I have the following XAML:
<TextBlock Text="{Binding ElementName=EditListBox, Path=SelectedItems.Count}" Margin="0,0,5,0"/>
<TextBlock Text="items selected">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=EditListBox, Path=SelectedItems.Count}" Value="1">
<Setter Property="TextBlock.Text" Value="item selected"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
The first text block happily changes with SelectedItems.Count, showing 0,1,2, etc. The datatrigger on the second block never seems to fire to change the text.
Any thoughts?
Alternatively, you could replace your XAML with this:
<TextBlock Margin="0,0,5,0" Text="{Binding ElementName=EditListBox, Path=SelectedItems.Count}"/>
<TextBlock>
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="Text" Value="items selected"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=EditListBox, Path=SelectedItems.Count}" Value="1">
<Setter Property="Text" Value="item selected"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
Converters can solve a lot of binding problems but having a lot of specialized converters gets very messy.
The DataTrigger is firing but the Text field for your second TextBlock is hard-coded as "items selected" so it won't be able to change. To see it firing, you can remove Text="items selected".
Your problem is a good candidate for using a ValueConverter instead of DataTrigger. Here's how to create and use the ValueConverter to get it to set the Text to what you want.
Create this ValueConverter:
public class CountToSelectedTextConverter : IValueConverter
{
#region IValueConverter Members
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if ((int)value == 1)
return "item selected";
else
return "items selected";
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
#endregion
}
Add the namespace reference to your the assembly the converter is located:
xmlns:local="clr-namespace:ValueConverterExample"
Add the converter to your resources:
<Window.Resources>
<local:CountToSelectedTextConverter x:Key="CountToSelectedTextConverter"/>
</Window.Resources>
Change your second textblock to:
<TextBlock Text="{Binding ElementName=EditListBox, Path=SelectedItems.Count, Converter={StaticResource CountToSelectedTextConverter}}"/>
Related
I have a ListView, with its items represented by an ItemTemplate like so:
<ListView dependencyObjects:InterestingItem.Interesting="{Binding InterestingItem}"
ItemsSource="{Binding Quotations}" >
<ListView.ItemTemplate>
<DataTemplate>
<Border>
<Grid>
<StackPanel x:Name="NotImportant">
</StackPanel>
<Grid x:Name="HiddenGrid"
Background="Red"
Visibility="Hidden" >
<Grid.Style>
<Style TargetType="Grid">
<Style.Triggers>
<Grid.Triggers>
<DataTrigger Binding="{Binding Path=DataContext.InterestingItem,
RelativeSource={RelativeSource AncestorType={x:Type ListView }}}"
Value="*this instance here*!">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
</Grid.Triggers>
</Style.Triggers>
</Style>
</Grid.Style>
</Grid>
</Grid>
</Border>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
The ListView has an attached property InterestingItem that is one of the items in the ListView.
What I can't hook up is when the InterestingItem is the same as one of the items, the second Grid should become visible.
I would prefer not to change and bind to the actual objects in the list - but rather have the ListView control which item is to be altered.
What is the Value in the DataTrigger that I need?
There are multiple issues in your XAML and conceptually that prevent it from working.
To bind attached properties, you have to use the correct syntax with parentheses.
Path="{Binding (local:InterestingItem.Interesting), RelativeSource={RelativeSource AncestorType={x:Type ListView}}}"
See the Binding path syntax documenation for reference.
The Triggers property does only support EventTriggers, see FrameworkElement.Triggers.
Note that the collection of triggers established on an element only supports EventTrigger, not property triggers (Trigger). If you require property triggers, you must place these within a style or template and then assign that style or template to the element either directly through the Style property, or indirectly through an implicit style reference.
You cannot bind the Value property of DataTrigger, since it is not a dependency property.
You could of course change the bound type to expose a property that indicates if it is a special object or not and bind that in XAML using a DataTrigger, similar to this (where IsSpecial is the new bool property).
