Develop Reference

Issue importing values from one file to another in react-native

I am learning ReactNative, and now I'm looking into how to organize the files (for now I am going to create a folder for each page, each with an index, functions and styles file). For some reason, though, I am not being able to import information to index.js, can't use the styles or functions, when I open the page, it doesn't return the func method.
I am wondering whether I am using import wrong. Using import { MenuFunctions} from './Menu' has resulted in an error saying nothing was imported, this error no longer appears, but nothing is being returned still.
This is my code, index, Menu and styles are all in the same folder.
index.js
import React from 'react';
import MenuFunctions from './Menu';
import MenuStyles from './styles'
import { Text, View } from 'react-native';
export default class MenuPage extends React.Component {
render(){
return(
<View>
<Text> Text: {MenuFunctions.func} </Text>
</View>
);
}
}
Menu.js
import React from 'react';
export default class MenuFunctions extends React.Component{
constructor(props){
super(props);
}
func = () => {return "Hello, World!"};
}
styles.js
import React from 'react';
import { StyleSheet } from 'react-native';
export default class MenuStyles extends React.Component{
styles = StyleSheet.create({
text: {
color: "red",
}
});
}

Menu.js and styles.js shouldn't be React.Component and you forgot to call to Func method, () is missing.
React.Component is a UI component only which include a render method that returns JSX element.
Your code should look like that:
index.js
import React from 'react';
import MenuFunctions from './Menu';
import MenuStyles from './styles';
import {Text, View} from 'react-native';
export default class MenuPage extends React.Component {
render() {
return (
<View>
<Text> Text: {MenuFunctions.func()} </Text>
</View>
);
}
}
Menu.js
import React from 'react';
class MenuFunctions {
func = () => {
return 'Hello, World!';
};
}
export default new MenuFunctions();
styles.js
import {StyleSheet} from 'react-native';
export default styles = StyleSheet.create({
text: {
color: Colors.red30,
}
});

The problem is that you are trying to import Menu.js using import MenuFunctions from './Menu' when you had to specify the file itself:'./Menu/Menu.js'. (remember to call the function using parentheses class.function())
Also, whenever you export as default you don't have to use curly braces {}
If you are wondering about your project structure, you can use the following as a common structure to create projects. Let's say you have the following
- index.js
- src
- assets
- screens
- MenuScreen
- components
- services
- menu
- index.js //this is Menu.js
- android
- ios
NOTE
Do not extend React.Component if you are not exporting a component.

You need an object to perform the function of the class you created.
Then declare and use the constructor.
index.js
import React from 'react';
import MenuFunctions from './Menu';
import MenuStyles from './styles'
import { Text, View } from 'react-native';
export default class MenuPage extends React.Component {
constructor(props){
super(props);
this.menu = new MenuFunctions()
MemuStyle = new MenuStyles()
}
render(){
return(
<View>
<Text style={MemuStyle.styles.text}> Text: {this.menu.func()}</Text>
</View>
);
}
}
Menu.js
import React from 'react';
export default class MenuFunctions extends React.Component {
func(){
return 'Hello, World!';
}
}
styles.js
import { StyleSheet } from 'react-native';
export default class MenuStyles extends React.Component {
styles = StyleSheet.create({
text: {
color: "red",
}
});
}
NOTE: The features you intend to use do not necessarily have to inherit React.

Function components do not support contextType

Function components do not support contextType.
I encountered an issue when trying to add context to a React component that was wrapped with a React Router withRouter(...) function.
import React, { Component } from 'react'
import UserContext from './UserContext'
class Toolbar extends Component {
render(){
return (
<div>username: this.context.username</div>
)
}
}
Toolbar.contextType = UserContext
export default withRouter(Toolbar)

The solution to this issue is simply switch the last two lines like so:
export default withRouter(Toolbar)
Toolbar.contextType = UserContext

Store subscribe not working in external component

So technically I have 2 components, I dispatch event from 1st, I want detect this change in 2nd.
I did everything as in Redux docs about Store subscribing : https://redux.js.org/api/store#subscribe. Unfortunatelly, it's not working for me.
This is my 1st react project.
(vue/x is better :] )
import React, {Component} from 'react';
import reducers from '../../reducers'
import { Dropdown } from 'semantic-ui-react'
import {translate} from "../../actions";
import createStore from "../../createStore";
const store = createStore(reducers)
class Component1 extends Component {
componentDidMount() {
store.subscribe(() => console.log(1));
}
updateTexts(lang) {
store.dispatch(translate(lang));
}
render() {
this.dropdown = <Dropdown
onChange={this.updateTexts}
/>
return (
<div className={"lang-switcher"}>
<div className={"select-lang"}>
{this.dropdown}
</div>
</div>
);
}
}
export default Component1
import React, {Component} from 'react';
import axios from 'axios';
import {Animate} from 'react-animate-mount';
import createStore from "../../createStore";
import reducers from "../../reducers";
const store = createStore(reducers);
export default class Component2 extends Component {
componentDidMount() {
store.subscribe(console.log(2));
}
render() {
return (
<div className="box">
{Something}
</div>
);
}
}
I want that Component2 will detect state change done by Component1.
Reducer is working correctly, updates state after dispatching.

