Develop Reference

In WPF is the contents of ListBox the same as its bound ItemsSource? and how do I seperate them?

I have a ListBox with its ItemsSource bound to some UserControl-s and shown based on their current states(IsVisible)
Here is the code
<ListBox x:Name="sidebarList" Margin="0,0,10,10" ItemsSource="{Binding Modules, Mode=TwoWay}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Margin="0 5 0 5" Visibility="{Binding IsVisible, Mode=TwoWay}">
<TextBlock Text="{Binding Title}" FontWeight="Bold" />
<TextBlock Margin="0 5 0 0" MaxWidth="200" Foreground="Gray" Text="{Binding Detail}"
TextWrapping="WrapWithOverflow">
</TextBlock>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
<ListBox.ItemContainerStyle>
<Style TargetType="{x:Type ListBoxItem}">
<Style.Triggers>
<DataTrigger Binding="{Binding IsVisible}" Value="Collapsed">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</Style>
</ListBox.ItemContainerStyle>
</ListBox>
And now I'm trying to only get "IsVisible"/selected parts when a button is pressed. As of right now, the ListBox actually contains every option but just showing the IsVisible ones(at least that's what I think).
How do I only get the selected options? I have tried to use a new List with the same type as the UserControl-s type(which I placed in app.xaml.cs to call from anywhere) and add to that list when their state changes to IsVisible
but the List doesn't show up in my classes where I check them.

Sounds like what you really need is a view-model. Bind your Listbox to a view model that has an observable collection that only shows view-models of the items you want to present.
I can give you a more "correct" answer about how to do it with style/data-triggers but you should really just learn about MVVM and use a view-model to simplify.

ListBox checklist SelectedItem returns null

I want to create a Listbox from where it's possible to select elements with checkboxes. It gets the elements through data-binding from a database. The items appear in the Listbox, but when I send the form, the code-behind doesn't receive a SelectedItem value.
The XAML section for the listbox looks like this:
<Grid x:Name="grMozik" Visibility="Visible" Margin="0,0,0,0" DataContext="{Binding}" Grid.Row="3" Grid.ColumnSpan="2">
<ListBox Name="lbMozik" Margin="15" Width="300" Height="200" ItemsSource="{Binding}">
<ListBox.ItemContainerStyle>
<Style TargetType="{x:Type ListBoxItem}">
<Setter Property="Focusable" Value="False"/>
</Style>
</ListBox.ItemContainerStyle>
<ListBox.ItemTemplate>
<DataTemplate>
<CheckBox Content="{Binding MoziNeve}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
And for test purposes the code that would show the selected item looks like this:
string text = ((ListBoxItem)lbMozik.SelectedItem).Content.ToString();
MessageBox.Show(text2);

ListBox.SelectedItem comes from a ListBoxItem which has IsSelected property set to true. If you want to select by CheckBoxes, then bind each of them to owner ListBoxItem.IsSelected:
<CheckBox Content="{Binding MoziNeve}"
IsChecked="{Binding IsSelected, RelativeSource={RelativeSource AncestorType=ListBoxItem}}"/>

UWP ListView DataTemplate Bindings

My ViewModel
BookingTakerViewModel
has a property
public List<string> Vias {get;set;}
I am wanting to bind a ListView with a DataTemplate but I can not find out how to do it. This is my code and it is throwing this error when it runs:
"Unable to cast object of type 'System.String' to type 'UI_Test_1.ViewModels.BookingTakerViewModel'."
I thought that the x:DataType should reference the class and in this case it is my Viewmodel.I presume that the x:Bind Vias is wrong beacuase this is a List so lost as to what to do.
<ListView
Name="viasList"
Width="300"
BorderBrush="Black"
BorderThickness="5"
ItemsSource="{x:Bind viewModel.Vias, Mode=OneWay}">
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="MinHeight" Value="1" />
<Setter Property="MaxHeight" Value="15" />
</Style>
</ListView.ItemContainerStyle>
<ListView.ItemTemplate>
<DataTemplate x:Name="dt" x:DataType="viewmodels:BookingTakerViewModel">
<Grid>
<TextBlock FontSize="14" Text="{x:Bind Vias, Mode=OneWay}" />
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
The Vias are intantiated with data so it's not that which is causing a NullReference Exception. I believe the XAML is incorrect.

Probably you are looking for something like this?
<ListView.ItemTemplate>
<DataTemplate x:Name="dt" x:DataType="x:String">
<Grid>
<TextBlock FontSize="14" Text="{x:Bind}" />
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
Inside the data template, the context of {x:Bind} is the templated object, which is a string item from the collection you set in ItemsSource.

ComboBox with fixed Header

I need to show a default text in my ComboBox, this text must not changed also when the user select an item of the Combobox, actually for do this I've created this structure:
<ComboBox ItemsSource="{Binding AvailableNations}" Width="160" Height="55" Margin="0, 0, 0, 15"
Text="Select Countries" IsEditable="True">
<ComboBox.ItemTemplate>
<DataTemplate>
<CheckBox IsChecked="{Binding IsChecked}" Content="{Binding Item.Name}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
this display as default text Select Countries but if I select an item the default text will disappear and the item selected will be displayed, how can I fix this?

