Winforms NotifyIcon NullReferenceException

Question

I have a simple winform program, that has 1 textbox. I want to hide it, if it loses focus (using Form1_Deactivate event for that) or user hits enter (then it also open up chrome with specific query) and show it's icon in the tray. After double-clicking tray icon I want to show the form again and give it focus. It works for the first two times (literally). Form shows, hides, shows, hides and next time it shows it doesn't have focus and also NullReferenceException related to NotifyIcon is being thrown.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void txtSlowo_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (e.KeyChar == (char)Keys.Enter)
        {
            Process.Start("chrome.exe", @"http:\\www.sjp.pl\" + txtSlowo.Text);

            txtSlowo.Text = "";
            this.notifyIcon1.Visible = true;
            this.Visible = false;
            e.Handled = true;
        }
    }

    private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
    {
        this.notifyIcon1.Visible = false;
        this.Show();
        txtSlowo.Text = "";
    }

    private void Form1_Deactivate(object sender, EventArgs e)
    {
        this.Hide();
        this.notifyIcon1.Visible = true; //this line throws the exception
    }
}

Github in case you want to see whole project

EDIT: I'm assuming this is the stacktrace of the exception:

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Forms.NotifyIcon.UpdateIcon(Boolean showIconInTray)
   at System.Windows.Forms.NotifyIcon.set_Visible(Boolean value)
   at SJPCheck.Form1.Form1_Deactivate(Object sender, EventArgs e) in c:\users\jan\documents\visual studio 2015\Projects\SJPCheck\SJPCheck\Form1.cs:line 42
   at System.Windows.Forms.Form.OnDeactivate(EventArgs e)
   at System.Windows.Forms.Form.set_Active(Boolean value)
   at System.Windows.Forms.Form.WmActivate(Message& m)
   at System.Windows.Forms.Form.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

"related to", can you point to the exact line that throws this exception? — Lasse V. Karlsen, Jun 01 '16 at 18:46
Yes, what line does the exception hit? Add the stack trace as well. — DonBoitnott, Jun 01 '16 at 18:51
My bad, I edited the original question. this.notifyIcon1.Visible = true; in Form1_Deactivate throws it. — JanRad, Jun 01 '16 at 18:53
in the OnFormClosed override, set `this.notifyIcon = null;`, then in your Deactivate method, check for null before setting the visible to true. — LarsTech, Jun 01 '16 at 19:19
Alright this works. To my understanding: Form1_Deactivate is also called when I close the form, so when closing, something weird was happening to notifyIcon (it wasn't set to null, thats why the override) and showing it caused the exception to be thrown. — JanRad, Jun 01 '16 at 19:29

Winforms NotifyIcon NullReferenceException

0 Answers0