反应 - 状态未更新 [英] React - State not updated

问题描述

这里我尝试将 state.autocomplete 设置为'hello'然后打印它，但状态似乎为null。当我刚刚使用 setState 更新状态时，怎么会这样？ data 设置为全局变量。

Here I try to set state.autocomplete to 'hello' and then print it, but state seems to be null. How can that be when I just updated the state using setState? data is set as a global variable.

  var data = {
    populate_at: ['web_start', 'web_end'],
    autocomplete_from: ['customer_name', 'customer_address']
  };


  var AutocompleteFromCheckboxes = React.createClass({
    handleChange: function(e) {
      this.setState( { autocomplete_from: 'event.target.value' } );
      console.log('autocompleteFrom state: ', this.state.autocomplete_from);
      // ^  => Uncaught TypeError: Cannot read property 'autocomplete_from' of null
      return 1;
    },
    render: function() {
      var autocompleteFrom = this.props.autocomplete_from.map(function(value) {
        return (
          <label for={value}>
            <input type="checkbox" name={value} value="{value}"
              onChange={this.handleChange.bind(this)}
              ref="autocomplete-from"/>
            {value}
          </label>
        );
      }, this);
      return (
        <div className="autocomplete-from">
          {autocompleteFrom}
        </div>
      );
    }
  });

  var DynamicForm = React.createClass({
    getInitialState: function() {
      return {
        name              : null,
        populate_at       : null,
        same_as           : null,
        autocomplete_from : "not set",
        title             : null
      };
    },
    saveAndContinue: function(e) {
      e.preventDefault();
      var data = {
        name     : this.refs.name.getDOMNode().value,
      };
      console.log('data: ' + data.name);
    },

    render: function() {
      return (
          <AutocompleteFromCheckboxes
            autocomplete_from={this.props.data.autocomplete_from} />
      );
    }
  });


  var mountpoint = document.getElementById('dynamic-form');
  if ( mountpoint ) {
    React.render(<DynamicForm data={data} />, mountpoint);
  }

});

推荐答案

来自reactjs docs：

From the reactjs docs:

setState（）不会立即变异 this.state 但创建一个待定状态转换。调用此方法后访问 this.state 可能会返回现有值。

setState() does not immediately mutate this.state but creates a pending state transition. Accessing this.state after calling this method can potentially return the existing value.

https://facebook.github.io/react/docs/component-api。 html

你可以做的是将一个回调函数传递给 setState 一旦状态被触发已更新：

What you can do is pass a callback function to setState which is triggered once the state has been updated:

this.setState(
    {autocomplete_from: ...}, 
    function () {
        ... at this point the state of the component is set ...
    }
)

这篇关于反应 - 状态未更新的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！