angular - Display custom validator error with mat-error

Angular - Display custom validator error with mat-error

To display custom validator errors with mat-error in Angular, you can create a custom validator function and then use it in your form controls. Here's an example:

Let's say you want to create a custom validator that checks if a password contains at least one uppercase letter. Here's how you can do it:

  1. Create a custom validator function:
import { AbstractControl, ValidationErrors, ValidatorFn } from '@angular/forms'; export function uppercaseValidator(): ValidatorFn { return (control: AbstractControl): ValidationErrors | null => { const value: string = control.value || ''; const hasUppercase = /[A-Z]/.test(value); return hasUppercase ? null : { uppercase: true }; }; }

This function returns a validator function that checks if the input contains at least one uppercase letter. If not, it returns a validation error with the key uppercase.

  1. Use the custom validator in your component:
import { Component } from '@angular/core'; import { FormBuilder, FormGroup, Validators } from '@angular/forms'; import { uppercaseValidator } from './path-to-your-validator'; @Component({ selector: 'app-your-component', template: ` <form [formGroup]="form"> <mat-form-field> <input matInput formControlName="password" placeholder="Password"> <mat-error *ngIf="form.get('password').hasError('uppercase')"> Password must contain at least one uppercase letter. </mat-error> </mat-form-field> </form> `, }) export class YourComponent { form: FormGroup; constructor(private fb: FormBuilder) { this.form = this.fb.group({ password: ['', [Validators.required, uppercaseValidator()]], }); } }

In this example, the uppercaseValidator is used in the Validators array for the password control. The mat-error element uses the hasError method to check for the specific error condition (uppercase) and displays an error message accordingly.

Remember to adjust the validation logic and error messages based on your specific requirements. This example illustrates the general process of creating a custom validator and using it with mat-error.

Examples

  1. "Angular custom validator error not showing in mat-error"

    • Code Implementation:
      <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customError')"> Custom error message </mat-error> </mat-form-field>
    • Description: Using the *ngIf directive with hasError method to conditionally display a custom error message in mat-error.

  2. "Angular display multiple custom validator errors with mat-error"

    • Code Implementation:
      <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customError1')"> Custom error message 1 </mat-error> <mat-error *ngIf="customFormControl.hasError('customError2')"> Custom error message 2 </mat-error> </mat-form-field>
    • Description: Handling multiple custom errors by using multiple mat-error elements with distinct conditions.

  3. "Angular display custom validator error with reactive forms"

    • Code Implementation:
      // In your component customFormControl = new FormControl('', [customValidator]); 
      <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customError')"> Custom error message </mat-error> </mat-form-field>
    • Description: Using a reactive form control with a custom validator and displaying the error message in mat-error.

  4. "Angular display custom validator error on submit"

    • Code Implementation:
      <form (ngSubmit)="onSubmit()"> <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customError') && customFormControl.touched"> Custom error message </mat-error> </mat-form-field> <button type="submit">Submit</button> </form> 
      // In your component onSubmit() { // Your form submission logic }
    • Description: Displaying custom validator error only after the form control has been touched and during form submission.

  5. "Angular display custom validator error with async validation"

    • Code Implementation:
      // In your component customAsyncValidator(control: AbstractControl): Observable<ValidationErrors | null> { return of({ customError: true }).pipe(delay(1000)); // Simulating async validation } customFormControl = new FormControl('', null, [this.customAsyncValidator.bind(this)]); 
      <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customError') && customFormControl.touched"> Custom async error message </mat-error> </mat-form-field>
    • Description: Implementing an async custom validator and displaying the error message once the async validation is complete.

  6. "Angular display custom validator error with template-driven forms"

    • Code Implementation:
      <form #myForm="ngForm"> <mat-form-field> <input matInput [(ngModel)]="model.property" name="property" #property="ngModel" required customValidator> <mat-error *ngIf="property.hasError('customError') && property.touched"> Custom error message </mat-error> </mat-form-field> </form>
    • Description: Using template-driven forms with ngModel and displaying the custom validator error in mat-error.

  7. "Angular display custom validator error for specific validation rule"

    • Code Implementation:
      // In your component customFormControl = new FormControl('', [customValidator]); 
      <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customRule1')"> Custom error for Rule 1 </mat-error> <mat-error *ngIf="customFormControl.hasError('customRule2')"> Custom error for Rule 2 </mat-error> </mat-form-field>
    • Description: Displaying different custom error messages for specific validation rules using distinct error codes.

  8. "Angular display custom validator error with custom directive"

    • Code Implementation:
      // In your custom validator directive @Directive({ selector: '[appCustomValidator]', providers: [{ provide: NG_VALIDATORS, useExisting: forwardRef(() => CustomValidatorDirective), multi: true }] }) export class CustomValidatorDirective implements Validator { validate(control: AbstractControl): ValidationErrors | null { // Your custom validation logic return { customError: true }; } } 
      <mat-form-field> <input matInput [formControl]="customFormControl" appCustomValidator> <mat-error *ngIf="customFormControl.hasError('customError')"> Custom error message </mat-error> </mat-form-field>
    • Description: Creating a custom validator directive and using it to display the custom error message in mat-error.

  9. "Angular display custom validator error with multiple validations"

    • Code Implementation:
      // In your component customFormControl = new FormControl('', [customValidator1, customValidator2]); 
      <mat-form-field> <input matInput [formControl]="customFormControl"> <mat-error *ngIf="customFormControl.hasError('customError1')"> Custom error message 1 </mat-error> <mat-error *ngIf="customFormControl.hasError('customError2')"> Custom error message 2 </mat-error> </mat-form-field>
    • Description: Using multiple custom validators and displaying distinct error messages for each validation rule.

  10. "Angular display custom validator error with form group"

    • Code Implementation:
      // In your component customFormGroup = this.fb.group({ property: ['', [customValidator]] }); 
      <mat-form-field> <input matInput formControlName="property" placeholder="Property"> <mat-error *ngIf="customFormGroup.get('property').hasError('customError')"> Custom error message </mat-error> </mat-form-field>
    • Description: Implementing a custom validator within a form group and displaying the error message in mat-error based on the specific form control.

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