You could use a Combined Template (ref post)
<Window.Resources>
<ResourceDictionary>
<DataTemplate x:Key="NormalItemTemplate" >
<CheckBox IsChecked="{Binding IsChecked}" Content="{Binding Item.Name}" />
</DataTemplate>
<DataTemplate x:Key="SelectionBoxTemplate" >
<TextBlock>Select Countries</TextBlock>
</DataTemplate>
<DataTemplate x:Key="CombinedTemplate">
<ContentPresenter x:Name="Presenter"
Content="{Binding}"
ContentTemplate="{StaticResource NormalItemTemplate}" />
<DataTemplate.Triggers>
<DataTrigger
Binding="{Binding RelativeSource={RelativeSource FindAncestor,ComboBoxItem,1}}"
Value="{x:Null}">
<Setter TargetName="Presenter" Property="ContentTemplate"
Value="{StaticResource SelectionBoxTemplate}" />
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ResourceDictionary>
</Window.Resources>
<Grid>
<ComboBox ItemsSource="{Binding AvailableNations}"
SelectedItem="{Binding SelectedNation}"
ItemTemplate="{StaticResource CombinedTemplate}"
Width="160" Height="55" Margin="0, 0, 0, 15" >
</ComboBox>
</Grid>
The way it works is described in the original answer. Note that the suggested solution will only work when IsEditable is set to false, I assume that won't be a problem in your case. Second, to get the text displayed at start up I bound SelectedItem (e.g. to the first item in the collection).

From the comments, it sounds like you just want the Select Countries text to display at all times, even when an item is selected.
Personally I would just go the simple route and place a TextBox on top of the ComboBox, and hide the Display Text of the ComboBox by using a Transparent Foreground color.
Here's a quick example demonstrating it :
<Grid>
<ComboBox SelectedIndex="1" Foreground="Transparent">
<ComboBox.Resources>
<Style TargetType="{x:Type ComboBoxItem}">
<!-- Make sure ComboBoxItems don't have transparent text -->
<Setter Property="Foreground" Value="{StaticResource {x:Static SystemColors.ControlTextBrushKey}}" />
</Style>
</ComboBox.Resources>
<ComboBoxItem>Test 1</ComboBoxItem>
<ComboBoxItem>Test 2</ComboBoxItem>
<ComboBoxItem>Test 3</ComboBoxItem>
</ComboBox>
<TextBlock Text="Select Countries" Margin="4,3" IsHitTestVisible="False" />
</Grid>
And the results (note that SelectedIndex = 1)
I'm sure there's other ways too, such as overwriting the way it paints the display text, or changing the control template, but this seemed like the easiest to me.

Passing DataContext in Telerik RadGridView

I use c# .NET 4.5 and WPF RadControls from Telerik.
On my MainWindow I have a RadTabControl and in my code behind I bind my MainViewModel like this:
this.DataContext = new MainViewmodel();
The ItemSource of the RadTabControl is bound in XAML:
<telerik:RadTabControl ... ItemsSourc={Binding Tabs} .. />
I also use a ContentSelector to load different Contents to my Tabs. These Contents are UserControls. On one UserControl I use a RadGRidView with it's own ItemsSource that I bind in the code behind:
TestGridView.ItemsSource = Tasks.GetTasks();
The RadGridView Columns bound to it's own style:
<telerik:RadGridView.Columns>
<telerik:GridViewDataColumn DataMemberBinding="{Binding ID}" Width="*" CellStyle="{StaticResource CellStyle}" />
</telerik:RadGridView.Columns>
<Style x:Key="CellStyle" TargetType="{x:Type telerik:GridViewCell}">
<Setter Property="BorderThickness" Value="0" />
<Setter Property="BorderBrush" Value="{x:Null}" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<Border BorderBrush="#f2f2f2" BorderThickness="0,0,0,2" Padding="0,5,0,5">
<StackPanel Orientation="Horizontal">
<StackPanel Orientation="Vertical" Margin="10,0,0,0" VerticalAlignment="Top">
<TextBlock Text="{Binding Titel}" />
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Start}" Foreground="#9fa2ae"/>
<TextBlock Text=" XXX - XXX " />
<TextBlock Text="{Binding Startzeit}" Foreground="#9fa2ae" />
<telerik:RadButton Height="30" Content="Right Button" Command="{Binding AddTabCommand}" CommandParameter="Tab9999"/>
</StackPanel>
</StackPanel>
</StackPanel>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
The Problem is that the RadButton does not fire the DelegateCommand of my MainViewModel. I have also the same Button in the UserControl out of the RadGridView, this works fine.
Please can somebody tell me how I can fix this problem of my RadButton in the RadGridView?
Thanks a lot
Best Regards
RR
PS: I have a simple project, but can't attach it

The reason why this is happening is that the binding on your RadButton is trying to find the AddTabCommand on the DataContext of the button, not the parent Window.
To fix this, I would advise setting the style inside the Window's resources, and instead of using this:
Command="{Binding AddTabCommand}"
Give the Window a name, and use this:
Command="{Binding ElementName=windowName, Path=DataContext.AddTabCommand}"

Agree with what Mike said its not finding AddTabCommand in your DataContext(ViewModel).
You can try with specifying whole path of the command :
Command="{Binding ElementName=windowName, Path=NameSapce_Name.ViewModelName.AddTabCommand}".