angular - 如何在 Angular 5 中动态设置选定的下拉值

Question

我正在尝试在 Angular 5 中设置下拉列表的选定值。

HTML:

<mat-form-field class="col-sm-3">
   <mat-select placeholder="State" name="state [formControl]="stateFormControl" required>
     <mat-option *ngFor="let state of states" value="{{state.key}}">{{state.name}}
     </mat-option>
   </mat-select>
   <mat-error *ngIf="stateFormControl.hasError('required')">State is required
   </mat-error>
</mat-form-field>

typescript :

stateFormControl = new FormControl('', [
    Validators.required
]);

this.vendorForm.controls["state"].setValue(this.state);

即使我在 FormControl 声明中设置了默认值，默认情况下也没有为下拉列表设置任何内容。

Answer 1

你应该试试这个:

this.stateFormControl.setValue(this.state);

或

<mat-form-field class="col-sm-3">
   <mat-select placeholder="State" name="state" formControlName="state" required>
     <mat-option *ngFor="let state of states" value="{{state.key}}">{{state.name}}
     </mat-option>
   </mat-select>
   <mat-error *ngIf="stateFormControl.hasError('required')">State is required
   </mat-error>
</mat-form-field>

如果您决定更改 html，请遵循 this tutorial react 形式

所以你会用这样的东西来构建你的表单

buildForm(){
    this.vendorForm = this.fb.group({
      state: ['', Validators.required ], // <--- You don't need to instantiate FormControls
    });
}

你会在别处得到这个

<form [formGroup]="vendorForm">