I am trying to select all Items in a ListView, using mvvm. Using code-behind, I have tried SelectAll() and foreach to select them, but I would like to use MVVM like the rest of my project. Any ideas?
Here is the listview:
<ListView x:Name="TransformerList" ItemsSource="{Binding CurrentStations}" Margin="16,250,0,10.4" SelectionMode="Multiple" HorizontalAlignment="Left" Width="411">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Select">
<i:InvokeCommandAction Command="{Binding SeeAllCustomersCommand}" CommandParameter="{Binding Item1}"/>
</i:EventTrigger>
<i:EventTrigger EventName="SelectionChanged">
<i:InvokeCommandAction Command="{Binding SelectedCustomersChangedCommand}" />
</i:EventTrigger>
</i:Interaction.Triggers>
<ListView.ItemContainerStyle>
<Style TargetType="{x:Type ListViewItem}">
<Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=IsSelected}" />
<Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=TransformerIsSelected}" />
</Style>
</ListView.ItemContainerStyle>
<ListView.View>
<GridView>
<GridViewColumn Header="Nettstasjon" Width="70" DisplayMemberBinding="{Binding Path=Name}" />
<GridViewColumn Header="Område" Width="210" DisplayMemberBinding="{Binding Path=Area}"/>
<GridViewColumn Header="Radial" Width="110" DisplayMemberBinding="{Binding Path=Radial}"/>
</GridView>
</ListView.View>
</ListView>
and the button:
public ICommand cmd_VelgAlle { get { return new RelayCommand(on_cmd_VelgAlle); } }
private void on_cmd_VelgAlle()
{
foreach (item i in CurrentStations) //the item here gives an error "type or namespace could not be found"
{
i.TransformerIsSelected = true;
}
}
And the mvvm:
private bool _TransformerIsSelected;
public bool TransformerIsSelected
{
get { return _TransformerIsSelected; }
set
{
_TransformerIsSelected = value;
RaisePropertyChanged("TransformerIsSelected");
}
}
You need to create a ListViewItem Style:
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="IsSelected" Value="{Binding IsSelected}" />
</Style>
</ListView.ItemContainerStyle>
Create a property in Model class:
public bool IsSelected
{
get { return isSelected; }
set
{
isSelected = value;
RaiseChange("IsSelected");
}
}
And iterate your ItemSource to set IsSelected true for all items.(In ViewModel)
foreach(item i in yourCollection)
{
i.IsSelected = true;
}
Update:
Use Style as:
<ListView.ItemContainerStyle>
<Style TargetType="{x:Type ListViewItem}">
<Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=TransformerIsSelected}" />
</Style>
</ListView.ItemContainerStyle>
Command:
private void on_cmd_VelgAlle()
{
//Item is the class your CurrentStations is made of(i guess something like `station` in your design)
//i.e if CurrentStations is list of string then Item will be string
foreach (Item i in CurrentStations)
{
i.TransformerIsSelected = true;
}
}
Related
I'm trying to dynamically hide elements in my ComboBox based on a boolean flag in the objects bound it it but I can't seem to get it working
Here is me XAML
<xctk:CheckComboBox Name="TagsDropDown" HorizontalAlignment="Left" Height="30" Margin="0,0,0,0" VerticalAlignment="Top" Width="450" IsEditable="True" IsTextSearchEnabled="True" ItemsSource="{Binding AllTags}" ItemSelectionChanged="TagsDropDown_OnItemSelectionChanged">
<xctk:CheckComboBox.ItemTemplate>
<DataTemplate>
<Grid HorizontalAlignment="Stretch">
<TextBlock Margin="2" Text="{Binding Name}"/>
<TextBlock Margin="2" HorizontalAlignment="Right" Text="{Binding Count}"/>
</Grid>
</DataTemplate>
</xctk:CheckComboBox.ItemTemplate>
<xctk:CheckComboBox.ItemContainerStyle>
<Style TargetType="xctk:SelectorItem">
<Setter Property="Visibility" Value="Visible"/>
<Style.Triggers>
<!-- <DataTrigger steamTools:TriggerTracing.TriggerName="is zero" steamTools:TriggerTracing.TraceEnabled="True" Binding="{Binding Path=IsZero, RelativeSource={RelativeSource Self} }" Value="True">-->
<DataTrigger Binding="{Binding Path=IsZero, RelativeSource={RelativeSource Self} }" Value="True">
<DataTrigger.Setters>
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger.Setters>
</DataTrigger>
</Style.Triggers>
</Style>
</xctk:CheckComboBox.ItemContainerStyle>
</xctk:CheckComboBox>
And the class bound to the control
public class CompTag : INotifyPropertyChanged
{
private int _count;
private bool _isZero;
public string Name { get; set; }
public bool IsZero
{
get { return _isZero; }
set
{
if (_isZero != value)
{
_isZero = value;
OnPropertyChanged("IsZero");
}
}
}
public int Count
{
get { return _count; }
set
{
if (_count != value)
{
_count = value;
OnPropertyChanged("Count");
}
}
}
Can anyone see what I am doing wrong?
