I want to check that the ListBox element has a specific type to assign a visual style to, but the constant check fails. Maybe I'm doing it wrong?
Problem with this line:
Condition Binding="{Binding}" Value="{x:Type econemodels:DishDTOAdvance}"
<ListBox.ItemTemplate>
<DataTemplate>
<ContentControl Content="{Binding}">
<ContentControl.Style>
<Style TargetType="ContentControl">
<Style.Triggers>
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding}"
Value="{x:Type econemodels:DishDTOAdvance}" />
</MultiDataTrigger.Conditions>
<Setter Property="ContentTemplate"
Value="{StaticResource DishNoImage}" />
</MultiDataTrigger>
</Style.Triggers>
</Style>
</ContentControl.Style>
</ContentControl>
</DataTemplate>
</ListBox.ItemTemplate>
The binding fails, because it binds an instance of type DishDTOAdvance and compares it with an instance of Type that describes the DishDTOAdvance type. Obviously they are different types and the condition is never true. In XAML x:Type is like typeof() or GetType() in code.
The x:Type markup extension has a similar function to the typeof() operator in C# or the GetType operator in Microsoft Visual Basic. The x:Type markup extension supplies a from-string conversion behavior for properties that take the type Type.
That is exactly the case for a custom DataTemplateSelector, no need for bindings.
Provides a way to choose a DataTemplate based on the data object and the data-bound element.
With a data template selector you can provide arbitrary logic to choose a data template for an item. In your case a switch statement for the type is enough to choose a template that can be found through FindResource in the resources up the visual tree. Of course you could also assign data templates trough properties if you do not want to search in all resources.
public class TypeTemplateSelector : DataTemplateSelector
{
public override DataTemplate SelectTemplate(object item, DependencyObject container)
{
var contentPresenter = (ContentPresenter)container;
switch (item)
{
case DishDTOAdvance _:
return (DataTemplate)contentPresenter.FindResource("DishNoImage");
// ...other type cases.
default:
return base.SelectTemplate(item, container);
}
}
}
Create and add an instance of the data template selector to your ListBox. Remove the ItemTemplate completely, it it now automatically assigned by the selector.
<ListBox ...>
<ListBox.ItemTemplateSelector>
<local:TypeTemplateSelector/>
</ListBox.ItemTemplateSelector>
<!-- ...other markup. -->
</ListBox>
The ContentControl is redundant. However in case you need it within an item template, it works just the same. ContentControl exposes an ContentTemplateSelector property for the same purpose.
Bonus round: Is the trigger impossible? No. You can create a converter that returns the type.
public class TypeConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value?.GetType();
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new InvalidOperationException();
}
}
Create an instance of the converter in a resource dictionary in scope.
<Window.Resources>
<local:TypeConverter x:Key="TypeConverter"/>
</Window.Resources>
Use the converter in the condition binding. Now types are compared.
<Condition Binding="{Binding Converter={StaticResource TypeConverter}}"
Value="{x:Type econemodels:DishDTOAdvance}"/>
Related
I understand the concept of Binding / Value converter well, but for some reasons the following binding doesn't work. I would like the change the FontWeight to Bold for some Descriptions (Description is a text field):
XAML:
<DataGridTextColumn Header="Description"
Binding="{Binding Description}"
FontWeight="{Binding Description, Converter={converters:DescriptionToFontWeightConverter}}"/>
Value converter method (simplified):
public class DescriptionToFontWeightConverter : ConverterMarkupExtension<DescriptionToFontWeightConverter>
{
public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
// Some logic based on the value
// ..
return "Bold"; // I believe I should use "Bold", and not "FontWeights.Bold" here (like it would be with a dependency property, but the problem is that it doesn't go inside the method.
}
public override object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) => Binding.DoNothing;
}
I believe the problem comes from the binding path of the FontWeight property. For example, if I replace (Path=)Description by RelativeSource={RelativeSource Self}, it goes inside the value converter method, but I don't think I can retrieve the value of the binding.. I think it isn't something abnormal (at least something I didn't expect), but I wonder if I shouldn't replace the DataGridTextColum by a DataGridTemplateColum and digs further?
