Can't bind static property in XAML (Xamarin Forms)

Question

I have a static class (Evp), which is located in Models folder. It has a Name string, with getter and setter and a PropertyChangedEventHandler and its code:

public static event PropertyChangedEventHandler StaticPropertyChanged;
private static string _name
public static string Name{
    get => _name;
    set{
        _name = value;
        OnStaticPropertyChanged("Name"); } }
private static void OnStaticPropertyChanged(string propertyName)
    {
        StaticPropertyChanged?.Invoke(null, new PropertyChangedEventArgs(propertyName));
    }

In my XAML file, this is how I tried to bind (it worked in WPF 4.5 if I recall correctly):

<Label Grid.Row="0" Grid.Column="1" TextColor="Beige" Text="{Binding Source={x:Static Models:Evp.Name}}" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" FontSize="30"></Label>

I specified the Models folder in the ContentPage in XAML:

xmlns:Models="clr-namespace:Rdb.Models;assembly=Rdb"

For some reason, it's not working. What am I doing wrong? Also, how can I set this binding in code-behind?

{Binding Source={x:Static Models:Evp}, Path=Name} It gives me an error before the comma: " , expected". Strange. I guess this will be some easy task, but I cannot figure out. — Laszlo, Jan 22 '18 at 21:50

Martin Zikmund · Accepted Answer · 2018-01-22T21:57:50.170

To support data binding, your class has to implement the INotifyPropertyChanged interface. Unfortunately, static classes cannot implement interfaces, so your solution will not work.

The solution would be to create a normal class that implements INotifyPropertyChanged and then create a singleton instance of this class which you will register as a resource:

App.Current.Resources["Evp"] = new Evp();

And then you reference it with StaticResource markup extension:

{Binding Name, Source={StaticResource Evp}}

To ensure the class is singleton would be a public static get-only property:

public static Evp Instance {get;} = new Evp();

And you would then also add a private constructor to make sure others cannot create instances of your class:

private Evp()
{
}

The resource would then be set as:

App.Current.Resources["Evp"] = Evp.Instance;

This makes using your class in C# code easier by just using Evp.Instance.

Can't bind static property in XAML (Xamarin Forms)

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