如何将数组分配给状态变量？

Question

我有一个看起来像这样的函数：

select(e) {
    let { selectedItems } = this.state;

    let arr: number[] = [];
    for (var i = 0; i < 2; i++) arr = [...arr, i];

    this.setState(
      {
        selectedItems: arr,
      }
    );
  console.log(selectedItems);
  }

但是当我尝试console.log(selectedItems) 时，我得到的只是一个空数组。当我 console.log(arr) 时，我得到了我正在寻找的正确输出 - 一个长度为 2 的数组。这里可能发生了什么以及如何将 selectedItems 分配给 arr 的值？

Answer 1

class A {
  select(e) {
    let { selectedItems } = this.state;
    let arr: number[] = [];
    for (var i = 0; i < 2; i++) arr = [...arr, i];
    this.setState({
      selectedItems: arr
    }, function callback() {
      console.log(this.state) // will have updated value
    });
    console.log(selectedItems); // wont print anything, coz u never assign
    selectedItems = arr;
    console.log(selectedItems); // will have updated value
  }
}

Answer 2

setState 采用回调函数。请尝试以下操作：

  select(e) {
    let { selectedItems } = this.state;

    let arr: number[] = [];
    for (var i = 0; i < 2; i++) arr = [...arr, i];

    this.setState({
      selectedItems: arr,
    }, function(){
        console.log(this.state);
    }.bind(this));
  }