I have a TextBox with a style that has a DataTrigger which changes the text, like this:
<Grid>
<TextBlock Text="Foo">
<TextBlock.Style>
<Style BasedOn="{StaticResource TextStyle}" TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding MyBool}" Value="True">
<Setter Property="Text" Value="Bar"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</Grid>
But it's not working, the text never changes to "Bar". I have tested using another TextBlock with Text="{Binding MyBool}" and this text changes from "False" to "True". Snoop reveals no errors that I can see and there is nothing in the output.
This question may seem like a duplicate of WPF Trigger binding to MVVM property, but my code does not seem different from the accepted answer there (http://www.thejoyofcode.com/Help_Why_cant_I_use_DataTriggers_with_controls_in_WPF.aspx, section "Using a style") in any relevant way. And using a DataTemplate as suggested in the actual answer seems wrong since I only want this to apply to a single TextBlock, but if it is correct, I'm not sure how to write a DataTemplate for this...
EDIT:
This is what the property I'm binding to looks like:
public bool MyBool
{
get { return _myBool; }
set
{
if (_myBool== value)
return;
_myBool= value;
NotifyPropertyChanged();
}
}
private bool _myBool;
Dependency Properties can be set from many different places; inline, animations, coercion, triggers, etc. As such a Dependency Property Value Precedence list was created and this dictates which changes override which other changes. Because of this order of precedence, we can't use a Trigger to update a property that is explicitly set inline in your XAML. Try this instead:
<Grid>
<TextBlock>
<TextBlock.Style>
<Style BasedOn="{StaticResource TextStyle}" TargetType="TextBlock">
<!-- define your default value here -->
<Setter Property="Text" Value="Foo" />
<Style.Triggers>
<DataTrigger Binding="{Binding MyBool}" Value="True">
<!-- define your triggered value here -->
<Setter Property="Text" Value="Bar" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</Grid>
Related
XAML
<utility:InvalidNotification x:Name="InvalidNotificationControl"/>
<Button Content="Clean AppV Cache" Click="Button_Click">
<Button.Style>
<Style TargetType="Button">
<Setter Property="IsEnabled" Value="True"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=InvalidNotificationControl, Path=Visibility}" Value="Visible">
<Setter Property="IsEnabled" Value="False"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>
NOTE
InvalidNotification is a custom UserControl
Now, the DataTrigger works fine initially and disable the button since the Usercontrol is visible.
The problem is when I collapse the Usercontrol based on another condition the button stays disable. I found this related answer which states that The properties changed by triggers are automatically reset to their previous value when the triggered condition is no longer satisfied. which is not my case. Why is that ?
EDIT
Thanks to #mm8 which led me to the solution. So if ever you're trying to bind a control on a UserControl's content (inner TextBlock in my case), just add a second trigger at the bottom of your Usercontrol like so,
<UserControl.Style>
<Style TargetType="UserControl">
<Setter Property="Visibility" Value="Collapsed"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=Notification, Path=Visibility}" Value="Visible">
<Setter Property="Visibility" Value="Visible"/>
</DataTrigger>
</Style.Triggers>
</Style>
</UserControl.Style>
where notification would be the name of my TextBlock
Your example works provided that you toggle/set the Visibility property of the InvalidNotification control itself, since it is this property that you bind to.
If you set the Visibility property of some element within the InvalidNotification control, you need to bind to this specific element.
You can't do this using an ElementName binding though because the Button and any element defined in the InvalidNotification control don't belong to the same namescope.
I am trying to set expander IsExpanded property inside DataTrigger with Setter.
<ItemsControl.ItemTemplate>
<DataTemplate>
<Expander x:Name="myExpander" />
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding ElementName=myExpander, Path=IsKeyboardFocusWithin}" Value="False">
<Setter TargetName="Self" Property="IsExpanded" Value="False" />
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ItemsControl.ItemTemplate>
The problem is when I write the code like
TargetName="myExpander"
I wanted some keyword like "self" or "." - something that associates the Setter target with its parent's elements and finds it.
I think what you're looking for is this:
<ItemsControl.ItemTemplate>
<DataTemplate>
<Expander x:Name="myExpander" />
<DataTemplate.Triggers>
<Trigger SourceName="myExpander" Property="IsKeyboardFocusWithin" Value="False">
<Setter TargetName="myExpander" Property="IsExpanded" Value="False" />
</Trigger>
</DataTemplate.Triggers>
</DataTemplate>
</ItemsControl.ItemTemplate>
Note that I used Trigger with SourceName rather than DataTrigger (although the latter would also work). As for the Setter, you need to set the TargetName="myExpander" in order to set the property of your expander - if you did not specify the TargetName, the setter would attempt to set the property on the DataTemplate itself.
