setState의 업데이트가 완료된 후 함수를 실행할 수 있습니까?

setState의 업데이트가 완료된 후 함수를 실행할 수 있습니까?

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나는 React JS를 처음 접했다 (지금 막 시작한 것처럼). setState 작동 방식을 잘 모르겠습니다. React와 Easel JS를 결합하여 사용자 입력을 기반으로 그리드를 그립니다. 여기 내 JS 빈이 있습니다 : http://jsbin.com/zatula/edit?js,output

코드는 다음과 같습니다.

        var stage;

    var Grid = React.createClass({
        getInitialState: function() {
            return {
                rows: 10,
                cols: 10
            }
        },
        componentDidMount: function () {
            this.drawGrid();
        },
        drawGrid: function() {
            stage = new createjs.Stage("canvas");
            var rectangles = [];
            var rectangle;
            //Rows
            for (var x = 0; x < this.state.rows; x++)
            {
                // Columns
                for (var y = 0; y < this.state.cols; y++)
                {
                    var color = "Green";
                    rectangle = new createjs.Shape();
                    rectangle.graphics.beginFill(color);
                    rectangle.graphics.drawRect(0, 0, 32, 44);
                    rectangle.x = x * 33;
                    rectangle.y = y * 45;

                    stage.addChild(rectangle);

                    var id = rectangle.x + "_" + rectangle.y;
                    rectangles[id] = rectangle;
                }
            }
            stage.update();
        },
        updateNumRows: function(event) {
            this.setState({ rows: event.target.value });
            this.drawGrid();
        },
        updateNumCols: function(event) {
            this.setState({ cols: event.target.value });
            this.drawGrid();
        },
        render: function() {
            return (
                <div>
                    <div className="canvas-wrapper">
                        <canvas id="canvas" width="400" height="500"></canvas>
                        <p>Rows: { this.state.rows }</p>
                        <p>Columns: {this.state.cols }</p>
                    </div>
                    <div className="array-form">
                        <form>
                            <label>Number of Rows</label>
                            <select id="numRows" value={this.state.rows} onChange={ this.updateNumRows }>
                                <option value="1">1</option>
                                <option value="2">2</option>
                                <option value ="5">5</option>
                                <option value="10">10</option>
                                <option value="12">12</option>
                                <option value="15">15</option>
                                <option value="20">20</option>
                            </select>
                            <label>Number of Columns</label>
                            <select id="numCols" value={this.state.cols} onChange={ this.updateNumCols }>
                                <option value="1">1</option>
                                <option value="2">2</option>
                                <option value="5">5</option>
                                <option value="10">10</option>
                                <option value="12">12</option>
                                <option value="15">15</option>
                                <option value="20">20</option>
                            </select>
                        </form>
                    </div>    
                </div>
            );
        }
    });
    ReactDOM.render(
        <Grid />,
        document.getElementById("container")
    );

드롭 다운 중 하나를 사용하여 행 또는 열 수를 변경하면 JS bin에서 볼 수 있습니다. 처음으로 아무 일도 일어나지 않습니다. 다음에 드롭 다운 값을 변경하면 그리드가 이전 상태의 행 및 열 값으로 그려집니다. setState가 완료되기 전에 this.drawGrid () 함수가 실행 중이기 때문에 이것이 발생하고 있다고 생각합니다. 다른 이유가 있을까요?

시간 내 주셔서 감사합니다!

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setState(updater[, callback]) 비동기 함수입니다.

https://facebook.github.io/react/docs/react-component.html#setstate

You can execute a function after setState is finishing using the second param callback like:

this.setState({
    someState: obj
}, () => {
    this.afterSetStateFinished();
});

---

render will be called every time you setState to re-render the component if there are changes. If you move your call to drawGrid there rather than calling it in your update* methods, you shouldn't have a problem.

If that doesn't work for you, there is also an overload of setState that takes a callback as a second parameter. You should be able to take advantage of that as a last resort.

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when new props or states being received (like you call setState here), React will invoked some functions, which are called componentWillUpdate and componentDidUpdate

in your case, just simply add a componentDidUpdate function to call this.drawGrid()

here is working code in JS Bin

as I mentioned, in the code, componentDidUpdate will be invoked after this.setState(...)

then componentDidUpdate inside is going to call this.drawGrid()

read more about component Lifecycle in React https://facebook.github.io/react/docs/component-specs.html#updating-componentwillupdate

---

Making setState return a Promise

In addition to passing a callback to setState() method, you can wrap it around an async function and use the then() method -- which in some cases might produce a cleaner code:

(async () => new Promise(resolve => this.setState({dummy: true}), resolve)()
    .then(() => { console.log('state:', this.state) });

And here you can take this one more step ahead and make a reusable setState function that in my opinion is better than the above version:

const promiseState = async state =>
    new Promise(resolve => this.setState(state, resolve));

promiseState({...})
    .then(() => promiseState({...})
    .then(() => {
        ...  // other code
        return promiseState({...});
    })
    .then(() => {...});

This works fine in React 16.4, but I haven't tested it in earlier versions of React yet.

Also worth mentioning that keeping your callback code in componentDidUpdate method is a better practice in most -- probably all, cases.

참고URL : https://stackoverflow.com/questions/34687091/can-i-execute-a-function-after-setstate-is-finished-updating