Win8.1/10引入了多显示器DPI特性，允许对不同显示器指定不同DPI，窗口拖到不同DPI的显示器时，会通知程序动态进行缩放。但是目前为止，WPF的稳定版是不支持Win8.1/10的这种特性的。为了支持这个特性，必须安装最新版.NET框架4.6.2 Preview。

对于低于4.6.2版本的编译，默认是不响应DPI变化的，开启DPI响应需要修改app.config，如下所示：

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <runtime>
    
    <appcontextswitchoverrides value="Switch.System.Windows.DoNotScaleForDpiChanges=false">
  </appcontextswitchoverrides></runtime>
  <startup>
    <supportedruntime version="v4.0.30319">
  </supportedruntime></startup>
</configuration>

以上只是开启了WPF内部的DPI响应支持。在目前的4.6.2 Preview版本中，默认DPI级别还是等于1（支持系统级DPI），需要手动设置DPI级别为2（支持多显示器DPI）。暂时还没有找到用一般的方法如何改，在这里提供了一个用C#代码调用系统函数修改的方法。

首先在AssemblyInfo.cs中加入这一句，不让WPF自己设置DPI缩放级别：

[assembly: System.Windows.Media.DisableDpiAwareness()]

然后在App.cs中改成如下所示：

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Threading.Tasks;
using System.Windows;
using System.Runtime.InteropServices; // DllImport
using System.Diagnostics; // Debug
  
namespace WpfApplication8
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        [DllImport("kernel32.dll")]
        private static extern IntPtr LoadLibrary(string libname);
        [DllImport("kernel32.dll")]
        private static extern void FreeLibrary(IntPtr hlib);
        [DllImport("kernel32.dll", CharSet = CharSet.Ansi)]
        private static extern IntPtr GetProcAddress(IntPtr hlib, string procname);
        private delegate int ProcSetProcessDpiAwareness(int level);
        private delegate void ProcSetProcessDPIAware();
  
        static void Win7SetDPIAware()
        {
            IntPtr hUser32 = LoadLibrary("user32.dll");
            if (hUser32 != IntPtr.Zero)
            {
                IntPtr addrSetProcessDPIAware = GetProcAddress(hUser32, "SetProcessDPIAware");
                if (addrSetProcessDPIAware != IntPtr.Zero)
                {
                    ProcSetProcessDPIAware SetProcessDPIAware =
                        (ProcSetProcessDPIAware)
                        Marshal.GetDelegateForFunctionPointer(addrSetProcessDPIAware,
                            typeof(ProcSetProcessDPIAware));
                    SetProcessDPIAware();
                }
                FreeLibrary(hUser32);
            }
        }
  
        // 需要在AssemblyInfo.cs里面设置
        // [assembly: System.Windows.Media.DisableDpiAwareness()]
        static bool Win81SetDPIAware()
        {
            IntPtr hShcore = LoadLibrary("shcore.dll");
            if (hShcore != IntPtr.Zero)
            {
                IntPtr addrSetProcessDpiAwareness = GetProcAddress(hShcore, "SetProcessDpiAwareness");
                if (addrSetProcessDpiAwareness != IntPtr.Zero)
                {
                    // Win8.1以上版本，支持多显示器DPI
                    ProcSetProcessDpiAwareness SetProcessDpiAwareness =
                        (ProcSetProcessDpiAwareness)
                        Marshal.GetDelegateForFunctionPointer(addrSetProcessDpiAwareness,
                            typeof(ProcSetProcessDpiAwareness));
  
                    Type t = typeof(Window);
                    var evt = t.GetEvent("DpiChanged");
                    if (evt != null)
                    {
                        // 4.6.2新版WPF，支持DPI响应
                        // 需在app.config里面设置
                        // <runtime>
                        //   <appcontextswitchoverrides value="Switch.System.Windows.DoNotScaleForDpiChanges=false">
                        // </appcontextswitchoverrides></runtime>
                        if (SetProcessDpiAwareness(2) < 0)
                        {
                            Debug.WriteLine("SetProcessDpiAwareness(2) failed!");
                        }
                        else
                        {
                            Debug.WriteLine("SetProcessDpiAwareness(2) succeeded!");
                        }
                    }
                    else
                    {
                        // 旧版WPF，不支持DPI响应
                        SetProcessDpiAwareness(1);
                    }
                    FreeLibrary(hShcore);
                    return true;
                }
                else // 找不到SetProcessDpiAwareness
                {
                    FreeLibrary(hShcore);
                    return false;
                }
            }
            else // 找不到shcore.dll
            {
                return false;
            }
        }
  
        static App()
        {
            if (!Win81SetDPIAware())
            {
                Win7SetDPIAware();
            }
        }
    }
}