At least that's the theoretical solution. In practice it will not work (or at least not as you expect), because a trigger based on the IsKeyboardFocusWithin is not a good choice for what I think you're trying to achieve. Better choice would be to subscribe to the LostFocus event.
I'm new to the styling part of WPF. What I want to do is to get the value of an attached property in a setter, e.g.:
<Trigger Property="SomeProperty" Value="SomeValue">
<Setter Property="SomeProperty"
Value="(My attached property, let's say lcl:MyClass.MyString)"/>
</Trigger>
I know that you can get something to this effect using a {TemplateBinding lcl:MyClass.MyString} in a ControlTemplate. My question is: can you do this in a style, without using a ControlTemplate?
You can try to use:
<Setter Property="SomeProperty" Value="{Binding Path=(lcl:MyClass.MyString), RelativeSource={RelativeSource self}}"/>
if your attached property applies to the element as your style. If not, you can use RelativeSource or ElementName to find the appropriate element.
I am not sure how you have done that since your code lacks of details. Below code works:
<UserControl.Resources>
<Style x:Key="LabelStyle" TargetType="{x:Type Label}">
<Style.Triggers>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Content"
Value="{Binding Path=(TestWebBrowser:AttachP.ValueEditorState), RelativeSource={RelativeSource self}}"/>
</Trigger>
</Style.Triggers>
</Style>
</UserControl.Resources>
<StackPanel>
<Label x:Name="label" TestWebBrowser:AttachP.ValueEditorState="HelloWorld" Style="{StaticResource LabelStyle}"/>
<Button Content="Disable Label" Click="Button_Click"/>
</StackPanel>
Button's click event handler will set Label's IsEnabled to false to trigger the trigger. And note that you have to use Path= with parenthesis in the binding.
I would like to implement a "NullText" behavior for a TextBlock that is bound to a property in a ViewModel. When that property in the ViewModel is null or empty, I would like to display gray italic text something like "No Data". I'd like this to follow MVVM pattern but I am lost...
Update
So after playing around with the solution James Webster suggested, I got it to work like this...
<UserControl.Resources>
<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" />
<c:NullOrEmptyValueConverter x:Key="NullOrEmptyValueConverter" Text="(No Data)"/>
</UserControl.Resources>
...
<TextBlock Name="SerialNumberTextBlock" Text="{Binding Path=SerialNumber, Converter={StaticResource NullOrEmptyValueConverter}}">
<TextBlock.Resources>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=SerialNumberTextBlock, Path=Text}" Value="(No Data)">
<Setter Property="FontStyle" Value="Italic"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Resources>
</TextBlock>
I'd recommend implementing an IValueConverter; if the source value is not null or empty, then pass it through to the TextBlock. If the source value is null or empty, then render your chosen text.
public class NullValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
string str = (string)value;
if (str.IsNullOrWhitespace())
{
return "No Data";
}
return str;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
... //An empty implementation I expect...
}
}
However I have just realised that you want to set the style as well... hmmm, probably a DataTrigger that sets the style if the value is 'No Data' required I expect;
<TextBlock Text="{Binding Path=SomeProperty, Converter={StaticResource keyToNullValueConverter}">
<TextBlock.Triggers>
<DataTrigger Binding="{Binding Path=Text}" Value="No Data">
<Setter Property="FontStyle" Value="Italic"/>
</DataTrigger>
</TextBlock.Triggers>
</TextBlock>
Something along those lines might work.
I think you don't need to create Converter Class, you can simply write your style code like this.
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=SerialNumberTextBlock, Path=Text}" Value="{x:Null}">
<Setter Property="FontStyle" Value="Italic"/>
</DataTrigger>
<DataTrigger Binding="{Binding ElementName=SerialNumberTextBlock, Path=Text}" Value="{x:Static System:String.Empty}">
<Setter Property="FontStyle" Value="Italic"/>
</DataTrigger>
</Style.Triggers>
</Style>
Note :- You need to include the system namespace as
xmlns:System="clr-namespace:System;assembly=mscorlib"
You could try to bind to a property that looks thus
private string _textBlockText;
public string TextBlockText
{
get
{
if(string.IsNullOrEmpty(_textBlockText))
{
return "No Data";
}
return _textBlockText;
}
set
{
_textBlockText = value;
}
}
and then use the XAML that James has mentioned for styling. Saves the need for a converter.
