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XAML DataTrigger Not Firing?

I have a property in my ModularClientModule class called ExistsOnDisk. When that property is set to false, I want to disable the CheckBox. For some reason, this does not seem to work despite me putting it last in the Triggers XAML block, which means it should be the last thing to fire. I.e, nothing should be interfering. I know my code-behind should be correct because as you will see below, I have another control which receives the update and fires fine.
This one here responds to the ExistsOnDisk property change without issue, and strikesthrough the text:
GridViewColumn x:Name="FileNameHeader" Header="File Name">
<GridViewColumn.CellTemplate>
<DataTemplate DataType="{x:Type local:ModularClientModuleUI}">
<TextBlock Text="{Binding Filename}">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Style.Triggers>
<DataTrigger Binding="{Binding ExistsOnDisk}" Value="False">
<Setter Property="TextDecorations" Value="Strikethrough"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</DataTemplate>
</GridViewColumn.CellTemplate>
</GridViewColumn>
This one here does not, and the checkbox remains enabled:
<GridViewColumn x:Name="StatusHeader" Header="Status">
<GridViewColumn.CellTemplate>
<DataTemplate DataType="{x:Type local:ModularClientModuleUI}">
<StackPanel>
<CheckBox x:Name="ClientModuleStatusCheckBox" Margin="5, 0" Click="ClientModuleStatusCheckBox_Click" IsEnabled ="{Binding Client.Online}">
<CheckBox.Style>
<Style TargetType="{x:Type CheckBox}" BasedOn="{StaticResource MahApps.Styles.CheckBox}">
<Setter Property="IsEnabled" Value="False" />
<Style.Triggers>
<DataTrigger Binding="{Binding LoadState}" Value="Loaded">
<Setter Property="IsChecked" Value="True" />
<Setter Property="IsEnabled" Value="True" />
</DataTrigger>
<DataTrigger Binding="{Binding LoadState}" Value="Unloaded">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
<DataTrigger Binding="{Binding LoadState}" Value="Loading">
<Setter Property="Visibility" Value="Collapsed" />
</DataTrigger>
<DataTrigger Binding="{Binding ExistsOnDisk}" Value="True">
<Setter Property="IsEnabled" Value="True" />
</DataTrigger>
<DataTrigger Binding="{Binding ExistsOnDisk}" Value="False">
<Setter Property="IsEnabled" Value="False" />
</DataTrigger>
</Style.Triggers>
</Style>
</CheckBox.Style>
</CheckBox>
What could be going on here?

Set the default value of the IsEnabled using a Setter and remove IsEnabled ="{Binding Client.Online}" from the <CheckBox> element:
<CheckBox x:Name="ClientModuleStatusCheckBox" Margin="5, 0" Click="ClientModuleStatusCheckBox_Click">
<CheckBox.Style>
<Style TargetType="{x:Type CheckBox}" BasedOn="{StaticResource MahApps.Styles.CheckBox}">
<Setter Property="IsEnabled" Value="False" />
<Style.Triggers>
<DataTrigger Binding="{Binding LoadState}" Value="Loaded">
<Setter Property="IsChecked" Value="True" />
<Setter Property="IsEnabled" Value="True" />
</DataTrigger>
<DataTrigger Binding="{Binding LoadState}" Value="Unloaded">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
<DataTrigger Binding="{Binding LoadState}" Value="Loading">
<Setter Property="Visibility" Value="Collapsed" />
</DataTrigger>
<DataTrigger Binding="{Binding ExistsOnDisk}" Value="True">
<Setter Property="IsEnabled" Value="True" />
</DataTrigger>
</Style.Triggers>
</Style>
</CheckBox.Style>
</CheckBox>
Also note that you shouldn't use more than one trigger on the same bool property.

ContentStringFormat never changes by Setter Property in DataTrigger

In my user control I want to have label displaying Text from resource depending on viewmodel property Location value and with different format.
I implemented it by defining DataTrigger for each Location value
<Style x:Key="LocationValueHelper" TargetType="{x:Type Label}">
<Style.Triggers>
<DataTrigger Binding="{Binding Location}" Value="HomeViewModel">
<Setter Property="Content" Value="" />
<Setter Property="ContentStringFormat" Value="{}{0}???"/>
</DataTrigger>
<DataTrigger Binding="{Binding Location}" Value="FirstViewModel">
<Setter Property="ContentStringFormat" Value="{}{0}+++"/>
<Setter Property="Content" Value="{localization:LanguageResource ResourceKey=First}" />
</DataTrigger>
<DataTrigger Binding="{Binding Location}" Value="SecondViewModel">
<Setter Property="ContentStringFormat" Value="{}{0}---"/>
<Setter Property="Content" Value="{localization:LanguageResource ResourceKey=Second}" />
</DataTrigger>
<DataTrigger Binding="{Binding Location}" Value="ThirdViewModel">
<Setter Property="ContentStringFormat" Value="{}{0}***"/>
<Setter Property="Content" Value="{localization:LanguageResource ResourceKey=Third}" />
</DataTrigger>
</Style.Triggers>
</Style>
<Label Foreground="White" HorizontalAlignment="Center" FontSize="40" Style="{StaticResource LocationValueHelper}" />
The problem is that format never changes from the first one (???) - HomeViewModel selected first - although text changing works.
I have
Home???
First???
Second???
Third???
instead of
Home???
First+++
Second---
Third***

