Angular- Disable button till dropdown option is selected

Question

I made a dropdown As you can see there are empty textareas and no option is selected. I want to disable all the buttons until any option is selected and textareas are full, means making selecting an option mandatory. How do I do it?

This is my code:

<div>
  <table class="justify-content-between">
    <tr *ngFor="let entity of rows">
      <td class="col-1" *ngIf="entity.value!=null">
        <mat-select [(ngModel)]="entity.code" (selectionChange)="onChangeValue($event)" required>
          <mat-option *ngFor="let lang of languages" [disabled]="!lang.canEdit" [value]="lang.code" disabled>{{ lang.title }}</mat-option>
        </mat-select>
      </td>
      <td class="col-1" *ngIf="entity.value!=null">
        <textarea style="height: 2rem" class="pl-5" >{{ entity.value }}</textarea>
      </td>
    </tr>
  </table>
  <div class="d-flex flex-column align-items-center mt-2">
    <button class="form-control" (click)="addNewLanguage()">Add new language</button>
      <div class="d-flex pt-2">
        <button class="form-control">Discard</button>
        <button class="form-control ml-4">Save Changes</button>
      </div>
  </div>
</div>

The ts file:

dialogData: DialogDataModel;

  languages: any[];

  rows: any[] = [];

  constructor(@Inject(MAT_DIALOG_DATA) public data: DialogDataModel) {
      this.dialogData = data;
      this.rows = this.dialogData.localisedEntities.filter(lang => lang.value);
      this.languages = this.dialogData.localisedEntities.map(item => ({ code: item.code, title: item.title, canEdit: item.canEdit }))
    }

  ngOnInit(): void {
  }

  addNewLanguage() {
    this.rows.push({
      code: '',
      title: '',
      value: '',
      canEdit: true
    });
  }

  onChangeValue(ev: any){
    this.rows = this.rows.map(row => {
      if (row.code == ev.value) {
        const lang = this.languages.find(lang => lang.code == ev.value);
        row.title =lang.title;
      }
      return row;
    });
    

    this.languages = this.languages.map(lang => {
      if (lang.code == ev.value) {
        lang.canEdit = false;
      }
      return lang;
    });

  }

Answer 1

You need to call on changeEvent whenever an option is selected or text field is changed For option selected

 <mat-select
            [(ngModel)]="entity.code"
            (selectionChange)="onChangeValue($event)"
            required
>

for text area you also need to bind the value to ngModel like this

 <textarea
            [(ngModel)]="entity.value"
            (change)="isDisabled()"
            style="height: 2rem"
            class="pl-5"
          ></textarea>

and the buttons you want to disable you need to add disable property like this

<button
        class="form-control"
        (click)="addNewLanguage()"
        [disabled]="isDisabled()"
      >
        Add new language
      </button>

 <button class="form-control ml-4" [disabled]="isDisabled()">
          Save Changes
        </button>

and in ts file you need to do this

 onChangeValue() {
    this.isDisabled();
  }
  isDisabled() {
    return this.rows.filter((item) => item.value == '' || item.code == '')
      .length > 0
      ? true
      : false;
  }

you will see both are calling the same function on event change

here is the stackblitz just for demo cahnge it as your ease https://stackblitz.com/edit/angular-mat-select-example-decme7