MessageBox.Show() fails after WebView2 is added to form

[ftppro]

The code below exemplifies that MessageBox.Show() fails after WebView2 is added to a form.

MessageBox.Show("ok2") throws the following error, even though it is in a try block: System.ArgumentException: 'Value does not fall within the expected range.';

Microsoft.Web.WebView2.WinForms.WebView2 objWebView2 = new Microsoft.Web.WebView2.WinForms.WebView2();
objWebView2.Location = new System.Drawing.Point(10, 10);
objWebView2.Size = new System.Drawing.Size(800, 600);
objWebView2.Source = new Uri("https://www.google.com");
MessageBox.Show("ok1");
this.Controls.Add(objWebView2);
try
{
    MessageBox.Show("ok2");
}
catch { }

My versions: Windows 10 Home Version 2004, installed 5/29/20 Microsoft.Web.WebView2 v.0.9.538-prerelease Visual Studio 2017 version 15.0 .NET Framework 4.8.04084 Microsoft Edge Version 86.0.569 (Canary 64-bit)

[michael-russin]

Could you post the whole call stack?

[ftppro]

Here is the call stack when the error occurs:

[External Code] 
MyApp.exe!MyApp.Form1.DoLogin() Line 116    C#
[Resuming Async Method] 
[External Code] 
MyApp.exe!MyApp.Program.Main() Line 19  C#

If I add any Button to the Form, the error does not occur. If I set the Visible property of that Button to false, the error occurs.

[cgeier]

This is occurring because of MessageBox.Show("ok1");. If you comment it out (or remove it), the issue doesn't occur.

The issue can be reproduced by creating a new form. (name: Form1). Then adding the following code to the form "Load" event handler. Then, from the menu, select "Debug", "Start Debugging".

*Note: The issue doesn't occur if you select "Debug", "Start Without Debugging"

        private void Form1_Load(object sender, EventArgs e)
        {
            Microsoft.Web.WebView2.WinForms.WebView2 objWebView2 = new Microsoft.Web.WebView2.WinForms.WebView2();
            objWebView2.Location = new System.Drawing.Point(10, 10);
            objWebView2.Size = new System.Drawing.Size(800, 600);
            objWebView2.Source = new Uri("https://www.google.com");
            MessageBox.Show("ok1");
            this.Controls.Add(objWebView2);
            try
            {
                MessageBox.Show("ok2");
            }
            catch { }
        }

As you also stated, the issue doesn't seem to occur if you add a button to the form, and run the program by selecting "Debug", "Start Debugging"--as long as the button is visible. If you change button's "Visible" property to false, the issue occurs again. This issue doesn't occur if you comment out (or remove) MessageBox.Show("ok1");

Here's the stack trace:

System.ArgumentException
  HResult=0x80070057
  Message=Value does not fall within the expected range.
  Source=Microsoft.Web.WebView2.Core
  StackTrace:
   at Microsoft.Web.WebView2.Core.Raw.ICoreWebView2Controller.MoveFocus(COREWEBVIEW2_MOVE_FOCUS_REASON reason)
   at Microsoft.Web.WebView2.Core.CoreWebView2Controller.MoveFocus(CoreWebView2MoveFocusReason reason)
   at Microsoft.Web.WebView2.WinForms.WebView2.OnEnter(EventArgs e)
   at System.Windows.Forms.Control.NotifyEnter()
   at System.Windows.Forms.ContainerControl.UpdateFocusedControl()
   at System.Windows.Forms.ContainerControl.AssignActiveControlInternal(Control value)
   at System.Windows.Forms.ContainerControl.ActivateControlInternal(Control control, Boolean originator)
   at System.Windows.Forms.ContainerControl.SetActiveControlInternal(Control value)
   at System.Windows.Forms.ContainerControl.set_ActiveControl(Control value)
   at System.Windows.Forms.Control.Select(Boolean directed, Boolean forward)
   at System.Windows.Forms.Form.set_Active(Boolean value)
   at System.Windows.Forms.Form.WmActivate(Message& m)
   at System.Windows.Forms.Form.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

[ftppro]

The error still happens when MessageBox.Show("ok1"); is removed.

[cgeier]

If you're trying to output some debugging messages. I think that you'll get better results if you use System.Diagnostics.Debug.WriteLine("your message"); instead of MessageBox.Show("your message");. If you really want to use a MessageBox, you can do the following:

Thread t = new Thread(() => MessageBox.Show(text));
t.Start();

It's from a post on StackOverflow.

[cgeier]

Try to "Clean" your project, then re-compile (Build => Clean . Then, Build => Rebuild )

[ftppro]

'Cleaning' did not fix the problem.

