Develop Reference

InvalidCastException while binding with converter

I have a problem with a binding, I want to change an icon when the column has at least one element filtered. But it is not working.
This is my converter:
public class FilteredToIconConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
int index = ((DataGridColumnHeader)((MahApps.Metro.IconPacks.PackIconMaterial)value).TemplatedParent).Column.DisplayIndex;
return !((AdvancedDataGrid)parameter).FilterLists[index].Any(item => item.NotFiltered);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
A filter for each column is generated with a contentTemplate, and I have 2 problems, If I set this style in controlTemplate.Resources the dataGrid reference is not found.
If I set the style in the DataGrid.Resources then I get
InvalidCastException: Can not convert an object from type 'System.Windows.Controls.DataGrid' to type 'MahApps.Metro.IconPacks.PackIconMaterial'.
This is the style:
<Style TargetType="iconPacks:PackIconMaterial">
<Style.Triggers>
<DataTrigger Binding="{Binding Converter={StaticResource FilteredToIcon}, ConverterParameter={x:Reference dataGrid}}" Value="True">
<Setter Property="Kind" Value="FilterMenu"/>
</DataTrigger>
</Style.Triggers>
</Style>
And this is a summary of the whole XAML of my custom AdvancedDataGrid:
<DataGrid x:Class="ZOT.GUI.Items.AdvancedDataGrid"
x:Name="dataGrid"
xmlns:iconPacks="http://metro.mahapps.com/winfx/xaml/iconpacks"
xmlns:local="clr-namespace:ZOT.GUI.Items">
<DataGrid.Resources>
<local:FilteredToIconConverter x:Key="FilteredToIcon" />
<!-- The style can be here-->
</DataGrid.Resources>
<DataGrid.ColumnHeaderStyle>
<Style TargetType="DataGridColumnHeader">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type DataGridColumnHeader}">
<ControlTemplate.Resources>
<!-- The style can be here as well, whatever that works-->
</ControlTemplate.Resources>
<Grid>
<ContentPresenter/>
<ToggleButton x:Name="Y">
<!-- This is the Icon I want to change -->
<iconPacks:PackIconMaterial Kind="Filter"/>
</ToggleButton>
<Popup x:Name="pop" Width="auto" IsOpen="{Binding IsChecked, ElementName=Y,Mode=TwoWay}">
<!-- .... -->
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</DataGrid.ColumnHeaderStyle>
</DataGrid>
If you have any clue, tell me please.
Thank you.

If you want to bind to the PackIconMaterial itself, you should set the RelativeSource property of the binding to RelativeSource.Self:
<Style TargetType="iconPacks:PackIconMaterial">
<Style.Triggers>
<DataTrigger Binding="{Binding Converter={StaticResource FilteredToIcon}, ConverterParameter={x:Reference dataGrid},
RelativeSource={RelativeSource Self}}" Value="True">
<Setter Property="Kind" Value="FilterMenu"/>
</DataTrigger>
</Style.Triggers>
</Style>
That's the only way you will be able to cast value to MahApps.Metro.IconPacks.PackIconMaterial in the converter.
There are probably better ways of solving whatever you're trying to do though.

Value Converter set in Style does not get file value, but whole datarow

I set up a style for a label which should be triggered if the value of the bound filed in the underlying DataTable is greater than zero:
<c:Groesser0BooleanValueConverter x:Key="G0" />
<Style x:Key="DashboardProzent" TargetType="{x:Type Label}">
<Style.Triggers>
<DataTrigger Binding="{Binding Converter={StaticResource G0}}" Value="{x:Null}">
<Setter Property="Foreground" Value="Red"/>
</DataTrigger>
</Style.Triggers>
</Style>
The label itself is set up this way (a DataTemplate in a resource Dictionary):
<Label Content="{Binding percentCol}" Style="{StaticResource DashboardPrzoent}" Grid.Row="0" Grid.Column="2"/>
The converter looks like this:
public class Groesser0BooleanValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (System.Convert.ToInt32(value) > 0)
{
return true;
}
else
{
return false;
}
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
If a run the whole thing, i get the error in the Convert method of the Groesser0BooleanValueConverter class:
Unable to cast object of type 'System.Data.DataRowView' to type
'System.IConvertible'
If I check the parameter of the Convert method of the Converter, it shows that a System.Data.DataRowView has been passed, instead of the value of the percentCol field, which I would have expected. How can I get the Label to pass the value instead of the whole row?
Update:
If I set the Label to
<Label Content="{Binding Path=percentCol}" Style="{StaticResource DashboardPrzoent}" Grid.Row="0" Grid.Column="2"/>
the error still occurs. If I disable the trigger, the value is shown (even without the Path= segment.
I don't want to state the field name in the style segment, as I would like to use it for other values to.