Very late to the party, but here is my answer.
<TextBox >
<TextBox.Style>
<Style TargetType="{x:Type TextBox}">
<Setter Property="Text" Value="{Binding MyText, TargetNullValue=No data}"/>
<Style.Triggers>
<DataTrigger Binding="{Binding MyText}" Value="{x:Null}">
<Setter Property="FontStyle" Value="Italic"/>
</DataTrigger>
<DataTrigger Binding="{Binding MyText}" Value="{x:Static System:String.Empty}">
<Setter Property="FontStyle" Value="Italic"/>
</DataTrigger>
<Trigger Property="IsFocused" Value="True">
<Setter Property="Text" Value="{Binding MyText}"/>
</Trigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
My answer assumes that you want the default text to disappear on focus, which is more in line how inputs with default text usually behave. Also this works only for null values. If you need a check for string empty or additional logic, you could instead use a converter like in other provided answers. The key idea is, that you remove null value text or converter in the binding when control gains focus and thus only display the default text when control has no focus. This also prevents the default value flowing back to your view model.
DataTriggers part for font style was kindly borrowed from pchajer's answer.
I have a collection of objects bound to a hierarchical data template, each of my objects have a property on them (lets call it Property "A") that is of a certain type. This type varies among each of the objects.
If the data template contains an image and some text, what would be the best way to change the image that is displayed in the template based on the type of property "A".
I know I could just stick this into a converter and do the binding translation manually in code, but with all the binding facilities available in WPF, I think theres probably a better way.
It's pretty simple to do this within your data template, if you create local data templates and use a ContentPresenter. This template presents objects of type MyObject, displaying an image whose source is determined by the type of the A property next to a TextBlock that displays the content of the Text property:
<DataTemplate DataType="{x:Type MyObject}">
<StackPanel Orientation="Horizontal">
<StackPanel.Resources>
<DataTemplate DataType="{x:Type Thing1}">
<Image Source="thing1.png"/>
</DataTemplate>
<DataTemplate DataType="{x:Type Thing2}">
<Image Source="thing2.png"/>
</DataTemplate>
</StackPanel.Resources>
<ContentPresenter Content="{Binding A}"/>
<TextBlock Text="{Binding Text}"/>
</StackPanel>
</DataTemplate>
If you want to use styles to do this instead, you're going to run into a problem, because data triggers want to look at property values, and the type of the A property is not, itself, exposed as a property.
Unless, of course, you implement one:
public Type AType { get { return A.GetType(); } }
(You'll also need to raise PropertyChanged for AType when the value of A changes.) Once you've done this, you should be able to implement a data trigger in a style, e.g.:
<Style TargetType="Image">
<Setter Property="Source" Value="default.png"/>
<Style.Triggers>
<DataTrigger Binding="{Binding AType}" Value="{x:Type Thing1}">
<Setter Property="Source" Value="thing1.png"/>
</DataTrigger>
<DataTrigger Binding="{Binding AType}" Value="{x:Type Thing2}">
<Setter Property="Source" Value="thing2.png"/>
</DataTrigger>
</Style.Triggers>
</Style>
I think You can do that with triggers.
<Image.Style>
<Style TargetType="{x:Type Image}">
<Setter Property="Source" Value="Path">
<Style.Triggers>
<DataTrigger Binding="{Binding TheProperty}" Value="TheValue">
<Setter Property="Source" Value="NewPath"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Image.Style>
DataTemplateSelector doesn't seem to be a good choice here since you have the same template for all values of A.
Use DataTriggers:
<DataTemplate>
<StackPanel>
<Image x:Name="image" />
<TextBlock>Your text</TextBlock>
</StackPanel>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Path=A}" Value="ValueToCheck1">
<DataTrigger.Setters>
<Setter Property="Source" Value="Image1.png" TargetName="image" />
</DataTrigger.Setters>
</DataTrigger>
<DataTrigger Binding="{Binding Path=A}" Value="ValueToCheck2">
<DataTrigger.Setters>
<Setter Property="Source" Value="Image2.png" TargetName="image" />
</DataTrigger.Setters>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
Haven't tested it, but the idea is like that.