[mikemeinz]

It appears that you are not waiting properly for WebView2 to initialize. Here is an example for you.

using System;
using System.Diagnostics;
using System.Windows.Forms;
using Microsoft.Web.WebView2.Core;
namespace WebView2
{
    public partial class WebView : Form
    {
        public WebView()
        {
            this.Load += WebView2Test_Load;
            InitializeComponent();
            webView2.CoreWebView2Ready += webView_CoreWebView2Ready;
            webView2.NavigationCompleted += browser_NavigationCompleted;
        }

        private void WebView2Test_Load(object sender, EventArgs e)
        {
            InitializeAsync();
        }

        async private void InitializeAsync()
        {
            await webView2.EnsureCoreWebView2Async(); // Wait for coreWebView2 initialization

        }
        private void browser_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Navigation Completed");
        }

        private void webView_CoreWebView2Ready(object sender, EventArgs e)
        {
            try
            {
                webView2.Source = new System.Uri("https://microsoft.com/", UriKind.Absolute);
            }
            catch (Exception ex)
            {
                Debug.Print(ex.ToString());
            }
        }
  }
}

[ftppro]

I took all the steps you suggested, and the problem still happens. Also, those steps don't explain why adding a button to the form causes the problem to not occur, and why that button must be visible.

[mikemeinz]

Show your source code.

[cgeier]

It looks like if one adds this.TopMost = true;, the issue doesn't occur.

private void Form1_Load(object sender, EventArgs e)
{
    this.TopMost = true;

    Microsoft.Web.WebView2.WinForms.WebView2 objWebView2 = new Microsoft.Web.WebView2.WinForms.WebView2();

    objWebView2.Location = new System.Drawing.Point(10, 10);
    objWebView2.Size = new System.Drawing.Size(800, 600);
    objWebView2.Source = new Uri("https://www.google.com");
    MessageBox.Show("ok1");
    this.Controls.Add(objWebView2);

    try
    {
        MessageBox.Show("ok2");
    }
    catch { }
}

This is the stack trace before adding this.TopMost = true;:

There's a post on StackOverflow, that may be useful.

[mikemeinz]

You are not properly waiting for Webview2 to initialize fully. That is root cause.

[ftppro]

I used exactly the code that was suggested, and the error still happened.

Adding "this.TopMost = true" just stopped the break from occurring when the error was thrown, and it made it impossible to close the app when debugging (by clicking the X in the upper right of the app's frame).

[mikemeinz]

The only code you have shown does not wait properly for Webview2 to fully initialize.

[ftppro]

Again, I used exactly the code that you suggested (including InitializeAsync, EnsureCoreWebView2Async(), and NavigationCompleted). The error still occurred. You still haven't explained why adding a do-nothing Button to the form eliminates the error.

[mikemeinz]

I can't answer any questions about causation until I see exactly what you are doing.

[cgeier]

It's probably better to know what you are trying to accomplish, rather than trying to figure out why your usage of MessageBox, for debugging purposes, isn't working. Or as @mikemeinz said, show your code. You can zip it up and attach it, if you don't want to paste it. If your project has a lot of code, create another project that only demonstrates your usage of the WebView2 control.

[mikemeinz]

I will try to explain the cause of the problem a bit differently. Because you are not properly waiting for initialization to finish before setting the Source property, Webview2 will eventually throw an exception. That exception will interrupt your program at whatever step it happens to be executing. Whether it is a Message Box, a For loop, a computation, etc. makes no difference. It fails because Webview2 throws the exception. The Call Stack display shows that it is Webview2 throwing the exception.

[cgeier]

Give the following code a try. It incorporates the code @mikemeinz posted, as well as some code from Getting started with WebView2 in Windows Forms apps (Preview). Add a form named "Form1" to your project, and then add the code below, changing the namespace name to your projects namespace.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Microsoft.Web.WebView2.Core;
using Microsoft.Web.WebView2.WinForms;
using Microsoft.Web.WebView2;
using System.Diagnostics;

namespace TestWebView2
{
    public partial class Form1 : Form
    {

        //create new instance of WebView2
        Microsoft.Web.WebView2.WinForms.WebView2 objWebView2 = new Microsoft.Web.WebView2.WinForms.WebView2();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            InitializeAsync();

            //set WebView2 properties and add to form
            objWebView2.Location = new System.Drawing.Point(10, 10);
            objWebView2.Size = new System.Drawing.Size(800, 600);
            objWebView2.Source = new Uri("about:blank");
            this.Controls.Add(objWebView2);

            try
            {
                MessageBox.Show("ok1");

                if (objWebView2 != null && objWebView2.CoreWebView2 != null)
                {
                    //navigate to website
                    objWebView2.CoreWebView2.Navigate("https://www.google.com"); //option 1
                    //objWebView2.Source = new Uri("https://www.google.com", UriKind.Absolute); //option 2
                }//if