I use the ConvertMarkupExtension method from this website which doesn't require to specify the value converters as static resources.
UPDATE with DataGridColumnTemplate
<DataGridTemplateColumn Header="Description">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Description}">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="FontWeight"
Value="{Binding Description, Converter={converters:DescriptionToFontWeightConverter}}"/>
</Style>
</TextBlock.Style>
</TextBlock>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<TextBox Text="{Binding Description}"/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>
Thanks for any insights :-)
A DataGridColumn doesn't inherit any DataContext so trying to bind to a Description property of the current item will always fail.
The Binding property is special. Its type is Binding and the binding that you define in XAML will eventually be applied to the element that gets created at runtime. In the case of a DataGridTextColumn, this is a TextBlock or a TextBox depending on whether you are in edit mode.
but I wonder if I shouldn't replace the DataGridTextColum by a DataGridTemplateColum and digs further
If you use a DataGridTemplateColumn and define a TextBlock in the CellTemplate (and a TextBox in the CellEditingTemplate), you can actually bind to a property of the current item as usual. This is because the element in the template is added to the element tree and inherits a DataContext like any other element.
I have a button control in a WPF application which is used for log-in purposes. The button is dual purpose: when logged-out, it shall display the text "log in". When logged-in, it shall display the text "log out".
I could do this with databinding to an appropriate string property in the viewmodel.
But it would be neater if I could simply databind to the "loggedIn" boolean (false for logged-out, true for logged-in) and then make the decision about what text to display on the button from within the view.
Is this possible?
You can achieve it using Style in Xaml without writing specific C# code.
Suppose you have IsLoggedIn property in ViewModel which is being changed on button bind command's execute method :
private void MyButtonCommandExecuteMethod()
{
this.IsLoggedIn = !this.IsLoggedIn;
}
private bool isLoggedIn;
public bool IsLoggedIn
{
get
{
return this.isLoggedIn;
}
set
{
this.isLoggedIn = value;
OnPropertyChanged(nameof(IsLoggedIn));
}
}
In the above code OnPropertyChanged is method implementation of INotifyPropertyChanged's PropertyChanged event. If you using any framework or defined own name, then replace it with appropriate name.
You could define a style such as:
<Button Command="{Binding YourButtonCommand}">
<Button.Style>
<Style TargetType="Button" BasedOn="{StaticResource {x:Type Button}}">
<Setter Property="Content" Value="Log In" />
<Style.Triggers>
<DataTrigger Binding="{Binding IsLoggedIn}" Value="True">
<Setter Property="Content" Value="Log out" />
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>
In the above code IsLoggedIn is bind to DataTrigger to update the Button's Content property based on it's value.
Another point, the button style is inherited from default style. If you any Keyed style then use it in BasedOn Property.
Solution
Yes that is possible using value converter, specifically IValueConverter. You can bind a bool property, say BoolProperty from your viewmodel to button using converter like this.
<Button Content="{Binding BoolProperty, Converter={StaticResource BoolConverter}}" />
Step 1: You need to create a converter that will accept bool value and return whatever string as you wish.
public class BoolConverter : System.Windows.Data.IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is bool)
{
return value.ToString();
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Step 2: Declare this converter as a resource in XAML (you will need to define local namespace alias that contains the converter in your <Window ..> start element.
<local:BoolConverter x:Key="BoolConverter" />
So now whenever property changed event is raised for BoolProperty, this converter will be triggered and button text will change appropriately.
Suggestion:
I am not sure why you think maintaining extra string property is not a clean way. It is clean and is much simpler approach than using converter. Whatever I have shown is unnecessary overhead for your case, IMO. However, since you asked about possibility, I detailed it. Choice is yours! :)
I am trying to create converter that shows me if something got value is Other then "None" just write X in cell so I have created simple element style:
<DataGridTextColumn.ElementStyle>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="Text" Value="{Binding Value, Converter={StaticResource SetBitConverter}}"/>
</Style>
</DataGridTextColumn.ElementStyle>
And converter is as well simple
public class SetBitConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var input = value as string;
switch (input)
{
case "None":
return "OK";
default:
return "X";
}
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotSupportedException();
}
}
Now problem is that on value set it will not enter converter, although if i change property from Text to Background for example, it will enter converter with no problem.
