How to Properly Minimize a WinForm Application to the System Tray and Prevent Unwanted Visibility?

Understanding Form Minimization to Tray

To minimize a WinForm application to the system tray, the NotifyIcon component is often employed. Upon closing the form, it can be successfully hidden from the desktop, taskbar, and alt-tab dialogue. However, challenges arise when attempting to start the application while already minimized.

Troubleshooting Window Visibility and Alt-Tab Behavior

Initially, the minimized form would appear in the alt-tab dialog. Setting the FormBorderStyle to a ToolWindow option resolved this issue, but introduced a new concern: the title bar of the minimized window became briefly visible upon startup.

Prevent Initial Visibility

The optimal solution to mitigate these problems is to prevent the form from becoming visible at the outset. This can be achieved by overriding the SetVisibleCore() method. Here's an example implementation:

protected override void SetVisibleCore(bool value) {
    if (!allowVisible) {
        value = false;
        if (!this.IsHandleCreated) CreateHandle();
    }
    base.SetVisibleCore(value);
}

This code checks the allowVisible flag, which indicates whether the user has explicitly requested the form to become visible (e.g., through a context menu command). If not, the visibility is forced to false.

Handle Form Closing

To prevent accidental closing of the form, handle the OnFormClosing event.

protected override void OnFormClosing(FormClosingEventArgs e) {
    if (!allowClose) {
        this.Hide();
        e.Cancel = true;
    }
    base.OnFormClosing(e);
}

This code checks the allowClose flag and cancels the closing event if the user has not explicitly chosen to close the form. By hiding the form instead of closing it, the NotifyIcon can continue to function.

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