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Force loop to wait for an event

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梦毁少年i
梦毁少年i 2020-12-12 05:07

I am trying to write a method that goes through a list of items - for each one adds it to a form, then waits for the user to input some data and click a button. However I ha

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  • 旧时难觅i
    旧时难觅i (楼主)
    2020-12-12 05:47

    While I agree in general with Jon Skeet, there was an interesting presentation by Mads Torgensen demonstrating how async/await can be used to simplify such scenarios (using the techniques mentioned by Jon). After all, isn't that the same as with enumerators - we can write own enumerator class using state like index etc., but we almost never do that and use iterator blocks instead.

    Anyway, here is the async/await technique we were talking about.

    First, the reusable part: 

    public static class Utils
{
    public static Task WhenClicked(this Button button)
    {
        var tcs = new TaskCompletionSource();
        EventHandler onClick = null;
        onClick = (sender, e) =>
        {
            button.Click -= onClick;
            tcs.TrySetResult(null);
        };
        button.Click += onClick;
        return tcs.Task;
    }
}



    and your code using it (note that you need to mark your method as async)
    


    foreach (string s in List)
{
    txtName.Text = s;
    await yourButton.WhenClicked();
}

    


    Sample test putting it all together:
    


    using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Samples
{
    static class Test
    {
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            var form = new Form();
            var txtName = new TextBox { Parent = form, Top = 8, Left = 8 };
            var buttonNext = new Button { Parent = form, Top = txtName.Bottom + 8, Left = 8, Text = "Next" };
            form.Load += async (sender, e) =>
            {
                var List = new List { "A", "B", "C", "D " };
                foreach (string s in List)
                {
                    txtName.Text = s;
                    await buttonNext.WhenClicked();
                }
                txtName.Text = "";
                buttonNext.Enabled = false;
            };
            Application.Run(form);
        }
    }
    public static class Utils
    {
        public static Task WhenClicked(this Button button)
        {
            var tcs = new TaskCompletionSource();
            EventHandler onClick = null;
            onClick = (sender, e) =>
            {
                button.Click -= onClick;
                tcs.TrySetResult(null);
            };
            button.Click += onClick;
            return tcs.Task;
        }
    }
}

    
    
             
    
                                                        
    
            
            
    
              
                
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