We Keep Coding

how to open new WPF window in stack panel in WPF mainwindow?

I get this error:- System.NullReferenceException: 'Object reference not set to an instance of an object.'
objectPlacement was null.
private void Button_Click(object sender, RoutedEventArgs e)
{
ObjectPlacement w = new ObjectPlacement() {Topmost = };// ObjectPlacement is new WPF window
objectPlacement.WindowStyle = WindowStyle.None;
settingpanel.Children.Add(objectPlacement);//settingpanel stack is panel name
w.Show();
}

It would be much more usual to define a usercontrol or datatemplate for whatever you're trying to show in your window. A window is a kind of content control. One way to think of a window ( or contentcontrol ) is something that shows you some UI. All the UI in a window is that content.
When you add window to a project it is templated out with a grid in it.
This is the content and everything you want to see in that window goes in it.
You could replace that grid with something else instead.
If you made that a contentpresenter then you can bind or set what that'll show to some encapsulated re-usable UI.
Usually the best way to encapsulate re-usable UI is as a usercontrol.
A datatemplate can reference a usercontrol.
It is not usually your entire UI for a window you want to switch out. But you can and that is occasionally useful - say if you want a generic way to show dialogs.
The usual way to write wpf is mvvm so most devs will want some mvvm way of switching out UI.
I'll show you some code might make the description clearer.
There are some corners cut in what follows, so this is illustrative. Don't just run with this for your next lead developer interview at a stock traders.
But, basically you click a button for Login you "navigate" to a LoginUC view. Click a button for User and you "navigate" to UserUC.
My mainwindow.
<Window.Resources>
<DataTemplate DataType="{x:Type local:LoginViewModel}">
<local:LoginUC/>
</DataTemplate>
<DataTemplate DataType="{x:Type local:UserViewModel}">
<local:UserUC/>
</DataTemplate>
</Window.Resources>
<Window.DataContext>
<local:MainWindowViewModel/>
</Window.DataContext>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="100"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<ItemsControl ItemsSource="{Binding NavigationViewModelTypes}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button Content="{Binding Name}"
Command="{Binding DataContext.NavigateCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
CommandParameter="{Binding VMType}"
/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<ContentPresenter Grid.Column="1"
Content="{Binding CurrentViewModel}"
/>
</Grid>
</Window>
Notice the datatemplates which associate the type of a viewmodel with a usercontrol.
https://learn.microsoft.com/en-us/dotnet/desktop/wpf/data/data-templating-overview?view=netframeworkdesktop-4.8
What will happen is you present your data in a viewmodel to the UI via that contentpresenter and binding. That viewodel is then templated out into UI with your viewmodel as it's datacontext. The datacontext of a UserUC view will therefore be an instance of UserViewModel. Change CurrentViewModel to an instance of LoginViewModel and you get a LoginUC in your mainwindow instead.
The main viewmodel.
public class MainWindowViewModel : INotifyPropertyChanged
{
public string MainWinVMString { get; set; } = "Hello from MainWindoViewModel";
public ObservableCollection<TypeAndDisplay> NavigationViewModelTypes { get; set; } = new ObservableCollection<TypeAndDisplay>
(
new List<TypeAndDisplay>
{
new TypeAndDisplay{ Name="Log In", VMType= typeof(LoginViewModel) },
new TypeAndDisplay{ Name="User", VMType= typeof(UserViewModel) }
}
);
private object currentViewModel;
public object CurrentViewModel
{
get { return currentViewModel; }
set { currentViewModel = value; RaisePropertyChanged(); }
}
private RelayCommand<Type> navigateCommand;
public RelayCommand<Type> NavigateCommand
{
get
{
return navigateCommand
?? (navigateCommand = new RelayCommand<Type>(
vmType =>
{
CurrentViewModel = null;
CurrentViewModel = Activator.CreateInstance(vmType);
}));
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Type and display relates the type for a viewmodel with text displayed in the UI.
public class TypeAndDisplay
{
public string Name { get; set; }
public Type VMType { get; set; }
}
This is "just" quick and dirty code to illustrate a principle which is usually called viewmodel first navigation. Google it, you should find a number of articles explaining it further.
For completeness:
<UserControl x:Class="wpf_Navigation_ViewModelFirst.LoginUC"
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:wpf_Navigation_ViewModelFirst"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<StackPanel Background="Yellow">
<TextBlock Text="This is the Login User Control"/>
<TextBox>
<TextBox.InputBindings>
<KeyBinding Key="Return" Command="{Binding LoginCommand}"/>
</TextBox.InputBindings>
</TextBox>
</StackPanel>
</UserControl>
public class LoginViewModel
{
private RelayCommand loginCommand;
public RelayCommand LoginCommand
{
get
{
return loginCommand
?? (loginCommand = new RelayCommand(
() =>
{
string s = "";
}));
}
}
}
<UserControl x:Class="wpf_Navigation_ViewModelFirst.UserUC"
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:wpf_Navigation_ViewModelFirst"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Grid Background="pink">
<TextBlock Text="This is the User module Control"
VerticalAlignment="Top"
/>
<TextBlock Text="{Binding Path=DataContext.MainWinVMString, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
VerticalAlignment="Bottom"
/>
</Grid>
</UserControl>
public class UserViewModel
{
}
I put this together some years ago, I would now recommend the community mvvm toolkit with it's code generation, base classes, messenger etc.