Thanks in advance!
Does your AllTags list have isZero member?(in model )
if yes
Try This
Binding="{Binding Path=IsZero, {RelativeSource FindAncestor, AncestorType={x:Type xctk:CheckComboBox}} }"
if no, and it in your datacontext class try to remove RelativeSource={RelativeSource Self}
How can I catch the Selection Changed event that fires on a ComboBox that is embedded into a DataGridComboBoxColum? I would like to use MVVM pattern for this so something like a EventToCommmand solution would be nice.
XAML:
<DataGridComboBoxColumn Header="ViewTemplate" Width="180" SelectedItemBinding="{Binding ViewTemplate}" DisplayMemberPath="Name">
<DataGridComboBoxColumn.ElementStyle>
<Style TargetType="{x:Type ComboBox}" BasedOn="{StaticResource {x:Type ComboBox}}">
<Setter Property="ItemsSource" Value="{Binding DataContext.ViewTemplates, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
<Setter Property="IsReadOnly" Value="True"/>
</Style>
</DataGridComboBoxColumn.ElementStyle>
<DataGridComboBoxColumn.EditingElementStyle>
<Style TargetType="{x:Type ComboBox}" BasedOn="{StaticResource {x:Type ComboBox}}">
<Setter Property="ItemsSource" Value="{Binding DataContext.ViewTemplates, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
</Style>
</DataGridComboBoxColumn.EditingElementStyle>
</DataGridComboBoxColumn>
I would like to use something like this but don't know where/how to set it up in this particular case.
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand PassEventArgsToCommand="True" Command="{Binding SelectionChangedCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
As requested this is my full code for XAML:
<UserControl x:Class="GrimshawRibbon.Revit.Views.ViewManager.ViewManagerView"
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:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:local="clr-namespace:GrimshawRibbon.Revit.Views.ViewManager"
xmlns:ex="clr-namespace:GrimshawRibbon.Revit.Wpf.Extensions"
xmlns:controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"
xmlns:cmd="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Platform"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="500">
<UserControl.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />
<ResourceDictionary Source="pack://application:,,,/GrimshawRibbon;component/Revit/Wpf/Style/GrimshawTheme.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
<Grid>
<ex:DataGridEx x:Name="dgViews"
Style="{StaticResource AzureDataGrid}"
Margin="10"
AutoGenerateColumns="False"
ItemsSource="{Binding Views, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
CanUserAddRows="False"
IsReadOnly="False"
SelectionMode="Extended"
SelectionUnit="FullRow"
SelectedItemsList="{Binding SelectedViews, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="CellEditEnding">
<cmd:EventToCommand PassEventArgsToCommand="True" Command="{Binding CellEditEndingCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<DataGrid.Columns>
<DataGridTextColumn Header="Name" Binding="{Binding Name, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="*"/>
<DataGridTextColumn Header="ViewType" Binding="{Binding ViewType}" Width="100" IsReadOnly="True"/>
<DataGridTextColumn Header="ViewGroup" Binding="{Binding ViewGroup, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="130" IsReadOnly="False"/>
