Callback return

[LeoDecking]

Could you implement the possibility to return something from c# to javascript?

Example:

C#:

WebView.AddLocalCallback("square", (str) => 
{
    int i = int.Parse(str);
    return i*i;
});

JavaScript:

var s = square(5);

[Jacko1394]

I'm also interested in this as it's the way the XLabs one does it.

How is the webapp to request data from the Native CSharp code?

[ravinderjangra]

Did you find any solution yet? @LeoDecking , @Jacko1394

[Jacko1394]

Without making changes to Ryan's source code, this is how I achieved a Callback return value from C# to Javascript:

C#

public class Bridge {
  public const string Wait = "WAIT";
  public static EventHandler<string> OnPromiseCompleted;

  public static async Task<string> TheNativeFunction(string json) {
    // json param is from javascript code
    Trace.WriteLine(json);
    // do c sharp stuff here...
    var result = "{\"success\": true}" // json value to return to javascript
    return result;
  }
}

public class ViewModel {

  public FormsWebView WebView { get; set; }

  public void Init() {
    // This is used to complete bridge functions that involve some time to complete:
    Bridge.OnPromiseCompleted += CompletePromise;

    FormsWebView.AddGlobalCallback("xamarinCode", async (string arg) => {

      string result;

      try {
        IsBusy = true;
        result = await Bridge.TheNativeFunction(arg);
      } catch (Exception ex) {
        result = ex.Message;
      }

      if (result == Bridge.Wait) {
        Trace.WriteLine("WAITING....");
        return;
      }
      CompletePromise(null, result);
    });

  }

  private async void CompletePromise(object sender, string result) {
    try {
      await WebView.InjectJavascriptAsync($"nativeReturn({result});");
    } catch (Exception ex) {
      Trace.WriteLine(ex.Message);
    }
    IsBusy = false;
  }
}

Javascript

var nativeReturn;

// Bridge function:
send: function(data) {
  return new Promise(function(resolve, reject) {
    try {
      nativeReturn = resolve; // sets reference for native code to return to
      let encoded = encodeURIComponent(JSON.stringify(data)); // this is the data to send to c#
      xamarinCode(encoded); // sends command to native c#
    } catch (e) {
      console.log(e);
      reject(e);
    }
  });
}

// USAGE:
send('command json goes here').then(function(result) {
  console.log(result); // promise completes
});

[ravinderjangra]

Thanks, @Jacko1394. I'll try using this and it'll be great if you can share other references as well (if you have something in mind).