Form Validator In Angular

Angular 的 ReactiveFormsModule 相當強大，包含了 two way binding data 以及好用的 validator，以下的範例示範怎麼針對單一欄位以及整體表單自製 validator，如果 username 填寫 chan 的話表示帳號重複，年齡大於 100 的話則錯誤，group 的部分兩者都要填寫。

ts

import { Component, OnInit } from '@angular/core';
import { AbstractControl, FormBuilder, ValidationErrors, ValidatorFn } from '@angular/forms';

@Component({
  selector: 'app-form-validator',
  templateUrl: './form-validator.component.html',
  styleUrls: ['./form-validator.component.scss']
})
export class FormValidatorComponent implements OnInit {
  public form = this.fb.group({
    username: ['', [this.userNameChecker()]],
    age: ['', [this.numberChecker()]]
  }, { validators: this.bothRequired() });
  public ageLimit: number = 100;

  constructor(
    private fb: FormBuilder
  ) { }

  ngOnInit(): void {
  }

  get username(): AbstractControl {
    return this.form.controls.username;
  }

  get age(): AbstractControl {
    return this.form.controls.age;
  }

  private userNameChecker(): ValidatorFn {
    return (control: AbstractControl): ValidationErrors | null => {
      if (control.value === '') {
        return null;
      }

      if (control.value === 'chan') {
        return { userNameExists: true };
      }

      return null;
    }
  }

  private numberChecker(): ValidatorFn {
    return (control: AbstractControl): ValidationErrors | null => {
      if (control.value === '') {
        return null;
      }

      if (control.value > this.ageLimit) {
        return { tooBig: true };
      }

      return null;
    }
  }

  private bothRequired(): ValidatorFn {
    return (group: AbstractControl): ValidationErrors | null => {
      return (group.get('username')?.value === '' || group.get('age')?.value === '') ? { bothRequired: true } : null;
    }
  }
}

html

<h3>{{ form.value | json }}</h3>
<div [formGroup]="form">
  <div>
    username: <input type="text" formControlName="username">
    <div *ngIf="username.errors?.userNameExists">username exists</div>
  </div>
  <div>
    age: <input type="number" formControlName="age">
    <div *ngIf="age.errors?.tooBig">age should lower than {{ ageLimit }}</div>
  </div>
  <div>
    <button [disabled]="form.invalid">submit</button>
  </div>
</div>

Stop The Process By Condition In Ansible

Ansible 的任務沒有下中斷的話，即便有使用 when 偵測，playbook 會繼續往下走，可以利用 fail 這個參數讓條件不符合時直接把 process 中斷，以 stat 偵測目錄是否存在來做範例。

- hosts: localhost

  vars:
    path: /tmp/sync/

  tasks:
    - name: "stat {{ path }}"
      stat:
        path: "{{ path }}"
      register: the_dir

    - name: "shutdown when {{ path }} is not exists"
      fail:
        msg: "{{ path }} not exists"
      when: the_dir.stat.exists == False

    - name: "echo yes when {{ path }} exists"
      debug:
        msg: 'yes'
      when: the_dir.stat.exists

當我們設定的 path 不存在時，會直接中斷，不會走道最後的 "echo yes when {{ path }} exists"。

Input And Output In Angular

Angular 的 @Input 以及 @Output 修飾器是用來讓父與子元件可以跨元件溝通資訊，應用範圍很廣，譬如說有些固定的表單功能我們可以把他切細，提供給各單元的表單套入使用，可以減少重複造輪子的問題，下面示範如何讓子元件改變父元件表單的內容。

父 ts

import { Component, OnInit } from '@angular/core';
import { FormBuilder } from '@angular/forms';

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html',
  styleUrls: ['./example.component.scss']
})
export class ExampleComponent implements OnInit {
  public form = this.fb.group({
    username: 'chan',
    amount: 100
  });

  constructor(
    private fb: FormBuilder
  ) { }

  ngOnInit(): void {
  }

  public patchAmount(amount: number): void {
    this.form.patchValue({
      amount: amount
    })
  }
}

