我有两个组成部分:
父组件
子组件
我试图从Parent调用Child的方法,我尝试了这种方式,但不能得到一个结果:
class Parent extends Component {
render() {
return (
<Child>
<button onClick={Child.getAlert()}>Click</button>
</Child>
);
}
}
class Child extends Component {
getAlert() {
alert('clicked');
}
render() {
return (
<h1 ref="hello">Hello</h1>
);
}
}
是否有一种方法从父调用子方法?
注意:子组件和父组件在两个不同的文件中。
这里有个虫子?注意:
我同意rossipedia的解决方案使用forwardRef, useRef, useImperativeHandle
网上有一些错误的信息说refs只能从React类组件创建,但如果你使用上面提到的钩子,你确实可以使用函数组件。注意,只有在我将文件更改为在导出组件时不使用withRouter()后,钩子才对我有效。例如,从
export default withRouter(TableConfig);
取而代之的是
export default TableConfig;
In hindsight the withRouter() is not needed for such a component anyway, but usually it doesn't hurt anything having it in. My use case is that I created a component to create a Table to handle the viewing and editing of config values, and I wanted to be able to tell this Child component to reset it's state values whenever the Parent form's Reset button was hit. UseRef() wouldn't properly get the ref or ref.current (kept on getting null) until I removed withRouter() from the file containing my child component TableConfig
如果你这样做只是因为你想让Child为它的父对象提供一个可重用的trait,那么你可以考虑使用render-props来代替。
这种技术实际上把结构颠倒过来了。Child现在包装了父对象,所以我将它重命名为AlertTrait。为了保持连续性,我保留了Parent这个名字,尽管它现在已经不是一个真正的Parent了。
// Use it like this:
<AlertTrait renderComponent={Parent}/>
class AlertTrait extends Component {
// You will need to bind this function, if it uses 'this'
doAlert() {
alert('clicked');
}
render() {
return this.props.renderComponent({ doAlert: this.doAlert });
}
}
class Parent extends Component {
render() {
return (
<button onClick={this.props.doAlert}>Click</button>
);
}
}
在这种情况下,AlertTrait提供了一个或多个特征,它将这些特征作为道具传递给renderComponent道具中给定的任何组件。
Parent接收doAlert作为道具,并在需要时调用它。
(为了清晰起见,我在上面的例子中调用道具renderComponent。但在上面链接的React文档中,他们只称之为渲染。)
Trait组件可以在它的渲染函数中渲染父元素周围的东西,但它不渲染父元素内部的任何东西。实际上,如果它将另一个道具(例如renderChild)传递给父对象,父对象就可以在它的渲染方法中使用它,它就可以在父对象内部渲染东西。
这与OP要求的有些不同,但有些人可能会在这里结束(就像我们所做的那样),因为他们想要创建一个可重用的trait,并且认为子组件是实现这一点的好方法。
从父函数触发子函数的另一种方法是在子组件中使用componentDidUpdate函数。我将一个道具triggerChildFunc从父对象传递给子对象,初始值为null。当单击按钮时,该值更改为一个函数,Child注意到componentDidUpdate中的更改并调用自己的内部函数。
因为道具triggerChildFunc变成了一个函数,我们也得到了一个回调到父类的函数。如果Parent不需要知道函数何时被调用,则triggerChildFunc值可以从null改为true。
const { Component } = React;
const { render } = ReactDOM;
class Parent extends Component {
state = {
triggerFunc: null
}
render() {
return (
<div>
<Child triggerChildFunc={this.state.triggerFunc} />
<button onClick={() => {
this.setState({ triggerFunc: () => alert('Callback in parent')})
}}>Click
</button>
</div>
);
}
}
class Child extends Component {
componentDidUpdate(prevProps) {
if (this.props.triggerChildFunc !== prevProps.triggerChildFunc) {
this.onParentTrigger();
}
}
onParentTrigger() {
alert('parent triggered me');
// Let's call the passed variable from parent if it's a function
if (this.props.triggerChildFunc && {}.toString.call(this.props.triggerChildFunc) === '[object Function]') {
this.props.triggerChildFunc();
}
}
render() {
return (
<h1>Hello</h1>
);
}
}
render(
<Parent />,
document.getElementById('app')
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id='app'></div>
CodePen: https://codepen.io/calsal/pen/NWPxbJv?editors=1010
这里是我的演示:https://stackblitz.com/edit/react-dgz1ee?file=styles.css
I am using useEffect to call the children component's methods. I have tried with Proxy and Setter_Getter but sor far useEffect seems to be the more convenient way to call a child method from parent. To use Proxy and Setter_Getter it seems there is some subtlety to overcome first, because the element firstly rendered is an objectLike's element through the ref.current return => <div/>'s specificity.
Concerning useEffect, you can also leverage on this approach to set the parent's state depending on what you want to do with the children.
在我提供的演示链接中,你会发现我完整的ReactJS代码和我的草稿,所以你可以欣赏我的解决方案的工作流程。
在这里,我只提供了相关代码的ReactJS片段。:
import React, {
Component,
createRef,
forwardRef,
useState,
useEffect
} from "react";
{...}
// Child component
// I am defining here a forwardRef's element to get the Child's methods from the parent
// through the ref's element.
let Child = forwardRef((props, ref) => {
// I am fetching the parent's method here
// that allows me to connect the parent and the child's components
let { validateChildren } = props;
// I am initializing the state of the children
// good if we can even leverage on the functional children's state
let initialState = {
one: "hello world",
two: () => {
console.log("I am accessing child method from parent :].");
return "child method achieve";
}
};
// useState initialization
const [componentState, setComponentState] = useState(initialState);
// useEffect will allow me to communicate with the parent
// through a lifecycle data flow
useEffect(() => {
ref.current = { componentState };
validateChildren(ref.current.componentState.two);
});
{...}
});
{...}
// Parent component
class App extends Component {
// initialize the ref inside the constructor element
constructor(props) {
super(props);
this.childRef = createRef();
}
// I am implementing a parent's method
// in child useEffect's method
validateChildren = childrenMethod => {
// access children method from parent
childrenMethod();
// or signaling children is ready
console.log("children active");
};
{...}
render(){
return (
{
// I am referencing the children
// also I am implementing the parent logic connector's function
// in the child, here => this.validateChildren's function
}
<Child ref={this.childRef} validateChildren={this.validateChildren} />
</div>
)
}