Prism WPF Binding RegionManager.RegionName

I have a Prism 7 application with two modules, called ModuleA and ModuleB. In my main window I would like to be able to show either ModuleA if "Show A" button is clicked or ModuleB if "Show B" button is clicked. I implemented the behaviour the following way:
MainWindow.xaml
<Window x:Class="ModulesTest.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">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<ContentControl prism:RegionManager.RegionName="{Binding Module}" />
<StackPanel Grid.Row="1">
<Button Command="{Binding ShowModuleCommand}"
CommandParameter="A">
Show A
</Button>
<Button Command="{Binding ShowModuleCommand}"
CommandParameter="B">
Show B
</Button>
</StackPanel>
</Grid>
MainWindowViewModel.cs
public class MainWindowViewModel : BindableBase
{
private string _title = "Prism Application";
public string Title
{
get { return _title; }
set { SetProperty(ref _title, value); }
}
private string fieldName;
public string Module
{
get { return fieldName; }
set { SetProperty(ref fieldName, value); }
}
private DelegateCommand<string> _showModuleCommand;
public DelegateCommand<string> ShowModuleCommand =>
_showModuleCommand ?? (_showModuleCommand = new DelegateCommand<string>(ExecuteShowModuleCommand));
void ExecuteShowModuleCommand(string module)
{
Module = "Module" + module;
}
public MainWindowViewModel()
{
Module = "ModuleA";
}
}
The problem is that the RegionManager.RegionName remains "ModuleA" as set in the constructor of the ViewModel and doesn't change when "Show B" is clicked. Is the binding of the RegionManager.RegionName not allowed by design or am I doing it wrong?
Here's also the link to the repo: https://github.com/moisejbraver/ModulesTest

A region is a structural part of your user interface. You should not reassign the region name once it has been assigned to a specific control.
If you need to navigate inside a region, consider using the IRegionNavigationService...

WPF UserControl Dependency Property not working

In a WPF project (code below) I have a UserControl of type MyUserControl with a dependency property, called MyOrientation of type Orientation.
On the MainWindow I have 2 instances of MyUserControl, where via XAML I set the Orientation property on one to be Horizontal and the other instance to be Vertical.
I have made the MyOrientation property a DP as I want the ability to set it directly in XAML as in this example or using a binding.
My problem is that when I run the project both instances of the UserControl show up with the Orientation = Horizontal?
Could someone please tell me what I am doing wrong and how to fix it?
Many thanks in advance.
Here is the code:
MYUSERCONTROLVIEWMODEL:
public class MyUserControlViewModel : ViewModelBase
{
private Orientation _myOrientation;
public Orientation MyOrientation
{
get { return _myOrientation; }
set
{
if (_myOrientation == value)
return;
_myOrientation = value;
OnPropertyChanged();
}
}
}
MYUSERCONTROL.XAML
<UserControl x:Class="TestUserControlDPProblem.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:TestUserControlDPProblem"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Grid x:Name="root">
<Grid.DataContext>
<local:MyUserControlViewModel/>
</Grid.DataContext>
<StackPanel Orientation="{Binding MyOrientation}">
<TextBlock>Hello</TextBlock>
<TextBlock>There</TextBlock>
</StackPanel>
</Grid>
MYUSERCONTROL CODE BEHIND:
public partial class MyUserControl : UserControl
{
MyUserControlViewModel _vm;
public MyUserControl()
{
InitializeComponent();
_vm = root.DataContext as MyUserControlViewModel;
}
public static readonly DependencyProperty MyOrientationProperty = DependencyProperty.Register("MyOrientation", typeof(Orientation), typeof(MyUserControl), new FrameworkPropertyMetadata(Orientation.Vertical, new PropertyChangedCallback(OnMyOrientationChanged)));
private static void OnMyOrientationChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
var myUserControl = o as MyUserControl;
myUserControl?.OnMyOrientationChanged((Orientation)e.OldValue, (Orientation)e.NewValue);
}
protected virtual void OnMyOrientationChanged(Orientation oldValue, Orientation newValue)
{
_vm.MyOrientation = newValue;
}
public Orientation MyOrientation
{
get
{
return (Orientation)GetValue(MyOrientationProperty);
}
set
{
SetValue(MyOrientationProperty, value);
}
}
}
MAINWINDOW.XAML
<Window x:Class="TestUserControlDPProblem.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:TestUserControlDPProblem"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<StackPanel>
<local:MyUserControl Margin="10" MyOrientation="Horizontal"/>
<local:MyUserControl Margin="10" MyOrientation="Vertical"/>
</StackPanel>
</Grid>

