Focus issue on Form Load

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你的背包 2021-01-29 05:32

I have an ActiveX control (written in VB 6.0 or C++ maybe) that we are using as an AxInterop in a C# WinForms program. It is very much like a text box but with some special logi

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-上瘾入骨i (楼主)

2021-01-29 06:06

You can use the WindowsApi.SetFocus method to set the focus.
This method can be used to set a focus on a specific control in an external application, so it should work in your application on a 3rd party control.

Here is another option - a working block of code to set focus for a control in an external application in winforms:

    [DllImport("user32.dll")]
    static extern IntPtr GetWindowThreadProcessId(IntPtr hWnd, IntPtr ProcessId);
    [DllImport("kernel32.dll")]
    static extern IntPtr GetCurrentThread();

    [DllImport("user32.dll")]
    static extern bool AttachThreadInput(IntPtr idAttach, IntPtr idAttachTo,  bool fAttach);

    [DllImport("user32.dll", SetLastError = true)]
    static extern bool BringWindowToTop(IntPtr hWnd);

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool SetForegroundWindow(IntPtr hWnd);

    [DllImport("User32.dll", EntryPoint = "FindWindow")]
    public static extern IntPtr FindWindow(String lpClassName, String lpWindowName);
    [DllImport("user32.dll")]
    static extern IntPtr SetFocus(IntPtr hWnd);

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool EnumChildWindows(IntPtr hwndParent, EnumWindowsProc lpEnumFunc, string  lParam);
    private delegate bool EnumWindowsProc(IntPtr hWnd, string className);

    [DllImport("user32.dll")]
    static extern uint RealGetWindowClass(IntPtr hwnd, [Out] StringBuilder pszType,   uint cchType);


    void SetFocus(IntPtr hwndTarget, string childClassName)
    {
        // hwndTarget is the other app's main window 
        // ...
        IntPtr targetThreadID = GetWindowThreadProcessId(hwndTarget, IntPtr.Zero); //target thread id
        IntPtr myThreadID = GetCurrentThread(); // calling thread id, our thread id

        bool lRet = AttachThreadInput(myThreadID, targetThreadID, true); // attach current thread id to target window

        // if it's not already in the foreground...
        lRet = BringWindowToTop(hwndTarget);
        SetForegroundWindow(hwndTarget);

        // Enumerate and find target to set focus on
        EnumChildWindows(hwndTarget, OnChildWindow, childClassName);
    }

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