Develop Reference

RoutedCommand in UserControl is not working as expected

I am trying to use RoutedCommands in my UserControls, following the example in this article:
https://joshsmithonwpf.wordpress.com/2008/03/18/understanding-routed-commands/
I defined the RoutedCommand and CommandBindings in the UserControl instead of in the article's example. I am trying to use it in my MainWindow, so that when the Button is clicked, the Command in the UserControl is executed. However, the Button is disabled and the Foo_CanExecute() method is never executed.
<UserControl x:Class="RoutedCommandTest.ViewControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:RoutedCommandTest"
mc:Ignorable="d"
d:DesignHeight="450" d:DesignWidth="800">
<UserControl.CommandBindings>
<CommandBinding
Command="{x:Static local:ViewControl.Foo}"
PreviewCanExecute="Foo_CanExecute"
PreviewExecuted="Foo_Executed"
/>
</UserControl.CommandBindings>
<Grid>
</Grid>
</UserControl>
Here is the code for ViewControl.xaml.cs:
public static readonly RoutedCommand Foo = new RoutedCommand();
void Foo_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
e.CanExecute = true;
}
void Foo_Executed(object sender, ExecutedRoutedEventArgs e)
{
MessageBox.Show("The Window is Fooing...");
}
public ViewControl()
{
InitializeComponent();
}
And here is the code for MainWindow.xaml:
<Window x:Class="RoutedCommandTest.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:RoutedCommandTest"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<local:ViewControl/>
<Button Content="Foo" Margin="0 5" Command="{x:Static local:ViewControl.Foo}"/>
</Grid>
</Window>
I would like to know how to fix the issue so that the Button is enabled and the Foo_CanExecute() method is executed when the Button is clicked.

Your command is in a usercontrol, whilst the button is in mainwindow.
Which presumably contains your usercontrol.
Like bubbling and routing events ( which are used to drive them ).
Executed looks for the command bubbling UP the visual tree to the binding.
PreviewExecuted looks for the command tunnelling DOWN the visual tree to the binding.
Since your button is in the parent of the usercontrol I'm not sure whether either bubbling or tunnelling will work.
But tunnelling would be PreviewExecuted And PreviewCanExecute.
https://learn.microsoft.com/en-us/dotnet/api/system.windows.input.commandbinding.previewexecuted?view=netframework-4.8
https://learn.microsoft.com/en-us/dotnet/api/system.windows.input.commandbinding.previewcanexecute?view=netframework-4.8
Routedcommands can be pretty tricky to get right.
One thing you sometimes have to do is to bind commandtarget to tell it where to go look.
eg:
<Grid>
<local:UserControl1 x:Name="UC1" Height="60" Width="100"/>
<Button Content="Foo" TextElement.FontSize="30" Command="{x:Static local:UserControl1.Foo}"
CommandTarget="{Binding ElementName=UC1}"
/>
</Grid>
Works for me.
I have rarely found them useful - this is one of the aspects makes them way less useful than you might at first imagine.
EDIT:
It's perhaps worth mentioning the other thing makes these unattractive compared to a regular icommand. You need to either use a static which means it's only suitable for very generic commands OR you need event handlers which will be in code behind.
On the other hand.
If you're writing something has to work generically with whatever has focus. Like say a text editor with multiple textboxes and you're doing text manipulation. A routed command might be suitable. I have never encountered such a requirement in apps I've worked on though.

ShowDialog in WPF

When I make two calls for ShowDialog in WPF the first window open normally, after closing it the second one doesn't appear.
<Application
x:Class="Test.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Startup="App_OnStartup">
</Application>
private void App_OnStartup(object sender, StartupEventArgs e)
{
var windowA = new WindowA();
windowA.ShowDialog();
var windowB = new WindowB();
windowB.ShowDialog();
}
WindowA:
<Window x:Class="Test.WindowA"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="WindowA" Height="129.452" Width="313.356">
<Grid>
<Button Content="Button" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Margin="139,54,0,0"/>
</Grid>
</Window>
public partial class WindowA : Window
{
public WindowA()
{
InitializeComponent();
}
}
WindowB:
<Window x:Class="Test.WindowB"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="WindowB" Height="221.918" Width="300">
<Grid>
<RadioButton Content="RadioButton" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="124,63,0,0"/>
</Grid>
</Window>
public partial class WindowB : Window
{
public WindowB()
{
InitializeComponent();
}
}

In WPF you can specify when application shuts down and by default Application.ShutdownMode is OnLastWindowClose which means that when last Window is closed applications shuts down and in your case first Window is also last. When you open and close first Window your application shuts down and that's why you don't see second Window. You would need to change ShutdownMode to OnExplicitShutdown
<Application ... ShutdownMode="OnExplicitShutdown"/>
but this means that even when you close all your windows application is still running so you have to explicitly call Application.Shutdown() to shutdown your application, for example when main window is closed.

