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Question

下面是我的代码示例：

（如果选择了两个，则显示一个输入）

https://stackblitz.com/edit/angular-fqkfyx

 <div class="offset-md-2">
  <form [formGroup]="usForm">
    <div class="div-champs">
      <p id="champs">Type
        <span id="required">*</span>
      </p>
      <div class="select-style ">
          <select [(ngModel)]="selectedOption" name="type">
              <option style="display:none">
              <option [value]="o.name" *ngFor="let o of options">
                {{o.name}}
              </option>
          </select>
      </div>
    </div>
    <p id="champs" *ngIf="selectedOption == 'two'">Appears
      <input type="appears" class="form-control" name="appears">
    </p>
  </form>
</div>

import { Component, OnInit } from '@angular/core';

import { FormGroup, FormBuilder } from '@angular/forms';

@Component({
  selector: 'app-create-us',
  templateUrl: './create-us.component.html',
  styleUrls: ['./create-us.component.css']
})
export class CreateUsComponent implements OnInit {

  public usForm: FormGroup;
  public selectedOption: string;

  constructor(private fb: FormBuilder) {
  }

  ngOnInit() {
    this.createForm();
  }

  createForm() {
    this.usForm = this.fb.group({
      'type': [null, ],
      'appears': [null, ],
    });
  }

  options = [
    { name: 'first', value: 1 },
    { name: 'two', value: 2 }
  ];
}

你好，瓦伦丁

Answer 1

您应该使用FormControlName而不是[(ngModel)]。

然后在比较中，您应该比较usform.value.type而不是selectedvalue。

试试看：

<div class="offset-md-2">
  <form [formGroup]="usForm">
    <div class="div-champs">
      <p id="champs">Type
        <span id="required">*</span>
      </p>
      <div class="select-style ">
          <select formControlName="type" name="type">
              <option style="display:none">
              <option [value]="o.name" *ngFor="let o of options">
                {{o.name}}
              </option>
          </select>
      </div>
    </div>
    <p id="champs" *ngIf="usForm.value.type == 'two'">Appears
      <input type="appears" class="form-control" name="appears">
    </p>
  </form>
</div>