Develop Reference

app:compileDebugJavaWithJavac'. > Could not find tools.jar Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds`

when I use this command in the terminal:
PS C:\web dev\practice-projects\react-native\myproject> react-native run-android --no-jetifier
I get this whole error:
info JS server already running.
'adb' is not recognized as an internal or external command,
operable program or batch file.
info Launching emulator...
error
Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds`.
warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
info Installing the app...
Starting a Gradle Daemon, 1 stopped Daemon could not be reused, use --status for details
> Task :app:compileDebugJavaWithJavac FAILED
Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.2/userguide/command_line_interface.html#sec:command_line_warning
14 actionable tasks: 2 executed, 12 up-to-date
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':app:compileDebugJavaWithJavac'.
> Could not find tools.jar. Please check that C:\Program Files\Java\jre1.8.0_271 contains a valid JDK installation.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 39s
error Failed to install the app. Make sure you have the Android development environment set up: https://reactnative.dev/docs/environment-setup. Run CLI with --verbose flag for more details.
Error: Command failed: gradlew.bat app:installDebug -PreactNativeDevServerPort=8081
My emulator isn't being launched and I have tried multiple fixes. I am getting started in react-native and don't understand the warnings or answers on similar questions. Please help.

There are few ways you can run your app,
Always works - Open the app from android studio. Select Open existing project and select android folder in your app to open the project and run from there after indexing is done.
Not sure would work and not recommended (might need release build) but you can drag your apk file that is auto generated to your simulator to install.
Add this line to gradle.properties file i.e. android/gradle.properties.
org.gradle.java.home=/Library/Java/JavaVirtualMachines/jdk1.8.0_271.jdk/Contents/Home. replace the jdk version name or directory if required.
Note for mac - this is not library folder within your user directory so search them in your main drive location - should be something like machintosh hd
For windows - just replace the path after org.gradle.java.home=. Should be something like C:\\Program Files\\Java\\jdk1.8.0_144

In my case it was because the JAVA_HOME path could not find it.
Close all terminals and open a new one
Find a directory like this on your Mac:
/Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home
What may change is the version, but once you have it, it runs in that
path:
export JAVA_HOME = / Library / Java / JavaVirtualMachines /
jdk1.8.0_91.jdk / Contents / Home
IN MY CASE I RUN THIS COMMAND AT THE ROOT OF THE REACT NATIVE PROJECT:
export JAVA_HOME=/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home
AND IT WORKED.

React Native Android

I already installed Android Studio and all the required tools and SDK version based on the documentation of react-native, I also followed all the instructions on the documentation. however , I dont understand this error, I'm new to react-native.
info Running jetifier to migrate libraries to AndroidX. You can disable it using "--no-jetifier" flag.
Jetifier found 967 file(s) to forward-jetify. Using 4 workers...
info JS server already running.
/bin/sh: adb: command not found
info Launching emulator...
error Failed to launch emulator. Reason: No emulators found as an output of emulator -list-avds.
warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
info Installing the app...
Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.2/userguide/command_line_interface.html#sec:command_line_warnings
FAILURE: Build failed with an exception.
What went wrong:
Could not determine the dependencies of task ':app:installDebug'.
SDK location not found. Define location with an ANDROID_SDK_ROOT environment variable or by setting the sdk.dir path in your project's local properties file at '/Users/rochesterpeduche/Desktop/AwesomeTSProject/android/local.properties'.
Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
Get more help at https://help.gradle.org
BUILD FAILED in 2s
error Failed to install the app. Make sure you have the Android development environment set up: https://reactnative.dev/docs/environment-setup. Run CLI with --verbose flag for more details.
Error: Command failed: ./gradlew app:installDebug -PreactNativeDevServerPort=8081

You need to set environment variable for android sdk like this :
Go to File explorer and right click
Then go to properties and select Advance system settings
Then select Environment Variables
Then select User Variables and path variable inside that
Then add path to your android SDK as shown in above image and click save and check!!!!

React Native run-android Only works on the first build

The first time I run my react-native app the emulator works (using Android Studio Galaxy Nexus). However, when I close the emulator and try again I get the errors below:
PS C:\Users\4chea\pexhouseV2> react-native run-android
info Running jetifier to migrate libraries to AndroidX. You can disable it using "--no-jetifier" flag.
Jetifier found 1197 file(s) to forward-jetify. Using 8 workers...
info Starting JS server...
info Launching emulator...
error Failed to launch emulator. Reason: Emulator exited before boot..
warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
info Installing the app...
> Task :app:stripDebugDebugSymbols UP-TO-DATE
Compatible side by side NDK version was not found.
> Task :app:installDebug FAILED
Skipping device 'emulator-5554' (emulator-5554): Device is OFFLINE.
Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.2/userguide/command_line_interface.html#sec:command_line_warnings
160 actionable tasks: 2 executed, 158 up-to-date
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':app:installDebug'.
> com.android.builder.testing.api.DeviceException: No online devices found.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 24s
error Failed to install the app. Make sure you have the Android development environment set up: https://reactnative.dev/docs/environment-setup. Run CLI with --verbose flag for more details.
Error: Command failed: gradlew.bat app:installDebug -PreactNativeDevServerPort=8081
My emulator is open while this happens and says "failed to connect to metro server"

