making a cross-thread call to hide a form visual c#

Question

Update: Solution arrived since and is now accepted. Due to the clarity of the pseudo codes on this question the solution took only a few seconds. Trying to figure out the solution from the other seemingly "duplicate" questions took a lot of time already. I had the solution in 20 minutes from the moment I asked this question. So it is not a duplicate, probably the clearest of them all to date.

While several similar questions have been asked on this, I was still not able to put together a working code from them. My main application is not on a form, but in a separate class that is a plugin and executed by a host application.

So while it seems a duplicate question it is not. Please read on.

I have my main class doing stuff. Then I have a form that displays information to the user. I need to hide this form when the user switches away from the application (host application loses focus).

I am using very limited APIs so the only methods I have at my disposal events triggered by the host application.

I created a timer that fires every 100ms and checks whether the user had the application in focus. And if not a command is sent to the form to hide itself.

The reason for this approach is because the host application loosing focus is just one of the many scenarios that I need to hide the form and I need to channel all these through the same exact method.

All works from within the rest of the classes (the Hide() method is called from the rest of the application no problem. But it does not work when the timer calls the Hide() method, because the timer is on a different thread when it fires. So the call becomes a cross-thread call.

The very specific question is that I need an exact sample code how to make this call from the timer event handler to the form's Hide() method thread-safe with Invoke.

Thanks.

This is the timer:

private void Controllel_Opened(object sender, EventArgs e)
{
    myTimer.Elapsed += new System.Timers.ElapsedEventHandler(DisplayTimeEvent);
    myTimer.Interval = 50;
    myTimer.Start();
}

public static System.Timers.Timer myTimer = new System.Timers.Timer();
// This method checks different scenarios when the tool tip should be hidden and calls the hiding method
public static void DisplayTimeEvent(object source, System.Timers.ElapsedEventArgs e)
{
    FormHandler.Hide();
}

Then the "FormHandler" class:

public static class FormHandler
{
    private static Form1 frm1 = new Form1();

    public delegate void Form1HideEventHandler();
    public static event Form1HideEventHandler Form1Hide;

    public static void Hide()
    {
        if (Form1Hide != null)
        {
            Form1Hide();
        }

    }
}

Then the form's code:

public partial class Form1 : Form
{   
    public Form1()
    {
        InitializeComponent();
        FormHandler.Form1Hide += FormHandler_Form1Hide;
    }

    private void FormHandler_Form1Hide()
    {
        Hide();
    }
}

I would like to get a solution with exact code if possible. Thanks.

Found a better duplicate: http://stackoverflow.com/questions/1523878/getting-cross-thread-operation-not-valid — Rob, Apr 22 '16 at 05:50
@Rob -- Thanks. That may lead me to a solution. But what is the exact code to use with the above pseudo code? — ib11, Apr 22 '16 at 05:54

score 3 · Accepted Answer · edited May 06 '16 at 02:56

3

private void FormHandler_Form1Hide()
{
    if (InvokeRequired)
    {
        this.Invoke(new Action(() => { FormHandler_Form1Hide(); }));
    }
    else
    {
        Hide();
    }
}

edited May 06 '16 at 02:56

Rob

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answered Apr 22 '16 at 05:54

or hor

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Excellent! Thank you. And yes, it was **perfect** with your edit on adding the `else` part. I already had this when I applied your sample. – ib11 Apr 22 '16 at 05:59
2

Just for *DRY*, I prefer to call self in the `InvokeRequired` part instead of repeating the same code as below... something like: `if(InvokeRequired) { this.Invoke(() => FormHandler_Form1Hide()); return; }` then in case the function gets longer you don't have to repeat your code – Jcl Apr 22 '16 at 06:07

score 1 · Answer 2 · answered Apr 22 '16 at 05:37

1

You need to use System.Windows.Forms.Timer instead. That will invoke back onto the dispatcher thread.

answered Apr 22 '16 at 05:37

satnhak

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That's the problem, I need to call the form from outside of the form. The reason is because the host application loosing focus is just one of the many scenarios that I need to hide the form and I need to channel all these through the same exact method. – ib11 Apr 22 '16 at 05:40
Yes, but if you use that timer it will dispatch back onto the UI thread. The method doesn't matter, all that matters is the thread. – satnhak Apr 22 '16 at 05:45

making a cross-thread call to hide a form visual c#

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