First I think the main problem is due to your Binding in the DataTrigger
<DataTrigger Binding="{Binding Converter={StaticResource G0}}" Value="{x:Null}">
This will pass on the direct DataContext of your Label to your Converter, which is obviously not what you want.
You should have:
<DataTrigger Binding="{Binding Converter={StaticResource G0}, Path=percentCol}" Value="False">
I also corrected the Value part, since your 'Converter' only sends back True/False. If you want to change back to Value="{x:Null}", you will have to modify your converter.
I would also advise to be safer in your Converter, otherwise the explicit conversion System.Convert.ToInt32(value) may (will...) raise an error.

I wanted to set the Binding Path and the Binding Converter in two different locations, for example a DataTemplate and a Style file.
This can be done by using {Binding Content, RelativeSource={RelativeSource Self}, Converter={StaticResource converterName}} in the Style and setting the Binding Path as usual in the DataTemplate
Converter
<Style x:Key="DashboardPrzoent" TargetType="{x:Type Label}">
...
<Style.Triggers>
<DataTrigger Binding="{Binding Content, RelativeSource={RelativeSource Self}, Converter={StaticResource G0}}" Value="True">
<Setter Property="Foreground" Value="{StaticResource Gruen}"/>
</DataTrigger>
<DataTrigger Binding="{Binding Content, RelativeSource={RelativeSource Self}, Converter={StaticResource G0}}" Value="False">
<Setter Property="Foreground" Value="{StaticResource Rot}"/>
</DataTrigger>
</Style.Triggers>
</Style>
DataTemplate
<Label Content="{Binding Path=percentCol}" ... />

WPF Trigger not working, what am i doing wrong?

I have the following code (only relevant snippets)
<ribbon:RibbonWindow .............>
<Grid>
<ribbon:Ribbon>
<ribbon:RibbonToggleButton
x:Name="Button2"
SmallImageSource="Images\SmallIcon.png"
Label="Properties">
<ribbon:RibbonToggleButton.Triggers>
<Trigger Property="ToggleButton.IsChecked" Value="True">
<Setter TargetName="SPanel1" Property="UIElement.IsVisible" Value="False"/>
<Setter TargetName="SPanel2" Property="UIElement.IsVisible" Value="True"/>
</Trigger>
</ribbon:RibbonToggleButton.Triggers>
</ribbon:RibbonToggleButton>
</ribbon:Ribbon>
</Grid>
</ribbon:RibbonWindow>
And when i run the application, it hangs up and te debugger pops up. What am i doing wrong?
I have tried setting the trigger on the grid, wrapping everything in a control template and setting a trigger there, same problem!
Edit
I have tried creating a button, and only the tag of trigger causes the Unhandled Exception error.
<Button Content="Button" Grid.Row="1" Height="23" HorizontalAlignment="Left" Margin="12,27,0,0" Name="TestButton" VerticalAlignment="Top" Width="75" >
<Button.Triggers>
<Trigger></Trigger>
</Button.Triggers>
</Button>
Edit 2
Using Data triggers makes the Unhandled Exception go away but the trigger is not responding:
<StackPanel.Style>
<Style TargetType="StackPanel">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=Button2, Path=ToggleButton.IsChecked}" Value="True">
<Setter Property="UIElement.Visibility" Value="Hidden"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</StackPanel.Style>
Edit 3
<ribbon:RibbonToggleButton
x:Name="Button2"
SmallImageSource="Images\SmallIcon.png"
Label="Properties">
</ribbon:RibbonToggleButton>
And The panel to be hidden
<StackPanel
Grid.Row="2"
Grid.Column="1"
x:Name="SPanel1"
Visibility="Visible">
<Label>*Deafult Grid*</Label>
<StackPanel.Style>
<Style TargetType="StackPanel">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=Button2, Path=ToggleButton.IsChecked}" Value="True">
<Setter Property="UIElement.Visibility" Value="Hidden"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</StackPanel.Style>
</StackPanel>
And for second StackPanel that i want to show
<StackPanel
Grid.Row="2"
Grid.Column="1"
x:Name="SPanel2"
Visibility="Hidden">
<Label>*Panel 2 *</Label>
<StackPanel.Style>
<Style TargetType="StackPanel">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=Button2, Path=IsChecked}" Value="True">
<Setter Property="UIElement.Visibility" Value="Visible"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</StackPanel.Style>
</StackPanel>

