WPF App.xaml.cs常用模板，包括：异常捕获，App只能启动一次

App.xaml.cs中的代码每次都差不多，故特地将其整理出来直接复用：

using System;
using System.Configuration;
using System.Diagnostics;
using System.Globalization;
using System.Net;
using System.Net.Sockets;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Windows;

namespace WpfDemo
{
    /// <summary>
    /// App.xaml 的交互逻辑
    /// </summary>
    public partial class App : Application
    {
        private LoginWindow login = new LoginWindow();
        private ILog logger;

        static App()
        {
            log4net.Config.XmlConfigurator.Configure();
        }

        public App()
        {
            logger = LogManager.GetLogger(typeof(this));
        }

        System.Threading.Mutex _mutex;
        protected override void OnStartup(StartupEventArgs e)
        {
            Assembly assembly = Assembly.GetExecutingAssembly();
            string mutexName = string.Format(CultureInfo.InvariantCulture, "Local\{{{0}}}{{{1}}}", assembly.GetType().GUID, assembly.GetName().Name);
            bool ret = false;
            _mutex = new System.Threading.Mutex(true, mutexName, out ret);
            if (!ret)
            {
                this.logger.Info("已经运行程序，激活至主窗口.");
                HandleRunningInstance();
                Environment.Exit(0);
                return;
            }

            base.OnStartup(e);
            this.logger.Info("App startup.");
            this.ShutdownMode = System.Windows.ShutdownMode.OnExplicitShutdown;

            AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException;
            this.DispatcherUnhandledException += App_DispatcherUnhandledException;

            this.login.Show();
        }

        void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
        {
            try
            {
                var exception = e.ExceptionObject as Exception;
                if (exception != null)
                {
                    this.logger.FatalFormat("非UI线程全局异常, Message:{0}, Error: {1}", exception.Message, exception.ToString());
                }
            }
            catch (Exception ex)
            {
                this.logger.FatalFormat("非UI线程全局异常, Message:{0}, Error: {1}", ex.Message, ex.ToString());
            }
        }

        void App_DispatcherUnhandledException(object sender, System.Windows.Threading.DispatcherUnhandledExceptionEventArgs e)
        {
            try
            {
                e.Handled = true;
                this.logger.FatalFormat("UI线程全局异常：Meassage:{0}, Error: {1}", e.Exception.Message, e.Exception.ToString());
            }
            catch (Exception ex)
            {
                this.logger.FatalFormat("UI线程全局异常：Meassage:{0}, Error: {1}", ex.Message, ex.ToString());
            }
        }

        
        protected override void OnExit(ExitEventArgs e)
        {
            this.logger.Info("App exit.");
            
            base.OnExit(e);
        }

        ///<summary>
        /// 该函数设置由不同线程产生的窗口的显示状态
        /// </summary>
        /// <param name="hWnd">窗口句柄</param>
        /// <param name="cmdShow">指定窗口如何显示。查看允许值列表，请查阅ShowWlndow函数的说明部分</param>
        /// <returns>如果函数原来可见，返回值为非零；如果函数原来被隐藏，返回值为零</returns>
        [DllImport("User32.dll")]
        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);

        /// <summary>
        ///  该函数将创建指定窗口的线程设置到前台，并且激活该窗口。键盘输入转向该窗口，并为用户改各种可视的记号。
        ///  系统给创建前台窗口的线程分配的权限稍高于其他线程。 
        /// </summary>
        /// <param name="hWnd">将被激活并被调入前台的窗口句柄</param>
        /// <returns>如果窗口设入了前台，返回值为非零；如果窗口未被设入前台，返回值为零</returns>
        [DllImport("User32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);

        static Process RunningInstance()
        {
            Process current = Process.GetCurrentProcess();
            Process[] processes = Process.GetProcessesByName(current.ProcessName);
            foreach (Process process in processes)
            {
                if (process.Id != current.Id)
                {
                    if (process.MainModule.FileName == current.MainModule.FileName)
                    {
                        return process;
                    }
                }
            }
            return null;
        }

        private const int SW_NORMAL = 1;     //正常弹出窗体
        private const int SW_MAXIMIZE = 3;     //最大化弹出窗体

        public static void HandleRunningInstance()
        {
            var instance = RunningInstance();
            if (instance != null)
            {
                ShowWindowAsync(instance.MainWindowHandle, SW_NORMAL);
                SetForegroundWindow(instance.MainWindowHandle);
            }
        }
    }
}