Observablecollection from interface add to listview via binding

Question

I have an application that draws use of Xabre.ble plugin.

When the application scans for devices, once a device is discovered the application appends it to an ObservableCollection which derives from an interface.

I have made a Data template in Xaml that i wish to populate, but for some reason i can't seem to get the BindingContext right.

Basically, what I want to achieve, is to add device objects to my ObservableCollection IDevice, and fetch just the name of the individual devices in the bindingcontext for the user to see in the listview

Xaml:

<ListView x:Name="deviceList">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto"/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"/> 
                        <ColumnDefinition Width="Auto"/>
                   </Grid.ColumnDefinitions>
                   <local:IconView Grid.Row="0" Grid.Column="0" Source="BLE.png" Foreground="#3b5998" WidthRequest="30" HeightRequest="30"/>
                   <Label Grid.Row="1" Text="{Binding DeviceName}" TextColor="Teal"/>
                </Grid>
            </ViewCell>
        </DataTemplate> 
    </ListView.ItemTemplate>
</ListView>

Cs:

public ObservableCollection<IDevice> Devices { get; set; }
IAdapter adapter = CrossBluetoothLE.Current.Adapter;
public ObservableCollection<string> DeviceName { get; set; }

public MainPage()
{
    //Instantiate observable collection
    Devices = new ObservableCollection<IDevice>();
    DeviceName = new ObservableCollection<string>();

    //Appending peripherals to list
    BindingContext = DeviceName;
    deviceList.ItemsSource = BindingContext;
    Content = deviceList;
    Refreshcmd();
}
public void Refreshcmd()
{
//DeviceDiscovered is an event, when it discovers a device, we fire the eventhandler
    adapter.DeviceDiscovered += (s, a) =>
    {
        if (a.Device.Name != null)
        {
            Devices.Add(a.Device);               
            DeviceName.Add(a.Device.Name);
        }
    };
    adapter.StartScanningForDevicesAsync();
}

As you can see, I have tried to make an object which contains a string with just the name of the IDevice. However, it doesn't append to my databinding DeviceName.

Furthermore, I don't really like this solution, as I would much rather be able to access the Devices.Name from the interface, but that is not allowed apparently. - the reason why I would much rather like that solution is that the user eventually will have to connect to a device from the list, meaning that it is much easier to have one object for all the "behind the scenes" details.

Its a different control but your problem is similar to this - stackoverflow.com/questions/5409259/… — Rand Random
– Rand Random, Commented Sep 27, 2018 at 12:10
Had another look at what you are doing - try to change <Label Grid.Row="1" Text="{Binding DeviceName}" TextColor="Teal"/> to this <Label Grid.Row="1" Text="{Binding}" TextColor="Teal"/> — Rand Random
– Rand Random, Commented Sep 27, 2018 at 12:12
Why are you messing with the BindingContext ? Why can't the MainPage be the BindingContext for your XAML ? — Greggz
– Greggz, Commented Sep 27, 2018 at 12:14
Is there a reason why you try to use two lists? Devices and DeviceName — Rand Random
– Rand Random, Commented Sep 27, 2018 at 12:16

Bruno Caceiro · Accepted Answer · 2018-09-27 12:20:58Z

2

You should refactor your code, to a MVVM approach.

namespace YourNameSpace.ViewModels
{
    public class YourViewModel
    {

        private ObservableCollection<IDevice> devices;
        public ObservableCollection<IDevice> Devices
        {
            get { return devices; }
            set
            {
                devices = value;
            }
        }
        public YourViewModel()
        {
            Devices = new ObservableCollection<IDevice>();
        }
    }
}

In your Page.xaml.cs

public partial class YourPage : ContentPage
    {
        public YourPage()
        {
            InitializeComponent();
            BindingContext = new YourViewModel();
        }
    }

    public void Refreshcmd()
{
//DeviceDiscovered is an event, when it discovers a device, we fire the eventhandler
    adapter.DeviceDiscovered += (s, a) =>
    {
        if (a.Device.Name != null)
        {
            (YourViewModel)Devices.Add(a.Device);               
            //DeviceName.Add(a.Device.Name);
        }
    };
    adapter.StartScanningForDevicesAsync();
}

Then in Page.xaml

 <ListView ItemsSource="{Binding Devices}"
              CachingStrategy="RecycleElement">

answered Sep 27, 2018 at 12:20

Bruno Caceiro

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6 Comments

Jeppe Christensen Over a year ago

It works, but if i for example want to show the IDevice.Id, would I then just go {Binding Id} ? cause it doesn't show anything in that case.

Bruno Caceiro Over a year ago

Yes, in your ViewCell, you just need to Bind to the IDevice Property you desire.

Jeppe Christensen Over a year ago

In that case, I just wrote {Binding Id} but it doesn't show anything. I guess it doesn't affect anything that it is Int. It still should show right?

Bruno Caceiro Over a year ago

Yes, it should show even though its int. Have you tried to Bind to other properties? Are they showing correctly?

Jeppe Christensen Over a year ago

Hmm, i just tried printing the Rssi state, and that actually seems to work just fine!

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