You need to use DataTrigger, and set the style property of the two panels to the IsChecked propery of the checkbox, here an example
<CheckBox Name="check" Content="Prova" IsChecked="True"> </CheckBox>
<Canvas Name="SPanel1" Background="Blue" Width="100" Height="100">
<Canvas.Style>
<Style TargetType="Canvas">
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=check, Path=IsChecked}" Value="True">
<Setter Property="Visibility" Value="Hidden"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</Canvas.Style>
</Canvas>

UIElement.IsVisible is not a mutable property. You'll have to set UIElement.Visibility, which is an enum.
The reason why you get an exception is because FrameworkElement.Triggers only accepts EventTrigger. This means that if you do UIElement.Triggers (Button.Triggers or ribbon:RibbonToggleButton.Triggers), you can only add EventTriggers under that. Style, DataTemplate and ControlTemplate accept all TriggerBase derived classes.
Edit
As Mackho pointed out, you cannot use TargetName under Style. You'd have to accomplish this using data binding.
Assuming SPanel1 is a StackPanel, here's what you can do:
Create a converter
public class BoolToVisibilityConverter : IValueConverter {
public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
return (bool)value ? Visibility.Visible : Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return null;
}
}
Somewhere in the root control's resources, add BoolToVisibilityConverter
Add x:Name to your toggle button; lets say you call it "MyToggleButton"
<StackPanel x:Name="SPanel1" ...
Visibility="{Binding IsChecked, ElementName=MyToggleButton, Converter={StaticResource BoolToVisibilityConverter}}" />
And do something very similar for SPanel2.

How to implement NullText in a TextBlock with 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.

Set IsEnabled Property of ComboBox Based on SelectedItem

I want to enable/disable a ComboBox based on if there is an item selected in another ComboBox. I was able to get it working by setting a trigger on the Style, but that overrides my custom global style for the combobox. Is there another way to get the same functionality without losing my style?
<ComboBox Grid.Column="1" Grid.Row="1"
Name="AnalysisComboBox"
MinWidth="200"
VerticalAlignment="Center" HorizontalAlignment="Left"
ItemsSource="{Binding Path=AvailableAnalysis}">
<ComboBox.Style>
<Style TargetType="{x:Type ComboBox}">
<Setter Property="IsEnabled" Value="True" />
<Style.Triggers>
<DataTrigger Binding="{Binding SelectedItem,ElementName=ApplicationComboBox}" Value="{x:Null}">
<Setter Property="IsEnabled" Value="False" />
</DataTrigger>
</Style.Triggers>
</Style>
</ComboBox.Style>
</ComboBox>

You don't need to do this via a Style, you can bind the IsEnabled property directly using a value converter as follows:
<ComboBox Grid.Column="1" Grid.Row="1"
Name="AnalysisComboBox"
MinWidth="200"
VerticalAlignment="Center" HorizontalAlignment="Left"
IsEnabled={Binding SelectedItem, ElementName=ApplicationComboBox, Converter={StaticResource NullToFalseConverter}}"
ItemsSource="{Binding Path=AvailableAnalysis}"/>
Where NullToFalseConverter is a key to an instance of the followsing converter:
public class NullToFalseConverter: IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value == null;
}
public object ConvertBack(object value, Type targetType,
object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}

Yes, you can set BasedOn attribute to "inherit" your global style:
<ComboBox Grid.Column="1" Grid.Row="1"
Name="AnalysisComboBox"
MinWidth="200"
VerticalAlignment="Center" HorizontalAlignment="Left"
ItemsSource="{Binding Path=AvailableAnalysis}">
<ComboBox.Style>
<Style TargetType="{x:Type ComboBox}"
BasedOn="{StaticResource {x:Type ComboBox}}">
<Setter Property="IsEnabled" Value="True" />
<Style.Triggers>
<DataTrigger Binding="{Binding SelectedItem,ElementName=ApplicationComboBox}" Value="{x:Null}">
<Setter Property="IsEnabled" Value="False" />
</DataTrigger>
</Style.Triggers>
</Style>
</ComboBox.Style>
</ComboBox>
Instead of {StaticResource {x:Type ComboBox}} you can set the key of you global style (if it is not implicit).
But for this particular task you don't need to define a style. You can just set a binding to IsEnabled property and use a converter to convert selected item of another combo box to a boolean:
<ComboBox Grid.Column="1" Grid.Row="1"
Name="AnalysisComboBox"
MinWidth="200"
VerticalAlignment="Center" HorizontalAlignment="Left"
ItemsSource="{Binding Path=AvailableAnalysis}"
IsEnabled="{Binding SelectedItem,ElementName=ApplicationComboBox, Converter={StaticResource NotNullConverter}"/>

You could simply have a "normal" binding, with a value converter for changing "value exists" => true, "value is null" => false.