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MouseEnter event does not fire on a Popup control after a mouse click on the Control

I was testing a Popup control in WPF with the following code
<Window x:Class="Popup1.MainWindow"
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:Popup1"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="250">
<Grid>
<TextBlock TextWrapping="Wrap">You can use a popup to provide a link for a specific
<Run TextDecorations="Underline" MouseEnter="ContentElement_OnMouseEnter">
term
</Run>
</TextBlock>
<Popup Name="popLink" StaysOpen="False" Placement="Mouse" MaxWidth="200"
PopupAnimation="Slide" AllowsTransparency="True">
<Border>
<TextBlock Margin="10" TextWrapping="Wrap">
For more information, see
<Hyperlink NavigateUri="http://en.wikipedia.org/wiki/Term" Click="Hyperlink_OnClick">Wikipedia</Hyperlink>
</TextBlock>
</Border>
</Popup>
</Grid>
</Window>
and the handlers
private void ContentElement_OnMouseEnter(object sender, MouseEventArgs e) {
popLink.IsOpen = true;
}
private void Hyperlink_OnClick(object sender, RoutedEventArgs e) {
Process.Start(((Hyperlink) sender).NavigateUri.ToString());
}
The result is a trivial window that contains a textblock with a link to a popup control that visually appears when the mouse hovers over the link to the popup.
The normal behavioris the popup to stay visible until a mouse click. This works fine as long as the mouse click is not on the link to the popup
The strange behaviorthat i can't explain happens when i click the mouse over the link to the popup.Then, the popup closes ( as expected ) but it never appears again when the mouse hovers over the link (as it should).
Can you explain this behavior?

As commented, the reason is probably a race condition between closing popup and re-opening because the mouse is over the textblock. You can prevent this situation by delaying the popup open action until current work is completed:
private void ContentElement_OnMouseEnter(object sender, MouseEventArgs e)
{
Dispatcher.BeginInvoke(new Action(() => popLink.IsOpen = true));
}
Regarding your title text: the MouseEnter event is actually fired (debug it!), just the action within is not working as expected because the popup is in an inconsistent state.

After some tweaking the best behaviour is achieved if we add an extra event (comparing to the initial code) handler for the Popup Close event that sets the IsOpen property to false when the popup closes
private void PopLink_OnClosed(object sender, EventArgs e) {
if (popLink.IsOpen) {
popLink.IsOpen = false;
}
}
and the ammenment in XAML
<Popup Name="popLink" StaysOpen="False" Placement="Mouse" MaxWidth="200"
PopupAnimation="Slide" AllowsTransparency="True"
Closed="PopLink_OnClosed">
<Border Background="Bisque">
<TextBlock Margin="10" TextWrapping="Wrap">
For more information, see
<Hyperlink NavigateUri="http://en.wikipedia.org/wiki/Term" Click="Hyperlink_OnClick">Wikipedia</Hyperlink>
</TextBlock>
</Border>
</Popup>

Open Window Activate not working with button inside menu

I have a really strange behaviour, and I hope someone can help me out.
I have the following XAML layout:
<StackPanel Orientation="Horizontal">
<Menu>
<Menu.Items>
<MenuItem Padding="2,0,2,0">
<MenuItem.Header>
<Button Content="Details"
Click="Details_Click" />
</MenuItem.Header>
</MenuItem>
</Menu.Items>
</Menu>
<Button Content="Details"
Click="Details_Click" />
</StackPanel>
Please notice that both buttons have the same Event registered.
The Details_Click Event looks like this:
private void Details_Click(object sender, RoutedEventArgs e)
{
var viewer = new DictionaryViewer();
viewer.ShowActivated = true;
viewer.Show();
viewer.Topmost = true;
viewer.Topmost = false;
viewer.Activate();
viewer.Focus();
e.Handled = true;
return;
}
Now I am facing the problem, even with all the code from above the Window doesnt show up activated when I press the button inside the Menu but outside of it works with just .Activate();.
(How I know that window isnt activated: need 2 clicks to close/minimize/maximize it)
Why would my XAML Layout ruin the Activation of the DictionaryViewer(); window, with the button inside Menu?
(To your information the DictionaryViewer is totally empty, its a fresh window nothing implemented yet)
Edit:
Yes, I know there is the MenuItem_Click Event that may make it work, but I need/want the button inside the Menu how can I fix this issue?

