setState()之后的Console.log()不返回更新状态 [英] Console.log() after setState() doesn't return the updated state

问题描述

我创建了一个简单的待办事项列表来学习反应，并且我正在尝试添加一些其他功能.目前，我正在尝试添加用于切换项目列表的按钮，因此它要么显示所有任务，要么仅显示已完成的任务.

I've created a simple todo list to learn react and i'm trying to add some additional features. At the moment i'm trying to add buttons that toggle the list of items, so it either shows all the tasks or just those that are completed.

我编写了一个函数来更改visabilityFilter的状态，因此以后可以使用它来切换列表中的项目，但它的行为不正确.

I've written a function to change the state of my visabilityFilter so I can later use this to toggle the items in the list, but it isn't behaving how it should be.

我在控制台上记录了visabilityFilter变量，但是在更改为正确状态之前，它始终显示错误状态.例如全部显示"按钮将控制台日志显示完成"，然后再次按下该按钮将控制台日志显示全部"

I console log the visabilityFilter variable but it always shows the wrong state before changing to the correct state. e.g. the 'show all' button will console log 'show completed' then if you press it again it will console log 'show all'

App.js

import React, { Component } from 'react';
import './App.css';
import TodoList from './components/TodoList.js'
import VisabilityFilter from './components/VisabilityFilter.js'

export const SHOW_ALL = 'show_all'
export const SHOW_COMPLETED = 'show_completed'

class App extends Component {
  constructor (props) {
    super(props)

    this.state = {
      inputValues: {
        'newTodo': ''
      },
      todos: [
        {
          task: 'My First Todo',
          completed: false
        }
      ],
      visabilityFilter: SHOW_ALL
    }

    this.addTodo = this.addTodo.bind(this)
    this.handleInputChange = this.handleInputChange.bind(this)
    this.handleKeyUp = this.handleKeyUp.bind(this)
    this.toggleCompleted = this.toggleCompleted.bind(this)
    this.removeTodo = this.removeTodo.bind(this)
    this.checkCompleted = this.checkCompleted.bind(this)
    this.setVisabilityFilter = this.setVisabilityFilter.bind(this)

  }

  handleInputChange (e) {
      const { inputValues } = this.state
      const { id, value } = e.target
      this.setState({
        inputValues: {
          ...inputValues,
          [id]: value
        }
      })
  }

  handleKeyUp (e) {
    var code = e.key
        if(code === 'Enter') {
          this.addTodo(e);
        }
  }

  toggleCompleted (e, index) {
    const { todos } = this.state

    todos[index].completed = !todos[index].completed

    todos.sort((a, b) => b.completed - a.completed)

    this.setState({ todos })
  }

  removeTodo (e, index) {
    const { todos } = this.state
    this.setState ({ todos: todos.filter((todo, i) => i !== index) })
  }

  addTodo (e) {
      const { todos, inputValues } = this.state
      const { dataset } = e.target

      if (inputValues[dataset.for] === '') return

      const newTodo = { task: inputValues[dataset.for], completed: false }
      todos.push(newTodo)

      this.setState({
        todos,
        inputValues: { ...inputValues, [dataset.for]: '' }
      })
  }

  checkCompleted (e, index) {
    const { todos } = this.state
    return { todos } && todos[index].completed
  }

  setVisabilityFilter (e) {
    const { visabilityFilter } = this.state
    const { dataset } = e.target

    this.setState({
      visabilityFilter: dataset.for
    })

    console.log ({ visabilityFilter })
  }

  render() {
    const { todos, inputValues, visabilityFilter } = this.state
    return (
      <div className="App">
        <TodoList
          todos={todos}
          inputValues={inputValues}
          addTodo={this.addTodo}
          handleInputChange={this.handleInputChange}
          removeTodo={this.removeTodo}
          toggleCompleted={this.toggleCompleted}
          handleKeyUp={this.handleKeyUp}
          checkCompleted={this.checkCompleted}
        />
        <VisabilityFilter setVisabilityFilter={this.setVisabilityFilter} />
      </div>
    );
  }
}

export default App;

VisabilityFilter.js

VisabilityFilter.js

import React from 'react'
import { func } from 'prop-types'

import { SHOW_ALL, SHOW_COMPLETED } from '../App'

const VisabilityFilter = props => {
  return (
    <div>
      <button data-for={SHOW_COMPLETED} onClick={ props.setVisabilityFilter } >
        Show Completed Tasks
      </button>
      <button data-for={SHOW_ALL} onClick={ props.setVisabilityFilter }>
        Show All Tasks
      </button>
    </div>
  )
}

VisabilityFilter.propTypes = {
  setVisabilityFilter: func.isRequired
}

export default VisabilityFilter

推荐答案

setState()是异步的(反应文档)，因此状态更改不会立即应用.如果要注销新状态，setState()接受一个函数作为第二个参数，并在状态更新时执行该函数.所以:

setState() is async (React docs), so the state changes won't be applied immediately. If you want to log out the new state,setState() takes in a function as the second argument and performs that function when the state is updated. So:

this.setState({ 
    abc: xyz 
  }, 
  () => console.log(this.state.abc),
)

或者您也可以使用componentDidUpdate()，建议使用

Or you can also use componentDidUpdate(), which is recommended

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