Angular Material - 带有错误状态的自定义反应表单控件答案

【问题标题】：Angular Material - Custom Reactive Form Control with Error StateAngular Material - 带有错误状态的自定义反应表单控件
【发布时间】：2018-08-25 11:46:29
【问题描述】：

我正在关注来自 Angular Material 网站的 this tutorial 关于创建自定义表单控件的信息。教程中没有关于在出现验证错误时如何处理表单控件错误的示例。

custom-text.component.html

<mat-form-field class="example-full-width">
    <mat-select [placeholder]="placeholder" #select [formControl]="control">
        <mat-option *ngFor="let food of foods" [value]="food">
            {{food}}
        </mat-option>
    </mat-select>
    <mat-error>This is required.</mat-error>
</mat-form-field>

custom-text.component.ts

import { Component, ViewChild, HostBinding, Input, ChangeDetectionStrategy, Optional, Self, DoCheck, OnInit, NgZone } from '@angular/core';
import { ControlValueAccessor, NgControl, NgForm, FormGroupDirective, FormControlDirective, FormControlName, FormControl, FormBuilder } from '@angular/forms';
import { MatFormFieldControl, MatSelect, CanUpdateErrorState, ErrorStateMatcher } from '@angular/material';

@Component({
    selector: 'custom-text',
    templateUrl: './custom-text.component.html',
    styleUrls: [
        './custom-text.component.scss'
    ],
    providers: [
        {
            provide: MatFormFieldControl,
            useExisting: CustomTextComponent
        }
    ],
    changeDetection: ChangeDetectionStrategy.OnPush
})
export class CustomTextComponent implements ControlValueAccessor, OnInit, DoCheck {

    @Input()
    foods: string[];

    @Input()
    get errorStateMatcher(): ErrorStateMatcher {
        return this.select.errorStateMatcher;
    }
    set errorStateMatcher(val) {
        this.select.errorStateMatcher = val;
    }

    @Input()
    get placeholder() {
        return this.select.placeholder;
    }
    set placeholder(plh) {
        this.select.placeholder = plh;
        this.stateChanges.next();
    }

    @Input()
    get value() {
        return this.select.value;
    }
    set value(val) {
        this.select.value = val;
        this.stateChanges.next();
    }

    @ViewChild('select')
    select: MatSelect;

    control: FormControl;

    constructor(
        @Optional() @Self() ngControl: NgControl,
        @Optional() private _controlName: FormControlName) {
        if (ngControl) {
            ngControl.valueAccessor = this;
        }
    }

    ngOnInit(): void {
        this.control = this._controlName.control;
    }

    ngDoCheck(): void {
        this.select.updateErrorState();
    }

    writeValue(obj: any): void {
        this.value = obj;
    }
    registerOnChange(fn: any): void {
        this.select.registerOnChange(fn);
    }
    registerOnTouched(fn: any): void {
        this.select.registerOnTouched(fn);
    }
    setDisabledState?(isDisabled: boolean): void {
        this.select.setDisabledState(isDisabled);
    }


}

app.component.html

<div style="text-align:center">
  <form class="example-form" [formGroup]="myForm" (submit)="submitForm()">
    <custom-text [foods]="[null, 'burger', 'spaghetti', 'fries']" 
      formControlName="selectedFood" 
      [errorStateMatcher]="matcher"></custom-text>
    <button>Submit</button>
  </form>
</div>

基本上，我将FormControlName 实例注入到自定义控件中。

constructor(
    @Optional() private _controlName: FormControlName) {
....
ngOnInit(): void {
    this.control = this._controlName.control;
}

然后我将它的control 属性绑定到内部mat-select 控件中。

<mat-select [placeholder]="placeholder" #select [formControl]="control">

然后我在ngDoCheck 中调用this.select.updateErrorState。

这是 StackBlitz 的链接： https://stackblitz.com/edit/angular-c4ufpp

有没有更好或更标准的方法？

【问题讨论】：

标签： angular angular-material2

【解决方案1】：

不要使用创建循环错误依赖项的 Validator 接口，而是在自定义组件中添加 errorState，以检查注入到构造函数中的 ngControl，如下所示：

get errorState() {
  return this.ngControl.errors !== null && !!this.ngControl.touched;
}

这使得DoCheck 变得不必要。在您的父组件中，不要使用errorMatcher，而是使用普通的 Angular 验证器，如下所示：

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

【讨论】：