How do I access a variable declared in one function from a second function?

Question

I'm new to programming in C#, and im looking for a quick solution. I have 2 buttons on form, one is calling the DownloadFileAsync(), and the second one should cancel this operation. Code of first button:

private void button1_Click(object sender, EventArgs e)
{
...
WebClient webClient = new WebClient();
webClient.DownloadFileAsync(new Uri(textBox1.Text), destination);
}

Code of second button:

private void button2_Click(object sender, EventArgs e)
{
webClient.CancelAsync(); // yes, sure, WebClient is not known here.
}

Im looking for an idea how to solve this problem quickly (use the webClient from first function, in block of second).

It is not private but local to the method and lives only as long as the method is executed. — Olivier Jacot-Descombes, Jul 15 '12 at 21:08

score 4 · Accepted Answer · edited Jul 15 '12 at 21:06

4

That isn't a private variable. webClient goes out of scope. You will have to make it a member variable of the class.

class SomeClass {
    WebClient webClient = new WebClient();

    private void button1_Click(object sender, EventArgs e)
    {
        ...
        webClient.DownloadFileAsync(new Uri(textBox1.Text), destination);
    }
}

edited Jul 15 '12 at 21:06

Olivier Jacot-Descombes

104,806
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answered Jul 15 '12 at 20:46

Daniel A. White

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Ria · Answer 2 · 2012-07-15T21:08:29.363

You must to define webClient globally in your class (scope of variable). webClient on button2_Click is out of scope.

Form MSDN: Scopes

The scope of a local variable declared in a local-variable-declaration is the block in which the declaration occurs.

and

The scope of a member declared by a class-member-declaration is the class-body in which the declaration occurs.

so that

class YourClass 
{
     // a member declared by a class-member-declaration
     WebClient webClient = new WebClient();

    private void button1_Click(object sender, EventArgs e)
    {
        //a local variable 
        WebClient otherWebClient = new WebClient();
        webClient.DownloadFileAsync(new Uri(textBox1.Text), destination);
    }

    private void button2_Click(object sender, EventArgs e)
    {
        // here is out of otherWebClient scope
        // but scope of webClient not ended
        webClient.CancelAsync();
    }

}

score 0 · Answer 3 · answered Jul 15 '12 at 20:48

The webclient is declared in button1_Click method and is avialble in the scope this method

Hence you cannot use it in button2_Click method

Instead the compiler will fail your build

To reslove this please move the webClient declaration outside the method and make it available at class level

How do I access a variable declared in one function from a second function?

3 Answers3