setState() inside of componentDidUpdate()

问题:

I'm writing a script which moves dropdown below or above input depending on height of dropdown and position of the input on the screen. Also I want to set modifier to dropdown according to its direction. But using setState inside of the componentDidUpdate creates an infinite loop(which is obvious)

I've found a solution in using getDOMNode and setting classname to dropdown directly, but i feel that there should be a better solution using React tools. Can anybody help me?

Here is a part of working code with getDOMNode (i a little bit neglected positioning logic to simplify code)

let SearchDropdown = React.createClass({
    componentDidUpdate(params) {
        let el = this.getDOMNode();
        el.classList.remove('dropDown-top');
        if(needToMoveOnTop(el)) {
            el.top = newTopValue;
            el.right = newRightValue;
            el.classList.add('dropDown-top');
        }
    },
    render() {
        let dataFeed = this.props.dataFeed;
        return (
            <DropDown >
                {dataFeed.map((data, i) => {
                    return (<DropDownRow key={response.symbol} data={data}/>);
                })}
            </DropDown>
        );
    }
});

and here is code with setstate (which creates an infinite loop)

let SearchDropdown = React.createClass({
    getInitialState() {
        return {
            top: false
        };
    },
    componentDidUpdate(params) {
        let el = this.getDOMNode();
        if (this.state.top) {
           this.setState({top: false});
        }
        if(needToMoveOnTop(el)) {
            el.top = newTopValue;
            el.right = newRightValue;
            if (!this.state.top) {
              this.setState({top: true});
           }
        }
    },
    render() {
        let dataFeed = this.props.dataFeed;
        let class = cx({'dropDown-top' : this.state.top});
        return (
            <DropDown className={class} >
                {dataFeed.map((data, i) => {
                    return (<DropDownRow key={response.symbol} data={data}/>);
                })}
            </DropDown>
        );
    }
});

回答1:

You can use setStateinside componentDidUpdate. The problem is that somehow you are creating an infinite loop because there's no break condition.

Based on the fact that you need values that are provided by the browser once the component is rendered, I think your approach about using componentDidUpdate is correct, it just needs better handling of the condition that triggers the setState.

回答2:

If you use setState inside componentDidUpdate it updates the component, resulting in a call to componentDidUpdate which subsequently calls setState again resulting in the infinite loop. You should conditionally call setState and ensure that the condition violating the call occurs eventually e.g:

componentDidUpdate: function() {
    if (condition) {
        this.setState({..})
    } else {
        //do something else
    }
}

In case you are only updating the component by sending props to it(it is not being updated by setState, except for the case inside componentDidUpdate), you can call setState inside componentWillReceiveProps instead of componentDidUpdate.

回答3:

The componentDidUpdate signature is void::componentDidUpdate(previousProps, previousState). With this you will be able to test which props/state are dirty and call setState accordingly.

Example:

componentDidUpdate(previousProps, previousState) {
    if (previousProps.data !== this.props.data) {
        this.setState({/*....*/})
    }
}

回答4:

I would say that you need to check if the state already has the same value you are trying to set. If it's the same, there is no point to set state again for the same value.

Make sure to set your state like this:

let top = newValue /*true or false*/
if(top !== this.state.top){
    this.setState({top});
}

回答5:

I had a similar problem where i have to center the toolTip. React setState in componentDidUpdate did put me in infinite loop, i tried condition it worked. But i found using in ref callback gave me simpler and clean solution, if you use inline function for ref callback you will face the null problem for every component update. So use function reference in ref callback and set the state there, which will initiate the re-render