THe reason this is happening is because the Button inside the MenuItem is gaining Focus after the Window has opened.
If you set the Focusable property of the button inside MenuItem, this fixes the issue.
E.g.
<StackPanel Orientation="Horizontal">
<Menu>
<Menu.Items>
<MenuItem Padding="2,0,2,0">
<MenuItem.Header>
<Button Content="Details"
Click="Details_Click"
Focusable="False" />
</MenuItem.Header>
</MenuItem>
</Menu.Items>
</Menu>
<Button Content="Details"
Click="Details_Click" />
</StackPanel>

Xaml TextBox not behaving

I am trying to create UI from XAML at runtime, with something like
private void Application_Startup (object esender, StartupEventArgs e)
{
this.RootVisual = (UIElement)(XmlReader.Load(e.InitParams["Xaml"])
If I feed it this XAML:
<Canvas
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sdk="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls">
<StackPanel>
<TextBox Width="120" Margin="8" Text="Edit Me" />
<CheckBox Margin="8">Normal</CheckBox>
<ComboBox Margin="8" Width="120" SelectedIndex="1">
<ComboBoxItem Content="First Normal Item" />
<ComboBoxItem Content="Second Normal Item" />
</ComboBox>
</StackPanel>
</Canvas>
then the check box and list behave as expected, but my TextBox does not respond to typing, it stays with its initial value.
The really weird (to me) part is that if I put a handler for KeyDown on to the RootVisual, and in there display a message box, it works. If I have an empty handler or no handler it doesn't.
Do I need to set up some explicit handling for some events? If so, which ones, and how do I handle them?
Upadate: as suggested, I tried putting the dynamic markup into the MainPage of a new app, like this:
public MainPage()
{
InitializeComponent();
var dynamic = XamlReader.Load(xaml);
this.LayoutRoot.Children.Add(dynamic as UIElement);
}
where xaml is a string literal containing the content as above, and everything else is just how VS2010 wizard left it. That works. But I can't see what the effective difference is.
Update update: that's a red herring; the difference is the environment. It works in VS, but not in the Silverlight ActiveX control that I am using in the real app.

Did you define the root namespace on your root element?
<param name="initParams" value="xaml=<TextBox xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' Text='hi'/>" />
Just a shot in the dark here, but have you tried adding the dynamically created content as the child of a static "MainPage.xaml" Grid instead of as RootVisual?

Check for IsEnabled="True" property in your main XAML file, if it is set to false then controls will not be editable.

How to implement "Mega Menus" in WPF?

I'm trying to implement "Mega Menu" style menus using WPF. To see examples of mega menus in web design, see here.
So far, I've tried creating a similar interface by using TextBlocks as the highest level of the menu, and then using the mouse hover event to display an additional window that appears positioned below the text block. This is cumbersome and inflexible, future changes would require adding/removing TextBlocks dynamically.
I have considered using the WPF Menu control, because I know the styles can be dramatically modified, but I haven't seen any way to produce multi-column layouts with the hierarchical model that the Menu control uses.
Is there a better way to do this? Am I going to have to stick with custom windows and relative positioning? Can someone point me to an example of this that has already been implemented?

