Working with Styles and Events

Handling Text Input

TextInput is a Core Component that allows the user to enter text. It has an onChangeText prop that takes a function to be called every time the text changed, and an onSubmitEditing prop that takes a function to be called when the text is submitted.

For example, let's say that as the user types, you're translating their words into a different language. In this new language, every single word is written the same way: 🍕. So the sentence "Hello there Bob" would be translated as "🍕🍕🍕".

In this example, we store text in the state, because it changes over time.

There are a lot more things you might want to do with a text input. For example, you could validate the text inside while the user types. For more detailed examples, see the React docs on controlled components, or the reference docs for TextInput.

Text input is one of the ways the user interacts with the app. Next, let's look at another type of input and learn how to handle touches.

import React, { Component } from 'react';
import { Text, TextInput, View } from 'react-native';

export default class PizzaTranslator extends Component {
  constructor(props) {
    super(props);
    this.state = {text: ''};
  }

  render() {
    return (
      <View style={{padding: 10}}>
        <TextInput
          style={{height: 40}}
          placeholder="Type here to translate!"
          onChangeText={(text) => this.setState({text})}
          value={this.state.text}
        />
        <Text style={{padding: 10, fontSize: 42}}>
          {this.state.text.split(' ').map((word) => word && '🍕').join(' ')}
        </Text>
      </View>
    );
  }
}

Handling Touches

Users interact with mobile apps mainly through touch. They can use a combination of gestures, such as tapping on a button, scrolling a list, or zooming on a map. React Native provides components to handle all sorts of common gestures, as well as a comprehensive gesture responder system to allow for more advanced gesture recognition, but the one component you will most likely be interested in is the basic Button.

Displaying a basic button

Button provides a basic button component that is rendered nicely on all platforms. The minimal example to display a button looks like this:

<Button
  onPress={() => {
    alert('You tapped the button!');
  }}
  title="Press Me"
/>

This will render a blue label on iOS, and a blue rounded rectangle with light text on Android. Pressing the button will call the "onPress" function, which in this case displays an alert popup. If you like, you can specify a "color" prop to change the color of your button.

Go ahead and play around with the Button component using the example below. You can select which platform your app is previewed in by clicking on the toggle in the bottom right, then click on "Tap to Play" to preview the app.

import React, { Component } from 'react';
import { Platform, StyleSheet, Text, TouchableHighlight, TouchableOpacity, TouchableNativeFeedback, TouchableWithoutFeedback, View } from 'react-native';

export default class Touchables extends Component {
  _onPressButton() {
    alert('You tapped the button!')
  }

  _onLongPressButton() {
    alert('You long-pressed the button!')
  }


  render() {
    return (
      <View style={styles.container}>
        <TouchableHighlight onPress={this._onPressButton} underlayColor="white">
          <View style={styles.button}>
            <Text style={styles.buttonText}>TouchableHighlight</Text>
          </View>
        </TouchableHighlight>
        <TouchableOpacity onPress={this._onPressButton}>
          <View style={styles.button}>
            <Text style={styles.buttonText}>TouchableOpacity</Text>
          </View>
        </TouchableOpacity>
        <TouchableNativeFeedback
            onPress={this._onPressButton}
            background={Platform.OS === 'android' ? TouchableNativeFeedback.SelectableBackground() : ''}>
          <View style={styles.button}>
            <Text style={styles.buttonText}>TouchableNativeFeedback {Platform.OS !== 'android' ? '(Android only)' : ''}</Text>
          </View>
        </TouchableNativeFeedback>
        <TouchableWithoutFeedback
            onPress={this._onPressButton}
            >
          <View style={styles.button}>
            <Text style={styles.buttonText}>TouchableWithoutFeedback</Text>
          </View>
        </TouchableWithoutFeedback>
        <TouchableHighlight onPress={this._onPressButton} onLongPress={this._onLongPressButton} underlayColor="white">
          <View style={styles.button}>
            <Text style={styles.buttonText}>Touchable with Long Press</Text>
          </View>
        </TouchableHighlight>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    paddingTop: 60,
    alignItems: 'center'
  },
  button: {
    marginBottom: 30,
    width: 260,
    alignItems: 'center',
    backgroundColor: '#2196F3'
  },
  buttonText: {
    textAlign: 'center',
    padding: 20,
    color: 'white'
  }
});

Touchables

If the basic button doesn't look right for your app, you can build your own button using any of the "Touchable" components provided by React Native. The "Touchable" components provide the capability to capture tapping gestures, and can display feedback when a gesture is recognized. These components do not provide any default styling, however, so you will need to do a bit of work to get them looking nicely in your app.

Which "Touchable" component you use will depend on what kind of feedback you want to provide:

• Generally, you can use TouchableHighlight anywhere you would use a button or link on web. The view's background will be darkened when the user presses down on the button.

• You may consider using TouchableNativeFeedback on Android to display ink surface reaction ripples that respond to the user's touch.

• TouchableOpacity can be used to provide feedback by reducing the opacity of the button, allowing the background to be seen through while the user is pressing down.

• If you need to handle a tap gesture but you don't want any feedback to be displayed, use TouchableWithoutFeedback.

In some cases, you may want to detect when a user presses and holds a view for a set amount of time. These long presses can be handled by passing a function to the onLongPress props of any of the "Touchable" components.

Let's see all of these in action: