second Form as a member field of the first. Then it can be
instantiated and shown from the first form. Afterwards, as long as you have
not closed the second Form, the first Form has access to all of the second
Form's public members.

--
HTH,

Kevin Spencer
Microsoft MVP
Chicken Salad Surgery

Orange you bland I stopped splaying bananas?
 
what is the best way to call a form from another and then return some value
to the original form?
Click to expand...
Kevin's way will work, but if you want to do this for modal dialogs,
such as in response to pressing a button on the first form, you can do
it like this:

using (MySecondForm f = new MySecondForm(..params..)) {
if (f.ShowDialog() == DialogResult.OK) {
string s = f.SomePropertyYouAdded;
int i = f.SomeIntProperty;
}
}

There are variations on this, e.g. you could write a method which
shows the form and returns a value, but I have settled on the above
pattern because it allows me to return multiple values in as many
properties as I need, and it is natural to show the form using
ShowDialog().
 
Hi John,

Kevin has provided you the general solution. Some additional info:

1. Since all the control references of a form is declared as private by
default, although the first form has the reference of second form, it can
not manipulate the controls on the second form yet. You have several
options if you want to manipulate certain control on second form. For
example, you may encapsulate the code you want to execute in a public
method of second form, since this method is a member method of second form
class, it can manipulate the privates fields/properties of second form
without any problem. And since it is public, the first form can call this
method now. Another option is just changing the modifier of the control
reference you want to access from "private" to "public". However, this will
break the encapsulation concept of OOP, so it is only convinient when you
want to get a lot of control over that control, which is not easy to
encapsulate as public methods.

2. If you want to get the opposite done, that is, calling the first form
from the new created second form, the normal solution is passing the first
form reference in second form's constructor. You may explicitly create a
customized constructor of second form, which accept a parameter of type
first_form, then in the constructor, you may again store the parameter
passed in as a private field of type first_form for later reference. Sample
logic like this:

Second_Form form=new Second_Form(this);
form.Show();

public class Second_Form
{
private First_Form m_firstform=null;
public Second_Form(First_Form f)
{
m_firstform=f;
}
...
}

Hope this helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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