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Problem with BindableProperty on custom control

InregoInrego DKMember ✭✭
in Xamarin.Forms

Hello.

I'm having problems binding text to a label inside a custom control.

I have made the following control:

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Frida3.Components.TestView">
  <ContentView.Content>
      <StackLayout>
          <Label Text="{Binding Text}" />
      </StackLayout>
  </ContentView.Content>
</ContentView>

With the following code-behind:

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class TestView : ContentView
{
    public TestView ()
    {
        InitializeComponent ();
        BindingContext = this;
    }

    public static readonly BindableProperty TextProperty =
        BindableProperty.Create("Text", typeof(string), typeof(TestView), default(string));

    public string Text
    {
        get => (string) GetValue(TextProperty);
        set => SetValue(TextProperty, value);
    }
}

When using the control and a binding to set the Text property, nothing is shown. Below is some sample code of showing the results:

<!-- Shows that the LoginText binding contains value -->
<Label Text="{Binding LoginText}" BackgroundColor="BurlyWood"/>
<!-- Nothing shown with same binding -->
<components:TestView Text="{Binding LoginText}" BackgroundColor="Aqua" />
<!-- Works without binding -->
<components:TestView Text="This is showing" BackgroundColor="Yellow" />

And here is the result of that:

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Best Answer

Answers

  • InregoInrego DKMember ✭✭

    @NMackay said:
    Just a guess but try

    <?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Frida3.Components.TestView"
             x:Name="MyPage">
  <ContentView.Content>
      <StackLayout>
          <Label Text="{Binding Path=Text, Source={x:Reference Name=MyPage}}" />
      </StackLayout>
  </ContentView.Content>
</ContentView>

    hard to say without seeing what your binding context is etc. You really need to post a repo.

    Thank you, that worked. Is there no "shorthand" to avoid adding Source to every single element in my that I want to databind to a property?

  • NMackayNMackay GBInsider, University mod
    edited November 2018

    @Inrego

    Well the default behaviour is to bind to the bindingcontext property of the page, not the page itself, you can actually specify BindingContext.Command etc in a data template etc within a listview which is really useful as it takes you to whatever Viewmodel is bound and whatever property if you like stuff to be loosely coupled. If your writing a reusable control like your doing then this approach works fine where the parent is the binding context.

  • InregoInrego DKMember ✭✭

    I won't even pretend to understand why it wasn't working before. I'm just happy it's working now! :smiley:

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