Develop Reference

Why is IValueConverter ConverterParameter not Bindable? [duplicate]

In Xamarin Forms I'm trying to create a xaml converter with properties.
This is to be used, for example, to show values from a list in different ways, based on a code behind property.
I based my code on this: https://stackoverflow.com/a/29869734.
Converter:
namespace App2.Converters
{
class MyConverter : IValueConverter
{
public int ConvParam { get; set; }
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return $"value: {value} - ConvParam: {ConvParam}";
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
XAML:
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:conv="clr-namespace:App2.Converters"
x:Class="App2.MainPage"
x:Name="MainPageXaml">
<ContentPage.Resources>
<conv:MyConverter x:Key="cnv" ConvParam="{Binding Source={Reference MainPageXaml}, Path=PropParam}" />
<!--<conv:MyConverter x:Key="cnv" ConvParam="333" />-->
</ContentPage.Resources>
<StackLayout Orientation="Vertical">
<!-- Place new controls here -->
<Label Text="{Binding Source={Reference MainPageXaml}, Path=PropVal}" />
<Label Text="{Binding Source={Reference MainPageXaml}, Path=PropParam}" />
<Label Text="{Binding Source={Reference MainPageXaml}, Path=PropVal, Converter={StaticResource cnv}}" />
</StackLayout>
Code behind:
public partial class MainPage : ContentPage
{
public int PropVal { get; set; } = 111;
public int PropParam { get; set; } = 222;
public MainPage()
{
InitializeComponent();
}
}
The goal is to bind ConvParam of my converter to PropParam in code behind.
But if I use:
<conv:MyConverter x:Key="cnv" ConvParam="{Binding Source={Reference MainPageXaml}, Path=PropParam}" />
the error Position 10:39. No property, bindable property, or event found for 'ConvParam', or mismatching type between value and property is shown and the app doesn't compile.
The property ConvParam itself is recognized inside xaml: if I replace the above line with
<conv:MyConverter x:Key="cnv" ConvParam="333" />
everything works.
The binding expression I used ({Binding Source={Reference MainPageXaml}, Path=PropParam}) actually works, if used as source for the text property of a label:
<Label Text="{Binding Source={Reference MainPageXaml}, Path=PropParam}" />
But if I use it in Resources, It doesn't work.

Thanks to Julipan I could make it work!
As he pointed out, ConvParam must be a BindableProperty, so I modified my converter to inherit from BindableObject and defined ConvParam as BindableProperty.
Converter:
namespace App2.Converters
{
class MyConverter : BindableObject, IValueConverter
{
public static readonly BindableProperty ConvParamProperty = BindableProperty.Create(nameof(ConvParam), typeof(int), typeof(MyConverter));
public int ConvParam
{
get { return (int)GetValue(ConvParamProperty); }
set { SetValue(ConvParamProperty, value); }
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return $"value: {value} - ConvParam: {ConvParam}";
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}

UWP Image.Source binding with converter

In my code I have a class with the following fields:
public class Source
{
public string Name { get; set; }
...
public string Path { get => $"/Assets/Images/{Name}.svg"; }
}
Path property is there just for debugging.
I also develop a converter in order to get rid of Path property.
public class SourceToImageConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
return $"/Assets/Images/{value}.svg";
}
}
When I use Path property as Image Source, everything works fine, but when I try to do the same with the SourceToImageConverter, app is not working.
I know converter is working as it Should cause when I use it on a TextBlock it shows the right value.
Xaml code looks like:
<Page.Resources>
<local:SourceToImageConverter x:Key="SourceToImage"/>
<DataTemplate x:Key="SourceListViewTemplate" x:DataType="models:Source">
<StackPanel Orientation="Horizontal">
<Image Source="{x:Bind Path}"/>
<Image Source="{x:Bind Name, Converter={StaticResource SourceToImage}}"/>
<TextBlock Text="{x:Bind Name, Converter={StaticResource SourceToImage}}"/>
</StackPanel>
</DataTemplate>
</Page.Resources>
...
<GridView
x:Name="Source"
ItemsSource="{x:Bind ViewModel.Sources}"
ItemTemplate="{StaticResource SourceListViewTemplate}"
IsItemClickEnabled="True"
SelectionMode="Single"/>

Apply XamlBindingHelper.ConvertValue() to the value just as auto-generated {x:Bind} code is doing backstage.
public class SourceToImageConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
//if (targetType == typeof(string)) return $"/Assets/Images/{value}.svg";
return XamlBindingHelper.ConvertValue(typeof(ImageSource), $"/Assets/Images/{value}.svg");
}
}

Binding to last array element

So far, i have an ObservableCollection<T> for objects.
I always want to display the last inserted element into a TextBlock. I implemented two solutions in XAML, but both not working:
<TextBlock Text="{Binding Path=entries.Last().message, FallbackValue=...}" />
<TextBlock Text="{Binding Path=entries[entries.Length-1].message, FallbackValue=...}" />
This one works, but references the first entry:
<TextBlock Text="{Binding Path=entries[0].message, FallbackValue=...}" />
Am i missing something? Is it possible to do with pure XAML?

