pass an arraylist of custom objects to react native side from android

Question

I have a list of custom objects (List) . I need to send this data to React Native side to display in flat list . How do i do this ?This list is present in

class NativeToReact(reactContext: ReactApplicationContext,userManager: IUserManager) : ReactContextBaseJavaModule(reactContext)`

Answer 1

Since you would like to send an ArrayList, you would have to send a WritableArray from the native side to react-native.

public class NativeToReactModule extends ReactContextBaseJavaModule {

  public NativeToReactModule(ReactApplicationContext reactContext) {
    super(reactContext);
  }

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

  private static WritableMap convertJsonToMap(JSONObject jsonObject) throws JSONException {
    WritableMap map = new WritableNativeMap();

    Iterator<String> iterator = jsonObject.keys();
    while (iterator.hasNext()) {
      String key = iterator.next();
      Object value = jsonObject.get(key);
      if (value instanceof JSONObject) {
        map.putMap(key, convertJsonToMap((JSONObject) value));
      } else if (value instanceof Boolean) {
        map.putBoolean(key, (Boolean) value);
      } else if (value instanceof Integer) {
        map.putInt(key, (Integer) value);
      } else if (value instanceof Double) {
        map.putDouble(key, (Double) value);
      } else if (value instanceof String) {
        map.putString(key, (String) value);
      } else {
        map.putString(key, value.toString());
      }
    }
    return map;
  }

  @ReactMethod
  public void returnArrayOfObjects(Callback successCallback) throws JSONException {
    List<CustomObject> aList = new ArrayList<CustomObject>();
    Gson g = new Gson();

    aList.add(new CustomObject("Nameone", 1));
    aList.add(new CustomObject("nametwo", 132));

    WritableArray array = new WritableNativeArray();
    for (CustomObject co : aList) {
      JSONObject jo = new JSONObject(g.toJson(co));
      WritableMap wm = convertJsonToMap(jo);
      array.pushMap(wm);
    }

    successCallback.invoke(array);
  }
}

On the react-native side, you can create a javascript module for your native module as follows:

import { NativeModules } from "react-native";
module.exports = NativeModules.NativeToReactModule;

You can then access the ArrayList you sent from the native side.

import NativeToReact from "./NativeToReactModule";

...
...
...

NativeToReact.returnArrayOfObjects(array => {
  console.log(array, "The array you sent from the native side");
});

NOTE: The answer does not show a complete setup for making use of a native module.

Answer 2

You have to map your list into a JSON object

Answer 3

Expanding (or reducing?) from 10101010's answer, you should/could use FB's helper classes to convert values instead.

import com.facebook.react.bridge.Arguments;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactMethod;
import com.facebook.react.bridge.WritableMap;
import com.myapp.SomeClass;

public class NativeToReactModule extends ReactContextBaseJavaModule {

  public NativeToReactModule(ReactApplicationContext reactContext) {
    super(reactContext);
  }

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

  @ReactMethod
  public void getArray(Callback successCallback) {
    WritableArray array = Arguments.fromList(SomeClass.SomeStaticListValue);
    successCallback.invoke(array);
  }
}

Then on the JS side, just call:

import { NativeModules } from "react-native"

NativeModules.NativeToReactModule.getArray(array => console.log(array, "The array you sent from the native side"))