Why Does My C# WebBrowser Control's AJAX Calls Differ From Internet Explorer, and How Can I Fix It?

Troubleshooting AJAX Inconsistencies in C# WebBrowser Controls

Problem: Your C# WPF application (.NET 4) using a WebBrowser control might experience AJAX call discrepancies compared to a full Internet Explorer (IE) browser. This often manifests as a persistent "Your request is being processed" message without completion.

Root Cause: The WebBrowser control's rendering engine doesn't always perfectly mirror IE's behavior. This incompatibility can affect JavaScript and AJAX functionality.

Solution: Feature Control via Registry Manipulation

The key to resolving this is adjusting the WebBrowser control's emulation mode using Feature Control. This involves modifying registry settings to align the control's behavior more closely with a specific IE version. The following code avoids requiring administrator privileges by targeting the current user's registry.

Code Example:

This code snippet sets the FEATURE_BROWSER_EMULATION registry key to match a detected IE version. It also demonstrates a function to retrieve the appropriate emulation mode based on the installed IE version. Remember to add the necessary using statements for Microsoft.Win32 and System.

<code class="language-csharp">private void SetBrowserFeatureControlKey(string feature, string appName, uint value)
{
    using (var key = Registry.CurrentUser.CreateSubKey(
        $@"Software\Microsoft\Internet Explorer\Main\FeatureControl\{feature}",
        RegistryKeyPermissionCheck.ReadWriteSubTree))
    {
        key.SetValue(appName, (uint)value, RegistryValueKind.DWord);
    }
}

private uint GetBrowserEmulationMode()
{
    uint mode = 11000; // Default to IE11 emulation
    try
    {
        using (var ieKey = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Internet Explorer"))
        {
            var version = ieKey?.GetValue("svcVersion") ?? ieKey?.GetValue("Version");
            if (version != null)
            {
                if (int.TryParse(version.ToString().Split('.')[0], out int browserVersion))
                {
                    switch (browserVersion)
                    {
                        case 7: mode = 7000; break;
                        case 8: mode = 8000; break;
                        case 9: mode = 9000; break;
                        case 10: mode = 10000; break;
                    }
                }
            }
        }
    }
    catch { /* Ignore registry access errors */ }
    return mode;
}

private void SetBrowserFeatureControl()
{
    uint mode = GetBrowserEmulationMode();
    SetBrowserFeatureControlKey("FEATURE_BROWSER_EMULATION", Application.ProductName, mode);
}


// Call SetBrowserFeatureControl() before initializing the WebBrowser control.  For example:
public MainWindow()
{
    SetBrowserFeatureControl();
    InitializeComponent();
}</code>

Important Considerations:

• Error Handling: The GetBrowserEmulationMode function includes basic error handling to gracefully manage potential registry access issues.
• Application Name: The Application.ProductName property is used to identify your application within the registry. You might need to adjust this if your application's name differs.
• Further Feature Controls: While FEATURE_BROWSER_EMULATION is crucial, other Feature Controls might be necessary depending on the specific AJAX issues encountered. Consult Microsoft's documentation for a comprehensive list.

By implementing this solution, you should achieve greater consistency between your WebBrowser control and full IE, resolving the AJAX problems. Remember to test thoroughly after implementing these changes.

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