The value applied by a Style will always be of lower priority than one that has been set directly or, as in your case, by a Binding. If you want to add a Converter, add it to the Binding property of the DataGridTextColumn or use a DataGridTemplateColumn instead.
E.g.:
<DataGridTextColumn Binding="{Binding Value, Converter={StaticResource SetBitConverter}}"/>
Here is a comparison of the auto-generated default column and the one from above:
Why does dependency property precedence exist?
Typically, you would not want styles to always apply and to obscure even a locally set value of an individual element (otherwise, it would be very difficult to use either styles or elements in general). Therefore, the values that come from styles operate at a lower precedent than a locally set value.
Technical Background on Value Precedence
Property system coercion
Active animations, or animations with a Hold behavior
Local value
TemplatedParent template properties
Implicit style
Style triggers
Template triggers
Style setters
Default (theme) style
Inheritance
Default value from dependency property metadata
I have a control which has a default value for a property. When the control first gets its dataContext set, it assigns this property automatically.
In the xaml now, I want it to be possible to UNset this property. I've tried setting it to x:Null of just the empty string, but then I get an error because there's no converter for the property. How do I simply unassign this property from the xaml in the rare cases where I want the feature disabled?
code where it is originally set:
void OmniBox_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
if( e.NewValue is BindingObjectBaseExtended )
{
BindingObjectBaseExtended value = (BindingObjectBaseExtended)e.NewValue;
this.SetBinding(OmniBox.ContextValidationMessagesProperty, new Binding() { Source = value, Path = new PropertyPath("ValidationMessages") });
}
}
xaml where I want to unset the property.
<Style TargetType="ui:OmniBox">
<Setter Property="ContextValidationMessages" Value="" />
</Style>
Note that if I do not set up the binding automatically when the data context changes, then by default there are no validation messages and I have to do the following in the xaml to set them up:
<Style TargetType="ui:OmniBox">
<Setter Property="ContextValidationMessages" Value="ValidationMessages" />
</Style>
What I'm trying to do is make the above binding the default for my custom OmniBox control, and allow the user to unset it or change it to something else.
DependencyProperty.UnsetValue cannot be used in XAML.
http://msdn.microsoft.com/en-us/library/system.windows.dependencyproperty.unsetvalue(v=vs.90).ASPX
Personally, I would create a separate dependency property, such as bool AutoBindValidation and make it default to true. If it is false, don't do anything when the DataContext changes. This is a little more self-documenting. Depending on what exactly you're trying to do, you might not want to publicly expose ContextValidationMessages at all.
If you really want to do it the way you posted, I'm not sure why setting it to {x:Null} would cause an error (unless the property type is not nullable). But this approach would have problems because DataContextChanged is going to occur after the XAML is parsed. So the user can set it to {x:Null}, but then the DataContext will change and your code will set up the default binding and trample the user's value. You could set up the binding in the control's contstructor, but then if the DataContext does not have a ValidationMessages property, your control will be spitting out binding errors.
This may be impossible, my best bet was this:
<Setter Property="ContextValidationMessages"
Value="{x:Static DependencyProperty.UnsetValue}" />
But that throws "Cannot unset setter value". So you better inverse your logic or keep the property unset another way.
I don't think there is any supported way to do this in the xaml itself. In your code you are setting a local value on the ContextValidationMessagesProperty. The Style setters you included would have a lower dependency property precedence and even if they were evaluated they would set a value based on the specified Value - not clear it. Maybe instead of setting the binding in code you could have a Setter in your default style for OmniBox that sets that property - e.g.
