如何强制执行我的应用程序的单个实例？

Question

如何确保我的应用程序只有一个实例，并在尝试打开第二个实例时为其设置焦点？

我试过了：

public partial class Form1 : Form {

    [DllImport("USER32.DLL", CharSet = CharSet.Unicode)]
    public static extern
    IntPtr FindWindow(String lpClassName, String lpWindowName);

    [DllImport("USER32.DLL")]
    public static extern
    Boolean SetForegroundWindow(IntPtr hWnd);

    private void Form1_Load(object sender, EventArgs e)
    {
        bool isRunning = Process.GetProcesses()
                                .Where(p => p.MainWindowTitle.Contains(Text))
                                .Count() > 1;

        if (isRunning)
        {
            FocusWindow(Text);
            Application.Exit();
        }
    }

    public static void FocusWindow(string title)
    {
        SetForegroundWindow(FindWindow(null, title));
    }
}

这不是应用程序的焦点。我该如何解决这个问题？

Answer 1

您可能想改用Mutex，这样可以避免以稍微不可靠的方式搜索窗口（假设您重命名主窗体或打开另一个窗体）。

bool createdNew;
Mutex m = new Mutex(true, "SomeNameHere", out createdNew);

if (!createdNew)
{
    // Application already running. Call it and ask to show it's form.
    IpcClientChannel clientChannel = new IpcClientChannel();
    ChannelServices.RegisterChannel(clientChannel, true);

    RemotingConfiguration.RegisterWellKnownClientType(typeof(ExchangeBase), "ipc://SomeNameHere/YourAppBase");

    ExchangeBase Exchange = new ExchangeBase();
    Exchange.ShowForm();
}
else
{
    IpcServerChannel serverChannel = new IpcServerChannel("SomeNameHere");
    ChannelServices.RegisterChannel(serverChannel, true);
    RemotingConfiguration.RegisterWellKnownServiceType(typeof(ExchangeBase), "YourAppBase", WellKnownObjectMode.SingleCall);

    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    MainForm = new FormMain();
    if (!MainForm.StopLoading)
    {
        Application.Run(MainForm);

        // Keep the mutex reference alive until the termination of the program.
        GC.KeepAlive(m);
    }
}

Answer 2

看起来您正在将 Text 作为参数传递给您的 FocusWindow 方法，但同时执行 Contains 检查。我敢打赌 Text 只是部分窗口标题，因此会导致 FindWindow 失败。尝试传递窗口句柄的全文，而不是像：

var proc = Process.GetProcesses()
                  .Where(p => p.MainWindowTitle.Contains(Text))
                  .FirstOrDefault();

        if (proc != null)
        {
            FocusWindow(p.MainWindowTitle);
            Application.Exit();
        }

Answer 3

可能是windows标题相同导致的，所以FindWindow获取实际的windows句柄，尝试使用EnumWindows函数代替FindWindow。

Answer 4

对表单加载执行此检查是不正确的。您应该使用Mutex 来确保只有一个应用程序实例正在运行。有关如何执行此操作以及将焦点设置到现有实例的示例，请参阅 this article。

Answer 5

将此代码放在您的 App.xaml.cs 文件中：

using System.Runtime.InteropServices;

#region SetWindowPos Definitions
[DllImport("user32.dll")]
static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter,
    int X, int Y, int cx, int cy, uint uFlags);

static readonly IntPtr HWND_TOPMOST = new IntPtr(-1);
static readonly IntPtr HWND_NOTOPMOST = new IntPtr(-2);
static readonly IntPtr HWND_TOP = new IntPtr(0);
static readonly IntPtr HWND_BOTTOM = new IntPtr(1);

const UInt32 SWP_NOSIZE = 0x0001;
const UInt32 SWP_NOMOVE = 0x0002;
const UInt32 SWP_NOZORDER = 0x0004;
const UInt32 SWP_NOREDRAW = 0x0008;
const UInt32 SWP_NOACTIVATE = 0x0010;
const UInt32 SWP_FRAMECHANGED = 0x0020;
const UInt32 SWP_SHOWWINDOW = 0x0040;
const UInt32 SWP_HIDEWINDOW = 0x0080;
const UInt32 SWP_NOCOPYBITS = 0x0100;
const UInt32 SWP_NOOWNERZORDER = 0x0200;
const UInt32 SWP_NOSENDCHANGING = 0x0400;
#endregion
#region OnStartup
protected override void OnStartup(StartupEventArgs e)
{
    // Only allow one instance of the application
    Process thisProc = Process.GetCurrentProcess();
    Process[] processes = Process.GetProcessesByName(thisProc.ProcessName);
    if (processes.Length > 1)
    {
        Application.Current.Shutdown();

        SetWindowPos(processes[1].MainWindowHandle, HWND_TOPMOST, 0, 0, 0, 0, 
            SWP_NOSIZE | SWP_NOMOVE);
        SetWindowPos(processes[1].MainWindowHandle, HWND_NOTOPMOST, 0, 0, 0, 0, 
            SWP_NOSIZE | SWP_NOMOVE);
    }
    else
    {
        base.OnStartup(e);
    }
}
#endregion