<Grid x:Name="HiddenGrid"
Background="Red">
<TextBlock Text="Hidden Grid"/>
<Grid.Style>
<Style TargetType="{x:Type Grid}">
<Setter Property="Visibility" Value="Hidden"/>
<Style.Triggers>
<DataTrigger Binding="{Binding IsSpecial}" Value="True">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Style>
</Grid>
If you want to stick to your current approach, you could create a custom IMultiValueConverter that enables binding multiple properties. It would check if all of the bound values are equal and return Visibility.Visible or Visibility.Hidden otherwise. This example uses Linq to check this and supports an arbitrary number of values bound, but there are many other options.
public class EqualityToVisibilityConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
if (values is null || values.Length < 2)
return Binding.DoNothing;
return values.Distinct().Count() == 1 ? Visibility.Visible : Visibility.Hidden;
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new InvalidOperationException();
}
}
Next, instantiate the converter in the resources of the ListView or any other resource dictionary in scope and bind the Visibility property of the Grid to both the current item (just <Binding/>) and the attached property local:InterestingItem.Interesting with a MultiBinding that uses the converter to convert them to a Visibility.
<ListView local:InterestingItem.Interesting="{Binding InterestingItem}"
ItemsSource="{Binding Quotations}">
<ListView.Resources>
<local:EqualityToVisibilityConverter x:Key="EqualityToVisibilityConverter"/>
</ListView.Resources>
<ListView.ItemTemplate>
<DataTemplate>
<Border>
<Grid>
<StackPanel x:Name="NotImportant">
<TextBlock Text="Not Important"/>
</StackPanel>
<Grid x:Name="HiddenGrid"
Background="Red">
<Grid.Visibility>
<MultiBinding Converter="{StaticResource EqualityToVisibilityConverter}">
<Binding/>
<Binding Path="(local:InterestingItem.Interesting)"
RelativeSource="{RelativeSource AncestorType={x:Type ListView}}"/>
</MultiBinding>
</Grid.Visibility>
<TextBlock Text="Hidden Grid"/>
</Grid>
</Grid>
</Border>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
There are two other things to note here. I have added two dummy TextBlocks, otherwise the result will not be visible, as the panels are empty. Replace them with your content. Furthermore, both the StackPanel and the Grid are overlapping in the parent Grid, I do not know if this is intentional or not, but you can change it by adding rows or columns and moving the elements there.
What is the Value in the DataTrigger that I need?
I am afraid XAML has no support for something like the this keyword in C#.
You may use a MultiBinding with an IMultiValueConverter implementation that determines whether the items are equal:
<Grid x:Name="HiddenGrid" Background="Red">
<Grid.Style>
<Style TargetType="Grid">
<Setter Property="Visibility" Value="Hidden" />
<Style.Triggers>
<DataTrigger Value="True">
<DataTrigger.Binding>
<MultiBinding>
<MultiBinding.Converter>
<local:MultiConverter />
</MultiBinding.Converter>
<Binding Path="{Binding Path=DataContext.InterestingItem,
RelativeSource={RelativeSource AncestorType={x:Type ListView }}}" />
<Binding Path="{Binding}" />
</MultiBinding>
</DataTrigger.Binding>
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Style>
</Grid>
Converter:
public class MultiConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) =>
values != null && values.Length == 2 && values[0] == values[1];
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) =>
throw new NotSupportedException();
}
Note that you cannot set the Visibility property of the Grid to a local value if you want to be able to override the value using a Style setter.
<Grid x:Name="HiddenGrid" Background="Red" Visibility="Hidden">
I have trouble defining a trigger for TreeViewItems. I believe it is just some syntax problem, but I don't know what else to write...
This is the Trigger:
<DataTrigger Binding="{Binding Path=., Converter=IsNodeConverter}" Value="True">
<Setter Property="Focusable" Value="False"/>
</DataTrigger>
Since it is defined inside TreeView.ItemContainerStyle, the DataContext should be the contained item itself. The Item can either be of type Node or Entry and I want to trigger for all Items that are of type Node. So I wrote a converter:
public class IsNodeConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is Node)
return true;
return false;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Which returns true if it gets a Node as input and false otherwise.
