Develop Reference

How do I define a constant in C# and use it in XAML?

I try to define constants for string values whenever necessary to avoid burying "magic strings" in the code. I recently found myself needing to define a custom format string for a converter, so I defined public const string MyFormat = "a"; in the converter. When using the converter, I need to pass in "a" as the ConverterParameter, but rather than typing ConverterParameter=a, I would like to refer to the named constant.
<TextBlock Text="{x:Bind SomeProperty, Converter={StaticResource MyConverter}, ConverterParameter=???}" />
I've tried ConverterParameter=local:MyConverter.MyFormat, but it just passes in the string "local:MyConverter.MyFormat" rather than "a".
I've tried ConverterParameter={x:Bind local:MyConverter.MyFormat} but I get an error Nested x:Bind expressions are not supported.
I've tried ConverterParameter={StaticResource MyFormat} and adding it as a resource, but that just moves the problem and introduces a new problem:
I don't know how to reference the constant in the resources either. I can add <x:String x:Key="MyFormat">a</x:String>, but then I've defined the constant in two different places and if it changes I have to remember to update it in two different places.
Even if I do this, the string is not passed as the parameter as expected. The parameter is null.
Is there any way to refer to a named constant in XAML? (Note: this is UWP, not WPF.)
Here's a simple repro:
MainPage.xaml
<Page
x:Class="XamlConstantReference.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="using:XamlConstantReference"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
mc:Ignorable="d">
<Page.Resources>
<local:MyConverter x:Key="MyConverter" />
<!-- How do I refer to MyConverter.MyFormat rather than defining it a second time? -->
<x:String x:Key="MyFormat">a</x:String>
</Page.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition />
</Grid.RowDefinitions>
<!-- How do I refer to MyConverter.MyFormat rather than passing in ConverterParameter=a? -->
<TextBlock Grid.Row="0" Text="{x:Bind SomeProperty, Converter={StaticResource MyConverter}, ConverterParameter=a}" />
<TextBlock Grid.Row="1" Text="{x:Bind SomeProperty, Converter={StaticResource MyConverter}, ConverterParameter=local:MyConverter.MyFormat}" />
<!-- <TextBlock Grid.Row="2" Text="{x:Bind SomeProperty, Converter={StaticResource MyConverter}, ConverterParameter={x:Bind local:MyConverter.MyFormat}}" /> -->
<TextBlock Grid.Row="3" Text="{x:Bind SomeProperty, Converter={StaticResource MyConverter}, ConverterParameter={StaticResource MyFormat}}" />
</Grid>
</Page>
MainPage.xaml.cs
using System.ComponentModel;
using Windows.UI.Xaml.Controls;
namespace XamlConstantReference
{
public sealed partial class MainPage : Page, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _someProperty = "Hello World!";
public string SomeProperty
{
get => _someProperty;
set
{
if (_someProperty != value)
{
_someProperty = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SomeProperty)));
}
}
}
public MainPage()
{
InitializeComponent();
}
}
}
MyConverter.cs
using System;
using Windows.UI.Xaml.Data;
namespace XamlConstantReference
{
public class MyConverter : IValueConverter
{
public const string MyFormat = "a";
public object Convert(object value, Type targetType, object parameter, string language)
{
if (parameter == null)
{
return $"Fail. Formatted '{value}' with null parameter.";
}
else if (parameter is string parameterString)
{
switch (parameterString)
{
case MyFormat:
return $"Success! Formatted '{value}' with parameter '{parameterString}'.";
default:
return $"Fail. Formatted '{value}' with parameter '{parameterString}'.";
}
}
throw new ArgumentException();
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}
}

How to choose grid Columns from some Tabs and display them in another Tab?

I'm creating a WPF application(UI) with a TabControl which contains four TabItems in it.
My Application --
From the User Tab, I want to choose somehow (maybe with a check box, or any other way) which of the GridColumns will be displayed at the User Tab. I can work with the other Tabs, but sometimes I need to give the user the opportunity to work only with the specific outputs he/she wants. How can I make this work? I am new to C# and wpf, so if you could explain a simple solution and offer some codes, I would appriciate it.

