[英]Can't set state in js react-native
嘗試在setState
Native 中設置狀態時出錯。
import React from "react";
import { TextInput, Text, View, Button, Alert } from "react-native";
const UselessTextInput = () => {
state = { currentDate: "" };
const setCurentDate = (val) => {
this.setState({currentDate : val});
};
const [value, onChangeText] = React.useState("");
return (
<View>
<Text
style={{
alignSelf: "center",
marginTop: 60,
fontWeight: "bold",
fontSize: "25",
}}
>
BirthReminder
</Text>
<Text style={{ alignSelf: "center", marginTop: 15, fontSize: 15 }}>
Enter your friend's birthdate, please
</Text>
<TextInput
clearTextOnFocus={true}
style={{
height: 40,
borderColor: "gray",
borderWidth: 1,
marginTop: 20,
width: 250,
alignSelf: "center",
}}
onChangeText={(value) => setCurentDate(value)}
value={value}
/>
<Button title="Add to list"></Button>
</View>
);
};
export default UselessTextInput;
TypeError: undefined is not an object(評估'_this.setState')
功能組件無權訪問setState
方法,但無法訪問useState掛鈎。
useState 鈎子通過定義值的名稱來工作,例如foo
后跟它的 setter。 按照慣例,將 setter 命名為與帶有set前綴的 value 的名稱相同的名稱,即setFoo
const [foo, setFoo] = useState('hi');
// pass the initial value here -^^-
import { useState } from 'react';
import { TextInput } from 'react-native';
const Component = () => {
const [value, setValue] = useState('');
return <TextInput value={value} onChangeText={setValue} />;
};
我覺得你有點搞混了
如果您使用 Class 組件,請替換它,因為這是語法
state = { currentDate: "" };
const setCurentDate = (val) => {
this.setState({currentDate : val});
};
和:
const [date, setDate] = React.useState();
const setCurentDate = (val) => {
setDate(val);
};
並查看文檔
this.setState
在功能組件中是不允許的。 嘗試對currentDate
使用React.useState
const [currentDate, setCurrentDate] = React.useState("");
...
const setCurentDate = (val) => {
setCurrentDate(val);
};
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