Applying a pipe or transform to a Reactive Form value

问题

I'm building a simple reactive form. For simplicity, lets say the only data I want to display is a date.

test.component.html

<form novalidate [formGroup]="myForm">
       <input type="date" formControlName="date">
</form>

test.component.ts

private date: Date = Date.now();
ngOnInit() {
        this.myForm = this.fb.group({
            date: [this.date, [Validators.required]]
        });
    }

The input type=date field on the template requires the date to be in the format of 'yyyy-MM-dd'. The value in event is a JavaScript Date object.

How can I modify the data at the template level so the input value is correct?

What I've tried:

One way to do this would be to inject the DatePipe into my component and apply the conversion in code.

date: [datePipe.transform(this.event.date, 'yyyy-MM-dd'), [Validators.required]]

But this ties the implementation detail of the template to the component. For example, what if a NativeScript template requires the date to be in the format MM/dd/yyyy? The formGroup is no longer valid.

回答1:

The only way I've been able come up, with the help of @n00dl3 is to wrap the md-input component and provide the proper value via a ControlValueAccessor

    import { Component, Input, ViewChild } from '@angular/core';
    import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';
    import { DatePipe } from '@angular/common';
    import { MdInput } from '@angular/material';

    @Component({
        selector: 'md-date-input',
        template: `
        <md-input [placeholder]="placeholder"
            type="date"
            (change)="update()"
            [value]="dateInput">
        </md-input>`,
        providers: [
            { provide: NG_VALUE_ACCESSOR, useExisting: DateInputComponent, multi: true }]
    })
    export class DateInputComponent implements ControlValueAccessor {
        @Input() placeholder: string;
        @ViewChild(MdInput) mdInput: MdInput;

        dateInput: string;

        onChange: (value: any) => void;

        constructor(private datePipe: DatePipe) {
        }

        writeValue(value: any) {
            this.dateInput = value == null ? '' : this.datePipe.transform(value, 'yyyy-MM-dd');
        }

        registerOnChange(fn: (value: any) => void) {
            this.onChange = fn;
        }

        registerOnTouched(fn: (value: any) => void) {
        }

        update() {
            this.onChange(this.mdInput.value ? new Date(this.mdInput.value) : '');
        }
}

来源：https://stackoverflow.com/questions/40637453/applying-a-pipe-or-transform-to-a-reactive-form-value

标签

date

angular

angular-pipe