CODEWITHSUNDEEP
c#xamarinxamarin.formsxamarin.android
user875234
user875234

Reputation: 1

Xamarin: Binding property not found

This app works just fine in UWP. I have ripped out everything except one of the more basic properties that is failing on Android. It looks like this:

MyPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:ViewModels="clr-namespace:MyApp.ViewModels"
             x:Class="MyApp.Views.MyApp">
    <ContentPage.BindingContext>
        <ViewModels:MyViewModel />
    </ContentPage.BindingContext>
    <ContentPage.Content>
        <ScrollView>

            <StackLayout Style="{StaticResource PageForm}">

                <Picker ItemsSource="{Binding Modes}"
                    ItemDisplayBinding="{Binding Value}"
                    SelectedItem="{Binding SelectedMode}" />

            </StackLayout>

        </ScrollView>

   </ContentPage.Content>
</ContentPage>

MyPage.cs

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace MyApp.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class MyApp : ContentPage
    {
        public MyApp ()
        {
            InitializeComponent ();
        }
    }
}

MyViewModel.cs

using MyApp.Models;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
namespace MyApp.ViewModels
{
    public class MyViewModel: INotifyPropertyChanged
    {
        List<Mode> _modes;
        Mode _selectedMode;

        public event PropertyChangedEventHandler PropertyChanged;

        public MyViewModel()
        {
            Modes = new List<Mode>()
            {
                new Mode() { Key=ModeType.Mode1, Value="Mode1" },
                new Mode() { Key=ModeType.Mode2, Value="Mode2" }
            };
            SelectedMode = Modes.Single(m => m.Key == ModeType.Mode1);
        }

        public List<Mode> Modes {
            get { return _modes; }
            set {
                _modes = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Modes"));
            }
        }

        public Mode SelectedMode {
            get {
                return _selectedMode;
            }
            set {
                _selectedMode = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("SelectedMode"));
            }
        }

    }
}

Mode.cs

namespace MyApp.Models
{
    public enum ModeType { Mode1, Mode2 };
    public class Mode
    {
        public ModeType _key;
        public string _value;
        public ModeType Key {
            get
            {
                return _key;
            }
            set
            {
                _key = value;
            }
        }
        public string Value {
            get
            {
                return _value;
            }
            set
            {
                _value = value;
            }
        }
    }
}

and what I see in the Debug console is

[0:] Binding: 'Value' property not found on 'MyApp.Models.Mode', target property: 'Xamarin.Forms.Picker.Display'

[0:] Binding: 'Value' property not found on 'MyApp.Models.Mode', target property: 'Xamarin.Forms.Picker.Display'

[0:] Binding: 'SelectedMode' property not found on 'MyApp.ViewModels.'MyApp', target property: 'Xamarin.Forms.Picker.SelectedItem'

Like I said this works if I run it as a UWP app but when I try it on Android it just doesn't work. That's about all I can say since it doesn't really say what the problem is other than the errors above which don't make sense.

The rest of the view model actually works. The main part of the app works, I can even run the code on this view model. If I create a simple string binding that will work, even on Android.

Any help is appreciated.

Upvotes: 4

Views: 8745

Answers (3)

ofthelit
ofthelit

Reputation: 1491

Use a one way binding to avoid having these binding errors in the debug console.

Text="{Binding [Name], Source={x:Static i18n:Translator.Instance}, Mode=OneWay}"

If you need TwoWay binding, make sure the bound model objects implement INotifyPropertyChanged as Markus Michel indicated.

Upvotes: 2

Markus Michel
Markus Michel

Reputation: 2299

Your mode model class also needs to implement INotifyPropertyChanged

Upvotes: 0

user875234
user875234

Reputation: 1

The answer is total magic to me. If someone can please explain this I will mark your answer as the accepted one.

Anroid Project File > Properties > Linking > Set to None.

It still didn't work so I closed Visual Studio and deleted the bin and obj directories in the PCL and Android projects. Finally it worked.

One other thing is this seems like I've now lost the ability to have linking be set to sdk and user assemblies. What if I need that at some point?

Upvotes: 2

Related Questions