分页后，分页工作正常

Question

这是我的jsFiddle示例：https://jsfiddle.net/0se06am5/

class Pagination extends React.Component {
    constructor(props) {
        super(props);

        this.state = { current: 1 };
        this.items = ['a', 'b', 'c'];
        this.filteredItems = [];

        this.prev = this.prev.bind(this);
        this.next = this.next.bind(this);
        this.set = this.set.bind(this);
        this.filter = this.filter.bind(this);
    }

    componentWillUpdate() {
        this.filter();
    }

    prev() {
        this.setState({ current: this.state.current - 1});
    }

    next() {
        this.setState({ current: this.state.current + 1});
    }

    set(val) {
        this.setState({ current: val });
    }

    filter() {
        this.filteredItems = this.items.filter((i, idx) => {
            return (idx + 1) === this.state.current;
        })
    }

    render() {
        return (
            <div>
                {this.filteredItems.map((i, idx) => {
                    return <span key={`item_${idx}`}>{i}</span>;
                })}<br />

                <span onClick={this.prev}>prev</span>

                <span onClick={this.set.bind(this, 1)}>1</span>
                <span onClick={this.set.bind(this, 2)}>2</span>
                <span onClick={this.set.bind(this, 3)}>3</span>

                <span onClick={this.next}>next</span>

                <br /><span>current: {this.state.current}</span>
            </div>
        )
    }
}

当您点击分页项目时，您意识到它无法正常工作。

为什么filter()方法会延迟运行？而不是componentWillUpdate()我应该移动这个方法或者我应该写什么不同？

Answer 1

componentWillUpdate在初始渲染中执行 。 将过滤移动到渲染，因为它不会更改状态本身，并且它应该在组件呈现时运行（demo）：

options
{
    backtrack=true;
    memoize=true;
}

您还可以将render() { const items = this.items.filter((i, idx) => { return (idx + 1) === this.state.current; }).map((i, idx) => { return <span key={`item_${idx}`}>{i}</span>; }); return ( <div> {items} <br /> <span onClick={this.prev}>prev</span> <span onClick={this.set.bind(this, 1)}>1</span> <span onClick={this.set.bind(this, 2)}>2</span> <span onClick={this.set.bind(this, 3)}>3</span> <span onClick={this.next}>next</span> <br /><span>current: {this.state.current}</span> </div> ) } 和.filter来电合并为一个.map来电（demo）：

.reduce