WPF使用Mutex创建单实例程序失效

vs2019

1.引入名称空间

using System.Threading;

using System.Runtime.InteropServices;

2.导入dll并声明方法

    [DllImport("User32", CharSet = CharSet.Unicode)]

 static extern IntPtr FindWindowW(string lpClassName, string lpWindowName);

   [DllImport("User32", CharSet = CharSet.Unicode)]

  static extern Boolean SetForegroundWindow(IntPtr hWnd);

3 修改后App.xaml.cs如下

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Runtime.InteropServices;
using System.Threading;
using System.Windows;

namespace WpfApp1
{
    /// <summary>
    /// App.xaml 的交互逻辑
    /// </summary>
    public partial class App : Application    {
        
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);
            Mutex mutex = new Mutex(true, "单实例", out bool isNewInstance);//“单实例”是MainWindow.xaml中的Title
            if (isNewInstance != true)
            {

                IntPtr intPtr = FindWindowW(null, "单实例");
                if (intPtr != IntPtr.Zero)
                {
                    SetForegroundWindow(intPtr);
                }
                Shutdown();
            }
        }
      
        [DllImport("User32", CharSet = CharSet.Unicode)]
        static extern IntPtr FindWindowW(string lpClassName, string lpWindowName);

        [DllImport("User32", CharSet = CharSet.Unicode)]
        static extern Boolean SetForegroundWindow(IntPtr hWnd);
    }

}

运行生成后的exe程序发现没有实现单实例的效果。

4重新修改App.xaml.cs文件

前面是将mutex声明为局部变量

Mutex mutex = new Mutex(true, "单实例", out bool isNewInstance);//“单实例”是MainWindow.xaml中的Title

这次将mutex声明为字段

...
Mutex mutex;
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);
             mutex = new Mutex(true, "单实例", out bool isNewInstance);
            if (isNewInstance != true)
            {

                IntPtr intPtr = FindWindowW(null, "单实例");
                if (intPtr != IntPtr.Zero)
                {
                    SetForegroundWindow(intPtr);
                }
                Shutdown();
            }
        }
...

重新生成后实现效果