But in the part Binding="{Binding Path=., Converter=IsNodeConverter}" the compiler complains: "IValueConverter cannot convert from string." (original: "Vom TypeConverter-Objekt für IValueConverter wird das Konvertieren aus einer Zeichenfolge nicht unterstützt.") I don't understand this at all: DataContext is an object of type Entry or Node, and Binding Path=. should keep it that way. So what is the problem? What string is the compiler talking about? How do I correct this so that the compiler does not complain?
Here is the full code of the TreeView for reference. The collection ´AllNodesAndEntries´ is an ObservableCollection<object> that contains both Nodes and Entrys.
<TreeView ItemsSource="{Binding AllNodesAndEntries}">
<TreeView.Resources>
<HierarchicalDataTemplate ItemsSource="{Binding Children}" DataType="{x:Type usrLibVM:Node}">
<TextBlock Text="{Binding Name}" Background="LightBlue"/>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type usrLibVM:Entry}">
<TextBlock Text="{Binding Name}" Background="LightSalmon"/>
</DataTemplate>
</TreeView.Resources>
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=., Converter=IsNodeConverter}" Value="True">
<Setter Property="Focusable" Value="False"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
Your converter is certainly declared in a ResourceDictionary, so it should be referenced as StaticResource:
Binding="{Binding Path=., Converter={StaticResource IsNodeConverter}}"
or shorter:
Binding="{Binding Converter={StaticResource IsNodeConverter}}"
Based on answer in thread Using Value Converters in WPF without having to define them as resources first :
<DataTrigger Value="False">
<DataTrigger.Binding>
<Binding> <!-- <Binding Path="."> is possible but not necessary -->
<Binding.Converter>
<converterNamespace:IsNodeConverter/>
</Binding.Converter>
</Binding>
</DataTrigger.Binding>
<Setter Property="Focusable" Value="False"/>
</DataTrigger>
I would like to hide a progressbar in WPF using databinding. Whenever a property is 0, the progressbar should hide: I try the following code
(Info: My current datacontext is a class that holds an integer property 'CurrentIndex')
<ProgressBar Minimum="0" Maximum="100" Value="{Binding CurrentIndex, UpdateSourceTrigger=PropertyChanged}" Visibility="Visible">
<ProgressBar.Style>
<Style TargetType="{x:Type ProgressBar}">
<Style.Triggers>
<DataTrigger Binding="{Binding CurrentIndex}" Value="0">
<Setter Property="Visibility" Value="Hidden"/>
</DataTrigger>
</Style.Triggers>
</Style>
</ProgressBar.Style>
</ProgressBar>
What is wrong with this code? Why does the progressbar still show up when the CurrentIndex is 0? (in the model behind, the value of 'CurrentIndex' is 0 by default, when the control is loaded)
DP precedence, do not set Visibility on the control itself (local value > style).
Other way to use visibility binding and a converter:
<Grid>
<Grid.Resources>
<App:VisibilityConverter x:Key="VisibilityConverter" />
</Grid.Resources>
<ProgressBar Minimum="0" Maximum="100" Value="{Binding CurrentIndex, UpdateSourceTrigger=PropertyChanged}"
Visibility="{Binding CurrentIndex, Mode=OneWay, Converter={StaticResource VisibilityConverter}}" />
</Grid>
The converter code (VisibilityConverter.cs):
public class VisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return (int)value == 0 ? Visibility.Hidden : Visibility.Visible;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Your XAML was almost right!
Define your progressbar as you did:
<ProgressBar Minimum="0"
Maximum="100"
Value="{Binding CurrentIndex, UpdateSourceTrigger=PropertyChanged}"
Name="MyAutoHidingProgressBar" />
Don't forget to add the Name property AND do not set the Visibility here.
It will always override what is set in your Style.
Then define a Style as normal in your <Window.Resources>
<Window.Resources>
<Style TargetType="ProgressBar" x:Key="MyAutoHidingProgressBarStyle">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=MyAutoHidingProgressBar, Path=Value}" Value="0">
<Setter Property="Visibility" Value="Hidden"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</Window.Resources>
What this is basically doing is to check the Value of the progressbar itself, rather than your binding.
As a last step add the Style to your progressbar:
Style="{StaticResource MyAutoHidingProgressBarStyle}"
Now your ProgressBar will auto hide if its Value is 0.
