Develop Reference

PointerPoint.Properties.MouseWheelDelta tilt or scroll

I have a function that listenes to PointerWheelChanged events of my UIElement.
I can retreive the MouseWheelDelta but this doesn't tell me if the mouse wheel was tilted or moved up/down.
How can I get this info?
This is my code to get the delta:
private void TestScrollViewer_PointerWheelChanged(object sender, PointerRoutedEventArgs e)
{
PointerPoint ptrPt = e.GetCurrentPoint((UIElement)sender);
int delta = ptrPt.Properties.MouseWheelDelta;
// positive: forward/right motion; negative: backward/left motion
}

You can use IsHorizontalMouseWheel inside Pointers. See this example below:
MainWindow.xaml
<Window
x:Class="MouseWheelTests.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:local="using:MouseWheelTests"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Grid RowDefinitions="Auto,*">
<StackPanel Grid.Row="0">
<TextBlock x:Name="WheelHorizontal" />
<TextBlock x:Name="WheelVertical" />
</StackPanel>
<Grid
Grid.Row="1"
Background="Transparent"
PointerWheelChanged="Grid_PointerWheelChanged" />
</Grid>
</Window>
MainWindow.xaml.cs
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Input;
namespace MouseWheelTests;
public sealed partial class MainWindow : Window
{
public MainWindow()
{
this.InitializeComponent();
}
private int WheelHorizontalValue { get; set; }
private int WheelVerticalValue { get; set; }
private void Grid_PointerWheelChanged(object sender, PointerRoutedEventArgs e)
{
var properties = e.GetCurrentPoint((UIElement)sender).Properties;
if (properties.IsHorizontalMouseWheel is true)
{
WheelHorizontalValue += properties.MouseWheelDelta;
this.WheelHorizontal.Text = $"Horizontal: {WheelHorizontalValue}";
}
else
{
WheelVerticalValue += properties.MouseWheelDelta;
this.WheelVertical.Text = $"Vertical: {WheelVerticalValue}";
}
}
}

RegisterViewWithRegion throws System.NullReferenceException for a View

I created a Prism WPF application and I tried to split it into modules. This is my MainWindow:
<Window x:Class="MyProject.WPF.Views.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:prism="http://prismlibrary.com/"
prism:ViewModelLocator.AutoWireViewModel="True"
Title="{Binding Title}" Height="350" Width="525"
WindowState="Maximized">
<Grid>
<TabControl prism:RegionManager.RegionName="TabRegion"
VerticalAlignment="Stretch"
HorizontalAlignment="Stretch"
BorderThickness="0"/>
</Grid>
</Window>
My InfoView:
<UserControl x:Class="Info.Views.InfoView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Info.Views"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
xmlns:prism="http://prismlibrary.com/"
prism:ViewModelLocator.AutoWireViewModel="True" >
<Grid>
<TextBlock Text="{Binding Message}"
HorizontalAlignment="Center"
VerticalAlignment="Center" />
</Grid>
</UserControl>
My App class:
public partial class App
{
protected override Window CreateShell()
{
return Container.Resolve<MainWindow>();
}
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.Register<MainWindowViewModel>();
containerRegistry.Register<InfoViewModel>();
}
protected override void ConfigureModuleCatalog(IModuleCatalog moduleCatalog)
{
moduleCatalog.AddModule<MainModule>();
moduleCatalog.AddModule<InfoModule>();
}
protected override void ConfigureRegionAdapterMappings(RegionAdapterMappings regionAdapterMappings)
{
base.ConfigureRegionAdapterMappings(regionAdapterMappings);
regionAdapterMappings.RegisterMapping(typeof(TabControl), Container.Resolve<TabControlAdapter>());
}
}
My TabControlAdapter which I copy pasted from somewhere in the past. It worked in a previous project:
class TabControlAdapter : RegionAdapterBase<TabControl>
{
public TabControlAdapter(IRegionBehaviorFactory regionBehaviorFactory) : base(regionBehaviorFactory)
{
}
protected override void Adapt(IRegion region, TabControl regionTarget)
{
region.Views.CollectionChanged += (s, e) =>
{
if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
{
foreach (UserControl item in e.NewItems)
{
regionTarget.Items.Add(new TabItem { Header = item.Name, Content = item });
}
}
else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
{
foreach (UserControl item in e.OldItems)
{
var tabToDelete = regionTarget.Items.OfType<TabItem>().FirstOrDefault(n => n.Content == item);
regionTarget.Items.Remove(tabToDelete);
}
}
};
}
protected override IRegion CreateRegion()
{
return new SingleActiveRegion();
}
}
And my MainModule:
public class MainModule : IModule
{
public void RegisterTypes(IContainerRegistry containerRegistry) {}
public void OnInitialized(IContainerProvider containerProvider)
{
var regionManager = containerProvider.Resolve<IRegionManager>();
regionManager.RegisterViewWithRegion("TabRegion", nameof(InfoView));
}
}
When I run the App it throws a System.NullReferenceException at line regionManager.RegisterViewWithRegion("TabRegion", nameof(InfoView));, which I think means that the InfoView is never initialized. What am I missing or doing wrong?

