How Can I Keep a C# Windows Forms Window Always Visible, Even When Other Topmost Windows Appear?

Strategy for keeping windows persistently visible in .NET

This article explores a common dilemma in desktop applications: how to keep a specific window always visible, even if other windows try to obscure it. This article focuses on C# and Windows Forms applications.

Initial method: TopMost attribute

Typically, the first approach is to set the window's TopMost property to true. This should promote the window to the top of the z-order. However, as our users have experienced, this isn't always enough.

Challenge: Overlapping TopMost windows

The problem occurs when another program creates its own TopMost window. These newly appeared windows may still overlap the original TopMost window, thus hiding it.

Super TopMost: Breaking Myths

To solve this problem, one might seek a "super TopMost" window that cannot be covered by other TopMost windows. Unfortunately, as Raymond Chen explains in his article, this is not possible with the current Windows design.

Solution: Keep track of Z order

Since absolute TopMost behavior is not possible, we can take another approach. We can monitor the z-order of our windows and periodically bring our window to the top to ensure it remains visible. Here is a C# code example:

private async void Timer_Tick(object sender, EventArgs e)
{
    // 如果窗口不再可见，则停止跟踪 z 顺序
    if (!this.Visible)
    {
        timer.Stop();
        return;
    }

    // 将窗口置于最前
    this.TopMost = true;
    this.BringToFront();
    this.TopMost = false;
}

This approach consistently keeps the window visible, even in the face of overlapping TopMost windows.

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