Install Android Studio and Emulator

Download Android Studio and copy to your Applications folder. Launch it and complete the install process using the provided wizard. Using the Configure menu at the bottom the welcome screen, open the SDK Manager.

Confirm the SDK location (we will need this later) and that you have the Android 9.0 (Pie) SDK installed.

Close the SDK Manager and open the AVD Manager (from the Configure menu on the Welcome screen).

Create a new Virtual Device accepting the default device.

Select the Pie system image (downloading it if necessary).

On the last page confirm the setup and click Finish.

Once you have a device, click the green triangle to start the emulator.

Once started, the emulator should show the phone starting up.

Install React Native

Install Node.js. It is helpful to have certain packages installed “globally” but it is considered a bad practice to use sudo for this. Instead follow these instructions. Install the remaining tools using the following command:
npm install -g react react-native react-native-cli

Build an App

From a command prompt, enter the following:
react-native init HelloWorld
cd HelloWorld
react-native run-android
This will open a new Terminal with the title “Running Metro Bundler on port 8081.”

Missing JDK

At this point I got an error that I need to install the Java Developer Kit.

Download the JDK.

Open the package and step through the install process. Then try the startup again:
react-native run-android

“SDK location not found”

“SDK location not found. Define location with sdk.dir in the local.properties file or with an ANDROID_HOME environment variable.

As we did to handle the global install of Node.js packages, we will add a line to .profile with the SDK, source the file, and try again:
echo “ANDROID_HOME=/Users/jfoster/Library/Android/sdk” >> ~/.profile
source ~/.profile
react-native run-android

This should have solved the problem, but didn’t for me. So, I added a line to the local.properties file:
echo “sdk.dir=/Users/jfoster/Library/Android/sdk/” >> ./android/local.properties

“adb: command not found”

The next error I got was “adb: command not found”. It turns out that there are some executables that are installed but not found. So we need more updates to our environment variables:
echo “export PATH=$ANDROID_HOME/platform-tools:$PATH” >> ~/.profile
source ~/.profile
react-native run-android
Finally, we get the app running!

Customize the App

Edit App.js to customize the message, save the file, and then in the emulator double tap R to reload the app.

Remote Debugging

Install RNDebugger to support debugging. With the emulator in the foreground, press <Ctrl>+<M> on the keyboard. This should bring up a developer menu. Select “Debug JS Remotely” the Reload (either from the menu or double tap R).

Add some debugging code to App.js; for example, add a line to the end of the file:
console.log(“This is a message from my code to the console”);
Save App.js, then in the emulator double tap R to reload the app. You should see your message in the debugger.

If in Doubt, Restart

Not infrequently things don’t seem to work right and I close the Metro Bundler terminal, quit the app on the phone (tap the share button at the bottom right on the phone then swipe the app up and away), then restart the app (react-native run-android). You could also try quitting the emulator and restart it as well.

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