You can also easily add a Trigger to hide it if its full.
In the previous question of mine, I have asked how to hide an empty TextBlock, so that it doesn't take space in the panel. I have a new challenge now. How am I supposed to hide an empty Hyperlink:
<TextBlock>
<Hyperlink
NavigateUri="{Binding Path=Email}"
RequestNavigate="Hyperlink_RequestNavigate">
<TextBlock Text="{Binding Path=Email}" />
</Hyperlink>
</TextBlock>
This is what made the hiding possible in the previous question:
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<Trigger Property="Text" Value="">
<Setter Property="Visibility" Value="Collapsed" />
</Trigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
Providing this style on first TextBlock won't work because the Text property is not set. Providing style on Hyperlink doesn't hide the parent TextBlock and same happens if I try to hide the TextBlock inside the Hyperlink.
I am certain that my style needs to be applied on the Hyperlink, but the trigger inside should target the Visibility property of the 'Hyperlink's parentTextBlock`. What is the style supposed to look like?
Just use DataTrigger on the top level TextBlock to check whether the bound property is an empty string:
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding Email}" Value="">
<Setter Property="Visibility" Value="Collapsed" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
EDIT:
Also you can try binding to the child hyperlink's NavigationUri property:
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Path=Inlines
[0].NavigateUri}" Value="">
<Setter Property="Visibility" Value="Collapsed" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
The solution provided by Foovanadil that solves the similar issue by implementing visibility converter works the best in my opinion. It is the easiest to implement and can be reused whenever needed.
The converter should be implemented like this:
using System;
using System.Globalization;
using System.Windows;
using System.Windows.Data;
public class VisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
if (string.IsNullOrEmpty(value as string))
{
return Visibility.Collapsed;
}
else
{
return Visibility.Visible;
}
}
public object ConvertBack(object value, Type targetType, object parameter,
CultureInfo culture)
{
throw new NotSupportedException();
}
}
}
And used like this:
<Window.Resources>
<!-- Visibility converter -->
<converters:VisibilityConverter x:Key="visibleConv" />
</Window.Resources>
...
<TextBlock Visibility="{Binding Something, Converter={StaticResource visibleConv}}">
<Hyperlink NavigateUri="{Binding Something}">
<TextBlock Text="{Binding Something}" />
</Hyperlink>
</TextBlock>
All credits go to the original solution provider: Foovanadil
I've been having trouble using a value converter with a data trigger. In some of my code it seems like the DataTrigger's Path is being applied to the root element, rather than the element which the style applies to.
I created a simple test case, and I don't understand its behavior. I'm expecting the Button to turn red or blue depending on which value is being fed to the DataTrigger's converter, but the Button isn't being affected at all!
<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:SimpleWpfApplication"
x:Class="SimpleWpfApplication.SimpleUserControl"
ToolTip="UserControl ToolTip">
<UserControl.Resources>
<local:SimpleConverter x:Key="SimpleConverter" />
</UserControl.Resources>
<Button ToolTip="Button ToolTip">
<Button.Style>
<Style TargetType="{x:Type Button}">
<Style.Triggers>
<DataTrigger
Binding="{Binding Path=ToolTip, Converter={StaticResource SimpleConverter}}"
Value="Button ToolTip">
<Setter Property="Background" Value="Red" />
</DataTrigger>
<DataTrigger
Binding="{Binding Path=ToolTip, Converter={StaticResource SimpleConverter}}"
Value="UserControl ToolTip">
<Setter Property="Background" Value="Blue" />
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>
</UserControl>
And a simple converter:
class SimpleConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new InvalidOperationException("SimpleConverter is a OneWay converter.");
}
}
Why isn't Convert being called? Why doesn't the Button turn red or blue?
Found the answer in another StackOverflow question: What’s wrong with my datatrigger binding?
The answer is to add RelativeSource={RelativeSource Self} to the binding:
<DataTrigger Binding="{Binding Path=ToolTip,
RelativeSource={RelativeSource Self},
Converter={StaticResource SimpleConverter}}" />