"undefined is not a function" when create android native module in ReactNative - react-native

Question

I'm following ReactNative Native Module Guide to write the java class that can be used in JS side. The exported method is show from class ToastModule(exported as ToastAndroid). The show method is below:
public void show(String message, int duration) {
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
All work as expected with the toast button appear when I invoke ToastAndroid.show from Button onPress handler.
import React, { Component } from 'react';
import {
AppRegistry,
StyleSheet,
Text,
View,
Button,
NativeModules,
} from 'react-native';
const ToastAndroid = NativeModules.ToastAndroid
export default class App extends Component {
handleBTNPressed(){
ToastAndroid.show('Awesome', ToastAndroid.SHORT);
}
render() {
return (
<View style={styles.container}>
<Text style={styles.welcome}>
Welcome to React Native!!
</Text>
<Button title='click me' onPress={()=>this.handleBTNPressed()}/>
</View>
);
}
}
However, when I further change the function name from
#ReactMethod
public void show(String message, int duration) {
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
to
#ReactMethod
public void showAgain(String message, int duration) {
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
I encounter the following error:"undefined is not a function"
this error shows again if I add a new exported method as following:
#ReactMethod
public void showAgain2(String message, int duration) {
String mes = "Hi " + message;
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
Is there anyone know which step I goes incorrectly?
EDIT==========================
There might already be a ToastAndroid in ReactNative, so I change the name to MyToastExample. However, now the error become the following
Does anyone encounter the same issue?

Answer 1

In this step, check if you have import the right ToastModule, because ReactNative also have a class Called ToastModule.
Check if this line import com.facebook.react.modules.toast.ToastModule; exist in *ReactPackage.java

Answer 2

Try using import instead of require.
In my situation, I was using:
var Contacts = require( "react-native-unified-contacts" );
and I was getting the undefined is not function error.
However, changing to:
import Contacts from "react-native-unified-contacts";
fixed the issue for me.
Clearly require and import treat the modules differently.