根据mat select在输入中显示不同的占位符的角度

<mat-form-field>
  <mat-label>选择一个选项</mat-label>
  <mat-select [(ngModel)]="selectedOption" (selectionChange)="onSelectionChange()">
    <mat-option *ngFor="let option of options" [value]="option">{{ option }}</mat-option>
  </mat-select>
</mat-form-field>

import { Component } from '@angular/core';

@Component({
  selector: 'app-select-example',
  templateUrl: './select-example.component.html',
  styleUrls: ['./select-example.component.css']
})
export class SelectExampleComponent {
  selectedOption: string;
  options: string[] = ['Option 1', 'Option 2', 'Option 3'];

  onSelectionChange() {
    if (this.selectedOption === 'Option 1') {
      // 根据选项1显示占位符
      // 例如：this.placeholder = "选项1的占位符";
    } else if (this.selectedOption === 'Option 2') {
      // 根据选项2显示占位符
      // 例如：this.placeholder = "选项2的占位符";
    } else if (this.selectedOption === 'Option 3') {
      // 根据选项3显示占位符
      // 例如：this.placeholder = "选项3的占位符";
    }
  }
}