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"
           }
        }
   })

当前回答

可以使用useReducer钩子来管理复杂的状态,而不是useState。要做到这一点,首先初始化状态和更新函数如下所示:

const initialState = { name: "Bob", occupation: "builder" };
const [state, updateState] = useReducer(
  (state, updates) => ({ ...state, ...updates }),
  initialState
);

然后你可以通过只传递部分更新来更新状态,就像这样:

updateState({ occupation: "postman" })

其他回答

我已经给出了两个追加,整个对象更新,具体的关键更新的解决方案的例子

追加和修改都可以通过一个简单的步骤来完成。我认为这是更稳定和安全的,没有不可变或可变的依赖。

这就是追加新对象的方法

setExampleState(prevState => ({
    ...prevState,
    masterField2: {
        fieldOne: "c",
        fieldTwo: {
            fieldTwoOne: "d",
            fieldTwoTwo: "e"
        }
    },
}))

假设您想再次修改masterField2对象。可能有两种情况。您想要更新整个对象或更新对象的特定键。

更新整个对象-这里masterField2键的整个值将被更新。

setExampleState(prevState => ({
    ...prevState,
    masterField2: {
        fieldOne: "c",
        fieldTwo: {
            fieldTwoOne: "d",
            fieldTwoTwo: "e"
        }
    },
}))

但是如果你只想改变masterField2对象中的fieldTwoOne键呢?你可以这样做。

let oldMasterField2 = exampleState.masterField2
oldMasterField2.fieldTwo.fieldTwoOne = 'changed';
setExampleState(prevState => ({
    ...prevState,
    masterField2: oldMasterField2
}))

如果有人正在搜索useState()钩子,则更新为对象

- Through Input

        const [state, setState] = useState({ fName: "", lName: "" });
        const handleChange = e => {
            const { name, value } = e.target;
            setState(prevState => ({
                ...prevState,
                [name]: value
            }));
        };

        <input
            value={state.fName}
            type="text"
            onChange={handleChange}
            name="fName"
        />
        <input
            value={state.lName}
            type="text"
            onChange={handleChange}
            name="lName"
        />
   ***************************

 - Through onSubmit or button click
    
        setState(prevState => ({
            ...prevState,
            fName: 'your updated value here'
         }));

你想要创建状态的对象

let teams = {
  team: [
    {
      name: "one",
      id: "1"
    },
  ]
}

使团队的状态为对象

const [state, setState] = useState(teams);

像这样更新状态

setState((prevState)=>({...prevState,team:[
     ...prevState.team,
     {
     name: "two",
      id: "2"
     }
]}))

更新后状态变为

{
  team: [
    {
      name: "one",
      id: "1"
    },
    {
      name: "two",
      id: "2"
    }
  ]
}

要渲染项目根据当前状态使用地图功能

{state.team.map((curr_team) => {
      return (
        <div>
           <p>{curr_team.id}</p>
           <p>{curr_team.name}</p>
        </div>
      )
})}

我给您留下了一个实用函数来不可变地更新对象

/**
 * Inmutable update object
 * @param  {Object} oldObject     Object to update
 * @param  {Object} updatedValues Object with new values
 * @return {Object}               New Object with updated values
 */
export const updateObject = (oldObject, updatedValues) => {
  return {
    ...oldObject,
    ...updatedValues
  };
};

你可以这样用

const MyComponent = props => {

  const [orderForm, setOrderForm] = useState({
    specialities: {
      elementType: "select",
      elementConfig: {
        options: [],
        label: "Specialities"
      },
      touched: false
    }
  });


// I want to update the options list, to fill a select element

  // ---------- Update with fetched elements ---------- //

  const updateSpecialitiesData = data => {
    // Inmutably update elementConfig object. i.e label field is not modified
    const updatedOptions = updateObject(
      orderForm[formElementKey]["elementConfig"],
      {
        options: data
      }
    );
    // Inmutably update the relevant element.
    const updatedFormElement = updateObject(orderForm[formElementKey], {
      touched: true,
      elementConfig: updatedOptions
    });
    // Inmutably update the relevant element in the state.
    const orderFormUpdated = updateObject(orderForm, {
      [formElementKey]: updatedFormElement
    });
    setOrderForm(orderFormUpdated);
  };

  useEffect(() => {
      // some code to fetch data
      updateSpecialitiesData.current("specialities",fetchedData);
  }, [updateSpecialitiesData]);

// More component code
}

如果没有,您可以在这里找到更多实用程序:https://es.reactjs.org/docs/update.html

我认为更优雅的解决方案是创建更新后的状态对象,同时保留以前的state值。需要更新的Object属性可以以这样的数组形式提供

import React,{useState, useEffect} from 'react'
export default function Home2(props) {
    const [x, setX] = useState({name : '',add : {full : '', pin : '', d : { v : '' }}})
    const handleClick = (e, type)=>{
        let obj = {}
        if(type.length > 1){
            var z = {}
            var z2 = x[type[0]]
        
        type.forEach((val, idx)=>{
            if(idx === type.length - 1){
                z[val] = e.target.value
            }
            else if(idx > 0){
                Object.assign(z , z2) /*{...z2 , [val]:{} }*/
                z[val] = {}
                z = z[val]
                z2 = z2[val]
            }else{
                z = {...z2}
                obj = z
            }
        })
    }else obj = e.target.value
    setX( { ...x ,   [type[0]] : obj  } )
    
}
return (
    <div>
        <input value = {x.name} onChange={e=>handleClick(e,["name"])}/>
        <input value = {x.add.full} onChange={e=>handleClick(e,["add","full"])}  />
        <input value = {x.add.pin} onChange={e=>handleClick(e,["add","pin"])}  /><br/>
        <input value = {x.add.d.v} onChange={e=>handleClick(e,["add","d","v"])}  /><br/>
        {x.name} <br/>
        {x.add.full} <br/>
        {x.add.pin} <br/>
        {x.add.d.v}
    </div>
)
}