touched and valid using reactive forms in Angular

问题

How can i use the touched and valid properties using reactive forms in angular 4. I've used in template driven forms and you can just put this <span class="text-muted" *ngIf="!fname.valid && fname.touched"> Please enter a valid first name</span> below the input field. I've also learned that reactive forms would be better since you have to write the logic in the component.ts. So i want it to implement in the reactive form and i'm stuck on how to use the touched and valid properties.

html

<form [formGroup]="form" (ngSubmit)="onSignIn(form)">
    <div class="form-group">
        <input type="text" class="form-control" id="email" placeholder="Enter email" formControlName="email">
    </div>
    <div class="form-group">
        <input type="password" class="form-control" id="password" placeholder="Password" formControlName="password">
    </div><button class="btn btn-primary btn-block" type="submit" [disabled]="!form.valid">Sign In</button>
</form>

ts

 ngOnInit() {
    this.form = this.formBuilder.group({
      email: [null, [Validators.required, Validators.email]],
      password: [null, Validators.required],
    });
  }

  onSignIn(form: FormGroup){
    const email = form.value.email;
    const password = form.value.password;
    this.authService.loginUser(email, password)
    .subscribe(
      data => {
        this.router.navigate(['/settings']);
        alert("Login Successful");
        console.log(data);
      },
      error => {
        alert("Invalid Email or Password");
        console.log(error);
      });
  }

回答1:

Try this

 <span class="text-muted" *ngIf="!form.controls['email'].valid && form.controls['email']?.touched"> Please enter a valid first name</span>

回答2:

You can use it in similar way. To get the FormControl use get method on FormGroup object and then hasError:

// in your template form.get('email').hasError('required') && form.get('email').touched form.get('email').hasError('email') && form.get('email').touched form.get('password').hasError('required') && form.get('password').touched

You can also create some nice methods/getters for that in your component.

---

edit (full code)

<form [formGroup]="form" (ngSubmit)="onSignIn(form)">
    <div class="form-group">
        <input type="text" class="form-control" id="email" placeholder="Enter email" formControlName="email">
      <span class="text-muted" *ngIf="form.get('email').hasError('required') && form.get('email').touched">Email is required</span>
    </div>
    <div class="form-group">
        <input type="password" class="form-control" id="password" placeholder="Password" formControlName="password">
         <span class="text-muted" *ngIf="form.get('password').hasError('required') && form.get('password').touched">Password is required</span>
    </div><button class="btn btn-primary btn-block" type="submit" [disabled]="!form.valid">Sign In</button>
</form>

来源：https://stackoverflow.com/questions/46499786/touched-and-valid-using-reactive-forms-in-angular