Hướng dẫn gọi function native từ js.

CrabstudioUtils.java

package com.devjobs;

import android.app.Dialog;
import android.content.ComponentName;
import android.content.DialogInterface;
import android.content.Intent;
import android.provider.ContactsContract;

import com.facebook.react.bridge.Callback;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;

/**
 * Created by anhtuank7c on 6/5/17.
 */

public class CrabstudioUtils extends ReactContextBaseJavaModule {

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

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

    @ReactMethod
    public void openContact() {
        Intent intent = new Intent();
        intent.setComponent(new ComponentName("com.android.contacts", "com.android.contacts.DialtactsContactsEntryActivity"));
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        getReactApplicationContext().getApplicationContext().startActivity(intent);
    }
}

CrabstudioUtilsPackge.java

package com.devjobs;

import com.facebook.react.ReactPackage;
import com.facebook.react.bridge.JavaScriptModule;
import com.facebook.react.bridge.NativeModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.uimanager.ViewManager;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * Created by anhtuank7c on 6/5/17.
 */

public class CrabstudioUtilsPackge implements ReactPackage {
    @Override
    public List<NativeModule> createNativeModules(ReactApplicationContext reactContext) {
        List<NativeModule> modules = new ArrayList<>();
        modules.add(new CrabstudioUtils(reactContext));
        return modules;
    }

    @Override
    public List<Class<? extends JavaScriptModule>> createJSModules() {
        return Collections.emptyList();
    }

    @Override
    public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) {
        return Collections.emptyList();
    }
}

Import vào js

import {
    Text,
    NativeModules
} from 'react-native';

const CrabstudioUtils = NativeModules.CrabstudioUtils;

Sau đó cần dùng ở đâu thì gọi ra ở đó:

<TouchableOpacity onPress={() => CrabstudioUtils.openContact()}>
   <Text>Open contact</Text>
</TouchableOpacity>

MainApplication.java

Sửa file MainApplication.java, cho package bên dưới vào 

@Override
    protected List<ReactPackage> getPackages() {
      return Arrays.<ReactPackage>asList(
          new MainReactPackage(),
          new CrabstudioUtilsPackge()  // HERE
      );
    }