Before answering your question, a brief hint for you: when you ask, post some code, otherwise it will be hard that someone spends time for helping you.
For implementing your application you need to consider:
ElementName data binding
ElementName data binding can't work in the ColumnDefinitions property
To solve the point number 2 you can read this very interesting article by Josh Smith.
Pratically he creates a special kind of ElementSpy with an attached property:
public class ElementSpy : Freezable
{
private DependencyObject element;
public static ElementSpy GetNameScopeSource(DependencyObject obj)
{
return (ElementSpy)obj.GetValue(NameScopeSourceProperty);
}
public static void SetNameScopeSource(DependencyObject obj, ElementSpy value)
{
obj.SetValue(NameScopeSourceProperty, value);
}
public static readonly DependencyProperty NameScopeSourceProperty =
DependencyProperty.RegisterAttached("NameScopeSource", typeof(ElementSpy), typeof(ElementSpy),
new UIPropertyMetadata(null, OnNameScopeSourceProperty));
private static void OnNameScopeSourceProperty(DependencyObject d, DependencyPropertyChangedEventArgs args)
{
INameScope nameScope;
ElementSpy elementSpy = args.NewValue as ElementSpy;
if (elementSpy != null && elementSpy.Element != null)
{
nameScope = NameScope.GetNameScope(elementSpy.Element);
if (nameScope != null)
{
d.Dispatcher.BeginInvoke(new Action<DependencyObject, INameScope>(SetScope),
System.Windows.Threading.DispatcherPriority.Normal,
d, nameScope);
}
}
}
private static void SetScope(DependencyObject d, INameScope nameScope)
{
NameScope.SetNameScope(d, nameScope);
}
public DependencyObject Element
{
get
{
if (element == null)
{
PropertyInfo propertyInfo = typeof(Freezable).GetProperty("InheritanceContext",
BindingFlags.NonPublic | BindingFlags.Instance);
element = propertyInfo.GetValue(this, null) as DependencyObject;
if (element != null)
{
Freeze();
}
}
return element;
}
}
protected override Freezable CreateInstanceCore()
{
return new ElementSpy();
}
}
Now we can use binding in our XAML
<Window.Resources>
<local:BooleanWidthConverter x:Key="BooleanWidthConverter" />
<local:ElementSpy x:Key="ElementSpy" />
</Window.Resources>
<StackPanel HorizontalAlignment="Stretch">
<Grid local:ElementSpy.NameScopeSource="{StaticResource ElementSpy}"
Margin="0,0,0,30">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="{Binding ElementName=cb1, Path=IsChecked, Converter={StaticResource BooleanWidthConverter}, Mode=OneWay}" />
<ColumnDefinition Width="{Binding ElementName=cb2, Path=IsChecked, Converter={StaticResource BooleanWidthConverter}, Mode=OneWay}" />
<ColumnDefinition Width="{Binding ElementName=cb3, Path=IsChecked, Converter={StaticResource BooleanWidthConverter}, Mode=OneWay}" />
</Grid.ColumnDefinitions>
<TextBlock HorizontalAlignment="Center" Text="Column 1" Margin="4" Grid.Column="0" />
<TextBlock HorizontalAlignment="Center" Text="Column 2" Margin="4" Grid.Column="1" />
<TextBlock HorizontalAlignment="Center" Text="Column 3" Margin="4" Grid.Column="2" />
</Grid>
<CheckBox x:Name="cb1" Content="Column 1" Margin="4" IsChecked="true" HorizontalAlignment="Center" />
<CheckBox x:Name="cb2" Content="Column 2" Margin="4" IsChecked="true" HorizontalAlignment="Center" />
<CheckBox x:Name="cb3" Content="Column 3" Margin="4" IsChecked="true" HorizontalAlignment="Center" />
</StackPanel>
To complete our code, we need a simple converter:
public class BooleanWidthConverter : IValueConverter
{
private static GridLength star = new GridLength(1, GridUnitType.Star);
private static GridLength zero = new GridLength(0, GridUnitType.Pixel);
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
bool boolValue = (bool)value;
return boolValue ? star : zero;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
Of course this is just a sample prototype, but I am sure it can help you with your application.

Change image in xaml based on a value from another xaml

I have a Views/Doc.xaml with:
<navigation:Page ....
<data:DataGrid>
<data:DataGridTemplateColumn Header="Actions" HeaderStyle="{StaticResource TextHeaderStyle}" >
<data:DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<Grid x:Name="gridDocumentColumns">
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<HyperlinkButton x:Name="hlEmail" Grid.Column="1" Tag="{Binding Index}" Click="hlEmail_Click" >
<ToolTipService.ToolTip>
<ToolTip Tag="ToolTipEmail" Opened="toolTip_ActionOpened" />
</ToolTipService.ToolTip>
<Image Source="../images/close.png" Stretch="None" />
</HyperlinkButton>
</Grid>
</DataTemplate>
</data:DataGridTemplateColumn.CellTemplate>
</data:DataGridTemplateColumn>
</data:DataGrid>
..............
I have a second class Views/Controls/ReadDocs.xaml (). If a certain condition in ReadDocs.xaml Code Behind is true i want to change the image source in Views/Doc.xaml to ../images/open.png
How can i achieve this?

You can define a converter and pass a flag value to it.
This converter will returns a specific path depending upon the value you have passed.
Kindly refer the below converter for reference...
public sealed class ImagetoPathConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
if (value == null)
{
return value = "ms-appx:///Assets/Images/bk/1.png";
}
else if (value.ToString() == "1")
{
return value = "ms-appx:///Assets/Images/bk/2.png";
}
else if (value.ToString() == "2")
{
return value = "ms-appx:///Assets/Images/bk/3.png";
}
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}
Bind the converter in Source and pass your conditional value.

