按标题激活表单 System.NullReferenceException

Question

所以我有一个带有 ComboBox 的表单，其中填充了一个打开的进程列表（在这种情况下，我将其限制为标题为 13 个字符的进程。）当我 select ComboBox 中的 Item 我想按标题找到 Form 和 BringToFront 但是当我这样做时，它会抛出 System.NullReferenceException.

这是我用来填充框的代码。

using HWND = IntPtr;
public static class OpenWindowGetter
{
    /// <summary>Returns a dictionary that contains the handle and title of all the open windows.</summary>
    /// <returns>A dictionary that contains the handle and title of all the open windows.</returns>
    public static IDictionary<HWND, string> GetOpenWindows()
    {
        HWND shellWindow = GetShellWindow();
        Dictionary<HWND, string> windows = new Dictionary<HWND, string>();

        EnumWindows(delegate (HWND hWnd, int lParam)
        {
            if (hWnd == shellWindow) return true;
            if (!IsWindowVisible(hWnd)) return true;

            int length = GetWindowTextLength(hWnd);
            if (length == 0) return true;

            StringBuilder builder = new StringBuilder(length);
            GetWindowText(hWnd, builder, length + 1);

            windows[hWnd] = builder.ToString();
            return true;

        }, 0);

        return windows;
    }

    private delegate bool EnumWindowsProc(HWND hWnd, int lParam);

    [DllImport("USER32.DLL")]
    private static extern bool EnumWindows(EnumWindowsProc enumFunc, int lParam);

    [DllImport("USER32.DLL")]
    private static extern int GetWindowText(HWND hWnd, StringBuilder lpString, int nMaxCount);

    [DllImport("USER32.DLL")]
    private static extern int GetWindowTextLength(HWND hWnd);

    [DllImport("USER32.DLL")]
    private static extern bool IsWindowVisible(HWND hWnd);

    [DllImport("USER32.DLL")]
    private static extern IntPtr GetShellWindow();
}

public void populateIncidents()
    {
        foreach (KeyValuePair<IntPtr, string> window in OpenWindowGetter.GetOpenWindows())
        {
            IntPtr handle = window.Key;
            string title = window.Value;
            if (title.Length == 13)
            {
                chooseIncidentBox.Items.Add(title);
            }
        }
    }

这是我用来显示表单的代码。

private void chooseIncidentBox_SelectedIndexChanged(object sender, EventArgs e)
    {
        sSelectedIncident = chooseIncidentBox.Text;
        Application.OpenForms[sSelectedIncident].BringToFront(); //Exception thrown here.
    }

我不太确定它为什么抛出异常，我知道表单存在，否则它不会填充 ComboBox。任何帮助将不胜感激。

Answer 1

您拥有的代码提供了所有活动 windows。现在，Application.OpenForms 仅适用于在您的应用程序中打开的表单。例如，如果您的应用程序中有 ParentForm 和 ChildForm 并且都已打开，则 OpenForms 集合将包含这两个。

你要找的是把任何进程window放在前面。您可以使用 User32.dll 中的 SetForegroundWindow 来做到这一点。 This SO 问题看起来与您需要的非常相似。看看公认的解决方案。

按标题激活表单 System.NullReferenceException

Activating Form By Title Throws System.NullReferenceException

c#

combobox

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bringtofront