Accessing value returned by method in another thread

Question

How can I access a value that has been returned by a method that is running in another thread?

Lets say:

public string[,] method1
{
    string a = "blah";
    return a;
}

private void btn_Click(object sender, EventArgs e)
{
    Thread thread = new Thread(method1);
    thread.Start();

    // here I want to use a ...
    Label1.Text = a;
}

Can anyone tell me please?

Hi, I'd like some information about the actual usage here as this may impact the answers you get. Do you really need a thread here? In this case, btn_Click would have to wait for the thread to complete, why not simply call the method directly? — Lasse V. Karlsen, Apr 09 '14 at 14:37
The way your code is at the minute its very possible that you will have tried to set the text before `a` has been returned, backgroundworkers have a `Result` property that may help here but I agree with Lasse — Sayse, Apr 09 '14 at 14:38
I want to load pretty huge xls file on that button click. This is taking about a minute or so. So I want to avoid freeying of GUI, while the xls is loading. That is why I want to use thread. This is just a example. The method1 should return 2D array where the loaded values should be. — Martin Nemeth, Apr 09 '14 at 14:42
@MartinNemeth, for several reasons, use a jagged array, `string[][]`, instead of a multidimensional array. Or, perhaps here, an `IEnumerable>` could be appropriate. — Jodrell, Apr 09 '14 at 15:00
There is nothing intrinsicly wrong with the concept of a multi-dimensional array but, there is with the framework implementation. http://stackoverflow.com/questions/597720/what-are-the-differences-between-a-multidimensional-array-and-an-array-of-arrays — Jodrell, Apr 09 '14 at 15:09

Jodrell · Accepted Answer · 2014-04-10T08:52:08.387

3

why not,

public Task<string> Method1()
{
    return Task.Run(() => "blah");
}

private async void btn_Click(object sender, EventArgs e)
{
    Label1.Text = await Method1();
}

or, if the function takes parameters,

public Task<string> Method1(string someString, int someInt)
{
    return Task.Run(() => string.Format("{0}{1}", someString, someInt));
}

private async void btn_Click(object sender, EventArgs e)
{
    Label1.Text = await Method1("EZ", 1);
}

or even,

private Task<string[][]> ArrayMaker(uint x, uint y)
{
    return Task.Run(() =>
    {
        var result = new string[x][]
        for (var i = 0; i < x; i++)
        {
            result[i] = new string[y];
            for (var j = 0; j < y; j++)
            {
                result[i][j] = ((long)i * j).ToString(
                    CultureInfo.InvariantCulture);
            }
        }

        return result;
    });
}


private async void btn_Click(object sender, EventArgs e)
{
    var bigArray = await ArrayMaker(1000000, 1000000);
}

edited Apr 10 '14 at 08:52

answered Apr 09 '14 at 14:42

Jodrell

34,946
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the work of the method1 will be done in the mainthread not im other thred but the UI is not blocked? – Bassam Alugili Apr 09 '14 at 14:45
@Servy thank you for fixing, I'm forced to use this flakey browser. – Jodrell Apr 09 '14 at 14:52
1

@BassamAlugili If the code you have to generate the string is doing a lot of CPU bound work you can use `Task.Run` to create a task representing the completion of that work in another thread. – Servy Apr 09 '14 at 14:53
@BassamAlugili, the work of `Method1` will be performed asynchronously as a `Task`. – Jodrell Apr 09 '14 at 14:54
:-) Thanks @Servy exactly what I need to hear. Jodrell I have just asked becuase the quesiton was not so clear but the code example was seem to be thread cross problem. – Bassam Alugili Apr 09 '14 at 15:21
@Servy Ok, and how can I pass parameters to such async task? – Martin Nemeth Apr 10 '14 at 06:50
@MartinNemeth like that. – Jodrell Apr 10 '14 at 08:17
@MartinNemeth now using `Task.Run` – Jodrell Apr 10 '14 at 08:52

score 0 · Answer 2 · answered Apr 09 '14 at 14:40

0

Label1.InvokeIfRequired(c => { c.Text = a; });

Where "a" is a string or text from another thread.

answered Apr 09 '14 at 14:40

Bassam Alugili

16,345
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1

This is necessary if you are setting a control property on the non-GUI thread. Not what the OP is asking I fear. – Jodrell Apr 09 '14 at 15:02
@Jodrell I hope that not you have downvote my answer! – Bassam Alugili Apr 09 '14 at 15:25

Accessing value returned by method in another thread

2 Answers2