Solution 1 :
You can use a custom converter to achieve this :
Converter class :
class LastItemConverter : IValueConverter
{
public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
IEnumerable<object> items = value as IEnumerable<object>;
if (items != null)
{
return items.LastOrDefault();
}
else return Binding.DoNothing;
}
public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new System.NotImplementedException();
}
}
Xaml :
<Application.Resources>
<local:LastItemConverter x:Key="LastItemConverter" />
</Application.Resources>
<TextBlock Text="{Binding Path=entries, Converter={StaticResource LastItemConverter}}" />
Solution 2 :
The other way is to create a new property in your model that returns the entry :
public Object LastEntry => entries.LastOrDefault();
Xaml :
<TextBlock Text="{Binding Path=LastEntry, ... " />

Binding inside of a binding

Ok I have a Observable collection containing string defined like so.
public ObservableCollection<string> OCGroundType { get; set; }
This collection is having resources key so what I'm trying to do is with this code
<ListBox HorizontalAlignment="Left" Height="110" Margin="156,23,0,0" VerticalAlignment="Top" Width="314" ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=OCGroundType}" >
<ListBox.ItemTemplate>
<DataTemplate>
<Label Content="{Binding Path=, Source={StaticResource Resources}}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
So what I'm trying to do is give the path the value of the itemsource is that possible?
Edit
That's what the staticresource is 'binded' to , a resourceDictionary
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:cultures="clr-namespace:Marcam.Cultures"
xmlns:properties="clr-namespace:Marcam.Properties">
<ObjectDataProvider x:Key="Resources" ObjectType="{x:Type cultures:CultureResources}" MethodName="GetResourceInstance"/>
</ResourceDictionary>
What the ObjectType is 'binded' to is a method who return the current Resources.resx, If I've understanded well how it's work because I've based this code on this WPF Localization

It's not possible, because a Binding is not a DependencyObject, so its properties cannot be bound.
However, you could achieve the desired result by using a converter that fetches the appropriate value from the resources.
EDIT: first, you need a converter like this:
public class ResourceConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
string key = (string)value;
return Properties.Resources.ResourceManager.GetObject(key, culture);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
}
Then, declare an instance of this converter in the XAML resources:
<local:ResourceConverter x:Key="resourceConverter" />
And finally, just use this converter in your binding:
<Label Content="{Binding Path=., Converter={StaticResource resourceConverter}}"/>

Assuming Resources are mere string values declared under resources section of Window or UserControl, you can achieve that using IMultiValueConverter.
First of all you need to pass resource key and second ResourceDictionary of Window/UserControl wherever your resources are defined.
XAML will look like this:
<Label>
<Label.Content>
<MultiBinding Converter="{StaticResource ResourceToValueConverter}">
<Binding/>
<Binding Path="Resources" RelativeSource="{RelativeSource
Mode=FindAncestor, AncestorType=Window}"/>
</MultiBinding>
</Label.Content>
</Label>
Ofcourse you need to add instance of ResourceToValueConverter in XAML.
Second here goes your converter code:
public class ResourceToValueConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
return ((ResourceDictionary)values[1])[values[0]];
}
public object[] ConvertBack(object value, Type[] targetTypes,
object parameter,
System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
UPDATE
As you edited the question to include that resource is ObjectDataProvider, you can modify converter code.
You have ObjectDataProvider in your converter which you can get and call it's method to get the resource file(.resx) file. Get string value from the resource file and return it.
var provider = ((ResourceDictionary)values[1])["Resources"] as ObjectDataProvider;
var output = provider.Data;
return // Get string from resource file and return it.

How to pass a static value to IValueConverter in XAML

I would like to use static texts fetched from a web service in my WP7 app. Each text has a Name (the indetifier) and a Content property.
For example a text could look like this:
Name = "M43";
Content = "This is the text to be shown";
I would then like to pass the Name (i.e. the identifier) of the text to an IValueConverter, which would then look up the the Name and return the text.
I figured the converter to look something like this:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(value)).Content;
}
return null;
}
}
Then in the XAML:
<phone:PhoneApplicationPage.Resources>
<Helpers:StaticTextConverter x:Name="StaticTextConverter" />
</phone:PhoneApplicationPage.Resources>
...
<TextBlock Text="{Binding 'M43', Converter={StaticResource StaticTextConverter}}"/>
However, this does not seem to work and I am not sure that I pass in the value to the converter correctly.
Does anyone have some suggestions?

I finally found the answer. The answer was a mix between that of #Shawn Kendrot and another question I asked here: IValueConverter not getting invoked in some scenarios
To summarize the solution for using the IValueConverter I have to bind my control in the following manor:
<phone:PhoneApplicationPage.Resources>
<Helpers:StaticTextConverter x:Name="TextConverter" />
</phone:PhoneApplicationPage.Resources>
<TextBlock Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />
Since the ID of the text is passed in with the converter parameter, the converter looks almost the same:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter != null && parameter is string)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
}
return null;
}
}
However, as it turns out, the binding and thus the converter is not invoked if it does not have a DataContext. To solve this, the DataContext property of the control just has to be set to something arbitrary:
<TextBlock DataContext="arbitrary"
Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />
And then everything works as intended!

The problem lies in your binding. It will check the DataContext, and on this object, it will try to evaluate the properties M62 and ValueboxConsent on that object.
You might want to add static keys somewhere in your application where you can bind to:
<TextBlock Text="{Binding Source="{x:Static M62.ValueboxConsent}", Converter={StaticResource StaticTextConverter}}" />
Where M62 is a static class where your keys are located.. like so:
public static class M62
{
public static string ValueboxConsent
{
get { return "myValueBoxConsentKey"; }
}
}

If you want to use a value converter, you'll need to pass the string to the parameter of value converter
Xaml:
<TextBlock Text="{Binding Converter={StaticResource StaticTextConverter}, ConverterParameter=M43}"/>
Converter:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter != null)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
}
return null;
}
}

xmlns:prop="clr-namespace:MyProj.Properties;assembly=namespace:MyProj"
<TextBlock Text="{Binding Source={x:Static prop:Resources.MyString}, Converter={StaticResource StringToUpperCaseConverter}}" />