Okay it was pretty obvious. I just had to register the InfoView in the MainModule:
public void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.Register<InfoView>();
}
I won't delete the question, though, because I think it gives a basic example on how to work with Prism, TabRegions and Modules.

WPF ItemsControl can't bind Command

I'm a newbie in wpf and i know that this question has been asked other times, and i tried to implement some solutions that i found. But it's not working. I'm doing something wrong but i can't see what it is.
I've created a new simple application to test this problem.
namespace WpfApp3
{
public class MyElement
{
public string Text { get; set; }
public MyElement(string t)
{
Text = t;
}
}
public class MyCommand : ICommand
{
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
_handler(parameter);
}
private Action<object> _handler;
public MyCommand(Action<object> handler) { _handler = handler; }
}
public class MyItemsControlViewModel
{
ObservableCollection<MyElement> _items;
public ObservableCollection<MyElement> MyElementItems { get { return _items; } set { _items = value; RaisePropertyChanged("MyElementItems"); } }
ObservableCollection<MyElement> _temporayList;
private ICommand _itemClicked;
public ICommand ItemClicked { get { return _itemClicked; } }
public MyItemsControlViewModel()
{
_items = new ObservableCollection<MyElement>();
_temporayList = new ObservableCollection<MyElement>();
_itemClicked = new MyCommand(OnItemSelected);
AddItem("Element 1");
AddItem("Element 2");
AddItem("Element 3");
UpdateList();
}
public void UpdateList()
{
MyElementItems = _temporayList;
}
public void AddItem(string t)
{
MyElement item = new MyElement(t);
_temporayList.Add(item);
}
public void OnItemSelected(object param)
{
Debug.WriteLine("Executed!");
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
XAML
<UserControl x:Class="WpfApp3.MyUserControl"
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:WpfApp3"
mc:Ignorable="d"
d:DesignHeight="1080" d:DesignWidth="570"
x:Name="myCustomControl">
<Grid >
<Button x:Name="btnOutsideItemsControl" Width="100" Height="100 " VerticalAlignment="Top" Command="{Binding ItemClicked}" />
<ItemsControl
x:Name="listItems"
ScrollViewer.PanningMode="None"
IsEnabled="False"
Background = "Transparent"
HorizontalAlignment="Center"
ItemsSource="{Binding MyElementItems}" Margin="0,152,0,0" Width="549">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<WrapPanel HorizontalAlignment="Left" Margin="50,0,0,0"
Background="Transparent" Orientation="Vertical"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button
Content="{Binding Text}"
Command="{Binding ElementName=listItems, Path=DataContext.ItemClicked}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Grid>
</UserControl>
The component is used in MainWindow.xaml.
namespace WpfApp3
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
private MyItemsControlViewModel _myViewModel;
public MyItemsControlViewModel MyViewModel { get { return _myViewModel; } }
public MainWindow()
{
_myViewModel = new MyItemsControlViewModel();
InitializeComponent();
myCustomControl.DataContext = MyViewModel;
}
}
}
XAML
<Window x:Class="WpfApp3.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:WpfApp3"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<local:MyUserControl x:Name="myCustomControl"/>
</Grid>
</Window>
When i run the application i can see correctly the list of 3 items with the correct text.
But if i click on one of the button of the list i can't see the output of Debug.WriteLine("Executed!");
But if i click on the button btnOutsideItemsControl that is outside the ItemsControl, it works. I can see the output of Debug.WriteLine("Executed!");
So i think that also the definition of the command is correct.
To bind correctly the Command property of Button inside the ItemsControl i try this
<Button Command="{Binding ElementName=listItems, Path=DataContext.ItemClicked}">
And also this
<Button Command="{Binding DataContext.ItemClicked, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=ItemsControl}}">
But it not works.
Please help!

