Both mat-error show when only one condition is true

Question

Both mat-error show when only one error appeared.

I'm trying to make custom validators with mat-error. Both input for email and confirm password are red when each of them has a true value for hasError('').

I think my MyErrorStateMatcher class logic is wrong somehow. Please help! I have tried anything I could. Thank you in advance!

Image

As you can see in the image. When confirmPassword throws an error, the email field is also red.

---

My ErrorStateMatcher:

export class MyErrorStateMatcher implements ErrorStateMatcher {
  isErrorState(control: FormControl | null, form: FormGroupDirective | NgForm | null): boolean {
    const invalidCtrl = !!(control && control.invalid && (control.dirty || control.touched));
    const invalidParent = !!(control && (control.parent.hasError('notTheSame') || control.parent.hasError('emailUsed')));

    return ((invalidCtrl || invalidParent));
  }
}

HTML: (focus on email and confimPassword)

<form [formGroup]="signupForm" (ngSubmit)="signup(signupForm)">
        <mat-form-field style="width: 100%;">
          <input matInput formControlName="email" placeholder="Email address" type="email" [errorStateMatcher]="matcher" required>
          <mat-error *ngIf="signupForm.controls.email.hasError('required')">Email required!</mat-error>
          <mat-error *ngIf="signupForm.controls.email.hasError('email')">Email invalid!</mat-error>
          <mat-error *ngIf="signupForm.hasError('emailUsed')">This email already exists!</mat-error>
        </mat-form-field>
        <mat-form-field style="width: 100%;">
          <input matInput formControlName="username" placeholder="User name" (blur)="signupForm.value.username != null ? isValidUsername(signupForm.value.username) : ''" required />
          <mat-error>Please enter your new username!</mat-error>
          <mat-error *ngIf="usernameInvalid">Username already exists!</mat-error>
        </mat-form-field>
        <mat-form-field style="width: 100%;">
          <input matInput formControlName="password" placeholder="New password" [type]="show ? 'text' : 'password'" required />
          <mat-icon matSuffix (click)="show = !show" style="cursor: pointer;">{{show ? 'visibility' : 'visibility_off'}}</mat-icon>
          <mat-error>Please enter your password!</mat-error>
        </mat-form-field>
        <mat-form-field style="width: 100%;">
          <input matInput formControlName="confirmPassword" placeholder="Confirm password" type="password" [errorStateMatcher]="matcher" required>
          <mat-error *ngIf="signupForm.controls.confirmPassword.hasError('required')">Please confirm your password!</mat-error>
          <mat-error *ngIf="signupForm.hasError('notTheSame') && signupForm.value.confirmPassword != ''">Password is not the same!</mat-error>
        </mat-form-field>
        <br>
      <button mat-raised-button class="sessionBtn" color="primary" [disabled]="signupForm.invalid">Submit!</button>
</form>

TS:

signupForm = new FormGroup({
    firstName: new FormControl(),
    lastName: new FormControl(),
    email: new FormControl('', [
      Validators.required,
      Validators.email
    ]),
    username: new FormControl(),
    password: new FormControl('', [
      Validators.required
    ]),
    confirmPassword: new FormControl('', [
      Validators.required
    ])
  }, { validators: [this.checkPassword, this.checkExistingEmail] });
  matcher = new MyErrorStateMatcher();

/////////Custom validator////////

  checkPassword(signupForm: FormGroup) {
    let password = signupForm.value.password;
    let confirmPassword = signupForm.value.confirmPassword;

    return password === confirmPassword ? null : { notTheSame: true };
  }

  checkExistingEmail(signupForm: FormGroup) {
    let inputEmail = signupForm.value.email;
    let dbEmail = "test@test.com";

    return inputEmail !== dbEmail ? null: { emailUsed: true };
  }

Error happend with input email and input confirmPassword, both have [errorStateMatcher]="matcher"

Answer 1

Creating a customErrorMatcher

Well, if we want to show an error in a <mat-form-field> when the input is valid, we use a customErrorMatcher.

This is a class like

class CrossFieldErrorMatcher implements ErrorStateMatcher {
  isErrorState(control: FormControl | null, form: FormGroupDirective | NgForm | null): boolean {
    //when we want to show the error
    return true 
    //when we want not show the error
    return false
  }
}

Normally we has in our component

  errorMatcher=new CrossFieldErrorMatcher()
  //and the .html
  <mat-form-field>
    <input matInput formControlName='verifyPassword' 
        [errorStateMatcher]="errorMatcher">
    <mat-error *ngIf="....">
      Passwords do not match!
    </mat-error>
  </mat-form-field>

Well, we are change the things a bit, adding a constructor in our customErrorMatcher

class CrossFieldErrorMatcher implements ErrorStateMatcher {
  constructor(private name:string){}  //<--add a constructor
  isErrorState(control: FormControl | null, form: FormGroupDirective | NgForm | null): boolean {
    //when we want to show the error, but we can use "name"
    return true 
    //when we want not show the error
    return false
  }
}

Then, our component becomes

  errorMatcher(name:string)
  {
    return new CrossFieldErrorMatcher(name);
  }

  //and the .html
  <mat-form-field>
    <input matInput formControlName='verifyPassword' 
        [errorStateMatcher]="errorMatcher('password')">
    <mat-error *ngIf="....">
      Passwords do not match!
    </mat-error>
  </mat-form-field>

Answer 2

The email address field shows an error because the error state matcher checks the parent - which is the form - which is in error because the password fields do not match. You need to use different error state matchers for the email field and password fields because the conditions are different - email does not need to be in error if the password fields don't match.