React Native 中的文本没有更新

Question

app.js

import { StatusBar } from "expo-status-bar";
import {
  TouchableOpacity,
  Button,
  StyleSheet,
  Alert,
  SafeAreaView,
  Text,
} from "react-native";

export default function App() {
  let count = 5;
  let counts = [count];
  return (
    <SafeAreaView style={styles.container}>
      <Text style={styles.Text}>Earn Money</Text>
      <TouchableOpacity
        onPress={() => {
          count += 0.25;
          console.log(count);
        }}
        style={{
          height: 70,
          width: 130,
          backgroundColor: "#ff5c5c",
          alignSelf: "center",
          top: 25,
        }}
      >
        <Text
          style={{
            fontWeight: "900",
            alignSelf: "center",
            position: "relative",
            top: 25,
          }}
        >
          Earn 0.20$
        </Text>
      </TouchableOpacity>
      <Text style={styles.Balance}>{count}</Text>
      <StatusBar style="auto" />
    </SafeAreaView>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    paddingTop: Platform.OS === "android" ? 90 : 0,
    paddingLeft: Platform.OS === "android" ? 10 : 0,
  },
  Text: {
    justifyContent: "center",
    alignSelf: "center",
    color: "orange",
    fontSize: 25,
    fontWeight: "900",
  },
  Balance: {
    justifyContent: "center",
    alignSelf: "center",
    color: "orange",
    fontSize: 25,
    fontWeight: "900",
    top: 100,
  },
});

So when I press touchableOpacity the count variable is supposed to add 0.25 to itself, That is working fine but the text

<Text style={styles.Balance}>{count}</Text>

is not updating.I would also want to know if the way I dispaly the variable count in <Text><Text/> is correct. THe text is just showing 5 I have no prior experience with React native if you would help pls do.

Answer 1

React uses some hooks for updating the DOM you can't just use variables and expect it to update the DOM, in this instance you need to use useState hook

import { StatusBar } from "expo-status-bar";
import { useState} from "react";
import {
  TouchableOpacity,
  Button,
  StyleSheet,
  Alert,
  SafeAreaView,
  Text,
} from "react-native";

export default function App() {
  let [count, setCount] = useState(0);
  return (
    <SafeAreaView style={styles.container}>
      <Text style={styles.Text}>Earn Money</Text>
      <TouchableOpacity
        onPress={() => {
          setCount(c => c + 0.5)
        }}
        style={{
          height: 70,
          width: 130,
          backgroundColor: "#ff5c5c",
          alignSelf: "center",
          top: 25,
        }}
      >
        <Text
          style={{
            fontWeight: "900",
            alignSelf: "center",
            position: "relative",
            top: 25,
          }}
        >
          Earn 0.20$
        </Text>
      </TouchableOpacity>
      <Text style={styles.Balance}>{count}</Text>
      <StatusBar style="auto" />
    </SafeAreaView>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    paddingTop: Platform.OS === "android" ? 90 : 0,
    paddingLeft: Platform.OS === "android" ? 10 : 0,
  },
  Text: {
    justifyContent: "center",
    alignSelf: "center",
    color: "orange",
    fontSize: 25,
    fontWeight: "900",
  },
  Balance: {
    justifyContent: "center",
    alignSelf: "center",
    color: "orange",
    fontSize: 25,
    fontWeight: "900",
    top: 100,
  },
});

You can read this article to better understand react and how it works.

Answer 2

import { useState} from "react";
const [count,setCount]=useState(5) // 5 is default value
const [update,setUpdate]=useState(0) // add this
export default function App() {
  let count = 5;
  let counts = [count];
  return (
    <SafeAreaView style={styles.container}>
      <Text style={styles.Text}>Earn Money</Text>
      <TouchableOpacity
        onPress={() => {
          count += 0.25;
          setCount(count)       // add this
          setUpdate(update+1)   // add this
           
          console.log(count);
        }}
        style={{
          height: 70,
          width: 130,
          backgroundColor: "#ff5c5c",
          alignSelf: "center",
          top: 25,
        }}
      >
        <Text
          style={{
            fontWeight: "900",
            alignSelf: "center",
            position: "relative",
            top: 25,
          }}
        >
          Earn 0.20$
        </Text>
      </TouchableOpacity>
      <Text style={styles.Balance}>{count}</Text>
      <StatusBar style="auto" />
    </SafeAreaView>
  );
}