C# 如何使用.Net Core在单个实例中更改主窗口状态

我正试图将我的应用程序只保留一个实例

public partial class App : Application {

private static Mutex _mutex = null;

protected override void OnStartup(StartupEventArgs e)
{
    const string appName = "MyAppName";
    bool createdNew;

    _mutex = new Mutex(true, appName, out createdNew);

    if (!createdNew)
    {
        Application.Current.Shutdown();
    }

    base.OnStartup(e);
}          

代码工作正常，但我想操纵已经打开的窗口

当我打开多个实例时，如何将已打开的窗口向前移动

public partial class App : Application {

private static Mutex _mutex = null;

protected override void OnStartup(StartupEventArgs e)
{
    const string appName = "MyAppName";
    bool createdNew;

    _mutex = new Mutex(true, appName, out createdNew);

    if (!createdNew)
    {
        Application.Current.Shutdown();
    }

    base.OnStartup(e);
}          

}

---

在

OnStartup

中，我尝试使用

MainWindow.WindowState=WindowState.Normal调用窗口但调用失败，注意到错误System.Windows.Application.MainWindow.get返回null
我在WPF中为单实例应用程序创建了一个示例项目。也许有帮助：


您需要以下本机方法：

public static class NativeMethod
{
    public static IntPtr BroadcastHandle => (IntPtr)0xffff;
    public static int ReactivationMessage => RegisterWindowMessage("WM_SHOWME");

    [DllImport("user32")]
    public static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);
    [DllImport("user32")]
    public static extern int RegisterWindowMessage(string message);
}

在应用程序主窗口中添加钩子到窗口消息，当您收到激活消息时，应将主窗口置于其他窗口的顶部。像这样：

public partial class MainWindow
{
    public MainWindow()
    {
        InitializeComponent();
        RegisterWndProcCallback();
    }

    private void RegisterWndProcCallback()
    {
        var handle = new WindowInteropHelper(this).EnsureHandle();
        var hock = new HwndSourceHook(WndProc);
        var source = HwndSource.FromHwnd(handle);

        source.AddHook(hock);
    }

    private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        if (msg == NativeMethod.ReactivationMessage)
            ReactivateMainWindow();

        return IntPtr.Zero;
    }

    private void ReactivateMainWindow()
    {
        if (WindowState == WindowState.Minimized)
            WindowState = WindowState.Normal;

        Topmost = !Topmost;
        Topmost = !Topmost;
    }
}

public partial class App
{
    private static readonly Mutex _singleInstanceMutex =
        new Mutex(true, "{40D7FB99-C91E-471C-9E34-5D4A455E35E1}");

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        if (_singleInstanceMutex.WaitOne(TimeSpan.Zero, true))
        {
            Current.MainWindow = new MainWindow();
            Current.MainWindow.Show();
            Current.MainWindow.Activate();

            _singleInstanceMutex.ReleaseMutex();
        }
        else
        {
            NativeMethod.PostMessage(
                NativeMethod.BroadcastHandle,
                NativeMethod.ReactivationMessage,
                IntPtr.Zero,
                IntPtr.Zero);

            Current.Shutdown();
        }
    }
}

在应用程序启动时，您应该检查应用程序实例，如果需要，您应该向旧实例发送消息并激活该实例。像这样：

public partial class MainWindow
{
    public MainWindow()
    {
        InitializeComponent();
        RegisterWndProcCallback();
    }

    private void RegisterWndProcCallback()
    {
        var handle = new WindowInteropHelper(this).EnsureHandle();
        var hock = new HwndSourceHook(WndProc);
        var source = HwndSource.FromHwnd(handle);

        source.AddHook(hock);
    }

    private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        if (msg == NativeMethod.ReactivationMessage)
            ReactivateMainWindow();

        return IntPtr.Zero;
    }

    private void ReactivateMainWindow()
    {
        if (WindowState == WindowState.Minimized)
            WindowState = WindowState.Normal;

        Topmost = !Topmost;
        Topmost = !Topmost;
    }
}

public partial class App
{
    private static readonly Mutex _singleInstanceMutex =
        new Mutex(true, "{40D7FB99-C91E-471C-9E34-5D4A455E35E1}");

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        if (_singleInstanceMutex.WaitOne(TimeSpan.Zero, true))
        {
            Current.MainWindow = new MainWindow();
            Current.MainWindow.Show();
            Current.MainWindow.Activate();

            _singleInstanceMutex.ReleaseMutex();
        }
        else
        {
            NativeMethod.PostMessage(
                NativeMethod.BroadcastHandle,
                NativeMethod.ReactivationMessage,
                IntPtr.Zero,
                IntPtr.Zero);

            Current.Shutdown();
        }
    }
}

从复制子进程使用Win32的
PostMessage
（通过其主窗口句柄）向原始进程发送消息。