Merge pull request #24473 from alexlyulkov:al/samples_with_maven

Updated Android samples for modern Android studio. Added OpenCV from Maven support. #24473

Updated samples for recent Android studio:

- added namespace field that is required in build.gradle files
- replaced _switch_ by _if-else_ because it doesn't work with constants from resources
- added missed log library dependency in face-detection/jni/CMakeLists.txt
- use local.properties to define NDK location

Added support for OpenCV from Maven. Now you can choose 3 possible sources of OpenCV lib in settings.gradle: SDK path, local Maven repository, public Maven repository. (Creating Maven repository from SDK is added here #24456 )

There are differences in project configs for SDK and Maven versions:

- different dependencies in build.gradle
- different OpenCV library names in CMakeLists.txt
- SDK version requires OpenCV_DIR definition

Requires:
- https://github.com/opencv/ci-gha-workflow/pull/124
- https://github.com/opencv-infrastructure/opencv-gha-dockerfile/pull/26

samples/android/tutorial-2-mixedprocessing/build.gradle.in

@@ -1,6 +1,7 @@
 apply plugin: 'com.android.application'
 
 android {
+    namespace 'org.opencv.samples.tutorial2'
     compileSdkVersion @ANDROID_COMPILE_SDK_VERSION@
     defaultConfig {
         applicationId "org.opencv.samples.tutorial2"
@@ -11,7 +12,14 @@ android {
 
         externalNativeBuild {
             cmake {
-                arguments "-DOpenCV_DIR=" + project(':opencv').projectDir + "/@ANDROID_PROJECT_JNI_PATH@"@OPENCV_ANDROID_CMAKE_EXTRA_ARGS@
+                if (gradle.opencv_source == "sdk_path") {
+                    arguments "-DOpenCV_DIR=" + project(':opencv').projectDir + "/@ANDROID_PROJECT_JNI_PATH@",
+                              "-DOPENCV_FROM_SDK=TRUE"@OPENCV_ANDROID_CMAKE_EXTRA_ARGS@
+
+                } else {
+                    arguments "-DOPENCV_VERSION_MAJOR=@OPENCV_VERSION_MAJOR@",
+                              "-DOPENCV_FROM_SDK=FALSE"@OPENCV_ANDROID_CMAKE_EXTRA_ARGS@
+                }
                 targets "mixed_sample"
             }
         }
@@ -35,9 +43,18 @@ android {
              path '@ANDROID_SAMPLE_JNI_PATH@/CMakeLists.txt'
         }
     }
+    buildFeatures {
+        if (gradle.opencv_source == "maven_local" || gradle.opencv_source == "maven_cenral") {
+            prefab true
+        }
+    }
 }
 
 dependencies {
     //implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation project(':opencv')
+    if (gradle.opencv_source == "sdk_path") {
+        implementation project(':opencv')
+    } else if (gradle.opencv_source == "maven_local" || gradle.opencv_source == "maven_cenral") {
+        implementation 'org.opencv:opencv:@OPENCV_VERSION_PLAIN@'
+    }
 }

samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt

@@ -3,7 +3,12 @@ cmake_minimum_required(VERSION 3.6)
 set(target mixed_sample)
 project(${target} CXX)
 
-set(ANDROID_OPENCV_COMPONENTS "opencv_java" CACHE STRING "")
+if (OPENCV_FROM_SDK)
+  set(ANDROID_OPENCV_COMPONENTS "opencv_java" CACHE STRING "")
+else()
+  set(ANDROID_OPENCV_COMPONENTS "OpenCV::opencv_java${OPENCV_VERSION_MAJOR}" CACHE STRING "")
+endif()
+
 message(STATUS "ANDROID_ABI=${ANDROID_ABI}")
 find_package(OpenCV REQUIRED COMPONENTS ${ANDROID_OPENCV_COMPONENTS})