Angular2 Reactive 表单 - 为带有下拉列表的表单字段设置默认值

Question

如何为 angular 2 个反应式表单中的所有表单字段设置默认值？

这是重现问题的 plnkr

下面的代码不会更新下拉值，因为它有一个关联的对象。

注意：这里我需要为所有表单字段设置默认值，并从后端收到响应API。

Component.html

<form [formGroup]="myForm" novalidate (ngSubmit)="save(myForm.value, myForm.valid)">
    <div class="form-group">
        <label>Country:</label>
        <select formControlName="country">
          <option *ngFor="let country of masterCountries" [ngValue]="country">{{country.countryName}}</option>
        </select>
    </div>

    <div class="form-group">
      <label for="">Name</label>
      <input type="text" class="form-control" formControlName="name">
      <small [hidden]="myForm.controls.name.valid || (myForm.controls.name.pristine && !submitted)" class="text-danger">
            Name is required (minimum 5 characters).
          </small>
      <!--<pre class="margin-20">{{ myForm.controls.name.errors | json }}</pre>-->
    </div>
    <button type="submit" class="btn btn-default">Submit</button>
    <div class="margin-20">
      <div>myForm details:-</div>
      <pre>Is myForm valid?: <br>{{myForm.valid | json}}</pre>
      <pre>Is myForm submitted?: <br>{{submitted | json}}</pre>
      <pre>myForm value: <br>{{myForm.value | json}}</pre>
    </div>

Component.ts

export class AppComponent implements OnInit {
    public myForm: FormGroup;
    public masterCountries: any[] = [{"countryCode":"AF","countryName":"Afghanistan"},{"countryCode":"AL","countryName":"Albania"},{"countryCode":"DZ","countryName":"Algeria"},{"countryCode":"AS","countryName":"American Samoa"},{"countryCode":"AD","countryName":"Andorra"}];

    // Sample response received from backend api
    public CountryResponse = {country: {"countryCode":"AF","countryName":"Afghanistan"}, name: 'test123'};
    constructor(private _fb: FormBuilder) { }

    ngOnInit() {

        // the short way
        this.myForm = this._fb.group({
            country: [''],
            name: ['', [<any>Validators.required, <any>Validators.minLength(5)]],
        });


        (<FormGroup>this.myForm)
            .setValue(this.CountryResponse, {onlySelf: true});


    }


    save(model: User, isValid: boolean) {
        this.submitted = true;
        console.log(model, isValid);
    }
}

如果有任何其他方法可以设置整个表单，请告诉我。

Answer 1

您的代码不起作用，因为虽然您的 this.selectedCountry 似乎具有与 this.masterCountries 的元素之一相同的字段值，但它们 不是同一个对象。这使得 select.value === option.value 比较总是 returns false.

让它工作很简单，只需将 setValue 函数更改为如下所示：

(<FormControl>this.form.controls['country'])
            .setValue(this.masterCountries[0], { onlySelf: true });

或者您可以在创建 FormGroup:

时设置它

    this.myForm = this._fb.group({
        country: [this.masterCountries[0]],
        name: ['', [<any>Validators.required, <any>Validators.minLength(5)]],
    });

Answer 2

只需更改此：

 (<FormGroup>this.myForm)
            .setValue(this.CountryResponse, {onlySelf: true});

进入这个：

const selectedCountry = this.masterCountries.find(country => country.countryCode === this.CountryResponse.country.countryCode)
this.CountryResponse.country = selectedCountry;
(<FormGroup>this.myForm)
            .setValue(this.CountryResponse, {onlySelf: true});

如前所述，您需要传递对象的完全相同的引用

Answer 3

当您声明表单控件或初始化时将默认值作为参数传递

  MyFormControl: FormControl = new FormControl('Default value');

Answer 4

我知道这是一个老问题，但如果有人寻找它，现在有一种更好的方法可以在整个表单中设置值，PatchValue :

this.myForm.patchValue({
   country: this.CountryResponse,
   name: 'Any Name'
});

这也允许部分，所以你仍然可以做这样的事情：

this.myForm.patchValue({ country: this.CountryResponse });

或者您可以将值设置到单个控件中：

this.myForm.get('country').setValue(this.CountryResponse);

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