Angular 6 Material <mat-select>使用表单控件设置多个默认值

Question

我正在使用表单控件，这是我的html组件的代码

<mat-form-field>
  <mat-select placeholder="Toppings" [formControl]="toppings" multiple>
    <mat-option *ngFor="let topping of toppingList" [value]="topping">{{topping.value}}</mat-option>
  </mat-select>
</mat-form-field>

我的ts文件是

export class SelectMultipleExample {
   toppings = new FormControl();
  toppingList: any[] = [
      { id:1,value:"test 1"},
      { id:2,value:"test 2"},
      { id:3,value:"test 4"},
      { id:4,value:"test 5"},
      { id:5,value:"test 6"},
      { id:6,value:"test 7"}
    ];

  

  constructor(){
    this.bindData();
  }

  bindData(){
    const anotherList:any[]=[
      { id:1,value:"test 1"},
      { id:2,value:"test 2"}
      ]

      this.toppings.setValue(anotherList)
  }
}

我想为mat select设置默认值，如何实现这一点的任何帮助都会很棒。我想设置多个默认值。

Answer 1

The problem is due to the fact that your options are objects. In order for the selections to be applied, the selected objects must be the same objects as the ones used for the options. Revise your code as follows:

export class SelectMultipleExample {
    toppings = new FormControl();
    toppingList: any[] = [
        { id:1,value:"test 1"},
        { id:2,value:"test 2"},
        { id:3,value:"test 4"},
        { id:4,value:"test 5"},
        { id:5,value:"test 6"},
        { id:6,value:"test 7"}
    ];

    constructor(){
        this.bindData();
    }

    bindData() {
        const anotherList: any[] = [
            this.toppingList[0],
            this.toppingList[1]
        ]

        this.toppings.setValue(anotherList)
    }
}