WPF 获取系统 DPI 的多种方法
由于 WPF 的尺寸单位和系统的 DPI 相关，我们有时需要获取 DPI 值来进行一些界面布局的调整，本文汇总了一些 WPF 程序中获取系统 DPI 的方法。

首先，定义如下结构体来分别保存 X 方向 和 Y 方向的分量值，通常情况下两个值是一致的。

public struct Dpi
{
public double X { get; set; }

public double Y { get; set; }

public Dpi(double x, double y)
{
X = x;
Y = y;
}
} 
CompositionTarget
public static Dpi GetDpiFromVisual(Visual visual)
{
var source = PresentationSource.FromVisual(visual);

var dpiX = 96.0;
var dpiY = 96.0;

if (source?.CompositionTarget != null)
{
dpiX = 96.0 * source.CompositionTarget.TransformToDevice.M11;
dpiY = 96.0 * source.CompositionTarget.TransformToDevice.M22;
}

return new Dpi(dpiX, dpiY);
} 
Win32 API
private const int LOGPIXELSX = 88;
private const int LOGPIXELSY = 90;

[DllImport(“gdi32.dll”)]
private static extern int GetDeviceCaps(IntPtr hdc, int index);

[DllImport(“user32.dll”)]
private static extern IntPtr GetDC(IntPtr hWnd);

[DllImport(“user32.dll”)]
private static extern int ReleaseDC(IntPtr hWnd, IntPtr hDc);

public static Dpi GetDpiByWin32()
{
var hDc = GetDC(IntPtr.Zero);

var dpiX = GetDeviceCaps(hDc, LOGPIXELSX);
var dpiY = GetDeviceCaps(hDc, LOGPIXELSY);

ReleaseDC(IntPtr.Zero, hDc);
return new Dpi(dpiX, dpiY);
} 
SystemParameters
public static Dpi GetDpiBySystemParameters()
{
const BindingFlags bindingFlags = BindingFlags.NonPublic | BindingFlags.Static;

var dpiXProperty = typeof(SystemParameters).GetProperty(“DpiX”, bindingFlags);
var dpiYProperty = typeof(SystemParameters).GetProperty(“DpiY”, bindingFlags);

var dpiX = 96.0;
var dpiY = 96.0;

if (dpiXProperty != null)
{
dpiX = (double)dpiXProperty.GetValue(null, null);
}

if (dpiYProperty != null)
{
dpiY = (double)dpiYProperty.GetValue(null, null);
}

return new Dpi(dpiX, dpiY);
} 
Graphics
添加 System.Drawing 引用

public static Dpi GetDpiByGraphics()
{
double dpiX;
double dpiY;

using (var graphics = Graphics.FromHwnd(IntPtr.Zero))
{
dpiX = graphics.DpiX;
dpiY = graphics.DpiY;
}

return new Dpi(dpiX, dpiY);
} 
ManagementClass
System.Management 引用

public static Dpi GetDpiByManagement()
{
var dpiX = 96.0;
var dpiY = 96.0;

using (var mc = new ManagementClass(“Win32_DesktopMonitor”))
{
using (var moc = mc.GetInstances())
{
// there may be many, to filter the ones you are interested in
foreach (var mo in moc)
{
dpiX = double.Parse(mo.Properties[“PixelsPerXLogicalInch”].Value.ToString());
dpiY = double.Parse(mo.Properties[“PixelsPerYLogicalInch”].Value.ToString());
}
}
}

return new Dpi(dpiX, dpiY);
} 
处于 跨平台、多屏幕、性能 等方面的综合考虑，推荐使用 CompositionTarget 方法。另外，监听系统 DPI 变化的方法：

SystemEvents.DisplaySettingsChanged – SystemEvents Class
WM_DPICHANGED message
参考资料
Best way to get DPI value in WPF
How can I get the DPI in WPF? 

原文链接：https://blog.csdn.net/Iron_Ye/article/details/83053393