How to return a Boolean from @ReactMethod in React Native?

Question

I want to return a Boolean from @ReactMethod in reactNative Android application.

But when I make method similar to

@ReactMethod
public boolean retBoolean() {
return true;
}

and call it from JS component ,it returns undefined. only when return type is void function gets called ,I am not able to return string or boolean.

Answer 1

Rather than using callback, you could also use Promise.

import com.facebook.react.bridge.Promise;

@ReactMethod
public void hasFlash(final Promise promise) {
    Camera camera = RCTCamera.getInstance().acquireCameraInstance();
    if (null == camera) {
        promise.reject("No camera found.");
        return;
    }
    List<String> flashModes = camera.getParameters().getSupportedFlashModes();
    promise.resolve(null != flashModes && !flashModes.isEmpty());
}

Then in your JS, call it with

const myFunction = async () => { 
    const hasFlash = await CameraManager.hasFlash(); 
}

Answer 2

According to react documentation

To expose a method to JavaScript a Java method must be annotated using @ReactMethod. The return type of bridge methods is always void. React Native bridge is asynchronous, so the only way to pass a result to JavaScript is by using callbacks or emitting events

So if you want to return some value like boolean or string you need to use callbacks.

Example:

@ReactMethod
public void isEqual(
        int a,
        int b,
        Callback booleanCallback) {
    boolean equal= a == b;
    booleanCallback.invoke(equal);
}

In javascript call like below...

YourClass.isEqual(
 5,
 10,
 (status) => {
  console.log('Result ',status);
 }
);

For more info refer this