angular 2无法读取undefined的属性

Question

我收到以下错误

无法读取未定义的属性“值”

以下是我的代码

模板

<select class="form-control form-control-lg" formControlName="contractor" (ngModelChange)="onChange($event.target.value)" >
                    <option *ngFor="let contrac of contractors" [ngValue]="contrac">{{contrac.name}}</option>
                </select>

 <label class="control-label col-lg-2">Agency</label>
            <div class="col-lg-10">
                <input type="text" class="form-control form-control-lg" placeholder="Payroll Number" formControlName ="selectedAgency">
            </div>

组件

 ngOnInit() {
        this.form = this.fb.group({
            agency: ['', Validators.required],
            contractor: ['', Validators.required],
            selectedAgency : ['', Validators.required]

        });

 onChange = (contrac) => {
        alert(contrac.vendor);
        this.form.patchValue({ selectedAgency: contrac.vendor });
    }

这里有什么遗漏吗？

-Alan -

Answer 1

应该是：

(ngModelChange)="onChange($event)"

...或者使用(change)：

(change)="onChange($event.target.value)"

但是，似乎你只是用它来为表单中的另一个控件设置一个值，对吗？

因此，您可以在要设置值的输入上使用[ngModel]，如下所示：

<select class="form-control form-control-lg" formControlName="contractor">
  <option *ngFor="let contrac of contractors" 
          [ngValue]="contrac">{{contrac.name}}</option>
</select>

<label class="control-label col-lg-2">Agency</label>
<div class="col-lg-10">      
  <input type="text" 
         class="form-control form-control-lg" 
         placeholder="Payroll Number" 
         formControlName ="selectedAgency" 
         [ngModel]="myForm.get('contractor').value.vendor">
</div>