WPF Loses Event Handler - wpf

Question

I have a simple WPF app in .NET 4.7. The main Window listens for a "Key Up" event. If the Escape key is pressed, the Main Window closes itself. This works fine (at least it starts out working fine).
The main Window also contains a Button that opens another Window (call it X). X is just an empty Window. It has no event handlers. When X opens, the Button in the main Window is disabled. Once X closes, the Button is re-enabled.
Here's the problem: Once X is closed, the main Window's Key Up event handler seems to be gone...sort of. I can no longer press Escape to close the main Window unless I first give the focus to one of the buttons. If I just click on the main Window and press Escape, it will not close the Window. Prior to showing Window X, this was not the case.
It turns out that if I do not disable and re-enable the Button, the Key Up event handler continues to work after X is closed -- I can still reliably close the main Window by pressing the Escape key.
Obviously, I'm new to WPF. I'm wondering if there is something weird going on with Windows events.
Here is the the Main Window's XAML followed by it's code behind. I have also included Window X's XAML and code behind (btw, Window X is the WrapPanelWindow).
<Window x:Class="Wpf_01.MainWindow" x:ClassModifier="internal"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Wpf_01"
mc:Ignorable="d"
Title="Main Window" Height="300" Width="300" Background="#FF6289A4" KeyUp="Key_Up">
<StackPanel Margin="20,10,20,10">
<Button Content="Canvas Example"/>
<Button Content="WrapPanel Example" Click="Button_Click"/>
<Button Content="DockPanel Example"/>
<Button Content="Grid Example"/>
<Button Content="StackPanel Example"/>
</StackPanel>
Here is the Main Window's code behind:
namespace Wpf_01 {
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
internal partial class MainWindow : Window {
public MainWindow() {
InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e) {
Button clickedButton = sender as Button;
Window newWindow = null;
switch(clickedButton.Content) {
case "Canvas Example":
newWindow = new CanvasWindow();
break;
case "WrapPanel Example":
newWindow = new WrapPanelWindow();
break;
}
if(newWindow != null) {
clickedButton.IsEnabled = false;
newWindow.Show();
newWindow.Closed += (x, y) => clickedButton.IsEnabled = true;
}
} // Button_Clicked()
private void Key_Up(object sender, KeyEventArgs e) {
if(e.Key == Key.Escape)
Close();
} // KeyHandler()
}
}
Here is the WrapPanelWindow XAML and code behind:
<Window x:Class="Wpf_01.WrapPanelWindow" x:ClassModifier="internal"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Wpf_01"
mc:Ignorable="d"
Title="Fun with WrapPanel Window" Height="200" Width="260">
<Grid>
</Grid>
</Window>
Finally, the WrapPanelWindow's code behind.
namespace Wpf_01 {
/// <summary>
/// Interaction logic for WrapPanelWindow.xaml
/// </summary>
internal partial class WrapPanelWindow : Window {
public WrapPanelWindow() {
InitializeComponent();
}
}
}

Answer 1

The main window is not getting the focus back when you close the CanvasWindow. When you disable the button, nothing else on the window is focusable.
If you select the App from the windows taskbar (minimize and restore) or switch programs and come back using Ctrl+Tab it works.
Try giving the clickedButton focus after you re-enable it:
newWindow.Closed += (x, y) =>
{
clickedButton.IsEnabled = true;
clickedButton.Focus();
};