The "internal" view model of the UserControl makes no sense and should not be there. You should instead bind directly to the dependency property by means of a RelativeSource or ElementName Binding:
<StackPanel Orientation="{Binding MyOrientation,
RelativeSource={RelativeSource AncestorType=UserControl}}">
You wouldn't even need the PropertyChangedCallback:
public partial class MyUserControl : UserControl
{
public MyUserControl()
{
InitializeComponent();
}
public static readonly DependencyProperty MyOrientationProperty =
DependencyProperty.Register(
nameof(MyOrientation), typeof(Orientation), typeof(MyUserControl),
new FrameworkPropertyMetadata(Orientation.Vertical));
public Orientation MyOrientation
{
get { return (Orientation)GetValue(MyOrientationProperty); }
set { SetValue(MyOrientationProperty, value); }
}
}

MVVM Binding not working when change from event firing

I make a simple MVVM sample. I have main window with two user control pages. The main window have two event to change the view to two user control.
This is my main window XAML
<Window
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:MVVC_Binding"
xmlns:views="clr-namespace:MVVC_Binding.Views"
xmlns:viewModel="clr-namespace:MVVC_Binding.ViewModels"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" x:Class="MVVC_Binding.MainWindow"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<DataTemplate DataType="{x:Type viewModel:Page1ViewModel}">
<views:Page1 />
</DataTemplate>
<DataTemplate DataType="{x:Type viewModel:Page2ViewModel}">
<views:Page2/>
</DataTemplate>
</Window.Resources>
<Window.DataContext>
<local:MainViewModel />
</Window.DataContext>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="0">
<TextBlock Text="Page1">
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonUp">
<i:InvokeCommandAction Command="{Binding NavCommand}" CommandParameter="page1"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBlock>
<TextBlock Text="Page2">
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonUp">
<i:InvokeCommandAction Command="{Binding NavCommand}" CommandParameter="page2"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBlock>
</StackPanel>
<DockPanel Grid.Column="1" HorizontalAlignment="Left" VerticalAlignment="Top" Background="Gainsboro">
<Grid x:Name="container" Background="Gainsboro" VerticalAlignment="Top">
<ContentControl Content="{Binding CurrentViewModel}"/>
</Grid>
</DockPanel>
</Grid>
</Window>
I am using the BindableBase class for my view model. This is my BindableBase class
namespace MVVC_Binding.Utilities
{
public class BindableBase : INotifyPropertyChanged
{
/// <summary>
/// Interface implementation
/// </summary>
public event PropertyChangedEventHandler PropertyChanged = delegate { };
protected virtual void SetProperty<T>(ref T member, T val, [CallerMemberName] string propertyName = null)
{
// Check for current set member and the new value
// If they are the same, do nothing
if (object.Equals(member, val)) return;
member = val;
// Invoke the property change event
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
protected virtual void OnPropertyChanged(string propName)
{
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
}
In my main view model, just simple click event to change the view binding
private BindableBase _CurrentViewModel;
public BindableBase CurrentViewModel
{
get { return _CurrentViewModel; }
set
{
SetProperty(ref _CurrentViewModel, value);
}
}
private void OnNav(string destination)
{
switch (destination)
{
case "page2":
CurrentViewModel = page2;
break;
default:
CurrentViewModel = page1;
break;
}
}
The problem is in user control Page 2, when it is display, and the event in side of it does not change the TextBlock binding value, but the text can change during the view model constructor event.
Here is my page 2 XAML
<UserControl x:Class="MVVC_Binding.Views.Page2"
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:MVVC_Binding.Views"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<StackPanel>
<TextBlock Name="txtPage2" Text="{Binding Page2Text}"></TextBlock>
<TextBlock Name="btn" Text="Click Button">
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonUp">
<i:InvokeCommandAction Command="{Binding BtnCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBlock>
</StackPanel>
</UserControl>
And here is the Page2ViewModel
namespace MVVC_Binding.ViewModels
{
public class Page2ViewModel : BindableBase
{
public MyICommand<string> BtnCommand { get; private set; }
public Page2ViewModel()
{
BtnCommand = new MyICommand<string>(OnBtnClick);
Page2Text = "Just a test";
}
private void OnBtnClick(string obj)
{
Page2Text = "Changing by button click";
}
private string _page2Text;
public string Page2Text
{
get { return _page2Text; }
set
{
_page2Text = value;
SetProperty(ref _page2Text, value);
}
}
}
}
Can you please see what I am doing wrong? Thanks so much

