CODEWITHSUNDEEP
c#async-await
super sahar
super sahar

Reputation: 425

Cannot convert lambda expression (async/await)

Cannot convert lambda expression to intended delegate type because some of the return types in the block are not implicitly convertible to the delegate return type

I want to run function in enother thread and I can do this without error, but only when calculating function is not void. I want to use void function. Tell me please how to do it or what kind of result it should return?

private async void buttonStep3_Click(object sender, EventArgs e)
        {
            DialogResult dialogResult = folderBrowserDialog1.ShowDialog();
            if (dialogResult != DialogResult.OK)
                return;

            SetAllButtonsStateEnabled(false);

            progressBar1.Value = 0;
            progressBar1.Visible = true;

            var progressProgressBarValue = new Progress<int>(s => progressBar1.Value = s);

            await Task.Run(() => SizeFilter3(
                                    Convert.ToInt32(textBoxSF1W.Text), Convert.ToInt32(textBoxSF1H.Text),
                                    Convert.ToInt32(textBoxSF2W.Text), Convert.ToInt32(textBoxSF2H.Text),
                                    Convert.ToInt32(textBoxSF3W.Text), Convert.ToInt32(textBoxSF3H.Text),
                                    Convert.ToInt32(textBoxSF4W.Text), Convert.ToInt32(textBoxSF4H.Text),
                                    Convert.ToInt32(textBoxSF5W.Text), Convert.ToInt32(textBoxSF5H.Text),
                                    progressProgressBarValue),
                                TaskCreationOptions.LongRunning);//this line gives an error


            progressBar1.Visible = false;
            progressBar1.Value = 0;

            SetAllButtonsStateEnabled(true);
        }
private void SizeFilter3(int filterW1, int filterH1,
                                   int filterW2, int filterH2,
                                   int filterW3, int filterH3,
                                   int filterW4, int filterH4,
                                   int filterW5, int filterH5,
                                       IProgress<int> progressProgressBarValue)
{
       //some actions
       progressBarValue += progressBarProgress;
       progressProgressBarValue.Report(progressBarValue);
       //some actions
}

Upvotes: 4

Views: 1450

Answers (2)

Haytam
Haytam

Reputation: 4733

You should use the Task factory to create a long running task, which accepts a lambda:

await Task.Factory.StartNew(() => SizeFilter3(Convert.ToInt32("0"), Convert.ToInt32("0"),
                                              Convert.ToInt32("0"), Convert.ToInt32("0"),
                                              Convert.ToInt32("0"), Convert.ToInt32("0"),
                                              Convert.ToInt32("0"), Convert.ToInt32("0"),
                                              Convert.ToInt32("0"), Convert.ToInt32("0"), 
                                              progressProgressBarValue), TaskCreationOptions.LongRunning);

Task.Run doesn't have a TaskCreationOptions argument.

Upvotes: 5

waldrumpus
waldrumpus

Reputation: 2590

You can cast your lambda expression explicitly into an Action:

Task.Run((Action) (() => SizeFilter3(
                                Convert.ToInt32(textBoxSF1W.Text), Convert.ToInt32(textBoxSF1H.Text),
                                Convert.ToInt32(textBoxSF2W.Text), Convert.ToInt32(textBoxSF2H.Text),
                                Convert.ToInt32(textBoxSF3W.Text), Convert.ToInt32(textBoxSF3H.Text),
                                Convert.ToInt32(textBoxSF4W.Text), Convert.ToInt32(textBoxSF4H.Text),
                                Convert.ToInt32(textBoxSF5W.Text), Convert.ToInt32(textBoxSF5H.Text),
                                progressProgressBarValue)),
                            TaskCreationOptions.LongRunning);

Note that you have to put the expression in parentheses as well for this to work.

Upvotes: -1

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