DataContext binding in Page's Resources - wpf

Question

I have a page that gets a datacontext objet in the behind code.
I would like to set an empty value to the TextList[11] when the Trigger variable loses the 1 value. The Trigger "int" and the TextList "ObservableCollection" are booth situated in the Datacontext object. The TextList is initialized 20pcs element before set the page datacontext. I have to solve it in wpf code, code behind excluded. My English is pretty poor, sorry!
<Page x:Class="LayerTemplates.Templates.example"
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:LayerTemplates.Templates"
mc:Ignorable="d"
d:DesignHeight="450" d:DesignWidth="800"
Title=""
xmlns:System="clr-namespace:System;assembly=mscorlib">
<Page.Resources>
<DataTemplate x:Key="myDataTemplate" DataType="{x:Type System:String}">
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Path=Trigger}" Value="1">
<DataTrigger.ExitActions>
<BeginStoryboard>
<Storyboard>
<StringAnimationUsingKeyFrames Storyboard.TargetName="Page.DataContext" Storyboard.TargetProperty="TextList[11]" Duration="1">
<DiscreteStringKeyFrame KeyTime="0" Value=""></DiscreteStringKeyFrame>
</StringAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</DataTrigger.ExitActions>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</Page.Resources>
<Grid>
...
</Grid>

Answer 1

If you just want to hide a text box or label try to use style triggers instead. As you are setting the value of a string to an empty value I think you might be able to use Visibility="Hidden".
In this example I hide the the label by default but whenever the MyIntProperty becomes 1 I change visibility to Visible.
My xaml code looks like this:
<Window x:Class="TestBinding.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid>
<Label Content="{Binding MyTextProperty}">
<Label.Style>
<Style TargetType="Label">
<Setter Property="Visibility" Value="Hidden"/>
<Style.Triggers>
<DataTrigger Binding="{Binding MyIntProperty}" Value="1">
<Setter Property="Visibility" Value="Visible"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>
</Grid>
Data binding class and codebehind looks like this:
public class MyViewModel
{
public int MyIntProperty { get; set; } = 1;
public string MyTextProperty { get; set; } = "This is my text";
}
public partial class MainWindow : Window
{
MyViewModel model;
public MainWindow()
{
InitializeComponent();
model = new MyViewModel();
this.DataContext = model;
}
}
Note that in order to get the visibility to update automatically you have let the view model class implement INotifyPropertyChanged for the MyIntProperty.