how to clear validation errors for Angular Material mat-error

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29-08-2024

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Clearing Angular Material mat-error Validation Messages: A Comprehensive Guide

Angular Material's mat-error elements provide a clean and user-friendly way to display validation messages in your forms. But sometimes, you need to clear these messages, especially when you want to reset a form or handle successful submission. This article will delve into the best practices for clearing validation errors associated with mat-error in Angular Material, drawing upon real-world examples and insights from Stack Overflow.

Understanding the Issue

As highlighted in the Stack Overflow question, simply resetting the form using form.reset() doesn't always clear the mat-error messages. This is because Angular Material's validation mechanism tracks both the form's state (pristine/dirty) and the individual control's state (touched/untouched).

Here's the breakdown:

• form.reset(): This clears the form values but doesn't necessarily change the form's or individual controls' state.
• form.markAsPristine(): This marks the entire form as pristine, indicating no user interaction, but doesn't necessarily affect individual controls.
• form.markAsUntouched(): This doesn't affect the form's pristine state, but only marks the individual control as untouched.

The Solution: Combining Form and Control Updates

To successfully clear the mat-error messages, you need to update both the form's and the individual control's state. Here's the recommended approach:

1. Resetting the Form:

onSubmit(form: FormGroup) {
  // do work
  form.reset(); 
  form.markAsPristine(); // Mark the form as pristine
}

2. Resetting Individual Controls:

onSubmit(form: FormGroup) {
  // do work
  form.reset(); 
  form.markAsPristine(); 

  // Reset and mark each control as untouched
  form.get('title')?.reset(); // Assuming 'title' is the control's name
  form.get('title')?.markAsUntouched(); 
}

Explanation:

• The form.reset() method clears the values in the form.
• The form.markAsPristine() method sets the form back to its initial state, marking it as pristine.
• The form.get('title')?.reset() method resets the specific control.
• The form.get('title')?.markAsUntouched() method marks the specific control as untouched, ensuring that any previous validation errors are cleared.

Practical Example

Let's assume you have a simple form for collecting a user's name and age with validation:

<form [formGroup]="userForm" fxLayout="column">
  <mat-form-field>
    <input matInput formControlName="name" placeholder="Name" required>
    <mat-error *ngIf="userForm.get('name')?.hasError('required')">Name is required</mat-error>
  </mat-form-field>

  <mat-form-field>
    <input matInput type="number" formControlName="age" placeholder="Age" required>
    <mat-error *ngIf="userForm.get('age')?.hasError('required')">Age is required</mat-error>
  </mat-form-field>

  <button mat-raised-button color="primary" type="submit" (click)="onSubmit(userForm)">Submit</button>
</form>

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

@Component({
  selector: 'app-user-form',
  templateUrl: './user-form.component.html',
  styleUrls: ['./user-form.component.css']
})
export class UserFormComponent {
  userForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.userForm = this.fb.group({
      name: ['', Validators.required],
      age: ['', Validators.required]
    });
  }

  onSubmit(form: FormGroup) {
    console.log(form.value); // Handle form submission

    // Clear validation errors
    form.reset();
    form.markAsPristine();
    form.get('name')?.reset();
    form.get('name')?.markAsUntouched();
    form.get('age')?.reset();
    form.get('age')?.markAsUntouched();
  }
}

In this example, the onSubmit() method resets the form and its controls, ensuring that mat-error messages are removed after successful submission.

Additional Notes

• Remember to update the mat-error conditions in your HTML template to reflect the reset state of the form and controls.
• In cases where you need to clear only specific error messages, you can use the hasError() method on the individual control to check for specific errors and conditionally clear the mat-error element.
• Consider using a dedicated reset function for your form to improve code readability and maintainability.

By applying these principles and understanding the relationship between form states and validation errors, you can effectively clear mat-error messages in Angular Material and achieve a seamless user experience.