You're gonna kick yourself once I tell you.
Your problem is that you set IsEnabled="False" on your ItemsControl. Remove it and all will be well with the universe.

AssociatedObject.DataContext is null in Behavior in ContentPresenter

I try to use a Behavior to trigger a method in the View from the VM. To this end, I use an object of type Trigger with an Event and invoker in the VM, and bind this to a dependency property in the behavior. The behavior does the subscription to the event in its Loaded callback. This works as expected, when the event in the VM is invoked, I can call the method in the view using AssociatedObject.
However, when the Behavior is inside a DataTemplate for a ContentPresenter, I see the following weird behavior (no pun intended...). Given a ContentPresenter with two DataTemplates, used depending on the type of Content (Tab1 or Tab2), when the Content is changed from Tab1 to Tab2, everything is fine. When it is changed from one instance of Tab1 to another instance of Tab1, however, AssociatedObject.DataContext is suddently null (and the method I try to call on the View fails due to this).
I tried to create a minimal example to demonstrate this. The code below should have everything to just run in a new WPF app. Observe the debug output in the following click paths to reproduce:
Tab -> Tab1 -> Invoke -> Output as expected
Tab -> Tab1a -> Tab1 -> Invoke -> DataContext is empty
Tab -> Tab1 -> Again as expected
I can think of ways to work around this problem, but I would like to understand it. I assume it is related to the DataTemplate not being rebuilt when the Content changes to the same type, but still I would expect AssociatedObject to point to the correct Grid (which I think it does not, since the DataContext in the actually shown Grid is fine). Any ideas are highly appreciated!
MainWindow.xaml
<Window x:Class="EmptyWpfApp.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:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:local="clr-namespace:EmptyWpfApp"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<local:ViewModel />
</Window.DataContext>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<ContentPresenter Grid.Row="0" Content="{Binding Tab}">
<ContentPresenter.Resources>
<DataTemplate DataType="{x:Type local:Tab1}">
<Grid>
<i:Interaction.Behaviors>
<local:TestBehavior Trigger="{Binding T}"/>
</i:Interaction.Behaviors>
<TextBlock>With behavior</TextBlock>
</Grid>
</DataTemplate>
<DataTemplate DataType="{x:Type local:Tab2}">
<Grid>
<TextBlock>Empty</TextBlock>
</Grid>
</DataTemplate>
</ContentPresenter.Resources>
</ContentPresenter>
<Button Grid.Row="1" Click="ButtonBase_OnClick">Tab</Button>
<Button Grid.Row="1" Grid.Column="1" Click="ButtonBase_OnClick1">Tab1</Button>
<Button Grid.Row="1" Grid.Column="2" Click="ButtonBase_OnClick1a">Tab1a</Button>
<Button Grid.Row="2" Grid.ColumnSpan="3" Click="ButtonBase_OnClick2">Invoke on VM</Button>
</Grid>
MainWindows.xaml.cs:
using System;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;
using EmptyWpfApp.Annotations;
namespace EmptyWpfApp
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
private Tab2 _tab = new Tab2();
private Tab1 _tab1 = new Tab1();
private Tab1 _tab1a = new Tab1();
public MainWindow()
{
InitializeComponent();
DataContext = new ViewModel();
}
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
((ViewModel)DataContext).Tab = _tab;
}
private void ButtonBase_OnClick1(object sender, RoutedEventArgs e)
{
((ViewModel)DataContext).Tab = _tab1;
}
private void ButtonBase_OnClick1a(object sender, RoutedEventArgs e)
{
((ViewModel)DataContext).Tab = _tab1a;
}
private void ButtonBase_OnClick2(object sender, RoutedEventArgs e)
{
(((ViewModel) DataContext).Tab as Tab1)?.T.OnE();
}
}
public class ViewModel : INotifyPropertyChanged
{
private ITab _tab;
public ITab Tab
{
get => _tab;
set
{
_tab = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
public interface ITab {}
public class Tab1 : ITab
{
public Trigger T { get; } = new Trigger();
}
public class Tab2 : ITab {}
public class Trigger
{
public event EventHandler E;
public virtual void OnE()
{
E?.Invoke(this, EventArgs.Empty);
}
}
public class TestBehavior : Behavior<Grid>
{
public static readonly DependencyProperty TriggerProperty = DependencyProperty.Register(
"Trigger",
typeof(Trigger),
typeof(TestBehavior),
new PropertyMetadata(default(Trigger)));
public Trigger Trigger {
get => (Trigger)GetValue(TriggerProperty);
set => SetValue(TriggerProperty, value);
}
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.Loaded += OnLoaded;
AssociatedObject.Unloaded += Cleanup;
}
private void Cleanup(object sender, RoutedEventArgs e)
{
Cleanup();
}
protected override void OnDetaching()
{
base.OnDetaching();
Cleanup();
}
private void Cleanup()
{
AssociatedObject.Loaded -= OnLoaded;
if (Trigger != null)
Trigger.E -= TriggerOnE;
}
private void OnLoaded(object sender, RoutedEventArgs e)
{
Subscribe();
}
private void Subscribe()
{
Trigger.E += TriggerOnE;
}
private void TriggerOnE(object sender, EventArgs e)
{
Debug.WriteLine("DC:" + AssociatedObject.DataContext);
}
}
}

