如何在Angular2/4/5中实现自定义异步验证器

Question

1.它甚至得到了Angular的支持吗？看到这个开放的问题

2.如果是的话,什么是错在下面的代码

export class someClass{

    myForm:ControlGroup;

    constructor(public http:Http, public formBuilder:FormBuilder)
       this.myForm = formBuilder.group({
            ImageId: ["", Validators.required, this.asynValidator]
    });

    asyncValidator(control: Control): {[key: string]: any} {

        return new Promise (resolve => {

          let headers = new Headers();
          headers.append('Content-Type', 'application/json');

          this.http.get('http://localhost/ImageIdValidate?id='+ control.value, {headers:headers})
                .map(res => res.json())
                .subscribe(data => {
                    console.log(data);
                    if(data != null) {
                        resolve({"duplicate": true})
                    }
                    else resolve(null);      
                })
            });
        });
      }
    }

它甚至没有提出服务器请求.

Answer 1

您需要在组件实例本身上绑定您的方法,如下所述:

this.myForm = formBuilder.group({
            ImageId: ["",    
               Validators.required, 
               this.asynValidator.bind(this)]
    });

否则,您将无法使用http属性来执行请求.

本文还可以为您提供有关异步表单验证的一些提示(请参阅"异步验证"一节):

• http://restlet.com/blog/2016/02/17/implementing-angular2-forms-beyond-basics-part-2/