Instead of using custom Windows and positioning, you could use a Popup control. Your can use the StaysOpen=false setting to have it close when the user clicks off-screen.
If you can settle for clicking a menu item instead of hovering, the following custom control will work:
[TemplatePart(Name="PART_HoverArea", Type=typeof(FrameworkElement))]
[TemplatePart(Name="PART_Popup", Type=typeof(Popup))]
public class MegaMenuItem : HeaderedContentControl
{
private FrameworkElement hoverArea;
private Popup popup;
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
// Unhook old template
if (hoverArea != null)
{
hoverArea.PreviewMouseUp -= ShowPopupOnMouseDown;
}
hoverArea = null;
popup = null;
if (Template == null)
return;
// Hook up new template
hoverArea = (FrameworkElement)Template.FindName("PART_HoverArea", this);
popup = (Popup)Template.FindName("PART_Popup", this);
if (hoverArea == null || popup == null)
return;
hoverArea.PreviewMouseUp += ShowPopupOnMouseDown;
}
private void ShowPopupOnMouseDown(object sender, MouseEventArgs e)
{
popup.PlacementTarget = hoverArea;
popup.Placement = PlacementMode.Bottom;
popup.StaysOpen = false;
popup.IsOpen = true;
}
}
You would need a style to display it - something like this. Note the PART_ template part names:
<Style TargetType="WpfApplication14:MegaMenuItem">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="WpfApplication14:MegaMenuItem">
<Grid>
<Border Name="PART_HoverArea" Background="#fb9c3b" BorderBrush="White" BorderThickness="0,0,1,0">
<ContentPresenter Content="{TemplateBinding Header}" />
</Border>
<Popup
Name="PART_Popup"
PlacementTarget="{Binding ElementName=HoverArea}"
>
<Border MinWidth="100" MaxWidth="400" MinHeight="40" MaxHeight="200" Background="#0d81c3">
<ContentPresenter Content="{TemplateBinding Content}" />
</Border>
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
The XAML for your menu would then be:
<StackPanel Orientation="Horizontal" VerticalAlignment="Top">
<WpfApplication14:MegaMenuItem Header="Parent 1">
<WrapPanel Margin="5">
<TextBlock Text="Put any content you want here" Margin="5" />
<TextBlock Text="Put any content you want here" Margin="5" />
<TextBlock Text="Put any content you want here" Margin="5" />
</WrapPanel>
</WpfApplication14:MegaMenuItem>
<WpfApplication14:MegaMenuItem Header="Parent 2">
<WrapPanel Margin="5">
<TextBlock Text="Put any content you want here" Margin="5" />
<TextBlock Text="Put any content you want here" Margin="5" />
<TextBlock Text="Put any content you want here" Margin="5" />
</WrapPanel>
</WpfApplication14:MegaMenuItem>
</StackPanel>
Making the menu appear on hover is much harder, because of the way Popups steal focus (you can show the menu, but you can't easily hide it if they mouse over another menu). For that a custom window might work better.

You could use a HeaderedItemsControl and swap out the Panel to suit your needs; by default it uses a StackPanel however a WrapPanel may suit you better. The pop out and mouse over behavior do not exist by default and would need to be implemented.
A more robust approach would be to leverage a custom Expander; as it provides the pop out behavior you are after and the linked to walkthrough provides the mouse over behavior.

I wonder if the Ribbon control can be retrofitted to do this? It provides tabs, labels, columns and all that.
Please use this UI design sparingly and make sure that it only opens and closes when the user specifically requests such. It's tremendously annoying when a popup mega-menu appears over a website I'm viewing, and I can't get it to close, except for when I want to click on it and it goes away.

Custom windows and relative position are essentially how the WPF Menu/MenuItem control works... but as you've found, it's non-trivial. Best bet would be to retemplate the Menu/MenuItem controls to meet your need.

How do i navigate from one Xaml file to another?

I am very new to XAML and WPF.I have a problem.
I have two files. first.xaml and second.Xaml. There is a button in first.xaml, on click of which it should navigate to second.xaml.How do i achieve this.

This is one way of organising the code:
Your second.xaml should contain your window definiton e.g.:
<Window x:Class="MediaCheckerWPF.AboutBox"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="About Media Checker" Height="300" Width="400" ResizeMode="NoResize"
Icon="/MediaCheckerWPF;component/Resources/checker.ico"
ShowInTaskbar="False">
<Grid>
...
</Grid>
</Window>
Your first.xaml has the button e.g.:
<Button Height="23" HorizontalAlignment="Right" Name="aboutButton"
VerticalAlignment="Top" Width="23" Click="AboutButton_Click"
Content="{DynamicResource TInformationButton}"
ToolTip="{DynamicResource TInformationButtonTooltip}" Margin="0,0,8,0"/>
Then in the code behind:
private void AboutButton_Click(object sender, RoutedEventArgs e)
{
var about = new AboutBox { Owner = this };
about.Initialise();
about.Show();
}

ChrisF's answer is a good way of popping up a new window in a Windows-style application, except you should not call Initialize that way (it should be called from the constructor).
If you want web-style navigation instead, you should use the Page class instead of Window, along with NavigationService. This also allows your WPF application to run inside an actual web browser.