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AddHostObjectToScript does not work in MAUI app (at least for WINDOWS). #26848

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eveselov opened this issue Dec 27, 2024 · 1 comment
Open

AddHostObjectToScript does not work in MAUI app (at least for WINDOWS). #26848

eveselov opened this issue Dec 27, 2024 · 1 comment
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area-controls-webview WebView platform/windows 🪟 t/bug Something isn't working

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@eveselov
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Description

I am struggling with adding HostObject to jscript for WebView in MAUI app (for WINDOWS). I created a simplest MAUI app from scratch to avoid any special aspects of my own code, It's now the simplest possible:

MainPage.xaml:

<ScrollView>
    <VerticalStackLayout
        <WebView
            x:Name="HtmlWebView"
            HeightRequest="500"
            WidthRequest="300" />

        <Button
            x:Name="CounterBtn"
            Text="Click me" 
            Clicked="OnCounterClicked"
            HorizontalOptions="Fill" />
    </VerticalStackLayout>
</ScrollView>

MainPage.xaml.cs:

namespace MauiApp1 {
public partial class MainPage : ContentPage {
public MainPage() {
this.InitializeComponent();
}

    private void OnCounterClicked(object sender, EventArgs e) {
        this.HtmlWebView.Source = new HtmlWebViewSource {
            Html = "<html><body><h1>Hello!</h1><button onclick='alert(\"Test\"); window.host.HelloWorld()'>Click Me</button></body></html>"
        };
    }
}

}

MauiProgram.cs:

namespace MauiApp1 {
public static class MauiProgram {
public static MauiApp CreateMauiApp() {
var builder = MauiApp.CreateBuilder();
builder = builder
.UseMauiApp();
#if WINDOWS
builder = builder.ConfigureMauiHandlers(handlers => {
handlers.AddHandler(typeof(WebView), typeof(MauiApp1.Platforms.Windows.CustomWebViewHandler));
});
#endif

        return builder.Build();
    }
}

}

JavaScriptHost.cs (in Platforms/Windows):

using Microsoft.Maui.Handlers;
using Microsoft.UI.Xaml.Controls;
using System.Diagnostics;

namespace MauiApp1.Platforms.Windows {
public class CustomWebViewHandler : WebViewHandler {
protected override async void ConnectHandler(WebView2 platformView) {
base.ConnectHandler(platformView);
try {
if (platformView.CoreWebView2 == null) {
await platformView.EnsureCoreWebView2Async();
if (platformView.CoreWebView2 == null) {
Debug.WriteLine("WebView2 initialization failed");
return;
}
}
platformView.CoreWebView2.AddHostObjectToScript("host", new JavaScriptHost());
Debug.WriteLine("WebView2 initialized");
} catch (Exception ex) {
Debug.WriteLine($"WebView2 initialization failed: {ex}");
}
}
}

public class JavaScriptHost {
    public JavaScriptHost() {
        Debug.WriteLine("JavaScriptHost created");
    }

    public void HelloWorld() {
        Debug.WriteLine("Call from jscript received");
    }
}

}

Whatever I am trying to do with this, I am having the same SystemError error in this call:

platformView.CoreWebView2.AddHostObjectToScript("host", new JavaScriptHost());

Steps to Reproduce

  1. Create a new MAUI app
  2. Replace the content of MainPage.xaml, MainPage.xaml.cs, MauiProgram.cs
  3. Add JavaScriptHost.cs under Platforms/Windows
  4. Run the app
  5. Set breakpoint in JavaScriptHost.cs on platformView.CoreWebView2.AddHostObjectToScript("host", new JavaScriptHost());
  6. Click "Click Me" button

Result: exception thrown from AddHostObjectToScript

Link to public reproduction project repository

No response

Version with bug

9.0.21 SR2.1

Is this a regression from previous behavior?

No, this is something new

Last version that worked well

No response

Affected platforms

Windows

Affected platform versions

WINDOWS

Did you find any workaround?

I have to use "post" from jscript to pass information from WebView to C#

Relevant log output


      		
    

      
  





        



            

              
            

        

      


      
    








      

    



      

  
            

    

      
    

    


      

          @eveselov
eveselov




          added
  the 

  t/bug

  Something isn't working
 label


      Dec 27, 2024

    

  








      

  
      



  

  @jfversluis





  


    

      

  

    

        
    
    

  


      
          
  
      
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Result: exception thrown from AddHostObjectToScript




What exception? Do you have some details?

      		
    

  





        


            

            

              
            

        

      


      

            
  

    
  
    
    

  

  



    












      

  
            











  
  

    

      

  





  




  
  

              

  
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          @eveselov