.NET 中的平台特定代码如何条件编译？

<span style="color:blue;">#if</span> WINDOWS
    Console.WriteLine("运行在 Windows 上");
<span style="color:blue;">#elif</span> LINUX
    Console.WriteLine("运行在 Linux 上");
<span style="color:blue;">#elif</span> OSX
    Console.WriteLine("运行在 macOS 上");
<span style="color:blue;">#else</span>
    Console.WriteLine("未知平台");
<span style="color:blue;">#endif</span>

<PropertyGroup Condition="'$(OS)' == 'Windows_NT'">
  <DefineConstants>WINDOWS;DEBUG</DefineConstants>
</PropertyGroup>

<PropertyGroup Condition="'$(OS)' == 'Unix'">
  <DefineConstants>UNIX;LINUX;DEBUG</DefineConstants>
</PropertyGroup>

<PropertyGroup Condition="'$(TargetFramework)' == 'net8.0-android'">
  <DefineConstants>ANDROID;MOBILE</DefineConstants>
</PropertyGroup>

<span style="color:blue;">#if</span> WINDOWS
    <span style="color:darkgreen;">// 使用 PowerShell</span>
    var cmd = "powershell.exe";
<span style="color:blue;">#else</span>
    <span style="color:darkgreen;">// 使用 shell</span>
    var cmd = "/bin/bash";
<span style="color:blue;">#endif</span>

<span style="color:blue;">#if</span> ANDROID || IOS
    // 移动设备专用逻辑
    var path = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
<span style="color:blue;">#else</span>
    // 桌面端路径
    var path = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "MyApp");
<span style="color:blue;">#endif</span>

<span style="color:blue;">#if</span> DEBUG && WINDOWS
    #error 正在 Windows 调试模式下编译
<span style="color:blue;">#endif</span>