在创建可观察时间时评估订阅回调 [英] Evaluate subscription callback at time observable is created

问题描述

我有一个反应式表单，在该表单中，当可观察对象发出数据(并调用订阅函数)时，以下订阅中的函数对itm["value"].length-1进行求值.

I have a Reactive Form in which it appears the function inside the following subscription evaluates itm["value"].length-1 at the time the observable emits data (and calls the subscription function).

      this.formCtls[controlName] = new FormControl('', {updateOn: 'blur'});
      this.userForm.addControl(controlName, this.formCtls[controlName]);
      this.formCtls[controlName].valueChanges.subscribe(val=>{
        itm["value"][itm["value"].length-1]=val;
        this.renderDataArray();
      });

但是，我希望在创建observable/(FormControl)时对订阅回调函数表达式itm["value"].length-1进行求值.

However I want the subscription callback function expression itm["value"].length-1 to be evaluated at the time the observable/(FormControl) is created.

例如，在创建表单控件时，itm["value"].length可能仅是2，但是在Observable发出itm["value"].length时，可能是6或7或任何其他数字.我如何(以编程方式)将2(或等同版本)硬连接"到订阅回调中?

For instance, at the time the form control is created, itm["value"].length might only be 2, but at the time the Observable emits itm["value"].length may be 6 or 7 or any other number. How can I (programatically) "hardwire" the 2 (or equivalent) into the subscription callback?

非常感谢！

推荐答案

我现在不太确定下面的答案.它在我的代码中有效，但是我不确定为什么起作用.我将重新评估此临时答案并发布更新.同时，我非常感谢专家的任何意见，因为我对这些Observable感到有些困惑和迷茫. . .

I'm not so sure about the answer below now. It worked in my code, but I'm not sure why it worked. I will re-evaluate this provisional answer and post an update. In the meantime, I'd be very grateful for any input from an expert as I'm a bit confused and lost amongst these Observables. . .

this.formCtls[controlName] = new FormControl('', {updateOn: 'blur'});
      this.userForm.addControl(controlName, this.formCtls[controlName]);
      const idx = itm["value"].length-1;
      this.formCtls[controlName].valueChanges.subscribe(val=>{
        itm["value"][idx]=val;
        this.renderDataArray();
      });

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