Conditional Delegate?

Question

After the user is done with form "f", the form will retain a value that I want to check before running doStuff(). Like, if f.value > 0 , then run doStuff(), else, don't run doStuff(). How can I most concisely modify my code to allow for this check? I don't quite understand when the delegate is assigned, if I pass f.value, will it take the value when I'm adding the delegate, or when it is running the delegate?

form f = new form();
f.Show();
f.FormClosing += delegate{doStuff();};

Thanks!

My answer was voted down before I changed it, but I changed it to what I would do. I agree with Viacheslav. I'd say code it into the form and let the form handle it. Should be no memory leaks there. See my response below. — Mike Webb, May 13 '11 at 14:40
To prevent memory leak you should unsubscribe delegate from the event, but you can't do that because your delegate is anonaymous. You should use regular syntax of C# to implement it. Please investigate my answer. — Viacheslav Smityukh, May 13 '11 at 15:03
The delegate remains in memory as long as the form exists, obviously, but when the form is garbage collected the last reference to the (anonymous) delegate disappears. That's not a real memory leak, is it? — MSalters, May 13 '11 at 15:27
You are right, that should work as you described it. But my expirience said "attention memory leaks!". I'll write test app right now to check it. — Viacheslav Smityukh, May 13 '11 at 17:24
Rechecked results and have different result, no memory leak. But I preffer to unsubscribe it by my self. — Viacheslav Smityukh, May 13 '11 at 17:39
http://stackoverflow.com/questions/1348150/how-do-i-unregister-anonymous-event-handler — Viacheslav Smityukh, May 13 '11 at 17:47

score 7 · Accepted Answer · answered May 13 '11 at 13:56

You can capture the value of the reference when making the delegate:

f.FormClosing += delegate { if(f.value > 0) doStuff(); };

When the event occurs, it will check the current value of the captured reference f, and if the condition matches, continue executing.

score 1 · Answer 2 · answered May 13 '11 at 13:56

1

form f = new form();
f.Show();
f.FormClosing += delegate{if(f.Value>0){doStuff();}};

I believe that it uses the value at the time it runs, not at the time it is assigned. So it would use the value of f.Value when the FormClosing event fires

answered May 13 '11 at 13:56

scott

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score 1 · Answer 3 · answered May 13 '11 at 13:57

Somthing like this?

        form f = new Form();
        f.Show();
        f.FormClosing += (s, a) =>
                             {
                                 if (f.Value > 0)
                                 {
                                     doStuff();
                                 }
                             };

score 1 · Answer 4 · answered May 13 '11 at 13:57

1

My understanding is that lambdas are run in the scope that they're defined, so...

form f = new form();
f.Show();
f.FormClosing += delegate
{
   if(f.Value > 0)
      doStuff();
};

answered May 13 '11 at 13:57

Antony Woods

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Mike Webb · Answer 5 · 2011-05-13T15:11:00.923

1

I wouldn't do it this way. I'd let the form handle it all. Just run the form...

public void showMyForm()
{
    form f = new form();
    f.Show();
}

...then define the form closing event in the form .cs file and link the event in the form itself...

public partial class form : Form
{

    //Link the event in the IDE and let InitializeComponent() add it. Then perform the
    //the things you want in the form itself based on your condition
    private void doStuff(object sender, FormClosingEventArgs e) //Think that's the right args
    {
        if (this.value > 0)
        {
            //code you want to execute.
        }
    }
}

edited May 13 '11 at 15:11

answered May 13 '11 at 13:57

Mike Webb

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this is anonymous delegate delegate{doStuff();}; – Viacheslav Smityukh May 13 '11 at 14:10
@Viacheslav Smityukh - I know. My original thoughts were wrong, so I have been editing my response. – Mike Webb May 13 '11 at 14:11

Viacheslav Smityukh · Answer 6 · 2011-05-13T15:04:32.553

1

You can use regular syntax to implement it

form f = new form();
f.FormClosing += FormClosingHandler; // Add unanonaymous delegate to the event handler
f.Show();

private void FormClosingHandler(object sender, FormClosingEventArgs e)
{
   var form = (form)sender;
   form.FormClosing -= FormClosingHandler; // Unsubscribe from the event to prevent memory leak

   if(form.value > 0)
   {
      doStuff();
   }
}

edited May 13 '11 at 15:04

answered May 13 '11 at 14:25

Viacheslav Smityukh

5,652
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score 0 · Answer 7 · answered May 13 '11 at 13:55

0

If f.Value is a member of the form it will be checked when the delegate is run and you will get the value that is assigned at that moment, not at the moment you assigned the delegate.

answered May 13 '11 at 13:55

Russell Troywest

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Conditional Delegate?

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