Angular 2 - 组件内部的 formControlName

Question

我想创建一个可以与 FormBuilder API 一起使用的自定义输入组件。如何在组件中添加 formControlName？

模板:

<label class="custom-input__label"
          *ngIf="label">
        {{ label }}
</label>
<input class="custom-input__input" 
       placeholder="{{ placeholder }}"
       name="title" />
<span class="custom-input__message" 
      *ngIf="message">
        {{ message }}
</span>

组件:

import {
    Component,
    Input,
    ViewEncapsulation
} from '@angular/core';

@Component({
    moduleId: module.id,
    selector: 'custom-input',
    host: {
        '[class.custom-input]': 'true'
    },
    templateUrl: 'input.component.html',
    styleUrls: ['input.component.css'],
    encapsulation: ViewEncapsulation.None,
})
export class InputComponent {
    @Input() label: string;
    @Input() message: string;
    @Input() placeholder: string;
}

用法:

<custom-input label="Title" 
           formControlName="title" // Pass this to input inside the component>
</custom-input>

Answer 1

您不应将 formControlName 属性添加到自定义组件模板中的输入字段。 根据最佳实践，您应该在自定义输入元素本身上添加 formControlName。

在这里，您可以在自定义输入组件中使用的是 controlValueAccessor 接口(interface)，只要您的自定义输入模板中出现输入字段事件，您的自定义输入就会更新值改变或模糊。

它在您的自定义输入的表单控件行为与您为该自定义表单控件提供的 UI 之间提供连接(以更新值或其他需求)。

以下是 TypeScript 自定义输入组件的代码。

import { Component, Input, forwardRef, AfterViewInit, trigger, state, animate, transition, style, HostListener, OnChanges, ViewEncapsulation, ViewChild, ElementRef } from '@angular/core';
import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms';

export const CUSTOM_INPUT_CONTROL_VALUE_ACCESSOR: any = {
    provide: NG_VALUE_ACCESSOR,
    useExisting: forwardRef(() => InputComponent),
    multi: true
};

@Component({
  selector: 'inv-input',
  templateUrl:'./input-text.component.html',
    styleUrls: ['./input-text.component.css'],
    encapsulation: ViewEncapsulation.None,
  providers: [CUSTOM_INPUT_CONTROL_VALUE_ACCESSOR],
    animations:[trigger(
        'visibilityChanged',[
            state('true',style({'height':'*','padding-top':'4px'})),
            state('false',style({height:'0px','padding-top':'0px'})),
            transition('*=>*',animate('200ms'))
        ]
    )]
})

export class InputComponent implements ControlValueAccessor, AfterViewInit, OnChanges {

    // Input field type eg:text,password
    @Input()  type = "text"; 

    // ID attribute for the field and for attribute for the label
    @Input()  idd = ""; 

    // The field name text . used to set placeholder also if no pH (placeholder) input is given
    @Input()  text = ""; 

    // placeholder input
    @Input()  pH:string; 

    //current form control input. helpful in validating and accessing form control
    @Input() c:FormControl = new FormControl(); 

    // set true if we need not show the asterisk in red color
    @Input() optional : boolean = false;

    //@Input() v:boolean = true; // validation input. if false we will not show error message.

    // errors for the form control will be stored in this array
    errors:Array<any> = ['This field is required']; 

    // get reference to the input element
    @ViewChild('input')  inputRef:ElementRef; 


    constructor() {

    }

    ngOnChanges(){

    }

    //Lifecycle hook. angular.io for more info
    ngAfterViewInit(){ 
        // set placeholder default value when no input given to pH property      
        if(this.pH === undefined){
            this.pH = "Enter "+this.text; 
        }

        // RESET the custom input form control UI when the form control is RESET
        this.c.valueChanges.subscribe(
            () => {
                // check condition if the form control is RESET
                if (this.c.value == "" || this.c.value == null || this.c.value == undefined) {
                    this.innerValue = "";      
                    this.inputRef.nativeElement.value = "";                 
                }
            }
        );
    }

   //The internal data model for form control value access
    private innerValue: any = '';

    // event fired when input value is changed . later propagated up to the form control using the custom value accessor interface
    onChange(e:Event, value:any){
        //set changed value
        this.innerValue = value;
        // propagate value into form control using control value accessor interface
        this.propagateChange(this.innerValue);

        //reset errors 
        this.errors = [];
        //setting, resetting error messages into an array (to loop) and adding the validation messages to show below the field area
        for (var key in this.c.errors) {
            if (this.c.errors.hasOwnProperty(key)) {
                if(key === "required"){
                    this.errors.push("This field is required");
                }else{
                    this.errors.push(this.c.errors[key]);
                }              
            }
        }
    }



    //get accessor
    get value(): any {
        return this.innerValue;
    };

    //set accessor including call the onchange callback
    set value(v: any) {
        if (v !== this.innerValue) {
            this.innerValue = v;
        }
    }

    //propagate changes into the custom form control
    propagateChange = (_: any) => { }

    //From ControlValueAccessor interface
    writeValue(value: any) {
        this.innerValue = value;
    }

    //From ControlValueAccessor interface
    registerOnChange(fn: any) {
        this.propagateChange = fn;
    }

    //From ControlValueAccessor interface
    registerOnTouched(fn: any) {

    }
}

下面是自定义输入组件的模板 HTML

<div class="fg">
      <!--Label text-->
      <label [attr.for]="idd">{{text}}<sup *ngIf="!optional">*</sup></label>
      <!--Input form control element with on change event listener helpful to propagate changes -->
      <input type="{{type}}" #input id="{{idd}}" placeholder="{{pH}}" (blur)="onChange($event, input.value)">
      <!--Loop through errors-->
      <div style="height:0px;" [@visibilityChanged]="!c.pristine && !c.valid" class="error">
            <p *ngFor="let error of errors">{{error}}</p>
      </div>
</div>

下面是自定义输入组件，可以在 fromGroup 中使用，也可以单独使用

<inv-input formControlName="title" [c]="newQueryForm.controls.title" [optional]="true" idd="title" placeholder="Type Title to search"
          text="Title"></inv-input>

以这种方式，如果您实现自定义表单控件，您可以轻松应用自定义验证器指令并在该表单控件上累积错误以显示您的错误。

可以仿照上面的样式开发自定义select组件，radio button group, checkbox, textarea, fileupload等，根据表单控件的行为需求稍作改动。