加载组件时如何在angular mat-select中设置值? [英] How to set value in angular mat-select when component loading?

问题描述

我使用了 angular material("@angular/material": "7.1.0") mat-select box 然后我使用了表单控件而不是 ng 模型，现在问题是我可以't 在组件加载时设置该值.我需要将列表中的第一个值设置为 mat-select 框，我试过了，但我不能这样做.

I used angular material("@angular/material": "7.1.0") mat-select box and then i used form control instead of ng model, now the problem is i can't set the value when the component is loading. I need to set the first value to mat-select box from the list, i tried but i cant do that.

我在 stackblitz 创建了一个代码，这里是链接:https://stackblitz.com/编辑/angular-zt1a9f

I have created a code at stackblitz, here is the link: https://stackblitz.com/edit/angular-zt1a9f

请帮助我.

推荐答案

使用 compareWith 通过比较函数内部的名称来选择默认值.另请注意，我已将 value 绑定更改为 [(value)] ="animal".并删除了 selectedValue.您可以通过在 formControl 中分配它来选择默认值，查看组件中的以下更改.

Use compareWith to select the default value by comparing the name inside the compare function. Also note, I've changed value binding to [(value)] ="animal". And removed selectedValue. You select the default by assigning it in the formControl, look below changes in the component.

<form [formGroup]="myGroup">
<mat-form-field>
  <mat-select placeholder="Favorite animal" [compareWith]="compareThem" formControlName="animalControl" required >
    <mat-option>--</mat-option>
    <mat-option *ngFor="let animal of animals" [(value)] ="animal"  >
      {{animal.name}}
    </mat-option>
  </mat-select>
</mat-form-field>
</form>

在您的组件中，添加:

export class AppComponent  {

  animals = [
    {name: 'Dog', sound: 'Woof!'},
    {name: 'Cat', sound: 'Meow!'},
    {name: 'Cow', sound: 'Moo!'},
    {name: 'Fox', sound: 'Wa-pa-pa-pa-pa-pa-pow!'},
  ];  

  myGroup = new FormGroup({
      animalControl: new FormControl(this.animals[1], [Validators.required]) //I'm assigining Cat by using this.animals[1], you can put any value you like as default.
  });


  compareThem(o1, o2): boolean{
    console.log('compare with');
    return o1.name === o2.name;
  }
}

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