在 Focus React Native 上更改 TextInput 样式

Question

First of all, I've researched through other posts and find this How to change styling of TextInput placeholder in React Native?

The issue with the solutions in the post is once fontStyle is set to italic, it won't go back to normal font (I'm guessing that it can't be overridden unless the component updates). Here is my code sample

  <TextInput
    style={
      this.state.value.length === 0
      ? {fontStyle: 'italic', color: 'white'} // font changed to white and italic
      : {fontStyle: 'normal', color: 'black'} // font changed to black but stays italic
    }
    value={this.state.value}
  />

I came up with some hack by forcing the TextInput to update using forceUpdate() or set a key to the component, but this caused the keyboard UI to close when user is typing which is bad for UX.

I'd like to simply comment on the linked post instead but my reputation is not enough.

Is that intended behavior or did I make any mistake? If anyone can provide some explanation / solution, it will be greatly appreciated.

PS Tested on Android using the latest React Native

Answer 1

Use onFocus for the text input to handle your case. Because whenever you focus text input and start typing it will update the state and component will re-render. Look at this expo snack with the example usage.

state = { isFocused: false }; 

onFocusChange = () => {
    this.setState({ isFocused: true });
}

<TextInput 
    onFocus={this.onFocusChange}
    placeholder='Enter Input Here'
    style={(this.state.isFocused) ? {fontStyle: 'normal', color: 'black'} : {fontStyle: 'italic', color: 'white'}} 
 />

so learn more about component lifecycle then you'll know how to handle more of these type of cases and also always read documentation before using a component then you'll easily find the solution for your specific case.

Answer 2

Usually a TextInput has some public styles, so you can use Stylesheet.compose to reduce your code like this:

    const styles = StyleSheet.create({
        input: {
            borderRadius: 5,
        },
        inputOnFocus: {
            borderBottomWidth: 2,
            borderBottomColor: 'green'
        }
    });
    
    const inputOnFocus = StyleSheet.compose(styles.input, styles.inputOnFocus);

then you can use setState or useState to change the style.

Answer 3

Here is another way using hooks (I'm using expo.io btw)

    import React, { useState } from 'react'
    import { View, StyleSheet, TextInput } from 'react-native'
    
    const TextInput = () => {
      const [isHighlighted, setIsHighlighted] = useState(false)
    
       return (
        <View>
          <TextInput
            style={[styles.textInput, isHighlighted && styles.isHighlighted]}
            onFocus={() => { setIsHighlighted(true)}
            onBlur={() => {setIsHighlighted(false)} />
        </View>
      )
    }
    
    const styles = StyleSheet.create({
      textInput: {
        borderColor: 'grey',
        borderWidth: StyleSheet.hairlineWidth,
        borderRadius: 8,
        height: 43,
      },
      isHighlighted: {
        borderColor: 'green',
      }
    })