ShowDialog() function invokes the window modally. Which means code after windowA.ShowDialog(); will not execute until that window is closed.

Why does my Page lose focus?

I have Page, and it loses focus when I tap on an empty part of it. I tried putting a Border as the background, but that loses focus too when I tap it. Why does this happen?
What I really need to do is disable a WebView when the user opens the AppBar or the Settings Charm
Some example code to demonstrate the problem (watch the output window):
XAML:
<Page
x:Name="Pagey"
x:Class="FocusTest.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:FocusTest"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d" GotFocus="Focus" LostFocus="LoseFocus">
<Grid x:Name="RootGrid" Background="{StaticResource ApplicationPageBackgroundThemeBrush}" GotFocus="Focus" LostFocus="LoseFocus">
<StackPanel>
<Button x:Name="Clicky" Content="Clicky" GotFocus="Focus" LostFocus="LoseFocus" HorizontalAlignment="Center"></Button>
<Border x:Name="Border" Width="100" Height="100" Background="Red" GotFocus="Focus" LostFocus="LoseFocus"></Border>
<Button x:Name="Clicky2" Content="Clicky2" GotFocus="Focus" LostFocus="LoseFocus" HorizontalAlignment="Center"></Button>
</StackPanel>
</Grid>
</Page>
Code behind:
using System.Diagnostics;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
namespace FocusTest
{
public sealed partial class MainPage : Page
{
public MainPage()
{
this.InitializeComponent();
}
void Focus(object sender, RoutedEventArgs e)
{
Debug.WriteLine("Focus({0})", (sender as FrameworkElement).Name);
}
void LoseFocus(object sender, RoutedEventArgs e)
{
Debug.WriteLine("LoseFocus({0})", (sender as FrameworkElement).Name);
}
}
}

Look like your Border is inside the RootGrid So that every time when you tap Border's tap event will occur and LostFocus Event fired. Better you can set LostFocus event on the same RootGrid. Then it may work fine. Please try it.
Thanks.

How can i link a canvas on a grid, to the mainwindow.xaml?

I have a canvas in a grid, i want to keep my canvas on that grid, because its the first window, that opens in my program.
In my MainWindow.xaml, i have a ContentPage, that always changes its content, the startup content is the authenticationPage. In this page i have a Canvas that shows my skeletal tracking, and is used for making a gesture. This gestureCanvas is on my authenticationPage. The code behind this gestureCanvas is on my MainWindow.xaml.cs.
I need to link the gestureCanvas with my MainWindow.xaml.cs, because the code is behind MainWindow, and it's going to be used there, because it's an Kinect application.
How to link these ?
partial class MainWindow
{
void LoadCircleGestureDetector()
{
using (Stream recordStream = File.Open(circleKBPath, FileMode.OpenOrCreate))
{
circleGestureRecognizer.TraceTo(gesturesCanvas, Colors.Red);
}
}
}
This is my authenticationPage
<UserControl
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:smartHome2011"
xmlns:MyUserControl="clr-namespace:MyUserControl;assembly=MyUserControl"
mc:Ignorable="d"
x:Class="smartHome2011.AuthenticationPage"
x:Name="UserControl"
d:DesignWidth="640" d:DesignHeight="480">
<Grid x:Name="LayoutRoot">
<Grid x:Name="kinectGrid" HorizontalAlignment="Left">
<Viewbox Margin="204,220,430,220">
<Grid ClipToBounds="True" Margin="204,220,430,220">
**<Canvas x:Name="gesturesCanvas" />**
<Canvas x:Name="kinectCanvas"></Canvas>
</Grid>
</Viewbox>
</Grid>
</Grid>

at your code behind MainWindow you can try following
var gesturesCanvas = YourContentPage.FindName("gesturesCanvas") as Canvas;
if (gesturesCanvas != null) {
// do something
}
hope this helps

WPF Close button not working when in Grid

When I place Button in grid and add to is's click action:
this.Close();
It's not working. I want to be able to ask user before exit so I want to use Close(). I don't want to use Application.Shutdown();
How to solve it.

Just tested it and it works fine! I created a new WPF application and a basic window:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Button Content="Close" x:Name="closeButton" Click="closeButton_Click" />
</Grid>
</Window>
and then added the following to the code-behind
private void closeButton_Click(object sender, RoutedEventArgs e)
{
if (MessageBox.Show("Are you sure?", "Application", MessageBoxButton.YesNo) == MessageBoxResult.Yes)
{
this.Close();
}
}
And it works 100%... Can you post more code to see if something else is wrong? What .NET version are you using, etc...