If I understand correctly, you're asking why the code in this function doesn't seem to have an effect on the view:
private void OnBtnClick(string obj)
{
_page2Text = "Changing by button click";
}
The problem is that you are changing the underlying _page2Text member, but in order for WPF to detect this change, you must use the Page2Text property, like this:
private void OnBtnClick(string obj)
{
Page2Text = "Changing by button click";
}
The specific part of your code that is indicating the property change to WPF is the OnPropertyChanged method in your BindableBase class.

Thanks everyone, I manage to solve it by updating the class BindableBase. The updated
namespace SilentUpdate.Utilities
{
public class BindableBase : INotifyPropertyChanged
{
/// <summary>
/// Interface implementation
/// </summary>
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void SetProperty<T>(ref T member, T val, [CallerMemberName] string propertyName = null)
{
// Check for current set member and the new value
// If they are the same, do nothing
// if (object.Equals(member, val)) return;
member = val;
// Invoke the property change event
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
protected virtual void OnPropertyChanged(string propName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
}
}
}
So I comment out the check for the Object.Equals and force it to run for every value

Proper databinding in WPF using TabControl and MVVM

Just when I thought I was getting better at this, TabControl is now giving me problems. I have read relevant posts here on StackOverflow, but have been unable to get my simple demo application to work the way I want it to.
To keep things focused, I'll start with a single question about something I don't understand.
I have a TabControl whose TabItems each host the same UserControl. When I set the TabControl.ContentTemplate's DataTemplate to my UserControl, a rendering of that control appears, but it looks like it's the same control for each tab. Or perhaps it's not tied to any of the tabs at all.
MainWindow.xaml
<Window x:Class="TabControlMvvm.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:localviews="clr-namespace:TabControlMvvm.Views"
Title="MainWindow" Height="350" Width="525">
<TabControl ItemsSource="{Binding Tabs}" SelectedIndex="{Binding Selected}">
<TabControl.ContentTemplate>
<DataTemplate>
<localviews:PersonMainPanel />
</DataTemplate>
</TabControl.ContentTemplate>
</TabControl>
</Window>
Code-behind just sets the ViewModel as its DataContext:
namespace TabControlMvvm {
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window {
public MainWindow()
{
InitializeComponent();
DataContext = new TabControlMvvm.ViewModels.MainViewModel();
}
}
}
The TabItem's Content should be another UserControl, PersonMainPanel.xaml:
<UserControl x:Class="TabControlMvvm.Views.PersonMainPanel"
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:localviews="clr-namespace:TabControlMvvm.Views"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Border BorderBrush="Red" BorderThickness="2">
<TabControl TabStripPlacement="Bottom">
<TabItem Header="Tab 1">
<localviews:MyTabItem />
</TabItem>
<TabItem Header="Tab 2">
<TextBlock Text="This was left blank intentionally" />
</TabItem>
<TabItem Header="Tab 3">
<TextBlock Text="This was also left blank intentionally" />
</TabItem>
</TabControl>
</Border>
</UserControl>
Code-behind:
namespace TabControlMvvm.Views {
/// <summary>
/// Interaction logic for PersonMainPanel.xaml
/// </summary>
public partial class PersonMainPanel : UserControl {
public PersonMainPanel()
{
InitializeComponent();
}
}
}
And the MainViewModel:
namespace TabControlMvvm.ViewModels {
public class MainViewModel : ViewModelBase {