                MessageBox.Show("ok2");

            }
            catch (Exception ex)
            {
                Debug.Print("Error (Form1_Load): " + ex.Message);
            }
        }

        private void ObjWebView2_CoreWebView2Ready(object sender, EventArgs e)
        {
            Debug.Print("Info: ObjWebView2_CoreWebView2Ready");  
        }

        private async void InitializeAsync()
        {
            // wait for coreWebView2 initialization
            await objWebView2.EnsureCoreWebView2Async();

            //add event handlers
            objWebView2.CoreWebView2Ready += ObjWebView2_CoreWebView2Ready;
            objWebView2.NavigationStarting += ObjWebView2_NavigationStarting;
            objWebView2.CoreWebView2.NavigationCompleted += CoreWebView2_NavigationCompleted;
            objWebView2.NavigationCompleted += ObjWebView2_NavigationCompleted;

        }
        private void ObjWebView2_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Info: ObjWebView2_NavigationCompleted");
        }

        private void CoreWebView2_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Info: CoreWebView2_NavigationCompleted");
        }

        private void ObjWebView2_NavigationStarting(object sender, CoreWebView2NavigationStartingEventArgs e)
        {
            Debug.Print("Info: Navigating to '" + objWebView2.Source + "'");
        }

    }
}

There isn't a lot of documentation yet, so any feedback on improvements to my code is welcomed.

[mikemeinz]

@cgeier I rearranged your code. It is important to not use WebView2 control until CoreWebView2Ready event is thrown.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Microsoft.Web.WebView2.Core;
using Microsoft.Web.WebView2.WinForms;
using Microsoft.Web.WebView2;
using System.Diagnostics;

namespace TestWebView2
{
    public partial class Form1 : Form
    {

        //create new instance of WebView2
        Microsoft.Web.WebView2.WinForms.WebView2 objWebView2 = new Microsoft.Web.WebView2.WinForms.WebView2();

        public Form1()
        {
            InitializeComponent();

            //add event handler
            objWebView2.CoreWebView2Ready += ObjWebView2_CoreWebView2Ready;
            //set WebView2 properties and add to form
            objWebView2.Location = new System.Drawing.Point(10, 10);
            objWebView2.Size = new System.Drawing.Size(800, 600);
            objWebView2.Source = new Uri("about:blank");
            this.Controls.Add(objWebView2);
         }

        private void Form1_Load(object sender, EventArgs e)
        {
            InitializeAsync();
        }

        private void ObjWebView2_CoreWebView2Ready(object sender, EventArgs e)
        {
            Debug.Print("Info: ObjWebView2_CoreWebView2Ready"); 
            try
            {
                MessageBox.Show("ok1");

                if (objWebView2 != null && objWebView2.CoreWebView2 != null)
                {
                    //navigate to website
                    objWebView2.CoreWebView2.Navigate("https://www.google.com"); //option 1
                    //objWebView2.Source = new Uri("https://www.google.com", UriKind.Absolute); //option 2
                }//if

                MessageBox.Show("ok2");
            }
            catch (Exception ex)
            {
                Debug.Print("Error (Form1_Load): " + ex.Message);
            } 
        }

        private async void InitializeAsync()
        {
            // wait for coreWebView2 initialization
            await objWebView2.EnsureCoreWebView2Async();

            //add event handlers
            objWebView2.NavigationStarting += ObjWebView2_NavigationStarting;
            objWebView2.CoreWebView2.NavigationCompleted += CoreWebView2_NavigationCompleted;
            objWebView2.NavigationCompleted += ObjWebView2_NavigationCompleted;

        }
        private void ObjWebView2_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Info: ObjWebView2_NavigationCompleted");
        }

        private void CoreWebView2_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Info: CoreWebView2_NavigationCompleted");
        }

        private void ObjWebView2_NavigationStarting(object sender, CoreWebView2NavigationStartingEventArgs e)
        {
            Debug.Print("Info: Navigating to '" + objWebView2.Source + "'");
        }

    }
}

[cgeier]

@mikemeinz thanks for the help improving the code. I've converted the code, that you re-arranged, to VB .NET. Perhaps it will be useful to someone.

Imports Microsoft.Web.WebView2.Core
Imports Microsoft.Web.WebView2.WinForms
Imports System.Diagnostics

Public Class Form1

    'create new instance of WebView2
    Dim objWebView2 As Microsoft.Web.WebView2.WinForms.WebView2 = New Microsoft.Web.WebView2.WinForms.WebView2()

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.

