javascript - 如何仅在OnInit之后启动iterableDiffer？

Question

我的问题是，当我只从数据库中初始化数据时，iterableDiffer 检测到更改。我不想进行第一次更改检测。我只想在用户编辑数组时获得更改检测。

我尝试将数据库请求放入构造函数中。没有改变任何东西。

  constructor(
    private route: ActivatedRoute,
    private StoreService: StoreService,
    private iterableDiffers: IterableDiffers
  ) {
     this.iterableDiffer = 
       this.iterableDiffers.find([]).create(null);
  }

  myArray: MyClass[] = [];

  iterableDiffer: IterableDiffer<unknown>;

  ngOnInit() {
    const id = this.route.snapshot.params.id;
    this.StoreService.getData(id)
       .subscribe(data => this.myArray = data);
    // on this subscribe, the Differ falsely gets triggered
  }

  ngAfterViewChecked() {
    const changes = this.iterableDiffer.diff(this.myArray);
    if (changes) {
      changes.forEachAddedItem((record: IterableChangeRecord<MyClass>) => {

        console.log('Added Changes detected');

        this.StoreService.addToDatabase(record.item);
      });
    }
  }

  // gets called by User Click, here i want to have the Differ called
  // This works fine
  addElmt(elmt: MyClass) {
    this.myArray.push(elmt);
  }

代码片段是真实代码的简化版本。我无法在函数 addElmt() 中调用 StoreService.addToDatabase()。这只是为了更好的解释。

感谢您的帮助!

Answer 1

总是可以有一个变量“myObserver”并执行

myObserver:any=null
ngAfterViewChecked() {
    const changes = this.iterableDiffer.diff(this.myArray);
    if (changes) {
      changes.forEachAddedItem((record: IterableChangeRecord<MyClass>) => {

        console.log('Added Changes detected');

        this.StoreService.addToDatabase(record.item);
      });
    }
    if (!myObserver)
    {
      const id = this.route.snapshot.params.id;
      myObserver=this.StoreService.getData(id)
         .subscribe(data => this.myArray = data);
    }
}