使用异步等待的顺序函数调用问题

时间:2019-07-10 18:35:43

标签: typescript ionic4

我发现当我尝试调用函数时,必须首先调用initializeItems()。但是checkList()在initializeItems()之前被调用

  initializeItems() {

    this.dataService.readLocalData().subscribe( data => {
      console.log('Local Data');
      this.items = data;
      // console.log(this.items);
      this.tempItems = [];
      for (const i of this.items.material ){
        console.log(i['material-name']);
        this.tempItems.push( i['material-name'] );
      }
      console.log('***********************************************');
      console.log(this.tempItems);
    });
  }

  checkList(ev: any){
    // set val to the value of the searchbar
    const val = ev.target.value;
    console.log(val);
    console.log(this.tempItems);
    // if the value is an empty string don't filter the items
    if (val && val.trim() !== '') {
      this.tempItems = this.tempItems.filter((item) => {
        return (item.toLowerCase().indexOf(val.toLowerCase()) > -1);
      });
    }
  }

  async getItems(ev: any) {
    // Reset items back to all of the items
    await this.initializeItems(); //This need to execute first
    await this.checkList(ev); //But this getting executed
  }

如果函数按顺序调用。我的结果将是

initializeItems()

可变的tempItem将是//完整列表

然后

checkList()

可变tempItems将// //可搜索的下拉列表中的过滤列表

1 个答案:

答案 0 :(得分:1)

await用于诺言。由于initializeItems不返回承诺,所以await实际上并不等待任何东西。您需要修改initializeItems才能返回承诺。我的猜测是,您希望subscribe回调仅被调用一次,然后应会解决promise,因此您需要这样做:

initializeItems() {
  return new Promise((resolve) => { // <---- creating a promise
    this.dataService.readLocalData().subscribe( data => {
      console.log('Local Data');
      this.items = data;
      // console.log(this.items);
      this.tempItems = [];
      for (const i of this.items.material ){
        console.log(i['material-name']);
        this.tempItems.push( i['material-name'] );
      }
      console.log('***********************************************');
      console.log(this.tempItems);
      resolve(); // <-- resolving the promise
    });
  }
}