XAMARIN.FORMS BLUETOOTH ISSUE

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Auger•12/10/23, 6:14 AM

I've worked on Bluetooth for xamarin applications before. What exactly were you asking about it?

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Auger•12/10/23, 4:51 PM

Xamarin has built-in libraries to handle Bluetooth. You don't need any extra ones. I only have experience with Android using Xamarin, so that'll be what info I can provide below, I imagine it is the same a protocol level.

By on and off, I assume you mean the Bluetooth adapter. This is an android service that you can acquire from an Android Context, which is something you get with platform specific code (eg. MainActivity, Android services, or broadcast receivers). It will tell you what state the adapter is in, and if it's transitioning between on and off as well as let you toggle that. Your app will likely need the "Bluetooth admin" permission though.
This depends on whether you're using Bluetooth, classic or Bluetooth Low Energy, since they're pretty different. In both cases you get the android Bluetooth service and are able to scan for specific MAC Addresses (off the top of my head, the device name might be available as well in the Bluetooth advertisement).

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Auger•12/10/23, 5:01 PM

I mentioned that Bluetooth classic and Bluetooth low energy are pretty different, what I meant by that is really the way that you read and write data.
With Bluetooth classic, it's a bit more straightforward, you have a stream of bytes that you can read to and a stream of bytes that you can write to.
For Bluetooth low energy there is this GATT protocol, where you have to find a specific "characteristic" and "service that you want to read/write to, which each have a UUID. It isn't unusual to hard code that guid to make discovery between apps easier. For Bluetooth low energy, you can think of data transfer as a property changing values, and then subscribe to be notified that the property ("characteristic") changed. When the property changes, you get a chunk of bytes at once, although probably not complete.

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Auger•12/10/23, 5:02 PM

In my opinion BLE is harder to do than BT Classic, but sounds like a better use case for your type of data transfer; since for BT Classic, it takes a lot more power and I constant connection that is likely to break frequently

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Auger•12/10/23, 5:22 PM

For more information: https://developer.android.com/develop/connectivity/bluetooth/ble/ble-overview

Android Developers

Bluetooth Low Energy | Connectivity | Android Developers

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Auger•12/10/23, 5:23 PM

An important call out is that you need to define app-level security since once you connect, any other apps on your phone can read this data too. I also don't trust Bluetooth's built in security all that much for protecting from other listening devices (Example of recent vuln, https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-24023).

CVE - CVE-2023-24023

The mission of the CVE® Program is to identify, define, and catalog publicly disclosed cybersecurity vulnerabilities.

Original message was deleted

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Auger•12/10/23, 8:37 PM

I wouldn't mix; there is no point. The scanning is the same with xamarin

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Auger•12/11/23, 11:07 PM

Did you ensure you granted all relevant permissions in Android itself for your app?
Example

Original message was deleted

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Auger•12/12/23, 2:04 AM

https://github.com/dotnet-bluetooth-le/dotnet-bluetooth-le if you aren't already following this. The docs there look pretty promising, and help explain the latter part of BLE data transfer.

For your first question, that is more XAML-related. You can use something like this, if you aren't already... I saw you had an observable collection already.
You may need to tweak the bindings or set the Binding Context to the class you have holding this property. I usually create a view model to hold my bindings for me, not in the view's code-behind. Check out the MVVM design pattern.

public partial class MyPage : ContentPage
{
  public MyPage()
  {
    BindingContext = new MyViewModel();
  }
}

public partial class MyPage : ContentPage
{
  public MyPage()
  {
    BindingContext = new MyViewModel();
  }
}

public partial class MyPage : ContentPage
{
  public MyPage()
  {
    BindingContext = new MyViewModel();
  }
}

public partial class MyPage : ContentPage
{
  public MyPage()
  {
    BindingContext = new MyViewModel();
  }
}

public partial class MyViewModel: INotifyPropertyChanged
{
  public ObservableCollection<IDevice> Devices { get; } = new();
  // ....
}

public partial class MyViewModel: INotifyPropertyChanged
{
  public ObservableCollection<IDevice> Devices { get; } = new();
  // ....
}

public partial class MyViewModel: INotifyPropertyChanged
{
  public ObservableCollection<IDevice> Devices { get; } = new();
  // ....
}

public partial class MyViewModel: INotifyPropertyChanged
{
  public ObservableCollection<IDevice> Devices { get; } = new();
  // ....
}

