我正在创建一个应用程序,用户可以设计自己的形式。例如,指定字段的名称和应该包括的其他列的详细信息。
该组件可作为JSFiddle使用。
初始状态是这样的
var DynamicForm = React.createClass({
getInitialState: function() {
var items = {};
items[1] = { name: 'field 1', populate_at: 'web_start',
same_as: 'customer_name',
autocomplete_from: 'customer_name', title: '' };
items[2] = { name: 'field 2', populate_at: 'web_end',
same_as: 'user_name',
autocomplete_from: 'user_name', title: '' };
return { items };
},
render: function() {
var _this = this;
return (
<div>
{ Object.keys(this.state.items).map(function (key) {
var item = _this.state.items[key];
return (
<div>
<PopulateAtCheckboxes this={this}
checked={item.populate_at} id={key}
populate_at={data.populate_at} />
</div>
);
}, this)}
<button onClick={this.newFieldEntry}>Create a new field</button>
<button onClick={this.saveAndContinue}>Save and Continue</button>
</div>
);
}
当用户改变任何值时,我想更新状态,但我很难找到正确的对象:
var PopulateAtCheckboxes = React.createClass({
handleChange: function (e) {
item = this.state.items[1];
item.name = 'newName';
items[1] = item;
this.setState({items: items});
},
render: function() {
var populateAtCheckbox = this.props.populate_at.map(function(value) {
return (
<label for={value}>
<input type="radio" name={'populate_at'+this.props.id} value={value}
onChange={this.handleChange} checked={this.props.checked == value}
ref="populate-at"/>
{value}
</label>
);
}, this);
return (
<div className="populate-at-checkboxes">
{populateAtCheckbox}
</div>
);
}
});
我该怎么做呢?setState让它更新项目[1].name ?
以下是如何在没有帮助库的情况下做到这一点:
handleChange: function (e) {
// 1. Make a shallow copy of the items
let items = [...this.state.items];
// 2. Make a shallow copy of the item you want to mutate
let item = {...items[1]};
// 3. Replace the property you're intested in
item.name = 'newName';
// 4. Put it back into our array. N.B. we *are* mutating the array here,
// but that's why we made a copy first
items[1] = item;
// 5. Set the state to our new copy
this.setState({items});
},
如果你愿意,你可以结合步骤2和3:
let item = {
...items[1],
name: 'newName'
}
或者你可以用一行写完:
this.setState(({items}) => ({
items: [
...items.slice(0,1),
{
...items[1],
name: 'newName',
},
...items.slice(2)
]
}));
注意:我将项目创建为数组。OP使用一个对象。然而,概念是一样的。
你可以看到在你的终端/控制台发生了什么:
❯ node
> items = [{name:'foo'},{name:'bar'},{name:'baz'}]
[ { name: 'foo' }, { name: 'bar' }, { name: 'baz' } ]
> clone = [...items]
[ { name: 'foo' }, { name: 'bar' }, { name: 'baz' } ]
> item1 = {...clone[1]}
{ name: 'bar' }
> item1.name = 'bacon'
'bacon'
> clone[1] = item1
{ name: 'bacon' }
> clone
[ { name: 'foo' }, { name: 'bacon' }, { name: 'baz' } ]
> items
[ { name: 'foo' }, { name: 'bar' }, { name: 'baz' } ] // good! we didn't mutate `items`
> items === clone
false // these are different objects
> items[0] === clone[0]
true // we don't need to clone items 0 and 2 because we're not mutating them (efficiency gains!)
> items[1] === clone[1]
false // this guy we copied
发现这令人惊讶地困难,没有一个ES6传播魔法似乎工作如预期。
正在使用这样的结构来获得用于布局目的的渲染元素属性。
在这个简化的例子中,使用immutability-helper中的update方法是最直接的:
constructor(props) {
super(props)
this.state = { values: [] }
this.updateContainerState = this.updateContainerState.bind(this)
}
updateContainerState(index, value) {
this.setState((state) => update(state, { values: { [index]: { $set: value } } }))
}
改编自https://github.com/kolodny/immutability-helper#computed-property-names
要更新的数组成员是一个嵌套更复杂的对象,使用适当的深度复制方法基于复杂性。
当然有更好的方法来处理布局参数,但这是关于如何处理数组。每个子元素的相关值也可以在它们之外计算,但我发现向下传递containerState更方便,因此它们的子元素可以随意获取属性并在给定的索引处更新父状态数组。
import React from 'react'
import update from 'immutability-helper'
import { ContainerElement } from './container.component.style.js'
import ChildComponent from './child-component'
export default class ContainerComponent extends React.Component {
constructor(props) {
super(props)
this.state = { values: [] }
this.updateContainerState = this.updateContainerState.bind(this)
}
updateContainerState(index, value) {
this.setState((state) => update(state, { values: { [index]: { $set: value } } }))
}
// ...
render() {
let index = 0
return (
<ContainerElement>
<ChildComponent
index={index++}
containerState={this.state}
updateContainerState={this.updateContainerState}
/>
<ChildComponent
index={index++}
containerState={this.state}
updateContainerState={this.updateContainerState}
/>
</ContainerElement>
)
}
}
如果你只需要改变数组的一部分,
你有一个状态设置为的react组件。
state = {items: [{name: 'red-one', value: 100}, {name: 'green-one', value: 999}]}
最好更新数组中的red-one,如下所示:
const itemIndex = this.state.items.findIndex(i=> i.name === 'red-one');
const newItems = [
this.state.items.slice(0, itemIndex),
{name: 'red-one', value: 666},
this.state.items.slice(itemIndex)
]
this.setState(newItems)