<DataGridTextColumn Header="ViewSubGroup" Binding="{Binding ViewSubGroup, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="130" IsReadOnly="False"/>
<DataGridCheckBoxColumn ElementStyle="{DynamicResource MetroDataGridCheckBox}"
EditingElementStyle="{DynamicResource MetroDataGridCheckBox}"
Header="OnSheet"
Binding="{Binding OnSheet, Mode=TwoWay}"
IsReadOnly="True"
Width="80">
</DataGridCheckBoxColumn>
<DataGridComboBoxColumn Header="ViewTemplate" Width="180" SelectedItemBinding="{Binding ViewTemplate}" DisplayMemberPath="Name">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand PassEventArgsToCommand="True" Command="{Binding DataContext.SelectChangeCommand, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<DataGridComboBoxColumn.ElementStyle>
<Style TargetType="{x:Type ComboBox}" BasedOn="{StaticResource {x:Type ComboBox}}">
<Setter Property="ItemsSource" Value="{Binding DataContext.ViewTemplates, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
<Setter Property="IsReadOnly" Value="True"/>
</Style>
</DataGridComboBoxColumn.ElementStyle>
<DataGridComboBoxColumn.EditingElementStyle>
<Style TargetType="{x:Type ComboBox}" BasedOn="{StaticResource {x:Type ComboBox}}">
<Setter Property="ItemsSource" Value="{Binding DataContext.ViewTemplates, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
</Style>
</DataGridComboBoxColumn.EditingElementStyle>
</DataGridComboBoxColumn>
</DataGrid.Columns>
</ex:DataGridEx>
</Grid>
</UserControl>
and view model:
public class ViewManagerViewModel : ViewModelBaseEx
{
public ViewManagerModel Model;
public ObservableCollection<ViewWrapper> Views { get; private set; }
public ObservableCollection<ViewWrapper> ViewTemplates { get; private set; }
public IList SelectedViews { get; set; }
public RelayCommand<DataGridCellEditEndingEventArgs> CellEditEndingCommand { get; set; }
public RelayCommand<SelectionChangedEventArgs> SelectChangeCommand { get; set; }
public ViewManagerViewModel(Document doc)
{
Model = new ViewManagerModel(doc);
Views = Model.CollectViews();
ViewTemplates = Model.CollectViewTemplates();
CellEditEndingCommand = new RelayCommand<DataGridCellEditEndingEventArgs>(args => OnCellEditEnding(args));
SelectChangeCommand = new RelayCommand<SelectionChangedEventArgs>(args => OnSelectionChanged(args));
}
private void OnSelectionChanged(SelectionChangedEventArgs e)
{
// do something
}
/// <summary>
/// Logic for handling cell editing events.
/// </summary>
/// <param name="e">DataGrid Row object.</param>
private void OnCellEditEnding(DataGridCellEditEndingEventArgs e)
{
var wrapper = e.Row.Item as ViewWrapper;
switch (e.Column.SortMemberPath)
{
case "Name":
Model.ChangeName(wrapper);
break;
case "ViewGroup":
Model.SetParameter(wrapper, "View Group", wrapper.ViewGroup);
break;
case "ViewSubGroup":
Model.SetParameter(wrapper, "View Sub Group", wrapper.ViewSubGroup);
break;
default:
break;
}
}
public override void Apply()
{
var vw = new List<ViewWrapper>();
foreach (ViewWrapper v in SelectedViews)
{
vw.Add(v);
}
Model.Delete(vw);
// update collection so that rows get deleted in datagrid
foreach (ViewWrapper i in vw)
{
Views.Remove(i);
}
}
}
Using the MVVM pattern you don't handle the SelectionChanged event for the ComboBox element in the view.