        'add event handler
        AddHandler objWebView2.CoreWebView2Ready, AddressOf ObjWebView2_CoreWebView2Ready

        'set WebView2 properties and add to form
        objWebView2.Location = New System.Drawing.Point(10, 10)
        objWebView2.Size = New System.Drawing.Size(800, 600)
        objWebView2.Source = New Uri("about:blank")
        Me.Controls.Add(objWebView2)

    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        InitializeAsync()

    End Sub

    Private Async Sub InitializeAsync()

        'wait for coreWebView2 initialization
        Await objWebView2.EnsureCoreWebView2Async()

        'add event handlers
        AddHandler objWebView2.NavigationStarting, AddressOf ObjWebView2_NavigationStarting
        AddHandler objWebView2.CoreWebView2.NavigationCompleted, AddressOf CoreWebView2_NavigationCompleted
        AddHandler objWebView2.NavigationCompleted, AddressOf ObjWebView2_NavigationCompleted

    End Sub

    Private Sub ObjWebView2_CoreWebView2Ready(ByVal sender As Object, ByVal e As System.EventArgs)

        Debug.Print("Info: ObjWebView2_CoreWebView2Ready")

        Try
            MessageBox.Show("ok1")

            If (objWebView2 IsNot Nothing AndAlso objWebView2 IsNot Nothing) Then
                objWebView2.CoreWebView2.Navigate("https://www.google.com") 'option 1
                'objWebView2.Source = New Uri("https://www.google.com", UriKind.Absolute) 'option 2

            End If

            MessageBox.Show("ok2")

        Catch ex As Exception
            Debug.Print("Error (ObjWebView2_CoreWebView2Ready): " + ex.Message)
        End Try

    End Sub

    Private Sub ObjWebView2_NavigationCompleted(ByVal sender As Object, ByVal e As Microsoft.Web.WebView2.Core.CoreWebView2NavigationCompletedEventArgs)

        Debug.Print("Info: ObjWebView2_NavigationCompleted")

    End Sub

    Private Sub CoreWebView2_NavigationCompleted(ByVal sender As Object, ByVal e As Microsoft.Web.WebView2.Core.CoreWebView2NavigationCompletedEventArgs)

        Debug.Print("Info: CoreWebView2_NavigationCompleted")

    End Sub

    Private Sub ObjWebView2_NavigationStarting(ByVal sender As Object, ByVal e As Microsoft.Web.WebView2.Core.CoreWebView2NavigationStartingEventArgs)

        Debug.Print("Info: ObjWebView2_NavigationStarting")

    End Sub
End Class

It's been a while since I've written any VB .NET code, so any suggestions for improvement are welcomed.

[cgeier]

@ftppro @mikemeinz

It appears that some of the code that I posted above is flawed.

C

Instead of:

private void Form1_Load(object sender, EventArgs e)
{
    ....
}

it should be:

private async void Form1_Load(object sender, EventArgs e)
{
    ....
}

Instead of:

private async void InitializeAsync()
{
    ....
}

it should be:

private async Task InitializeAsync()
{
    ....
}

This allows one to do the following:

private async void Form1_Load(object sender, EventArgs e)
{
    //initialize CoreWebView2
    await InitializeAsync();
}

without this "await" in the "Load" event handler, the code won't execute in the expected order.

Here's a corrected example:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Microsoft.Web.WebView2.Core;
using Microsoft.Web.WebView2.WinForms;
using System.Diagnostics;

namespace TestWebView2
{
    public partial class Form1 : Form
    {
        //create new instance of WebView2
        Microsoft.Web.WebView2.WinForms.WebView2 webView21 = new Microsoft.Web.WebView2.WinForms.WebView2();
        public Form1()
        {
            InitializeComponent();

            //set WebView2 properties and add to form
            webView21.Location = new System.Drawing.Point(10, 10);
            webView21.Size = new System.Drawing.Size(800, 600);

            //don't set source property here

            this.Controls.Add(webView21);
        }

        private async void Form1_Load(object sender, EventArgs e)
        {
            // add event handler
            webView21.CoreWebView2Ready += webView21_CoreWebView2Ready;

            Debug.Print("Info: initializing CoreWebView2");

            //initialize CoreWebView2
            await InitializeAsync();

            Debug.Print("Info: after initializing CoreWebView2");

            if (webView21 != null && webView21.CoreWebView2 != null)
            {
                //navigate to website - option 1
                webView21.Source = new Uri("https://www.microsoft.com", UriKind.Absolute);

