WPF DataTrigger not firing if value remains same - wpf

Question

I have a WPF data trigger that is set to fire when a value is true.
I want this trigger to fire everytime this value is set to true, even if it was true before. Unfortunately it seems only to fire if the value is changed from true to false or vise versa. My underlying data model is firing the PropertyChanged event of INotifyPropertyChanged even if the value is set to true twice in succession but the Trigger doesn't seem to pick this up.
Is there anyway to make the trigger run regardless of whether the bound value has changed?
Some of you have asked for the code so here it is. Interesting to note that converters will be called each time. The problem is more specific to running an animation.
Update
If I change my code to reset the value to false and then back to true again it does fire the animation. Obviously this is not ideal and doesn't make the code nice to read. I'm hoping there is a better way to do this.
Any help greatly appreciated.
WPF code
<Grid>
<Grid.Resources>
<Storyboard x:Key="AnimateCellBlue">
<ColorAnimation Storyboard.TargetProperty="Background.Color" From="Transparent" To="Blue" Duration="0:0:0.1" AutoReverse="True" RepeatBehavior="1x" />
</Storyboard>
</Grid.Resources>
<TextBox Name="txtBox" Text="{Binding DataContext.DisplayText, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}">
<TextBox.Style>
<Style TargetType="TextBox">
<Style.Triggers>
<DataTrigger Binding="{Binding DataContext.IsTrue, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}" Value="True">
<DataTrigger.EnterActions>
<BeginStoryboard Name="BidSizeUpStoryB" Storyboard="{StaticResource AnimateCellBlue}" />
</DataTrigger.EnterActions>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
</Grid>
Code Behind:-
public partial class MainWindow : Window
{
private DataItem _dataItem;
private DispatcherTimer _dispatcherTimer;
public MainWindow()
{
InitializeComponent();
_dataItem = new DataItem();
_dataItem.DisplayText = "Testing";
_dataItem.IsTrue = true;
this.DataContext = _dataItem;
_dispatcherTimer = new DispatcherTimer(TimeSpan.FromSeconds(1), DispatcherPriority.Normal, TimerCallbackHandler, Dispatcher);
}
private void TimerCallbackHandler(object s, EventArgs args)
{
Console.WriteLine("In Timer");
_dataItem.IsTrue = true;
_dataItem.DisplayText = "Timer " + DateTime.Now.Ticks;
}
}
DataItem:-
public class DataItem : INotifyPropertyChanged
{
private bool _isTrue;
private string _displayText;
public bool IsTrue
{
get { return _isTrue; }
set
{
_isTrue = value;
NotifyPropertyChanged("IsTrue");
}
}
public string DisplayText
{
get
{
return _displayText;
}
set
{
_displayText = value;
NotifyPropertyChanged("DisplayText");
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
private void NotifyPropertyChanged(string info)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}

Answer 1

The trigger will be fire irrespective of the value set. Whenever PropertyChanged event is raised for the property binded with trigger, the trigger will be get called. Here's the sample on which i have verified -
<TextBox>
<TextBox.Style>
<Style TargetType="TextBox">
<Style.Triggers>
<DataTrigger Binding="{Binding DataContext.IsTrue, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window},
Converter={StaticResource MyConverter}}" Value="True">
<Setter Property="Background" Value="Red"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
I put the breakpoint on my converter and it got called whenever i raise PropertyChanged event for property IsTrue.
There msut be some other issue in your code. Can you please show bit of your code where you are facing this issue??

Answer 2

Update: it seems that my first answer was dependent on my ValueConverters. So, I did a bit more research and discovered ConditionalBehavior and PropertyChangedTrigger
Here's one that I tested.
<UserControl
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:ei="http://schemas.microsoft.com/expression/2010/interactions"
x:Class="WpfControlLibrary1.UserControl1"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<UserControl.Triggers>
<EventTrigger RoutedEvent="FrameworkElement.Loaded"/>
</UserControl.Triggers>
<Grid>
<i:Interaction.Triggers>
<!--Use multiple PropertyChangedTriggers to handle multiple conditions-->
<!--True State-->
<ei:PropertyChangedTrigger Binding="{Binding DataContext.IsTrue,
RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}" >
<i:Interaction.Behaviors>
<!--This is just a humble demonstration of Conditional Behavior, it's has so much potential that you can replicate complex if conditions-->
<ei:ConditionBehavior>
<ei:ConditionalExpression ForwardChaining="And">
<ei:ComparisonCondition Operator="Equal"
LeftOperand="{Binding DataContext.IsTrue, RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}"
RightOperand="True"
/>
</ei:ConditionalExpression>
</ei:ConditionBehavior>
</i:Interaction.Behaviors>
<!--I'm not sure why, but I needed to apply the default state first so that the true state plays it's storyboard.-->
<!--If you don't do this, this behaves like a data trigger.-->
<ei:GoToStateAction StateName="DefaultState"/>
<ei:GoToStateAction StateName="TrueState"/>
</ei:PropertyChangedTrigger>
<!--False state-->
<ei:PropertyChangedTrigger Binding="{Binding DataContext.IsTrue,
RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}" >
<i:Interaction.Behaviors>
<ei:ConditionBehavior>
<ei:ConditionalExpression ForwardChaining="And">
<ei:ComparisonCondition Operator="Equal"
LeftOperand="{Binding DataContext.IsTrue, RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}"
RightOperand="False"
/>
</ei:ConditionalExpression>
</ei:ConditionBehavior>
</i:Interaction.Behaviors>
<ei:GoToStateAction StateName="DefaultState"/>
</ei:PropertyChangedTrigger>
</i:Interaction.Triggers>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="VisualStateGroup">
<VisualState x:Name="DefaultState"/>
<VisualState x:Name="TrueState">
<Storyboard Storyboard.TargetName="txtBox" >
<ColorAnimation Storyboard.TargetProperty="Background.Color" From="Transparent" To="Blue" Duration="0:0:0.1" AutoReverse="True" RepeatBehavior="1x" />
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<TextBox x:Name="txtBox" Text="{Binding DataContext.DisplayText, RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}"/>
</Grid>
</UserControl>
You can use Visual State Groups for this. What's more, behavior property and value can both be databound!
I did this quickly in blend and did not test. this is similar to my solution.
<UserControl
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:ei="http://schemas.microsoft.com/expression/2010/interactions"
x:Class="WpfControlLibrary1.UserControl1"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Grid>
<i:Interaction.Behaviors>
<ei:DataStateBehavior Binding="{Binding DataContext.IsTrue,
RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}"
Value="True"
TrueState="TrueState"/>
</i:Interaction.Behaviors>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="VisualStateGroup">
<VisualState x:Name="DefaultState"/>
<VisualState x:Name="TrueState">
<Storyboard Storyboard.TargetName="txtBox" >
<ColorAnimation Storyboard.TargetProperty="Background.Color" From="Transparent" To="Blue" Duration="0:0:0.1" AutoReverse="True" RepeatBehavior="1x" />
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<TextBox x:Name="txtBox" Text="{Binding DataContext.DisplayText, RelativeSource={RelativeSource AncestorType={x:Type Window}, Mode=FindAncestor}}"/>
</Grid>
</UserControl>