Instead you should implement your selection changed logic in the setter of the ViewTemplate property, or in a method that you call from there, that gets set whenever a new item is selected in the ComboBox, .e.g.:
private ViewWrapper _viewTemplate;
public ViewWrapper ViewTemplate
{
get { return _viewTemplate; }
set { _viewTemplate = value; SelectionChanged(); }
}
This is one of corner stones of MVVM. Whenever the source property gets set by the view, the view model can perform some logic. The view only sets a property. It doesn't handle any event.
Edit: If this is not an option for some reason you should replace the DataGridComboBoxColumn with a DataGridTemplateColumn because you cannot apply an EventTrigger to a Style:
<DataGridTemplateColumn Header="ViewTemplate" Width="180">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding ViewTemplate.Name}" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox ItemsSource="{Binding DataContext.ViewTemplates, RelativeSource={RelativeSource AncestorType=DataGrid}}"
SelectedItem="{Binding ViewTemplate}"
DisplayMemberPath="Name">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand PassEventArgsToCommand="True"
Command="{Binding DataContext.SelectionChangedCommand, RelativeSource={RelativeSource AncestorType=DataGrid}}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</ComboBox>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>
You can add eventhandler to your combobox. I added to grid's showing event, you can add another event of course.
private void Grid1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
ComboBox cb = e.Control as ComboBox;
if (cb!=null)
{ cb.SelectionChangeCommitted -= new EventHandler(cb_SelectedIndexChanged);
// now attach the event handler
cb.SelectionChangeCommitted += new EventHandler(cb_SelectedIndexChanged);
}
}}
what i would do is something like this
so inside your viewmodel, you will have something like
Viewmodel.cs
public class ViewModel
{
public ViewModel()
{
_selectChangeCommand= new RelayCommand(OnSelectChange, CanSelectChange);
}
private RelayCommand _selectChangeCommand;
public ICommand SelectChangeCommand { get { return _selectChangeCommand; } }
private bool CanSelectChange()
{
return true;
}
private void OnSelectChange()
{
..//do something in here when you change something in your combo box
}
}
In your MainWindow.xaml.cs
do something like this:
this.DataContext = new ViewModel();
In your ViewModel.xaml file
<ComboBox....>
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<cmd:EventToCommand PassEventArgsToCommand="True" Command="{Binding SelectChangeCommand }"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</ComboBox>
One important thing is to make sure that your viewmodel.xaml knows where it references from so that it can see where the SelectionChangeCommand is located so it can do the binding. FYI, for the relaycommand, my advice is to use the Galasoft.MVVMlight so you don't have to implement relaycommand yourself.
I want to create a playlist.
But I have a problem to highlight the selected item indicated by the user and change the background color or the color of the text item that is played now.
Properties i want to show - what is play now (int IndexToPlay) what user selects (SelectedIndex)
The user should select only one item
I use WPF, MVVM, and I read a lot of posts, but unfortunately I have not found a solution.
<ListView Name="List"
Grid.ColumnSpan="11" Margin="7,0,7,0.4" Grid.Row="9"
ItemsSource="{Binding MusicList, UpdateSourceTrigger=PropertyChanged}"
SelectedIndex="{Binding SelectedIndex}"
>
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" />
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
If you have IsSelected and IsPlaying properties in your ViewModel class:
public class MusicItem
{
private bool _isPlaying;
public bool IsPlaying
{
get
{
return _isPlaying;
}
set
{
_isPlaying = value;
OnPropertyChanged();
}
}
private bool _isSelected;
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
OnPropertyChanged();
}
}
}
You can set the ItemContainerStyle to bind the IsSelected property and then you can use a style on the ItemTemplate with a DataTrigger to change the appearance of the ItemTemplate:
<ListView Name="List"
ItemsSource="{Binding MusicList, UpdateSourceTrigger=PropertyChanged}"
SelectedIndex="{Binding SelectedIndex}">
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="IsSelected" Value="{Binding Path=IsSelected, Mode=TwoWay}"/>
</Style>
</ListView.ItemContainerStyle>
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}">
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding IsPlaying}" Value="True">
<Setter Property="Foreground" Value="Red"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsSelected}" Value="True">
<Setter Property="Background" Value="Blue"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
I have a listview in my WPF application and the first column is a Checkbox. This checkbox is bound to the IsSelected property of my model and the event propogation happens correctly.
