ReactContext: currentActivity is null when onActivityResult is called

[fab1an]

I use addActivityEventListener to listen for the result of an Intent.

1. when I start the Intent RN calls onHostPause and releases the reference mCurrentActivity in ReactContext.java.
2. my onActivityResult fires, but there is no currentActivity set yet, because onHostResume is called afterwards.

0.29 / Android / Mac

[charpeni]

Can you provide some code?

[fab1an]

Yes, but it's in Kotlin, do you mind?

[charpeni]

I'm not familiar with Kotlin, but for other people who will check this that will be better than nothing I guess.

[fab1an]

Stripped version:

package at.feibra.mobileqm

class ControllerModule(ctx: ReactApplicationContext) : ReactContextBaseJavaModule(ctx) {

    // ~ Constructors ----------------------------------------------------------------------------------

    init {
        /* forward activity event to controller */
        ctx.addActivityEventListener { requestCode, resultCode, data ->
            L.info("activity result: requestCode: {}, resultCode: {}, data: {}", requestCode, resultCode, data);
        }

        /* forward resume, pause, destroy to controller */
        ctx.addLifecycleEventListener(object : LifecycleEventListener {
            override fun onHostResume() {
                L.info("host resumed")
            }

            override fun onHostPause() {
                L.info("host paused")
            }

            override fun onHostDestroy() {
            }
        })
    }
}

[fab1an]

This line: https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContext.java#L157

is called AFTER this: https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContext.java#L208

[satya164]

I can confirm this that I've run into this issue.

cc @foghina

[foghina]

Yeah, this is how Android works, unfortunately. If you have a plain Activity you will see the same thing: onActivityResult is called before onResume. We're not going to make hacks to work around this at the platform level (since we want to mimic Android as much as possible), but feel free to work around it yourself by e.g. storing the result and dealing with it in onHostResume. Even better, you can handle both cases easily, like this:

@Override
public void onHostResume() {
  if (mActivityResult != null) {
    // getCurrentActivity() will never return null here
    handleActivityResult(getCurrentActivity(), mActivityResult);
    mActivityResult = null;
  }
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
  final Activity activity = getCurrentActivity();
  if (activity != null) {
    handleActivityResult(activity, data);
  } else {
    mActivityResult = data;
  }
}

private void handleActivityResult(Activity activity, Intent result) {
  // insert business logic
}

I'd write this in Kotlin but I'm pretty rusty 🙃

[fab1an]

I've worked around it like that already.

I still think this needs fixing: Usually, without RN, people would override onActivityResult and have their Activity around using this.

Please reopen.

[fab1an]

@foghina Please reopen this issue. You said RN wants to mimic Android as much as possible. In a regular Android application you have access to your Activity on onActivityResult. In RN you don't…

[foghina]

Fine. Feel free to send a PR that e.g. adds an Activity arg to onActivityResult().

[fab1an]

@foghina Awesome thanks. I can do that, but I noticed another problem which might be related. I worked around like you said by storing the result and waiting for the Activity to return.

Now I tested my app for low-memory using "Don't keep activities". When using that onActivityResult is actually never called at all, because apparently the Host is destroyed?