WPF ComboBox Conditional ItemTemplate

I have a ComboBox Binded to a List of Possible values is the ViewModel.
<ComboBox ItemsSource="{Binding PossibleOperands}" SelectedValue="{Binding Operand, Mode=TwoWay}" VerticalAlignment="Center" Foreground="Black" FontSize="13" FontFamily="Calibri" Height="23" Grid.Column="1" Margin="7,2,0,2"/>
For most values I want the display a simple string (in The example above, "Operand Name"),
but for one of the values, I want to display a string + 2 comboBoxes.
Mockup:

Use ItemTemplateSelector class as described in MSDN

You can define a single ItemTemplate with a textblock and 2 combobox. Bind the Visibility of ComboBoxes with the required property. This way only for certain items the ComboBoxes will be visible.

I have done something like that before:
Assuming you have a class like this: (for the ComboBox's Content)
public class Content
{
private String _Texty;
public String Texty
{
get{return _Texty;}
set { _Texty = value; }
}
public List<String> Comb1{get ; set;}
public List<String> Comb2 { get; set; }
public Content(string t, List<String> comb1, List<String> comb2)
{
Texty = "Some Text";
Comb1 = comb1;
Comb2 = comb2;
}
}
You will need a Converter, defined in your xaml part like this:
<utils:ContentToVisibleConverter x:Key="MyConverter" />
where utils is something like:
xmlns:utils="clr-namespace:YOUR CONVERTER CLASS NAMESPACE"
So, define your Combobox like this in the xaml:
<ComboBox x:Name="Combo" Margin="4"
Height="23"
Width="250" ItemsSource="{Binding Collection}" >
<ComboBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal" >
<TextBlock Text="{Binding Texty}" Margin="4,0"/>
<Grid Margin="20 0 0 0">
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0" Text="Entity Type:"
Visibility="{Binding Path=Comb1, Converter={StaticResource MyConverter}}" />
<ComboBox Grid.Column="1" ItemsSource="{Binding Comb1}" Width="80" Margin="4,0"
Visibility="{Binding Path=Comb1, Converter={StaticResource MyConverter}}"/>
<TextBlock Grid.Column="2" Text="Entity:"
Visibility="{Binding Path=Comb2, Converter={StaticResource MyConverter}}"/>
<ComboBox Grid.Column="3" ItemsSource="{Binding Comb2}" Width="80" Margin="4,0"
Visibility="{Binding Path=Comb2, Converter={StaticResource MyConverter}}"/>
</Grid>
</StackPanel>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
Somewhere in my code, I use a Binding Collection this way:
private ObservableCollection<Content> _Collection;
public ObservableCollection<Content> Collection
{
get { return _Collection; }
set { _Collection = value; NotifyPropertyChanged("Collection"); }
}
// Fill it like this:
Collection = new ObservableCollection<Content>();
Collection.Add(new Content("Some Stuff", null, null));
Collection.Add(new Content("Some Stuff", null, null));
Collection.Add(new Content("Some Stuff", null, null));
Collection.Add(new Content("Some Stuff",
new List<String>() { "One", "Two" },
new List<String>() { "One", "Two" }));
Finally, I define a class for the converter it only contains:
public class ContentToVisibleConverter : System.Windows.Markup.MarkupExtension, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var s = value as List<string>;
if (s != null)
return s.Count > 0 ? Visibility.Visible : Visibility.Collapsed;
else return Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
That's all, let me know if it worked for you.

Conversion from ReadOnlyObservableCollection to List<MyClass>

I have a datagrid with grouping and I am trying to style the template to add in some summary about the group.
IN XAML DataGrid.RowGroupHeaderStyle
<Grid Grid.Column="3" Grid.Row="1" VerticalAlignment="Center" HorizontalAlignment="Stretch" Margin="0,1,0,1" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="200"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0" Text="{Binding Name}" Margin="4,0,0,0" />
<TextBlock Grid.Column="1" Text="{Binding Items, Converter="{StaticResource summaryConverter}"}" />
</Grid>
Binding of data grid items source
PagedCollectionView collection = new PagedCollectionView(e.Result.ToList<MyClass>());
collection.GroupDescriptions.Add(new PropertyGroupDescription("Name"));
dataGrid.ItemsSource = collection;
MyClass
class MyClass {
public string Name;
public double Value;
}
I have created a converter to grab the Items of the same group but I am facing problem in converting the object into List<MyClass>(). I receive this error
Unable to cast object of type 'System.Collections.ObjectModel.ReadOnlyObservableCollection1[System.Object]' to type 'System.Collections.Generic.List1[MyClass]'.
`
In Converter.cs
public object Convert(object values, Type targetType, object param, CultureInfo culture) {
var source = (List<MyClass>)values;
}
Does anyone know how should I do the conversion??

Use LINQ.
public object Convert(object values, Type targetType, object param, CultureInfo culture) {
var source = (ReadOnlyObservableCollection<object>) values;
List<MyClass> list = source.OfType<MyClass>().ToList();
...
}