                //navigate to website - option 2
                //webView21.CoreWebView2.Navigate("https://www.microsoft.com");
            }//if
        }

        private void webView21_CoreWebView2Ready(object sender, EventArgs e)
        {
            Debug.Print("Info: webView21_CoreWebView2Ready");

            //subscribe to events (add event handlers) - CoreWebView2
            webView21.CoreWebView2.NavigationCompleted += CoreWebView2_NavigationCompleted;

            //subscribe to events (add event handlers) - WebView2
            webView21.NavigationStarting += webView21_NavigationStarting;
            webView21.NavigationCompleted += webView21_NavigationCompleted;

            Debug.Print("Info: leaving webView21_CoreWebView2Ready");
        }

        private async Task InitializeAsync()
        {
            Debug.Print("Info: before EnsureCoreWebView2Async");

            // wait for coreWebView2 initialization
            await webView21.EnsureCoreWebView2Async();

            Debug.Print("Info: after EnsureCoreWebView2Async");
        }
        private void webView21_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Info: webView21_NavigationCompleted");
        }

        private void CoreWebView2_NavigationCompleted(object sender, CoreWebView2NavigationCompletedEventArgs e)
        {
            Debug.Print("Info: CoreWebView2_NavigationCompleted");
        }

        private void webView21_NavigationStarting(object sender, CoreWebView2NavigationStartingEventArgs e)
        {
            Debug.Print("Info: webView21_NavigationStarting - Navigating to '" + e.Uri.ToString() + "'");
        }
    }
}

[cgeier]

The VB .NET code I posted has the same flaw as mentioned for the C# code. One needs to call "InitializeAsync" with "Await" in the "Load" event handler, otherwise the code doesn't execute in the expected order. Below is the corrected code with some modifications.

VB .NET

Imports Microsoft.Web.WebView2.Core
Imports Microsoft.Web.WebView2.WinForms
Imports System.Threading.Tasks
Imports System.Diagnostics
Public Class Form1

    Private WithEvents WebView21 As Microsoft.Web.WebView2.WinForms.WebView2 = New Microsoft.Web.WebView2.WinForms.WebView2
    Private WithEvents CoreWebView21 As Microsoft.Web.WebView2.Core.CoreWebView2

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        'set WebView2 properties And add to form
        WebView21.Location = New System.Drawing.Point(10, 10)
        WebView21.Size = New System.Drawing.Size(800, 600)

        'don't set source property here

        Me.Controls.Add(WebView21)

    End Sub

    Private Async Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        Debug.Print("Info: initializing CoreWebView2")

        'initialize CoreWebView2
        Await InitializeAsync()

        Debug.Print("Info: after initializing CoreWebView2")

        'set value 
        CoreWebView21 = WebView21.CoreWebView2

        If (WebView21 IsNot Nothing AndAlso WebView21.CoreWebView2 IsNot Nothing) Then

            'navigate to website - option 1
            WebView21.Source = New Uri("https://www.microsoft.com", UriKind.Absolute)

            'navigate to website - option 2
            'WebView21.CoreWebView2.Navigate("https://www.microsoft.com")
        End If
    End Sub

    Private Async Function InitializeAsync() As Task

        Debug.Print("Info: before EnsureCoreWebView2Async")

        'wait for coreWebView2 initialization
        Await WebView21.EnsureCoreWebView2Async()

        Debug.Print("Info: after EnsureCoreWebView2Async")
    End Function

    Private Sub CoreWebView21_NavigationCompleted(sender As Object, e As CoreWebView2NavigationCompletedEventArgs) Handles CoreWebView21.NavigationCompleted
        Debug.Print("Info: CoreWebView21_NavigationCompleted")
    End Sub

    Private Sub WebView21_CoreWebView2Ready(ByVal sender As Object, ByVal e As System.EventArgs) Handles WebView21.CoreWebView2Ready
        Debug.Print("Info: WebView21_CoreWebView2Ready")

        Debug.Print("Info: leaving WebView21_CoreWebView2Ready")
    End Sub

    Private Sub WebView21_NavigationCompleted(sender As Object, e As CoreWebView2NavigationCompletedEventArgs) Handles WebView21.NavigationCompleted
        Debug.Print("Info: WebView21_NavigationCompleted")
    End Sub
    Private Sub WebView21_NavigationStarting(sender As Object, e As CoreWebView2NavigationStartingEventArgs) Handles WebView21.NavigationStarting
        Debug.Print("Info: WebView21_NavigationStarting - Navigating to '" & e.Uri.ToString() & "'")
    End Sub

End Class

[champnic]

Closing old issue. Please let me know if we need to re-open this for any reason.