WPF阻止窗体被系统缩放，使用显示器DPI

WPF默认是跟随系统DPI变化（缩放与布局）而缩放窗体的；

微软把它称为默认DPI感知，当DPI发生变化时WPF感知到后缩放窗体，介绍链接：设置进程的默认 DPI 感知 (Windows) - Win32 apps | Microsoft Learn

如果我们不希望窗体被缩放，而是让窗体使用显示器DPI该怎么办呢?

首先修改app.manifest，如下xml改到对应的xml

  <application xmlns="urn:schemas-microsoft-com:asm.v3">
    <windowsSettings>
      <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true/pm</dpiAware>
      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
      <longPathAware xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">true</longPathAware>
    </windowsSettings>
  </application>

然后在创建窗体前添加如下代码就可以阻止窗体跟随系统缩放。

//TypeUtil -> https://www.cnblogs.com/RedSky/p/18215093
TypeUtil.InvokeMethod(null, 
    TypeUtil.GetType("PresentationCore", "System.LocalAppContext"), "DefineSwitchDefault",
    new Type[] { typeof(string), typeof(bool) },
    new object[] { "Switch.System.Windows.DoNotScaleForDpiChanges", true });
var v = TypeUtil.GetType("WindowsBase", "MS.Win32.NativeMethods+PROCESS_DPI_AWARENESS").GetEnumValues().GetValue(0);
TypeUtil.SetProperty(null, typeof(HwndTarget), "ProcessDpiAwareness", v);
TypeUtil.SetProperty(null, typeof(HwndTarget), "AppManifestProcessDpiAwareness", v);

但是之后Window的DpiChanged就不会起作用了，如果想要监听DPI变化可以重写窗体OnSourceInitialized，使用如下方法：

protected override void OnSourceInitialized(EventArgs e)
{
    var aa = (HwndSource)HwndSource.FromDependencyObject(this);
    aa.AddHook(new HwndSourceHook(HwndTargetFilterMessage));
    base.OnSourceInitialized(e);
}
private IntPtr HwndTargetFilterMessage(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    IntPtr result = IntPtr.Zero;
    //WindowMessage: https://referencesource.microsoft.com/#WindowsBase/Base/MS/Internal/Interop/NativeValues.cs
    result = HandleMessage((WindowMessage)msg, wParam, lParam);
    if (result != IntPtr.Zero)
        handled = true;

    return result;
}
internal IntPtr HandleMessage(WindowMessage msg, IntPtr wparam, IntPtr lparam)
{
    IntPtr result = IntPtr.Zero;
    switch (msg)
    {
        case WindowMessage.WM_DPICHANGED:
            Debug.WriteLine("WindowMessage.WM_DPICHANGED");
            break;
        case WindowMessage.WM_DPICHANGED_AFTERPARENT:
            Debug.WriteLine("WindowMessage.WM_DPICHANGED_AFTERPARENT");
            break;
    }
    return result;
}