Execution failed for task ‘:app:installDebug’. com.android.builder.testing.api.DeviceException: No connected devices!

The error No connected devices! occurs when React Native cannot find any Android device or emulator to run your app on. This can happen if you don’t have a physical device connected or if you haven’t set up an Android emulator.

Step 1: Check if a Device is Connected

Here’s how to resolve this issue:

First, ensure that you have a physical Android device connected or a virtual Android device (emulator) running.

1. Connect a Physical Device:
   • Make sure your Android device is connected via USB.
   • Ensure that Developer Options and USB Debugging are enabled on your Android device. Here’s how:
     • Enable Developer Options:
       • Go to Settings > About phone > Tap Build number 7 times.
     • Enable USB Debugging:
       • Go to Settings > Developer options > Enable USB debugging.
   • Run the following command to ensure your device is detected:

adb devices 

1. If your device is listed, it’s connected properly.
2. Enable USB Debugging for Windows (if required):
   • Ensure that ADB drivers are installed on your Windows machine to allow the device to be detected.
   • Download and install Google USB Driver from Android Developer Site.

Step 2: Set Up an Android Emulator

If you don’t have a physical device, you can set up an Android emulator in Android Studio. Here’s how to do it:

1. Open Android Studio.
2. Create an Android Virtual Device (AVD):
   • Go to Tools > AVD Manager.
   • Click Create Virtual Device.
   • Choose a device model (e.g., Pixel 4).
   • Select a system image (e.g., a recent version of Android, such as API 29 or 30).
   • Follow the prompts to complete the setup.
3. Start the Emulator:
   • Once the AVD is created, click the green Play button next to your virtual device to start the emulator.
4. Verify the Emulator is Running:
   • Open Command Prompt and run:

adb devices 

1. This should list your emulator as a connected device (it will be labeled with something like emulator-5554).

Step 3: Run the React Native App Again

Now that your physical device or emulator is ready, try running the app again:

1. Navigate to your React Native project folder:

cd D:\ReactNativeProject\InsuranceApp

2. Run the app:

npx react-native run-android 

Step 4: Troubleshooting

If you’re still facing issues, here are a few troubleshooting steps:

1. Check Device Connection:
   • Run adb devices again to check if the device is listed. If not, unplug and reconnect your device, or restart your emulator.
2. Ensure Your Emulator is Running:
   • If using an emulator, make sure it’s running and not idle.
3. Restart the Metro Bundler:
   • Stop the current Metro bundler if it’s running (press Ctrl + C).
   • Start it again by running:

npx react-native start

1. Rebuild the Project:
   • Sometimes clearing build caches can help. Try cleaning the project and rebuilding it:

cd android 
gradlew clean 
cd .. 
npx react-native run-android

These steps should help you get your Android device or emulator connected and running the app. Let me know if you encounter any further issues!