Dynamically load multiple dropdown in formarray in angular 6

Question

I want to load two dropdown one dropdown is based on another dropdown.

I am using formarray to load the form values. In my actual scenario, first i am loading values in *ngfor loop with form data(formarray). below image shows my example scenario.

Img Brief: name, age, dob are like label field. only dropdowns are form.

first i am loading values in view using *ngFor then i am loading values using form array.

here on load it should load the dropdown values. if i am selecting first dropdown. it should change the second dropdown values. on load it self i am load the data in both the dropdown using service.

component.ts

this.wholedata.foreach({ x =>
 this.sampleservice.dropdown(x.firstdropdownvalue).subscribe({
  this.samplevalue = res;
  control.push({
   dropdownvalue1: x.firstdropdownvalue,
   dropdownvalue2: x.seconddropdownvalue
  })
 })
})

component.html

<div *ngFor="let data of datas">
 //formarray codes here placed
 <span>name: {{data.name}}</span>
 <span>age: {{data.age}}</span>
 <span>dob: {{data.dob}}</span>
 <span>
  <select formControlName="dropdownvalue1" (change)="changevalues($event)">
   <option *ngFor="let data of dropdownvalue">{{data.values}}</option>
  </select>
 </span>
 <span>
  <select formControlName="dropdownvalue2">
   <option *ngFor="let data of samplevalue">{{data.values}}</option>
  </select>
 </span>
 <button type="submit" (click)="submitValues()">
</div>

Currently samplevalue variable values loading to last *ngfor loop because the dynamic dropdown value is changing every array based on firstdropdown so i cant able to set the value.

Answer 1

you must use different list for each dropdown. So

//you have a variable "options"
options:any;

//when you change one drop
this.sampleservice.dropdown(x.firstdropdownvalue).subscribe({
  //Your response I supouse will be like ["one","two","three"..] (1)
  //or [{value:1,data:"one"},{value:2,data:"two"}...] (2)
  this.options[x.firsdropdownvalue]= res; //<--store the res in the object ...
  })

//So, your dropdowns can be like
<span>
  <select formControlName="dropdownvalue1" (change)="changevalues($event)">
  </select>
 </span>
 <span>
  <select formControlName="dropdownvalue2">
   <option *ngFor="let data of options[myForm.get('dropdownvalue1').value]">  
   <!--if your data is like (1) -->
   {{data}}   
   <!--if your data is like (2)
   {{data.values}}
    -->
   </option>
  </select>
 </span>

Another option if your dropdowns don't have a large ammount of items is have some like

options=[
   {value:1,data:"one",values:[{value:1,data:"one-one"},{value:2,data:"one-two"},..]},
   {value:2,data:"two",values:[{value:1,data:"two-one"},{value:2,data:"two-two"},..]},
   ...]

// Then you can write
<span>
  <select formControlName="dropdownvalue1" >
   <option *ngFor="let data of options" [ngValue]="data">{{data.data}}</option>
  </select>
 </span>
 <span>
  <select formControlName="dropdownvalue2">
   <option *ngFor="let data of myForm.get('dropdownvalue1').value.values">{{data.values}}</option>
  </select>
 </span>

but be carefull! dropdownvalue if an object (the whole object of the selection)