public ICollectionView Tabs { get; set; }
public int Selected { get; set; }
public class Person
{
public string Name { get; set; }
}
public class DummyController {
public List<Person> Persons { get; private set; }
public DummyController()
{
Persons = new List<Person> {
new Person { Name = "Larry" },
new Person { Name = "Darryl" },
new Person { Name = "Other brother Darryl" }
};
}
}
public DummyController Controller { get; private set; }
public RelayCommand HelloCommand { get; set; }
public MainViewModel()
{
Controller = new DummyController();
/*
IEnumerable<TabItem> tabs = Enumerable.Range( 1, _controller.Persons.Count())
.Select( x => new TabItem { Header = String.Format( "Person {0}", x),
Content = new PersonMainPanel() });
*/
IEnumerable<TabItem> tabs = Enumerable.Range( 1, Controller.Persons.Count())
.Select( x => new TabItem { Header = String.Format( "Person {0}", x)});
Tabs = CollectionViewSource.GetDefaultView( tabs.ToList());
Tabs.MoveCurrentToFirst();
InitializeCommands();
}
private void InitializeCommands()
{
HelloCommand = new RelayCommand( () => { MessageBox.Show( String.Format( "Hello, Person {0} named {1}!",
Selected, Controller.Persons[Selected].Name)); });
}
}
}
PersonMainPanel hosts another TabControl, where Tab 1's Content is MyTabItem.xaml:
<UserControl x:Class="TabControlMvvm.Views.MyTabItem"
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"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<StackPanel Orientation="Vertical">
<StackPanel Orientation="Horizontal">
<TextBlock Text="Name:" />
<TextBox Text="{Binding Name}" Width="100" />
</StackPanel>
<Button Command="{Binding HelloCommand}" Content="Say Hello" />
</StackPanel>
</UserControl>
Code-behind:
namespace TabControlMvvm.Views {
/// <summary>
/// Interaction logic for MyTabItem.xaml
/// </summary>
public partial class MyTabItem : UserControl {
public MyTabItem()
{
InitializeComponent();
}
}
}
Which looks like this at runtime:
Issues I have so far:
When I enter Person 1's Name and then click the Person 2 tab, Person 1's Name is still visible, hence my assumption that the controls are not databound properly. I understand that ItemsControls do not pass their DataContext down to their children, but I am not sure how to fix this without associating the View in code-behind.
I would have expected to get databinding errors in the Output window because of the missing DataContext, but I don't get any errors. I assume the DataContext is null, but wouldn't this still result in a binding error?
How can I use Snoop effectively to debug problems like this?
Here's the sample solution: http://www.filedropper.com/tabcontrolmvvm

Here is solution:
In MainWindow modify your TabControl template, to bind Header from your Model:
<TabControl ItemsSource="{Binding Tabs}" SelectedIndex="{Binding Selected}">
<TabControl.ContentTemplate>
<DataTemplate>
<localviews:PersonMainPanel />
</DataTemplate>
</TabControl.ContentTemplate>
<TabControl.ItemContainerStyle>
<Style TargetType="TabItem">
<Setter Property="Header" Value="{Binding Header}"/>
</Style>
</TabControl.ItemContainerStyle>
</TabControl>
In MyTabItem.xaml, set UpdateTrigger, because default one 'OnLostFocus' can sometimes not save your data:
<TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" Width="100" />
In MainViewModel modify creating of your tabs, so it will have Name property too:
IEnumerable<TabItem> tabs = Enumerable.Range( 1, Controller.Persons.Count())
.Select( x => new TabItem { Header = String.Format("Person {0}", x), Name = Controller.Persons[x-1].Name });
Also, the most important, create own TabItem class to contain some bounded data:
public class TabItem
{
public string Name { set; get; }
public string Header { set; get; }
}