CODEWITHSUNDEEP
c#.netwinforms
paul6734
paul6734

Reputation: 121

Enabling and disabling forms in C#

I have created two forms in C#: form1 is the main application and form2 is a logon window. form1 has a button that disable itself and show form2 and form2 has button that enable the main form and closes itself. The problem is when I try to enable form1 using a form2 button (I get "An unhandled exception of type 'System.NullReferenceException' occurred in Application.exe")

Here is the form1 code:

Login  Login = new Login();
Login.Show();
this.Enabled = false;

form2(Login) code:

(this.Owner as Form1).Enabled = true;  ===> this line gets highlighted
 Close();

Upvotes: 0

Views: 630

Answers (2)

GvS
GvS

Reputation: 52538

You could use ShowDialog, this will make all other forms (of the same application) inaccessable during the show of the form:

using (var login = new Login()) {
    login.ShowDialog(this);
}

And you can pass one of the DialogResult values, as the return code, to pass success or failure to the calling method.

Upvotes: 1

Andrey Korneyev
Andrey Korneyev

Reputation: 26886

Change this line of code in form1 from 

Login.Show();

to 

Login.Show(this);

or set owner explicitly before showing like:

Login.Owner = this;
Login.Show();

Otherwise that login form will not has owner and this.Owner will be null leading to NullReferenceException when you're trying to access its members.

Upvotes: 5

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