Hiding Button on Main Form from Form2

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Hi
How can I hide a button on the Main Form from the second form? I tried to write the following code but it is not working:

//Main Form

private void button1_Click(object sender, EventArgs e)
        {
            frmtwo formtwo = new frmtwo();
            formtwo.ShowDialog();
        }

//Form Two

private void button1_Click(object sender, EventArgs e)
       {
           frmMain  formMain = new frmMain();
           formMain.button1.Hide();
           this.Close();
       }

Posted 28-Feb-12 22:15pm

JacoBosch

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3 solutions

Solution 1

The problem here is that you are not working with the original instance of the main form, you are just working with a new instance. You have to have the reference to your main form in your second form. You declare a member (of typemain form) and set it to the original instance of the main form, either through a property or an overloaded constructor and then hide the button using the member variable.

Posted 28-Feb-12 22:42pm

Shameel

Comments

OriginalGriff 29-Feb-12 4:49am

That is a very bad idea - it ties the two forms together and makes it difficult to maintain. Consider using an event instead.

[no name] 29-Feb-12 8:48am

I was just giving him a heads up on what was causing the problem. I didn't think of explaining design guidelines :-)

OriginalGriff 29-Feb-12 9:03am

The problem is that with a beginner if you give them a solution at all, they assume it is the right thing to do. And then because it worked, they always use it in future.
Then you or I end up trying to sort out the code when they leave the company...:laugh:

[no name] 29-Feb-12 13:09pm

Agree, will keep in mind for future :-)

Solution 3

You now create a new instance of the mainForm and you want to get a reference to the existing instance. You have several options. To name a few:
1. You can add a property to Form2 for specifying the form when creating formtwo and use that. ie:

formtwo.some_form = frmMain;

2. You can get the form using Application.OpenForms, ie (assuming the mainform is at index 0:

Application.OpenForms[0]

Good luck!

Posted 28-Feb-12 22:48pm

E.F. Nijboer

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OriginalGriff · Accepted Answer · 2012-02-28T22:47:00

No, that wont work - you need the current instance of the main form, not a new one.
What you have tried to do is put your mobile phone in the glove box of your car, then expect to be able to open the glove box in my car and find your phone.

It is possible - if you hand an instance of the main form to the second when you open it, but it is a very bad idea - it locks the design of the two forms together, so you can't use form2 without the main form, or change the main form without considering teh effects on form2. This is against the principles of OOP and considered very bad practice.

Instead, construct an event in form2 which the main form subscribes to when it creates it. When the event is signalled, the main form can then hide it's own button, or take whatever other measures it sees fit.

It's pretty easy to do. In form2:

C#

// Signal operation disabled
public event EventHandler DisableOperation;

protected virtual void OnDisableOperation(EventArgs e)
   {
   EventHandler eh = DisableOperation;
   if (eh != null)
      {
      eh(this, e);
      }
   }

private void DoSomethingToDisableOperation()
   {
   OnDisableOperation(null);
   }

In your main form:

C#

private void ShowChildForm()
    {
    // Link in his event so if it changes, we detect it.
    frmChild fd = new frmChild();
    fd.DisableOperation += new EventHandler(DisableOperation);
    fd.ShowDialog();
    }

//
// Fired when the file is changed at a lower level.
//
private void DisableOperation(object sender, EventArgs e)
    {
    myButton.Enabled = false;
    }