If you're using React, you should be using the React-Redux library to handle interacting with the store.
That said, it also looks like you're creating two different store instances, one in each component file. So, Component 2 doesn't know about the store instance in Component 1's file.

Please create a script Store.js, and import for each component.
When you use export, that will create a singleton from your export const:
Store.js
import reducers from '../../reducers'
import createStore from "../../createStore"
export default createStore(reducers)
and use as:
import store from "./Store";
/* REMOVE const store = createStore(reducers); */

React global component

I am coming from a vue.js background and I have just recently started looking into react.
I have a component: PageContent.jsx and I wish to use it without constantly having to import it to be able to use it inside the render function (JSX).
In vue it is possible to globalise a component using:
Vue.component(componentName, componentObject)
Is there anything similar in react?

Hmm, there isn't any kind of "global" component in React. Each component has to be imported or passed as a prop. You have a few options if you want to avoid adding an import to each file though:
1) Create a Higher Order Component that renders the PageContent and the wrapped component.
import PageContent from './PageContent';
const withPageContent = WrappedComponent => {
return class extends React.Component {
render () {
return (
<PageContent>
<WrappedComponent />
</PageContent>
)
}
}
};
export default withPageContent;
// Usage
import withPageContent from './withPageContent';
class MyComponent extends React.Component {
render () {
return (
<div>
I'm wrapped in PageContent!
</div>
)
}
}
export default withPageContent(MyComponent);
2) Pass PageContent as a prop to a component:
import PageContent from './PageContent';
export default class App extends React.Component {
render() {
return (
<React.Fragment>
<Child1 content={PageContent} />
<Child2 content={PageContent} />
</React.Fragment>
)
}
}
// Usage
export default class Child1 extends React.Component {
render () {
const PageContent = this.props.content;
return (
<PageContent>
I'm wrapped in PageContent!
</PageContent>
)
}
}
export default class Child2 extends React.Component {
render () {
const PageContent = this.props.content;
return (
<PageContent>
I'm wrapped in PageContent!
</PageContent>
)
}
}

I very much agree with Chase's answer.
Still if you need another approach you can use the context api. You can declare in the App root, or another nested components tree, a collection of components that you want to easily access.
Here is an example with the useContext hook, but hooks is not a must. The structure is the standard create-react-app structure.
The component we would like to access globally - src/deep/Header.js:
function Header() {
return (
<h1>
I am a global component
</h1>
);
}
export default Header;
The context creation - src/global-components-context.js:
import React from 'react';
const MyContext = React.createContext(null);
export default MyContext;
The grouping of the global-components - src/global-components.js:
import Header from './deep/Header';
const contextValue = {
Header,
};
export default contextValue;
The app init file - src/index.js:
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import MyContext from './global-components-context';
import contextValue from './global-component';
ReactDOM.render(
<MyContext.Provider value={contextValue}>
<App />
</MyContext.Provider>,
document.getElementById('root')
);
Using the component without importing it - src/App.js:
import { useContext } from 'react';
import globalComponent from './global-components-context';
function App() {
const Context = useContext(globalComponent);
return (
<div className="App">
<Context.Header />
</div>
);
}
export default App;
I think this is the most global components you can have in react. Note that you still need to import the context wherever you would like to use a global component.
Also one more disclaimer, global components are very hard to test and often to reason about. I believe that is why there is no standard solution for it in react.
Hope I could help

redux-form Element type is invalid

"Element type is invalid" I still keep getting this error and don't know what to do. Tried <form> and <Form> still same. Please help:
This is my AzForm.js saved at: "./components/testComponent"
import React from 'react'
import { Provider } from 'react-redux'
import { Container, Content, Text, Form } from 'native-base';
//import { createStore } from 'redux' //NOT sure whether I need it, but I still get the same error
import { reduxForm } from 'redux-form'
const SignInForm = props => {
return (
<Form>
</Form>
);
};
export default reduxForm({
form: 'simple' // a unique identifier for this form
})(SignInForm)
and this is an extract from index.js
import React, { Component } from 'react';
import { AppRegistry, StyleSheet, Image } from 'react-native';
import { SignInForm } from "./components/AzForm";
export class HomeScreen extends Component {
render() {
return (
<SignInForm />
);
}
}

Change
export class HomeScreen
to
export default class HomeScreen`
When you export without the default, the component that is exported becomes what is known as a named export (you can have many of these per file). You would import these as import {HomeScreen} from 'HomeScreen'
The React convention is to one component per file. This is achieved by using the export default option as provided above. You would then import it using import HomeScreen from 'HomeScreen';