可以通过使用MatAutocompleteSelectedEvent来获取当前所选项的值，并将它作为输入框的初始值进行设置，以阻止值的更改。下面是代码示例：

  
  
    
      {{option}}
    
  

import { Component, OnInit } from '@angular/core';
import { FormControl } from '@angular/forms';
import { Observable } from 'rxjs';
import { startWith, map } from 'rxjs/operators';
import { MatAutocompleteSelectedEvent } from '@angular/material/autocomplete';

@Component({
  selector: 'app-autocomplete',
  templateUrl: './autocomplete.component.html',
  styleUrls: ['./autocomplete.component.css']
})
export class AutocompleteComponent implements OnInit {
  myControl = new FormControl();
  options: string[] = ['Angular', 'React', 'Vue'];
  filteredOptions: Observable;

  constructor() { }

  ngOnInit(): void {
    this.filteredOptions = this.myControl.valueChanges.pipe(
      startWith(''),
      map(value => this._filter(value))
    );
  }

  private _filter(value: string): string[] {
    const filterValue = value.toLowerCase();

    return this.options.filter(option => option.toLowerCase().includes(filterValue));
  }

  onOptionSelected(event: MatAutocompleteSelectedEvent): void {
    this.myControl.setValue(event.option.value, {emitEvent: false});
  }
}

在这个示例中，选中一个选项时，它不会改变输入框的值，而是将该选项设置为输入框的初始值。值的更改会被阻止。