[Hello-NativeAOTFromAndroid] Add instructions for building on Windows

samples/Hello-NativeAOTFromAndroid/Hello-NativeAOTFromAndroid.csproj

@@ -17,6 +17,8 @@
     <RuntimeIdentifier Condition=" '$(RuntimeIdentifier)' == '' ">linux-bionic-arm64</RuntimeIdentifier>
     <!-- Needed for cross-compilation, e.g. build linux-bionic-arm64 from osx-x64 -->
     <PlatformTarget>AnyCPU</PlatformTarget>
+    <!-- Needed so that we can use NativeAOT to cross-compile for Android (linux) from Windows -->
+    <DisableUnsupportedError Condition=" '$(OS)' == 'Windows_NT' ">true</DisableUnsupportedError>
   </PropertyGroup>
 
   <ItemGroup>

samples/Hello-NativeAOTFromAndroid/Hello-NativeAOTFromAndroid.targets

@@ -15,20 +15,29 @@
     <_NdkClangPrefix Condition=" '$(RuntimeIdentifier)' == 'linux-bionic-arm64' ">aarch64-linux-android21-</_NdkClangPrefix>
     <_NdkSysrootAbi Condition=" '$(RuntimeIdentifier)' == 'linux-bionic-x64' ">x86_64-linux-android</_NdkSysrootAbi>
     <_NdkClangPrefix Condition=" '$(RuntimeIdentifier)' == 'linux-bionic-x64' ">x86_64-linux-android21-</_NdkClangPrefix>
-    <_NdkPrebuiltAbi Condition=" '$(NETCoreSdkRuntimeIdentifier)' == 'osx-x64' ">darwin-x86_64</_NdkPrebuiltAbi>
+    <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('osx')) ">darwin-x86_64</_NdkPrebuiltAbi>
+    <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('linux')) ">linux-x86_64</_NdkPrebuiltAbi>
+    <_NdkPrebuiltAbi Condition=" $([MSBuild]::IsOSPlatform('windows')) ">windows-x86_64</_NdkPrebuiltAbi>
     <_NdkSysrootLibDir>$(AndroidNdkDirectory)/toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/sysroot/usr/lib/$(_NdkSysrootAbi)</_NdkSysrootLibDir>
     <_NdkBinDir>$(AndroidNdkDirectory)/toolchains/llvm/prebuilt/$(_NdkPrebuiltAbi)/bin</_NdkBinDir>
   </PropertyGroup>
 
   <PropertyGroup Condition="$(RuntimeIdentifier.StartsWith('linux-bionic'))">
-    <CppCompilerAndLinker>$(_NdkBinDir)/$(_NdkClangPrefix)clang</CppCompilerAndLinker>
-    <ObjCopyName>$(_NdkBinDir)/llvm-objcopy</ObjCopyName>
+    <CppCompilerAndLinker Condition=" '$(OS)' == 'Windows_NT' ">$(_NdkClangPrefix)clang.cmd</CppCompilerAndLinker>
+    <CppCompilerAndLinker Condition=" '$(OS)' != 'Windows_NT' ">$(_NdkBinDir)/$(_NdkClangPrefix)clang</CppCompilerAndLinker>
+    <ObjCopyName Condition=" '$(OS)' == 'Windows_NT' ">llvm-objcopy.exe</ObjCopyName>
+    <ObjCopyName Condition=" '$(OS)' != 'Windows_NT' ">$(_NdkBinDir)/llvm-objcopy</ObjCopyName>
   </PropertyGroup>
 
   <ItemGroup Condition="$(RuntimeIdentifier.StartsWith('linux-bionic'))">
     <LinkerArg Include="-Wl,--undefined-version" />
   </ItemGroup>
 
+  <PropertyGroup>
+    <_HomeDir Condition=" '$(OS)' != 'Windows_NT' ">$(HOME)/</_HomeDir>
+    <_HomeDir Condition=" '$(OS)' == 'Windows_NT' ">$(HOMEDRIVE)$(HOMEPATH)\</_HomeDir>
+  </PropertyGroup>
+
   <Target Name="_ValidateEnvironment"
       BeforeTargets="Build">
     <Error
@@ -43,6 +52,20 @@
         Condition=" '$(AndroidSdkDirectory)' == '' Or !Exists($(AndroidSdkDirectory)) "
         Text="Set the %24(AndroidSdkDirectory) MSBuild property or the %24ANDROID_HOME environment variable to the path of the Android SDK."
      />
+    <PropertyGroup>
+      <_DebugKeystorePath>$(_HomeDir).android/debug.keystore</_DebugKeystorePath>
+    </PropertyGroup>
+    <Error
+        Condition=" !Exists($(_DebugKeystorePath)) "
+        Text="Keystore file `$(_DebugKeystorePath)` does not exist.  This is needed to sign .apk files.  See README.md for details."
+    />
+    <PropertyGroup>
+      <_WinNdkBinDir>$(_NdkBinDir.Replace('/', '%5c'))</_WinNdkBinDir>
+    </PropertyGroup>
+    <Error
+        Condition=" '$(OS)' == 'Windows_NT' And !$(PATH.Contains($(_WinNdkBinDir))) "
+        Text="The %PATH% environment variable must contain: $(_WinNdkBinDir)"
+    />
   </Target>
 
   <ItemGroup>

samples/Hello-NativeAOTFromAndroid/README.md

@@ -6,6 +6,46 @@ by a Java Virtual Machine (JVM).
 
 Extend this idea for Android!
 
+## Prerequisites
+
+In order to build this sample, the Android SDK and Android NDK must be present.
+*An* easy way to provision these is to build dotnet/android:
+
+  * [Windows build instructions](https://github.com/dotnet/android/blob/155709f9917666ca046c79a4e9769924ff4ab9bb/Documentation/building/windows/instructions.md)
+  * [Linux and macOS build instructions](https://github.com/dotnet/android/blob/main/Documentation/building/unix/instructions.md)
+
+Once you've run `make prepar` or `dotnet  msbuild Xamarin.Android.sln -t:Prepare`,
+then an `android-toolchain` directory will exist in your home directory.
+
+A `.android/debug.keystore` file must also exist within your home directory.
+This file can be created by using
+[`keytool -genkeypair`](https://docs.oracle.com/en/java/javase/11/tools/keytool.html).
+
+  * On **Windows**, run the following command within a `CMD.EXE` window:
+
+    ```cmd
+    %HOMEDRIVE%%HOMEPATH%\android-toolchain\jdk-17\bin\keytool.exe -genkeypair ^
+      -keyalg RSA -validity 10950 -dname "CN=Android Debug,O=Android,C=US" ^
+      -keystore %HOMEDRIVE%%HOMEPATH%\.android\debug.keystore ^
+      -alias androiddebugkey -storepass android -keypass android
+    ```
+
+  * On **Linux** and **macOS**, run:
+
+    ```sh
+    $HOME/android-toolchain/jdk-17/bin/keytool -genkeypair \
+      -keyalg RSA -validity 10950 -dname "CN=Android Debug,O=Android,C=US" \
+      -keystore $HOME/.android/debug.keystore \
+      -alias androiddebugkey -storepass android -keypass android
+    ```
+
+The NativeAOT toolchain on Windows also requires that the NDK "prebuilt"
+directory be located within `%PATH%`
+
+```cmd
+set PATH=%HOMEDRIVE%%HOMEPATH%\android-toolchain\ndk\toolchains\llvm\prebuilt\windows-x86_64\bin;%PATH%
+```
+
 ## Building
 
 Building a native library with NativeAOT requires a Release configuration build.