父 html

<h1>Input Output Example</h1>
<h3>{{ form.value | json }}</h3>
<form [formGroup]="form">
  <div>
    <input type="text" formControlName="username">
  </div>
  <div>
    <app-example-number [amount]="form.get('amount')?.value" (patchParentAmount)="patchAmount($event)"></app-example-number>
  </div>
</form>

子 ts

import { Component, EventEmitter, Input, OnInit, Output } from '@angular/core';

@Component({
  selector: 'app-example-number',
  templateUrl: './example-number.component.html',
  styleUrls: ['./example-number.component.scss']
})
export class ExampleNumberComponent implements OnInit {
  @Input() amount: number = 0;
  @Output() patchParentAmount = new EventEmitter<number>();

  constructor() { }

  ngOnInit(): void {
  }

  public updateAmount(): void {
    this.patchParentAmount.emit(this.amount);
  }
}

子 html

<input type="number" [(ngModel)]="amount" (ngModelChange)="updateAmount()">

父元件傳了預設的 amount 過去給子元件，子元件透過監聽 ngModelChange 將改變的數字 emit 到父元件執行 patch form value 的動作，就可以做到互動更新了。

Dynamic Form Field In Angular

Angular 的 form builder 蠻強大的，two way binding data 以及 validator 相當好用，其中有一個特性 FormArray 可以做許多運用，來做一個動態產生表單欄位的範例。

ts

import { Component, OnInit } from '@angular/core';
import { FormArray, FormBuilder, FormGroup } from '@angular/forms';

@Component({
  selector: 'app-dy-demo',
  templateUrl: './dy-demo.component.html',
  styleUrls: ['./dy-demo.component.scss']
})
export class DyDemoComponent implements OnInit {
  public form = this.fb.group({
    username: 'chan',
    family: this.fb.array([])
  })

  constructor(
    private fb: FormBuilder
  ) { }

  ngOnInit(): void {
  }

  public newLine(): FormGroup {
    return this.fb.group({
      name: '',
      age: ''
    })
  }

  public family(): FormArray {
    return this.form.get('family') as FormArray;
  }

  public add(): void {
    return this.family().push(this.newLine());
  }

  public remove(i: number): void {
    this.family().removeAt(i);
  }
}

html

<h3>{{ form.value | json }}</h3>
<div>
  <button (click)="add()">add</button>
</div>
<form action="" [formGroup]="form">
  <div>
    <input type="text" formControlName="username">
  </div>
  <div formArrayName="family">
    <ng-container *ngFor="let f of family().controls; let i=index" [formGroupName]="i">
      <div>
        username: <input type="text" formControlName="name"> age: <input type="number" formControlName="age">
        <button (click)="remove(i)">remove</button>
      </div>
    </ng-container>
  </div>
</form>

目前覺得 Angular 的內容真是易學難精啊。

Array Object In Angular

angular 使用了 typescript，強型別是 ts 大殺器之一，除了簡單的 string、number 那些定義以外，array object 使用度也很高，最常見的作法如下。

interface Member {
    username: string;
    password: string;
}

const members: Member[] = [
    {
        username: 'chan',
        password: '123456'
    }
];

console.log(members);

這樣做沒什麼大問題，但設計上我覺得有點卡，因為 interface Member 就是一個單一物件，另一種寫法比較囉唆一點，但我覺得比較好：

interface Member {
    username: string;
    password: string;
}

interface Members extends Array<Member> {}

const members: Members = [
    {
        username: 'chan',
        password: '123456'
    }
];

console.log(members);

這樣調用 Members 時很明確就是要用陣列，而 Member 則可以給 member detail 使用，職責比較清楚，detail 理論上應該是最小單位，但如果 list 部分有自己的需求也可以自行擴充，type alias 也有相同的作法：

type Member = {
    username: string;
    password: string;
}

type Members = Member[];

const members: Members = [
    {
        username: 'chan',
        password: '123456'
    }
];

console.log(members);