React Native: Is it possible to persist native Java variable values on app reload?

Question

Is it possible to maintain the value of Java variables in a custom react native module when reloading the JS? I would like to maintain components in the below code for debugging purposes. It persists on onHostResume if the app goes into the background but on reload the value is lost.

public class CustomModule extends ReactContextBaseJavaModuleWithEvents implements LifecycleEventListener {

    public List<JsonObject> components = new ArrayList<>();

    public CustomModule(ReactApplicationContext reactContext) {
        super(reactContext);
        reactContext.addLifecycleEventListener(this);
    }

    @ReactMethod
    void addComponents(component) {
        // add some components...
        components.add(component);
    }

    @Override
    public String getName() {
        return "CustomModule";
    }

    @Override
    public void onHostResume() {
        getReactApplicationContext()
            .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
            .emit("DEBUG_TAG", components.toString());
    }

}

The method of storing variables using local storage looks good. — hong developer
– hong developer, Commented Jul 18, 2019 at 2:30
I reversed the edit as I’m not using Expo at all for my app and this is part of a custom native module which is why I added the current tags — Brien Crean
– Brien Crean, Commented Jul 18, 2019 at 5:57
In the case of the Expo, the React-native is used equally. The more tags involved, the more your expert in the field will see your question. — hong developer
– hong developer, Commented Jul 18, 2019 at 6:14
Thanks but I resolved the issue. I should have set the List as a static class variable so that it is only initialized once rather than initialized every time on reload. — Brien Crean
– Brien Crean, Commented Jul 18, 2019 at 19:11

Brien Crean · Accepted Answer · 2019-07-18 19:20:51Z

0

Every reload the JS code is creating a new instance of CustomModule reinitializing components. I should have set the components List as a static class variable so that it is only initialized once.

public class CustomModule extends ReactContextBaseJavaModuleWithEvents implements LifecycleEventListener {

    public static List<JsonObject> components = new ArrayList<>();

}

edited Jul 18, 2019 at 19:20

answered Jul 18, 2019 at 19:13

Brien Crean

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