There are a lot of discussions, using Labels and ContentStringFormat does not work like expected or desired:
WPF StringFormat on Label Content
StringFormat VS ContentStringFormat
...
The reason seems to be the template based implementation under the hood, since the content also could contain other data than strings. To solve your problem, my proposal is to use a TextBlock, which works quite smooth like this:
<StackPanel>
<CheckBox IsChecked="{Binding MyFlag}"/>
<TextBlock HorizontalAlignment="Center" FontSize="40">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Style.Triggers>
<DataTrigger Binding="{Binding MyFlag}" Value="False">
<Setter Property="Text" Value="{Binding Path=MyText, StringFormat='{}{0}+++'}" />
</DataTrigger>
<DataTrigger Binding="{Binding MyFlag}" Value="True">
<Setter Property="Text" Value="{Binding Path=MyText, StringFormat='{}{0}???'}" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</StackPanel>

How to bind to a SelectedValue data context property in WPF?

I have a listbox that display some model items.
I would like to hide some control below the listbox based on the boolean value of the model item associated with the selected listbox item.
I tried the following but it did not work:
1) set the ListBox SelectedValuePath="MyModelBooleanProperty"
2) add a data trigger to the control that I want to hide as follows
<DataTrigger Binding="{Binding ElementName=FolderList, Path=SelectedValue}" Value="False">
<Setter Property="Visibility" Value="Collapsed"></Setter>
</DataTrigger>
<DataTrigger Binding="{Binding ElementName=FolderList, Path=SelectedValue}" Value="True">
<Setter Property="Visibility" Value="Visible"></Setter>
</DataTrigger>

I used this and it worked. Also make sure you don't explicitly set Visibility of TextBlock that overrides whatever the Style does.
<ListBox
x:Name="FolderList"
ItemsSource="{Binding Source={StaticResource ViewModel}, Path=List}"
SelectedValuePath="SomeBooleanProperty">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding SomeStringProperty}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<TextBlock>
<TextBlock.Style>
<Style TargetType="TextBlock">
<Setter Property="Visibility" Value="Visible" />
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=FolderList, Path=SelectedValue}" Value="False">
<Setter Property="Visibility" Value="Collapsed" />
</DataTrigger>
<DataTrigger Binding="{Binding ElementName=FolderList, Path=SelectedValue}" Value="True">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
My Text Block
</TextBlock>

WPF - Hide/Show Image Based on Expander IsExpanded

I would like to show an image if the expander is collapsed and hide it when it's expanded. I tried the following but it doesn't work. Is there a way to do so without using a converter?
<Image x:Name="fgImage" Source="Resources/Images/MissingImage.png" Margin="0,96,258,-75" Height="110" VerticalAlignment="Top" HorizontalAlignment="Right" Width="110">
<Image.Style>
<Style TargetType="Image">
<Setter Property="Visibility" Value="Visible"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=orderDetailsExpander, Path=IsExpanded}">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>

your DataTrigger must be like that
<DataTrigger Binding="{Binding ElementName=orderDetailsExpander, Path=IsExpanded}" Value="True">
all the Image property
<Image x:Name="fgImage" Source="Resources/Images/MissingImage.png" Margin="0,96,258,-75" Height="110" VerticalAlignment="Top" HorizontalAlignment="Right" Width="110">
<Image.Style>
<Style TargetType="Image">
<Setter Property="Visibility" Value="Visible"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=orderDetailsExpander, Path=IsExpanded}" Value="True">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>

You DataTrigger needs a value, for example
Value="True"
According to the documentation, the default value is null

Text.IsEmpty Opposite

i have this CheckBox
<CheckBox VerticalAlignment="Center" Name="CheckItem"
IsChecked="{Binding ElementName=Faccette, Path=Text.isEmpty, Mode=OneWay}"
/>
Faccette is a TextBlock, i need the opposite of the Text.isEmpty.
Is it possible without a Converter?

You may use a Style with DataTriggers:
<CheckBox>
<CheckBox.Style>
<Style TargetType="CheckBox">
<Setter Property="IsChecked" Value="True"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=Faccette, Path=Text}" Value="">
<Setter Property="IsChecked" Value="False"/>
</DataTrigger>
<DataTrigger Binding="{Binding ElementName=Faccette, Path=Text}" Value="{x:Null}">
<Setter Property="IsChecked" Value="False"/>
</DataTrigger>
</Style.Triggers>
</Style>
</CheckBox.Style>
</CheckBox>