ChromeDevToolsSystemMenu does not exist in the current context in CefSharp

To resolve the issue, you need to create the missing method, as it’s not included in the CefSharp library.

This solution involves using DllImport to reference system functions. You’ll need to import System.Runtime.InteropServices in your form.

using System.Runtime.InteropServices;

Create the ChromeDevToolsSystemMenu class:

private static class ChromeDevToolsSystemMenu
{
    // P/Invoke constants
    public const int WM_SYSCOMMAND = 0x112;
    private const int MF_STRING = 0x0;
    private const int MF_SEPARATOR = 0x800;

    // ID for the Chrome DevTools item on the system menu
    public const int SYSMENU_CHROME_DEV_TOOLS = 0x1;

    // P/Invoke declarations
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern bool AppendMenu(IntPtr hMenu, int uFlags, int uIDNewItem, string lpNewItem);

    // Method to create the system menu
    public static void CreateSysMenu(Form frm)
    {
        // Override OnHandleCreated in your form and call this method:
        // protected override void OnHandleCreated(EventArgs e)
        // {
        //     ChromeDevToolsSystemMenu.CreateSysMenu(frm);
        // }

        // Get the handle for the form's system menu
        var hSysMenu = GetSystemMenu(frm.Handle, false);

        // Add a separator to the menu
        AppendMenu(hSysMenu, MF_SEPARATOR, 0, string.Empty);

        // Add the "Chrome Dev Tools" menu item
        AppendMenu(hSysMenu, MF_STRING, SYSMENU_CHROME_DEV_TOOLS, "&Chrome Dev Tools");
    }
}

You’ll need to initialize it and handle the events by overriding the WndProc method in your form class.

Override the WndProc method:

/// <summary>
/// Note: Replace the <chromeBrowser> variable with your own instance of ChromiumWebBrowser.
/// </summary>
protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);

    // Check if the "Chrome Dev Tools" menu item was selected
    if ((m.Msg == ChromeDevToolsSystemMenu.WM_SYSCOMMAND) && ((int)m.WParam == ChromeDevToolsSystemMenu.SYSMENU_CHROME_DEV_TOOLS))
    {
        chromeBrowser.ShowDevTools();  // Show Chrome DevTools
    }
}

Make sure to replace chromeBrowser with your own instance of ChromiumWebBrowser as indicated in the summary.

Call the ChromeDevToolsSystemMenu.CreateSysMenu method in your form's constructor:

public Form1()
{ 
    // Initialize components and Chromium
    InitializeComponent();
    InitializeChromium();

    // Add the "Show Chrome Dev Tools" option to the form's icon menu
    ChromeDevToolsSystemMenu.CreateSysMenu(this);
}

Now, you can use the ChromeDevToolsSystemMenu method in your form class without encountering errors. It’s a good practice to enable this functionality in your form's constructor for proper initialization.