<Setter Property="ContextValidationMessages" Value="{Binding ValidationMessages}" />
If you have to conditionally set the Binding then you could create a custom IValueConverter that checks for the specified type (passed as the parameter). e.g.
public class IsAssignableFromConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
Type typeParameter = parameter as Type;
if (typeParameter == null)
return DependencyProperty.UnsetValue;
return value != null && typeParameter.IsAssignableFrom(value.GetType());
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return DependencyProperty.UnsetValue;
}
}
Then you might use it like this:
<local:IsAssignableFromConverter x:Key="isAssignableConverter" />
<Style TargetType="ui:OmniBox">
<Style.Triggers>
<DataTrigger Binding="{Binding Converter={StaticResource isAssignableConverter}, ConverterParameter={x:Type ui:BindingObjectBaseExtended}}" Value="True">
<Setter Property="ContextValidationMessages" Value="{Binding ValidationMessages}" />
</DataTrigger>
</Style.Triggers>
</Style>
In the case where you don't want this property to be applied you might set the Style for that instance of the OmniBox to a new style and make sure to set the OverridesDefaultStyle property to true.
I suppose another option is to create another dependency property that will call ClearValue on the ContextValidationMessages property but this seems like it could be a maintenance issue.
For certain cases you can 'reset' to the default value of the parent control by using a RelativeSource. For instance I'm using a DataGrid and this worked for me to reset back to the 'default'.
This is a textblock inside a datagrid cell.
<TextBlock Text="{Binding ServiceName}">
<TextBlock.Style>
<Style>
<Style.Triggers>
<!-- Change text color to purple for FedEx -->
<Trigger Property="TextBlock.Text" Value="FedEx">
<Setter Property="TextBlock.Foreground" Value="Purple"/>
</Trigger>
<!-- Reset if the cell is selected, since purple on blue is illegible -->
<DataTrigger Binding="{Binding IsSelected, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGridCell}}}" Value="True">
<Setter Property="TextBlock.Foreground" Value="{Binding Foreground, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGridCell}}}"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
This seems clever enough to inherit the correct color even when the window is inactive.
I have a scenario where I need to specify Functions like
void SomeFunction(int value)
For this I'm using two DataGrids.
The left DataGrid holds the Functions
The right DataGrid holds the Parameters for the selected Function
I only want the Parameter DataGrid to be enabled when a valid Function is selected in the Function DataGrid. If the NewItemPlaceHolder (the Last Row when CanUserAddRows="True" for a DataGrid) is selected or if the selection is empty I want it to be disabled. I experimentet with a DataTrigger but I couldn't get it to work
<Style TargetType="DataGrid">
<Setter Property="IsEnabled" Value="False"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=functionDataGrid,
Path=SelectedItem}"
Value="{x:Type systemData:DataRowView}">
<Setter Property="IsEnabled" Value="True"/>
</DataTrigger>
</Style.Triggers>
</Style>
Is it possible to check if the value produced by the Binding is of a specific Type? Otherwise, does anyone have any other solutions to this? As of now, I'm handling this with the SelectedCellsChanged event but I would prefer not using code behind
Thanks
If anyone else comes across the same problem, here's what I did to solve it. I created a TypeOfConverter that returns the Type of the value produced by the Binding.
<DataTrigger Binding="{Binding ElementName=functionsDataGrid,
Path=SelectedItem,
Converter={StaticResource TypeOfConverter}}"
Value="{x:Type data:DataRowView}">
<Setter Property="IsEnabled" Value="True"/>
</DataTrigger>
TypeOfConverter
public class TypeOfConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return (value == null) ? null : value.GetType();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
Have you considered a DataTemplate for the right DataGrid (parameters)?
Then you could bind the DataContext of your right DataGrid to the SelectedItem of the left DataGrid.
And in your DataTemplate, you can make your right side look like an enabled DataGrid parameter entry form when the DataTemplate's DataType={x:Type local:FunctionObject}. When a 'FunctionObject' is not selected you can have a DataTemplate for that too which shows a disabled DataGrid parameter entry form, or you could choose to display nothing as well.