ControlValueAccessor with Error Validation in Angular Material

I had the same problem. I tried all and then finally could resolve using this method:

I added this listener on the custom component. You can also do it 'blur' event.

@HostListener('focusout', ['$event.target'])
  onFocusout() {
    this.onTouched();
  }

And also calling onTouched when setting any value.

 writeValue(value: any) {
    this.onTouched();
    this.Value = value ? value : '';
}

This will create error validation from Angular Material

Typescript:

import { Component, OnInit, Input, EventEmitter, Output, forwardRef, Injector } from '@angular/core';
import { ControlValueAccessor, NG_VALUE_ACCESSOR, FormControl, NgForm, FormGroupDirective, NgControl } from '@angular/forms';
import { ErrorStateMatcher } from '@angular/material';

export class CustomFieldErrorMatcher implements ErrorStateMatcher {
  constructor(private customControl: FormControl,private errors:any) { }

  isErrorState(control: FormControl | null, form: FormGroupDirective | NgForm | null): boolean {
    return this.customControl && this.customControl.touched &&(this.customControl.invalid || this.errors);
  }
}

@Component({
  selector: 'app-input-textbox',
  templateUrl: './input-textbox.component.html',
  styleUrls: ['./input-textbox.component.scss'],
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => InputTextboxComponent),
      multi: true
    }
  ]
})

export class InputTextboxComponent implements OnInit, ControlValueAccessor {
  @Input() MaxLength: string;
  @Input() FocusIn: boolean;
  @Input() Width: string;
  @Input() Value: string;
  @Input() type: string;
  @Input() Label: string;
  @Input() Hint: string;
  @Input() PlaceHolder: string;
  @Output() saveValue = new EventEmitter();
  @Output() onStateChange = new EventEmitter();
  @Input() errors: any = null;
  disabled: boolean;
  control: FormControl;

  constructor(public injector: Injector) {}

  ngOnInit(){}

  ngAfterViewInit(): void {
    const ngControl: NgControl = this.injector.get(NgControl, null);
    if (ngControl) {
      setTimeout(() => {
        this.control = ngControl.control as FormControl;
      })
    }
  }

  saveValueAction(e) {
    this.saveValue.emit(e.target.value);
  }

  //control value accessor init
  writeValue(value: any) {
    this.Value = value ? value : '';
  }

  onChange(e) {
    this.Value = e;
  }

  onTouched() {
    this.onStateChange.emit();
  }

  registerOnChange(fn: any) { this.onChange = fn; }

  registerOnTouched(fn: any) { this.onTouched = fn; }

  setDisabledState(isDisabled) { this.disabled = isDisabled; }

  errorMatcher() {
    return new CustomFieldErrorMatcher(this.control,this.errors)
  }

  readonly errorStateMatcher: ErrorStateMatcher = {
    isErrorState: (ctrl: FormControl) => (ctrl && ctrl.invalid)
  };

}

HTML

<div class="input-wrap">
    <mat-form-field>
        <mat-label>{{Label}}</mat-label>   
        <input 
            matInput 
            [attr.maxlength] = "MaxLength"
            [value]="Value ? Value : ''"
            [placeholder]="PlaceHolder ? PlaceHolder : ''"
            [type]="type ? type: 'text'"
            [ngModel]="Value" 
            [errorStateMatcher]="errorMatcher()"

            (input)="onChange($event.target.value)"
            (blur)="onTouched()"
            (change)="saveValueAction($event)"
            (ngModelChange)="Value=$event;onChange($event)"
        >
        <mat-hint>{{Hint}}</mat-hint>
    </mat-form-field>
</div>

Kinda used your answer and the link you provided to come up with this solution:

@Component({
  selector: 'app-custom-input',
  templateUrl: './custom-input.component.html',
  styleUrls: ['./custom-input.component.css'],
  providers: [{
    provide: NG_VALUE_ACCESSOR,
    useExisting: forwardRef(() => CustomInputComponent),
    multi: true
  }]
})
export class CustomInputComponent implements OnInit, ControlValueAccessor {
  ...
  _control: NgControl;
  disabled: boolean;

  constructor(@Inject(INJECTOR) private injector: Injector) {
  }

  ngOnInit() {
    this._control = this.injector.get(NgControl);
  }
  
  ...

custom-input.component.html

<div class="input-wrap">
    <mat-form-field appearance="outline">
        <mat-label>{{Label}}</mat-label>   
        <input matInput
            [formControl]="_control.control" // <== this what makes it work
            [attr.maxlength]="MaxLength"
            [placeholder]="PlaceHolder ? PlaceHolder : ''"
            [type]="type ? type: 'text'"
        >
    </mat-form-field>
</div>

Note: I'm not binding to MatInput's outputs (yea). the formControl directive that passes the control to MatInput handles that for us.

made an example for you