This here tells you the problem.
info Launching emulator...
error Failed to launch emulator. Reason: Emulator exited before boot..
warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
Something is wrong with your emulator. Try rebooting your system. If that doesn't work, try making a new emulator and see if that one works better. Also, I would turn off the Quickstart feature on your emulator - it may ask you as you shut it down if you want to save its memory state for faster boot times. I've had issues with that in the past similar to this.
Let me know if that changes anything. Good luck.

React Native not detecting Android emulator

When I do react-native run-android I get this error:
info Running jetifier to migrate libraries to AndroidX. You can disable it using "--no-jetifier" flag.
Jetifier found 960 file(s) to forward-jetify. Using 6 workers...
info Starting JS server...
/bin/sh: 1: adb: not found
info Launching emulator...
error Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds`.
warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
info Installing the app...
Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.0.1/userguide/command_line_interface.html#sec:command_line_warnings
FAILURE: Build failed with an exception.
* What went wrong:
Task 'installDebug' not found in project ':app'.
* Try:
Run gradlew tasks to get a list of available tasks. Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 4s
error Failed to install the app. Make sure you have the Android development environment set up: https://reactnative.dev/docs/environment-setup. Run CLI with --verbose flag for more details.
Error: Command failed: ./gradlew app:installDebug -PreactNativeDevServerPort=8081
FAILURE: Build failed with an exception.
* What went wrong:
Task 'installDebug' not found in project ':app'.
* Try:
Run gradlew tasks to get a list of available tasks. Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
I dont get it, before I run my React Native app I open the Android emulator first. I also noticed that my android studio doesn't have 'configure' on welcome page, so I have to start a project if I want to acces the sdk manager and avd manager.

Try in the same terminal that you put npx react-native run-android , set environment variables again like :
source $HOME/.zprofile (if you use zsh)
source $HOME/.bash_profile (if you use bash)

React Native WebStorm Emulator cannot start - error Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds`

I'm new to WebStorm and React Native and I encountered an error while setting up my environment that appears unique compared to the other post I've seen.
Objective
I've set up a default project in WebStorm, my goal is to run that project on an Android emulator, I'm using a Windows PC.
What I've tried
I've set up a simple Debug configuration in WebStorm
I've also downloaded an Android Emulator thru Android Studio and I have it running on my computer.
Now when I click on run for my debug emulator I get the following error:
info Running jetifier to migrate libraries to AndroidX. You can disable it using "--no-jetifier" flag.
Jetifier found 864 file(s) to forward-jetify. Using 4 workers...
info JS server already running.
'adb' is not recognized as an internal or external command,
operable program or batch file.
info Launching emulator...
infoerror Installing the app...
Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds`.
warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
FAILURE: Build failed with an exception.
* What went wrong:
A problem occurred configuring project ':app'.
> SDK location not found. Define location with an ANDROID_SDK_ROOT environment variable or by setting the sdk.dir path in your project's local properties file at 'C:\Users\Nicol\WebstormProjects\Dog\android\local.properties'.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 13s
Error: Command failed: gradlew.bat app:installDebug -PreactNativeDevServerPort=8081
FAILURE: Build failed with an exception.
* What went wrong:
A problem occurred configuring project ':app'.
> SDK location not found. Define location with an ANDROID_SDK_ROOT environment variable or by setting the sdk.dir path in your project's local properties file at 'C:\Users\Nicol\WebstormProjects\Dog\android\local.properties'.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 13s
at checkExecSyncError (child_process.js:621:11)
at execFileSync (child_process.js:639:15)
at runOnAllDevices (C:\Users\Nicol\WebstormProjects\Dog\node_modules\#react-native-community\cli-platform-android\build\commands\runAndroid\runOnAllDevices.js:94:39)
at processTicksAndRejections (internal/process/task_queues.js:93:5)
error Failed to install the app. Make sure you have the Android development environment set up: https://facebook.github.io/react-native/docs/getting-started.html#android-development-environment. Run CLI with --verbose flag for more details.
Other Information
Here is a picture of my Path System variables:

adb is not on your %PATH%; make sure to add the folder where adb.exe is located (usually $ANDROID_HOME/platform-tools, where $ANDROID_HOME is your Android SDK install dir, usually C:\Users\Your.Name\AppData\Local\Android\sdk, you can run where adb command in Windows cmd console to find it) to %PATH% under System environment variables and then restart WebStorm.
You also need defining %ANDROID_SDK_ROOT% environment variable per suggestion in the error message

Just to add, windows environment variables are case sensitive and adding %LOCALAPPDATA%\Android\Sdk like the react-native website says will not work, you need to add %localappdata%\Android\Sdk