Addressing code review comments

build-android.cmd

@@ -2,15 +2,14 @@
 pushd "%~dp0"
 
 REM Users may override the default %ANDROID_SDK_ROOT% location if necessary
-if not "%ANDROID_SDK_ROOT%" == "" goto proceed
-  echo Set default Android SDK paths
-  set "ANDROID_NDK_VERSION=21.1.6352462"
-  set "ANDROID_CMAKE_VERSION=3.10.2.4988404"
-  set "ANDROID_SDK_ROOT=C:\Android\android-sdk"
-  set "ANDROID_HOME=%ANDROID_SDK_ROOT%"
-  set "ANDROID_NDK=%ANDROID_SDK_ROOT%\ndk\%ANDROID_NDK_VERSION%"
-  set "ANDROID_NDK_HOME=%ANDROID_NDK%"
-:proceed
+
+if "%ANDROID_SDK_ROOT%"      == "" set "ANDROID_SDK_ROOT=C:\Android\android-sdk"
+if "%ANDROID_NDK_VERSION%"   == "" set "ANDROID_NDK_VERSION=21.1.6352462"
+if "%ANDROID_CMAKE_VERSION%" == "" set "ANDROID_CMAKE_VERSION=3.10.2.4988404"
+if "%ANDROID_HOME%"          == "" set "ANDROID_HOME=%ANDROID_SDK_ROOT%"
+if "%ANDROID_NDK%"           == "" set "ANDROID_NDK=%ANDROID_SDK_ROOT%\ndk\%ANDROID_NDK_VERSION%"
+if "%ANDROID_NDK_HOME%"      == "" set "ANDROID_NDK_HOME=%ANDROID_NDK%"
+REM Consider using %ANDROID_NDK_ROOT% environment variable
 
 REM Install Android tools if necessary
 call tools\setup-buildtools-android.cmd

docs/cpp-start-android.md

@@ -17,6 +17,21 @@ The Room database implementation adds one additional initialization requirement,
 
 If you are building on Windows, this helper script [build-android.cmd](../build-android.cmd) is provided to illustrate how to deploy the necessary SDK and NDK dependencies. Once you installed the necessary dependencies, you may use Android Studio IDE for local builds. See [ide.cmd](../lib/android_build/ide.cmd) that shows how to build the project from IDE. The `app` project (`maesdktest`) allows to build and run all SDK tests on either emulator or real Android device. While the tests are running, you can monitor the test results in logcat output.
 
+Default environment variables used by `build-android.cmd` script:
+
+```console
+
+set "ANDROID_NDK_VERSION=21.1.6352462"
+set "ANDROID_CMAKE_VERSION=3.10.2.4988404"
+set "ANDROID_SDK_ROOT=C:\Android\android-sdk"
+set "ANDROID_HOME=%ANDROID_SDK_ROOT%"
+set "ANDROID_NDK=%ANDROID_SDK_ROOT%\ndk\%ANDROID_NDK_VERSION%"
+set "ANDROID_NDK_HOME=%ANDROID_NDK%"
+
+```
+
+You can specify your own versions of dependencies as needed.
+
 ## 3. Integrate the SDK into your C++ project
 
 If you use the lib/android_build Gradle files, they build the SDK into maesdk.aar in the output folders of the maesdk module in lib/android. You can package or consume this AAR in your applications modules, just as you would any other AAR.

lib/android_build/ide.cmd

@@ -6,13 +6,12 @@ for /F "usebackq skip=2 tokens=1-2*" %%A in (`reg.exe QUERY "HKLM\Software\Andro
 
 echo Android Studio Path: %AndroidStudioPath%
 set "PATH=%AndroidStudioPath%\bin;%PATH%"
-if "%ANDROID_SDK_ROOT%"== "" (
-  echo Set default Android SDK path ...
-  set "ANDROID_SDK_ROOT=C:\Android\android-sdk"
-  set "ANDROID_HOME=%ANDROID_SDK_ROOT%"
-  set "ANDROID_NDK=%ANDROID_SDK_ROOT%\ndk\21.1.6352462"
-  set "ANDROID_NDK_HOME=%ANDROID_NDK%"
-)
+
+if "%ANDROID_SDK_ROOT%"   == "" set "ANDROID_SDK_ROOT=C:\Android\android-sdk"
+if "%ANDROID_HOME%"       == "" set "ANDROID_HOME=%ANDROID_SDK_ROOT%"
+if "%ANDROID_NDK_VERSION%"== "" set "ANDROID_NDK_VERSION=21.1.6352462"
+if "%ANDROID_NDK%"        == "" set "ANDROID_NDK=%ANDROID_SDK_ROOT%\ndk\%ANDROID_NDK_VERSION%"
+if "%ANDROID_NDK_HOME%"   == "" set "ANDROID_NDK_HOME=%ANDROID_NDK%"
 
 where studio.bat >NUL 2>NUL
 if %ERRORLEVEL% neq 0 (

lib/android_build/tools.gradle

@@ -1,10 +1,14 @@
 android {
-    compileSdkVersion 29
-    buildToolsVersion "29.0.3"
-    ndkVersion "21.1.6352462"
+
+    compileSdkVersion    = 29
+
+    buildToolsVersion    = "29.0.3"
+
+    ndkVersion           = System.getenv("ANDROID_NDK_VERSION") ?: "21.1.6352462"
+
     defaultConfig {
-        minSdkVersion 19
-        targetSdkVersion 29
+        minSdkVersion    = 19
+        targetSdkVersion = 29
     }
 }
 

tools/setup-buildtools-android.cmd

@@ -26,7 +26,7 @@ if exist ".buildtools" (
   echo y | call sdkmanager.bat --include_obsolete --verbose --sdk_root=%ANDROID_SDK_ROOT% "platforms;android-29" "sources;android-29"
   echo y | call sdkmanager.bat --include_obsolete --verbose --sdk_root=%ANDROID_SDK_ROOT% "build-tools;29.0.3"
   echo y | call sdkmanager.bat --include_obsolete --verbose --sdk_root=%ANDROID_SDK_ROOT% "platform-tools"
-  echo y | call sdkmanager.bat --install --include_obsolete --verbose --sdk_root=%ANDROID_SDK_ROOT% "ndk-bundle" "cmake;3.10.2.4988404" "ndk;21.1.6352462"
+  echo y | call sdkmanager.bat --install --include_obsolete --verbose --sdk_root=%ANDROID_SDK_ROOT% "ndk-bundle" "cmake;%ANDROID_CMAKE_VERSION%" "ndk;%ANDROID_NDK_VERSION%"
   popd
   popd
   copy NUL .buildtools