C# Class instance

Question

I'm a beginner in programming and I've read several tutorials. I'm still unclear about the following:

When clicking on a button, that event creates an instance of a class:

private void button2_Click(object sender, RoutedEventArgs e)
{
    int a = 1;
    myClass test = new myClass(a);
}

myClass is doing a long processing job (several minutes). If I click 5 times on my button, is it gonna create 5 instances? Or is the "test" going to be "overwritten" 4 times?

Thanks

Below, are two very good answers to a good beginner question -- its important to note that if the constructor of myClass is synchronous, you will be blocking on your UI thread for quite some time. — Jess
– Jess, Commented Apr 23, 2011 at 19:38
Just to add - if you didn#t want to create additional objects in this case, in the event of the user being over zealous with their clicking, you can always disable the button once clicked using Button.Enabled = false; — Darren
– Darren, Commented Apr 23, 2011 at 20:47

BrokenGlass · Accepted Answer · 2011-04-23 19:15:56Z

8

If I click 5 times on my button, is it gonna create 5 instances ? Or the "test" instance will be "overwritten" 4 times ?

Yes its going to create 5 separate instances. You are creating an object that immediately falls out of scope after it is constructed, so the next time a different instance of the same class is constructed.

I assume you were planning to do the processing as part of your constructor, keep in mind this will block the UI thread, your program will "freeze" - if you are looking to do a long processing job, you shouldn't do it on the UI thread - look into i.e. the BackgroundWorker.

answered Apr 23, 2011 at 19:15

BrokenGlass

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2 Comments

snipef Over a year ago

Thank you. Where should I use the BackgroundWorker ? Not inside the class I guess, but rather in the button function ?

BrokenGlass Over a year ago

@snipef: You can make the BackgroundWorker a variable on your form, then you can use it directly in the button click handler, provided you also add the additional DoWork() and WorkCompleted() (if needed) methods.

David · Accepted Answer · 2011-04-23 19:18:58Z

3

It will create however many instances that you click. However, if the work is synchronous and blocks the UI thread you can't click it again until the work has completed. If your work is asynchronous it will create a new instance every time you click.

Instead try...

private myClass _test;
private void button2_Click(object sender, RoutedEventArgs e)
{
    int a = 1;

    if (_test == null)
    {
        _test = new myClass(a);
    }
}

Though, I would not recommend doing synchronous work on the UI thread.

edited Apr 23, 2011 at 19:18

David

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answered Apr 23, 2011 at 19:16

Chad Moran

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