<CollectionView ItemSource={Binding Items}>
  <CollectionView.ItemTemplate>
    <DataTemplate>
      <Label Text={Binding Name}> <!--Idk what the property of \'Device\' is, but I assume it has a name or MAC addr.-->
    </DataTemplate>
  </CollectionView.ItemTemplate>
</CollectionView>

<CollectionView ItemSource={Binding Items}>
  <CollectionView.ItemTemplate>
    <DataTemplate>
      <Label Text={Binding Name}> <!--Idk what the property of \'Device\' is, but I assume it has a name or MAC addr.-->
    </DataTemplate>
  </CollectionView.ItemTemplate>
</CollectionView>

<CollectionView ItemSource={Binding Items}>
  <CollectionView.ItemTemplate>
    <DataTemplate>
      <Label Text={Binding Name}> <!--Idk what the property of \'Device\' is, but I assume it has a name or MAC addr.-->
    </DataTemplate>
  </CollectionView.ItemTemplate>
</CollectionView>

<CollectionView ItemSource={Binding Items}>
  <CollectionView.ItemTemplate>
    <DataTemplate>
      <Label Text={Binding Name}> <!--Idk what the property of \'Device\' is, but I assume it has a name or MAC addr.-->
    </DataTemplate>
  </CollectionView.ItemTemplate>
</CollectionView>

https://developer.android.com/reference/android/bluetooth/BluetoothDevice

The second, you can probably grab the Android service bluetoothadapter from the static default or from a Context (need MainActivity for this one) and call Enable();

BluetoothAdapter bluetoothAdapter = BluetoothAdapter.DefaultAdapter; 
bluetoothAdapter.Enable();

BluetoothAdapter bluetoothAdapter = BluetoothAdapter.DefaultAdapter; 
bluetoothAdapter.Enable();

BluetoothAdapter bluetoothAdapter = BluetoothAdapter.DefaultAdapter; 
bluetoothAdapter.Enable();

BluetoothAdapter bluetoothAdapter = BluetoothAdapter.DefaultAdapter; 
bluetoothAdapter.Enable();

https://learn.microsoft.com/en-us/dotnet/api/android.bluetooth.bluetoothadapter?view=xamarin-android-sdk-13
https://learn.microsoft.com/en-us/dotnet/api/android.bluetooth.bluetoothadapter.enable?view=xamarin-android-sdk-13

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Auger•12/12/23, 2:07 AM

@Bogdan , hope that helps

Original message was deleted

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Auger•12/12/23, 2:16 PM

Bluetooth sounds like the wrong technology for that kind of chat, and a more traditional, centralized backend sounds more appropriate. If location should be considered, you could make chat "rooms" based on the client's location with some radius requirement

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Auger•12/16/23, 5:01 PM

How many times is your Scan method invoked? You're probably registering to the DeviceDiscovered event multiple times causing your list to grow exponentially

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Auger•12/16/23, 5:01 PM

@Bogdan

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Auger•12/16/23, 5:02 PM

What you need to do is only register to that DeviceDiscovered event once, ever

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Auger•12/16/23, 5:03 PM

The constructor for your class is as good a place as any. Move that logic there, and keep the scan start logic where you've got it

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Auger•12/16/23, 5:17 PM

If you are starting a new scan, that's fine. You have to ask yourself if the old results are still relevant , or if they become stale

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Auger•12/16/23, 5:18 PM

A common way to display Bluetooth devices nearby is to also show the signal strength for each one

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Auger•12/16/23, 5:19 PM

Since devices can continuously come into range, go out of range, or similarly start broadcasting or stop broadcasting

XAMARIN.FORMS BLUETOOTH ISSUE

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