CODEWITHSUNDEEP
c#winformsmultithreadingdialog
Moinonime
Moinonime

Reputation: 304

C# : Show dialog on UI thread from another thread

I'm new to C#, but i've done a lots of java. Here's my problem : I'm trying to open a "SaveFileDialog" from a thread that is not the UI thread.

This is exactly what I try to do:

public partial class Form1: Form
{
    public string AskSaveFile()
    {
        var sfd = new SaveFileDialog();
        sfd.Filter = "Fichiers txt (*.txt)|*.txt|Tous les fichiers (*.*)|*.*";
        sfd.FilterIndex = 1;
        sfd.RestoreDirectory = true;
        DialogResult result = (DialogResult) Invoke(new Action(() => sfd.ShowDialog(this)));
        if(result == DialogResult.OK)
        {
            return sfd.FileName;
        }

        return null;
    }
}

This method will always be called from a thread different from the one who owns the Form. The problem is that when I execute this code, the "Form1" freeze and the "SaveFileDialog" doesn't show up.

Do you have some clue to help me to show the dialog from an independant thread?

Upvotes: 10

Views: 13214

Answers (2)

Hans Passant
Hans Passant

Reputation: 941218

Make it look like this:

    public string AskSaveFile() {
        if (this.InvokeRequired) {
            return (string)Invoke(new Func<string>(() => AskSaveFile()));
        }
        else {
            var sfd = new SaveFileDialog();
            sfd.Filter = "Fichiers txt (*.txt)|*.txt|Tous les fichiers (*.*)|*.*";
            sfd.FilterIndex = 1;
            sfd.RestoreDirectory = true;
            return sfd.ShowDialog() == DialogResult.OK ? sfd.FileName : null;
        }
    }

If you still get deadlock then be sure to use the debugger's Debug > Windows > Threads window and look at what the UI thread is doing. Control.Invoke() cannot complete unless the UI thread is idle and executing Application.Run(). If it isn't, like waiting for the worker thread to finish, then this code is always going to deadlock.

Also consider that this kind of code is risky from a UI usability perspective. The user might not expect this dialog to suddenly show up and could accidentally close it while mousing or keyboarding in the window(s) owned by the UI thread.

Upvotes: 15

Marco
Marco

Reputation: 57573

Try this:

public partial class Form1: Form
{
    public string AskSaveFile()
    {
        if (this.InvokeRequired)
        {
            Invoke( new MethodInvoker( delegate() { AskSaveFile(); } ) );
        }
        else
        {
            var sfd = new SaveFileDialog();
            sfd.Filter = "Fichiers txt (*.txt)|*.txt|Tous les fichiers (*.*)|*.*";
            sfd.FilterIndex = 1;
            sfd.RestoreDirectory = true;
            if(sfd.ShowDialog() == DialogResult.OK) return sfd.FileName; 
        }               
        return null;
    }
}

Upvotes: 7

Related Questions