com.android.builder.testing.api.DeviceException: No connected devices

Question

Scanning folders for symlinks in /home/sino/Desktop/we-clone/node_modules (4ms) Starting JS server... Building and installing the app on the device (cd android && ./gradlew installDebug)... Incremental java compilation is an incubating feature. :app:preBuild UP-TO-DATE :app:preDebugBuild UP-TO-DATE :app:checkDebugManifest :app:preReleaseBuild UP-TO-DATE :app:prepareComAndroidSupportAppcompatV72301Library UP-TO-DATE :app:prepareComAndroidSupportSupportV42301Library UP-TO-DATE :app:prepareComFacebookFbuiTextlayoutbuilderTextlayoutbuilder100Library UP-TO-DATE :app:prepareComFacebookFrescoDrawee130Library UP-TO-DATE :app:prepareComFacebookFrescoFbcore130Library UP-TO-DATE :app:prepareComFacebookFrescoFresco130Library UP-TO-DATE :app:prepareComFacebookFrescoImagepipeline130Library UP-TO-DATE :app:prepareComFacebookFrescoImagepipelineBase130Library UP-TO-DATE :app:prepareComFacebookFrescoImagepipelineOkhttp3130Library UP-TO-DATE :app:prepareComFacebookReactReactNative0493Library UP-TO-DATE :app:prepareComFacebookSoloaderSoloader010Library UP-TO-DATE :app:prepareOrgWebkitAndroidJscR174650Library UP-TO-DATE :app:prepareDebugDependencies :app:compileDebugAidl UP-TO-DATE :app:compileDebugRenderscript UP-TO-DATE :app:generateDebugBuildConfig UP-TO-DATE :app:mergeDebugShaders UP-TO-DATE :app:compileDebugShaders UP-TO-DATE :app:generateDebugAssets UP-TO-DATE :app:mergeDebugAssets UP-TO-DATE :app:generateDebugResValues UP-TO-DATE :app:generateDebugResources UP-TO-DATE :app:mergeDebugResources UP-TO-DATE :app:bundleDebugJsAndAssets SKIPPED :app:processDebugManifest UP-TO-DATE :app:processDebugResources UP-TO-DATE :app:generateDebugSources UP-TO-DATE :app:incrementalDebugJavaCompilationSafeguard UP-TO-DATE :app:compileDebugJavaWithJavac UP-TO-DATE :app:compileDebugNdk UP-TO-DATE :app:compileDebugSources UP-TO-DATE :app:transformClassesWithDexForDebug UP-TO-DATE :app:mergeDebugJniLibFolders UP-TO-DATE :app:transformNative_libsWithMergeJniLibsForDebug UP-TO-DATE :app:processDebugJavaRes UP-TO-DATE :app:transformResourcesWithMergeJavaResForDebug UP-TO-DATE :app:validateSigningDebug :app:packageDebug UP-TO-DATE :app:assembleDebug UP-TO-DATE :app:installDebug 07:52:34 E/adb: * daemon not running; starting now at tcp:5037 07:52:37 E/adb: * daemon started successfully :app:installDebug FAILED  FAILURE: Build failed with an exception.  * What went wrong: Execution failed for task ':app:installDebug'. > com.android.builder.testing.api.DeviceException: No connected devices!  * Try: Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.  BUILD FAILED  Total time: 8.916 secs Could not install the app on the device, read the error above for details. Make sure you have an Android emulator running or a device connected and have set up your Android development environment: https://facebook.github.io/react-native/docs/android-setup.html 

Answer 1

If you have android studio installed(if not install it) launch android studio with a dummy project, go to Tools -> AVD Manager. Make sure that you create a virtual device and start it.

Note: To create this virtual device you will need to download and install a compatible OS (compatible with your project's Android SDK version - SDK version can be found inside build.gradle file) on it before launching. AVD Manager will guide you with the process.

Another thing, you may be using a real Android device not an emulator and still get this message. If your device is connected through USB to your laptop you need to first enable the developer options:

If using stock Android, go to Settings > About phone > Build number. On a Samsung Galaxy device, go to Settings > About device > Build number. On an HTC device, go to Settings > About > Software information > More > Build number. On an LG device, go to Settings > About phone > Software info > Build number. Tap Build number seven times. After the first few taps, you should see the steps counting down until you unlock the developer options. Once activated, you will see a message that reads, “You are now a developer!” Go back to Settings, where you’ll find a Developer options entry in the menu. (https://www.digitaltrends.com/mobile/how-to-get-developer-options-on-android/)

Then inside developer options, you should enable USB debugging.