I also have a Checkbox in the same column's header and want to implement a 'Select All' feature where it checks all the listview items.
I'm using pattern MVVM.
The Event doesn't fire!
Can someone explain what I am doing wrong here..
The relevant code portions are mentioned below..
XAML:
<ListView Grid.Row="0"
ItemsSource="{Binding Path=WorkOrders}"
Margin="5,10,5,5"
Name="WorkOrders"
SelectionMode="Multiple"
FontSize="13"
Background="AliceBlue"
BorderBrush="AliceBlue">
<!--Style of items-->
<ListView.ItemContainerStyle>
<Style TargetType="{x:Type ListViewItem}">
<!--Properties-->
<Setter Property="Control.HorizontalContentAlignment" Value="Stretch" />
<Setter Property="Control.VerticalContentAlignment" Value="Center" />
<!--Trigger-->
<Style.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter Property="Background" Value="{x:Null}" />
<Setter Property="BorderBrush" Value="{x:Null}" />
</Trigger>
</Style.Triggers>
</Style>
</ListView.ItemContainerStyle>
<ListView.View>
<GridView >
<GridViewColumn CellTemplate="{StaticResource CheckBoxDataTemplate}" Width="80" >
<GridViewColumn.HeaderTemplate>
<DataTemplate>
<CheckBox Command="{Binding Path=SelectAllCommand}" />
</DataTemplate>
</GridViewColumn.HeaderTemplate>
</GridViewColumn>
<GridViewColumn Header="WorkOrder" CellTemplate="{StaticResource DetailIdenTemplate}" Width="300"/>
</GridView>
</ListView.View>
</ListView>
Model:
public class WorkOrder
{
public int CD_WORK_ORDER { get; set; }
public string ID_WORK_ORDER { get; set; }
public bool IsSelected { get; set; }
}
ViewModel:
public class LockWorkOrderSelectionViewModel : ViewModelBase
{
RelayCommand _selectAllCommand;
public ICommand SelectAllCommand
{
get
{
if (_selectAllCommand == null)
{
_selectAllCommand = new RelayCommand(
param => SelectAllElement(),
param => CanSelectAll);
}
//RaiseEvent(new RoutedEventArgs(SearchEvent));
return _selectAllCommand;
}
}
private bool _selectedAllElement;
public bool SelectAllElement()
{
foreach (var item in WorkOrders)
{
item.IsSelected = true;
}
return true;
}
public bool CanSelectAll
{
get { return true; }
}
public List<string> WorkOrdersList
{
get { return _workOrdersList; }
}
private ObservableCollection<WorkOrder> _workOrders = new ObservableCollection<WorkOrder>();
public ObservableCollection<WorkOrder> WorkOrders
{
get
{
int progr = 1;
foreach (var item in WorkOrdersList)
{
if (_workOrders.FirstOrDefault(i => i.ID_WORK_ORDER == item) == null)
{
_workOrders.Add(new WorkOrder { CD_WORK_ORDER = progr, ID_WORK_ORDER = item, IsSelected = false });
progr++;
}
}
return _workOrders;
}
}
}
<CheckBox IsChecked="{Binding DataContext.SelectAll, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}" />
Works for me.
I have a combobox which has 2 items. Each item is an objet deriving from a common interface. There is a DisplayText property on each object. Each object is templated so as to have a different visual. Everything works fine, except while selecting one of those objects, the visual is getting displayed in the combobox textbox. I want it to display the SelectedText property of the selected object in the textbox and the DisplayText inside the item template. How do I specify my binding for that please?