checkbox checked or click event not firing in datatemplate

I have a checkbox in my datatemplate and for some reason the events are not firing. see code below. my datatemplate is in a resource dictionary with code behind file. Any Ideas?
<ResourceDictionary x:Class="ArmyBuilder.Templates.EquipmentDataTemplate"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>
<DataTemplate x:Key="EquipmentDataTemplate">
<Grid>
<CheckBox Content="{Binding Name}" Checked="ToggleButton_OnChecked" Click="CheckBox_Click"/>
</Grid>
</DataTemplate>
//code behind
namespace ArmyBuilder.Templates
{
public partial class EquipmentDataTemplate : ResourceDictionary
{
public EquipmentDataTemplate()
{
InitializeComponent();
}
private void ToggleButton_OnChecked(object sender, RoutedEventArgs e)
{
// breakpoint not hit
}
private void CheckBox_Click(object sender, RoutedEventArgs e)
{
// breakpoint not hit
}
}
}

I am not sure how you use it, but the your code works for me and the click event got fired. Check the following and if you still cannot find the point, share a repro project to show how you used it.
Template XAML:
<ResourceDictionary x:Class="App10.EquipmentDataTemplate"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>
<DataTemplate x:Key="EquipmentDataTemplate">
<Grid>
<CheckBox Content="Click Me" Checked="ToggleButton_OnChecked" Click="CheckBox_Click"/>
</Grid>
</DataTemplate>
</ResourceDictionary>
Template cs:
namespace App10
{
public sealed partial class EquipmentDataTemplate : ResourceDictionary
{
public EquipmentDataTemplate()
{
this.InitializeComponent();
}
private void ToggleButton_OnChecked(object sender, RoutedEventArgs e)
{
// breakpoint not hit
}
private void CheckBox_Click(object sender, RoutedEventArgs e)
{
// breakpoint not hit
}
}
}
In MainPage.Xaml, use the template in a ListView:
<Page
x:Class="App10.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:App10"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Page.Resources>
<local:EquipmentDataTemplate></local:EquipmentDataTemplate>
</Page.Resources>
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<ListView x:Name="listView" CanReorderItems="True" AllowDrop="True" ItemTemplate="{StaticResource EquipmentDataTemplate}">
</ListView>
</Grid>
</Page>
In MainPage cs:
namespace App10
{
/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class MainPage : Page
{
public MainPage()
{
this.InitializeComponent();
var list = new ObservableCollection<string>();
for (int i = 0; i < 10; i++)
{
list.Add("Item " + i);
}
listView.ItemsSource = list;
}
}
}