A few improvements

build.gradle

@@ -1,6 +1,7 @@
 
 allprojects {
     repositories {
+        mavenLocal()
         mavenCentral()
         maven { url 'https://repo.gradle.org/gradle/libs-releases' }
     }

plugin/src/main/java/com/ahasbini/tools/androidopencv/Constants.java

@@ -9,5 +9,6 @@ public class Constants {
     public static final String OPENCV_VERSION_ANDROID_SDK_EXTRACTED_DIRECTORY_NAME = "opencv-%s-android-sdk";
     public static final String OPENCV_AAR_NAME_PREFIX = "opencv";
     public static final String EXTRACTED_OPENCV_ROOT_DIRECTORY_NAME = "OpenCV-android-sdk";
+    public static final String GRADLE_VERSION = null;
 
 }

plugin/src/main/java/com/ahasbini/tools/androidopencv/task/BuildAndroidOpenCVAarsTask.java

@@ -17,12 +17,14 @@
 import org.gradle.tooling.BuildLauncher;
 import org.gradle.tooling.GradleConnector;
 import org.gradle.tooling.ProjectConnection;
+import org.gradle.util.GradleVersion;
 
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.StandardOpenOption;
 import java.util.ArrayList;
+import java.util.Optional;
 import java.util.ResourceBundle;
 
 /**
@@ -182,10 +184,14 @@ private void performBuildAndroidOpenCVAars() {
                     ExceptionUtils.getCauses(e, messages.getString("caused_by")), e);
         }
 
+        String gradleVersion = Optional.ofNullable(Constants.GRADLE_VERSION)
+                .orElse(GradleVersion.current().getVersion());
+        logger.info("Use GradleVersion: " + gradleVersion);
+
         // Build AAR binaries
         try (ProjectConnection buildCacheProjectConnection = GradleConnector.newConnector()
                 .forProjectDirectory(androidOpenCVBuildCacheDir)
-                .useGradleVersion("4.1")
+                .useGradleVersion(gradleVersion)
                 .connect()) {
 
             BuildLauncher launcher = buildCacheProjectConnection.newBuild()

sample/build.gradle

@@ -5,6 +5,7 @@ buildscript {
         google()
         maven { url "https://plugins.gradle.org/m2/" }
         maven { url 'https://repo.gradle.org/gradle/libs-releases' }
+        mavenLocal()
     }
     dependencies {
         //noinspection GradleDependency
@@ -18,6 +19,7 @@ repositories {
     jcenter()
     google()
     mavenCentral()
+    mavenLocal()
 }
 
 apply plugin: 'com.android.application'

sample/src/main/java/com/ahasbini/sample/MainActivity.java

@@ -58,7 +58,7 @@ protected void onResume() {
         super.onResume();
         if (!OpenCVLoader.initDebug()) {
             Log.i(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initiation");
-            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_4_0, this, mLoaderCallback);
+            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, mLoaderCallback);
         } else {
             Log.i(TAG, "OpenCV library found inside package. Using it");
             mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);