Here is my code:
public interface IMyDate
{
string DisplayText { get; }
string SelectedText { get; }
}
public class TodayMinus1 : IMyDate
{
public string DisplayText { get { return "Yesterday"; } }
public string SelectedText{get { return DateTime.Today.AddDays(-1).ToString(); }}
}
public class Today : IMyDate
{
public string DisplayText { get { return "TODAY"; } }
public string SelectedText { get { return DateTime.Today.ToString(); } }
}
public class MyMainViewModel
{
public MyMainViewModel()
{
MyDates = new List<IMyDate>() {new Today(), new TodayMinus1()};
}
public List<IMyDate> MyDates { get; set; }
public IMyDate SelectedDate { get; set; }
}
<ComboBox MaxHeight="26" VerticalAlignment="Center" x:Name="contextDropdown" ItemsSource="{Binding MyDates}" SelectedItem="{Binding SelectedDate}" Grid.Column="1" Width="150" Margin="5">
<ComboBox.Resources>
<DataTemplate DataType="{x:Type local:TodayMinus1}">
<TextBlock Text="{Binding DisplayText}"/>
</DataTemplate>
<DataTemplate DataType="{x:Type local:Today}">
<TextBlock Text="{Binding DisplayText}"/>
</DataTemplate>
</ComboBox.Resources>
</ComboBox>
Please note that this is an oversimplified example and I have implemented INPC for all my objects.
Try this:
<ComboBox MaxHeight="26" VerticalAlignment="Center" x:Name="contextDropdown" ItemsSource="{Binding MyDates}"
SelectedItem="{Binding SelectedDate}" Grid.Column="1" Width="150" Margin="5">
<ComboBox.Resources>
<DataTemplate DataType="{x:Type local:TodayMinus1}">
<TextBlock>
<TextBlock.Style>
<Style TargetType="TextBlock">
<Setter Property="Text" Value="{Binding DisplayText}" />
<Style.Triggers>
<DataTrigger Binding="{Binding Path=IsSelected, RelativeSource={RelativeSource AncestorType=ComboBoxItem}}" Value="{x:Null}">
<Setter Property="Text" Value="{Binding SelectedText}" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</DataTemplate>
<DataTemplate DataType="{x:Type local:Today}">
<TextBlock>
<TextBlock.Style>
<Style TargetType="TextBlock">
<Setter Property="Text" Value="{Binding DisplayText}" />
<Style.Triggers>
<DataTrigger Binding="{Binding Path=IsSelected, RelativeSource={RelativeSource AncestorType=ComboBoxItem}}" Value="{x:Null}">
<Setter Property="Text" Value="{Binding SelectedText}" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</DataTemplate>
</ComboBox.Resources>
</ComboBox>
Added a DataTrigger inside the DataTemplate to achieve your requirement. Try this.
<ComboBox MaxHeight="26" VerticalAlignment="Center" x:Name="contextDropdown" ItemsSource="{Binding MyDates}" SelectedItem="{Binding SelectedDate}" Grid.Column="1" Width="150" Margin="5">
<ComboBox.Resources>
<DataTemplate DataType="{x:Type local:TodayMinus1}">
<TextBlock Text="{Binding DisplayText}" x:Name="DisplayBox"/>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor,ComboBoxItem,1}}" Value="{x:Null}">
<Setter TargetName="DisplayBox" Property="Text" Value="{Binding SelectedText}"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
<DataTemplate DataType="{x:Type local:Today}">
<TextBlock Text="{Binding DisplayText}" x:Name="DisplayBox"/>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor,ComboBoxItem,1}}" Value="{x:Null}">
<Setter TargetName="DisplayBox" Property="Text" Value="{Binding SelectedText}"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ComboBox.Resources>
</ComboBox>