在嵌套对象中,在React with Hooks中更新状态的正确方法是什么?
export Example = () => {
const [exampleState, setExampleState] = useState(
{masterField: {
fieldOne: "a",
fieldTwo: {
fieldTwoOne: "b"
fieldTwoTwo: "c"
}
}
})
如何使用setExampleState将exampleState更新为a(附加字段)?
const a = {
masterField: {
fieldOne: "a",
fieldTwo: {
fieldTwoOne: "b",
fieldTwoTwo: "c"
}
},
masterField2: {
fieldOne: "c",
fieldTwo: {
fieldTwoOne: "d",
fieldTwoTwo: "e"
}
},
}
}
b(改变值)?
const b = {masterField: {
fieldOne: "e",
fieldTwo: {
fieldTwoOne: "f"
fieldTwoTwo: "g"
}
}
})
您必须使用Rest参数和扩展语法(https://javascript.info/rest-parameters-spread),并设置一个以preState作为setState参数的函数。
不起作用(功能缺失)
[state, setState] = useState({})
const key = 'foo';
const value = 'bar';
setState({
...state,
[key]: value
});
确实工作!
[state, setState] = useState({})
const key = 'foo';
const value = 'bar';
setState(prevState => ({
...prevState,
[key]: value
}));
最初我在useState中使用object,但后来我移动到useReducer钩子用于复杂的情况。重构代码时,我感到性能有所提高。
当您有涉及多个子值的复杂状态逻辑时,或者当下一个状态依赖于前一个状态时,useReducer通常比useState更可取。
useReducer React文档
我已经实现了这样的钩子供我自己使用:
/**
* Same as useObjectState but uses useReducer instead of useState
* (better performance for complex cases)
* @param {*} PropsWithDefaultValues object with all needed props
* and their initial value
* @returns [state, setProp] state - the state object, setProp - dispatch
* changes one (given prop name & prop value) or multiple props (given an
* object { prop: value, ...}) in object state
*/
export function useObjectReducer(PropsWithDefaultValues) {
const [state, dispatch] = useReducer(reducer, PropsWithDefaultValues);
//newFieldsVal={[field_name]: [field_value], ...}
function reducer(state, newFieldsVal) {
return { ...state, ...newFieldsVal };
}
return [
state,
(newFieldsVal, newVal) => {
if (typeof newVal !== "undefined") {
const tmp = {};
tmp[newFieldsVal] = newVal;
dispatch(tmp);
} else {
dispatch(newFieldsVal);
}
},
];
}
更多相关的钩子。
您必须使用Rest参数和扩展语法(https://javascript.info/rest-parameters-spread),并设置一个以preState作为setState参数的函数。
不起作用(功能缺失)
[state, setState] = useState({})
const key = 'foo';
const value = 'bar';
setState({
...state,
[key]: value
});
确实工作!
[state, setState] = useState({})
const key = 'foo';
const value = 'bar';
setState(prevState => ({
...prevState,
[key]: value
}));
答案已经有了,但是这种类型没有被提到,所以看看这种类型的例子…
const[data,setdata]= useState({
username: [
email,
"required",
//...some additional codes
],
password: [
password,
"required|password-5",
//..additional code if any..
],
})
**要在输入字段中更新状态变量email,您可以添加类似的代码与您的变量名**
<Input
onChangeText={(t) => setdata(prevState=>({...prevState,username:{[0]:t}}))}
value={data.username[0]}
/>