How to Ensure a WinForm App Starts Minimized to the System Tray Without Showing Unexpectedly?

Minimizing a WinForm Application to the Tray at Start

Problem

Creating a WinForm application that can minimize to the tray is straightforward. However, attempts to start the application in a minimized state result in the application appearing in the alt-tab dialog with its titlebar occasionally visible.

Solution

To prevent the application from being visible at startup, the SetVisibleCore() method can be overridden. This involves:

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

Here, allowVisible is a flag set to indicate when the application should be visible (e.g., when the user clicks "Show" in the NotifyIcon context menu). If allowVisible is false, the value parameter is set to false to prevent the form from being visible. However, if the form's handle has not been created, it must be created before setting value to false.

Additionally, to prevent the application from closing when the user double-clicks the taskbar icon, the OnFormClosing method can be overridden:

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

Here, allowClose is a flag set to indicate when the application should be closed (e.g., when the user clicks "Exit" in the NotifyIcon context menu). If allowClose is false, the form is hidden and the e.Cancel property is set to true to prevent the application from closing.

Additional Note

The Load event for the main form will not fire until the form is first shown. Therefore, any initialization should be done in the form's constructor rather than in the Load event handler.

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