A brief analysis of two types of Form forms in Angular

This article will take you through the two Form forms in Angular, and briefly introduce their usage. I hope it will be helpful to everyone!

In Angular, there are two types of forms, namely template-driven and model-driven. [Related tutorial recommendations: "angular tutorial"]

1. Template driver

##1.1 Overview

The control logic of the form is written in the component template, which is suitable for simple form types

1.2 Get started quickly

Introduce dependent modules

FormsModule

import { FormsModule } from "@angular/forms"

@NgModule({
  imports: [FormsModule],
})
export class AppModule {}

Convert the

DOM form to ngForm

<form #f="ngForm" (submit)="onSubmit(f)"></form>

Declare the form fields as

ngModel

<form #f="ngForm" (submit)="onSubmit(f)">
  <input type="text" name="username" ngModel />
  <button>提交</button>
</form>

Get form field value

import { NgForm } from "@angular/forms"

export class AppComponent {
  onSubmit(form: NgForm) {
    console.log(form.value)
  }
}

Form grouping

<form #f="ngForm" (submit)="onSubmit(f)">
  <div ngModelGroup="user">
    <input type="text" name="username" ngModel />
  </div>
  <div ngModelGroup="contact">
    <input type="text" name="phone" ngModel />
  </div>
  <button>提交</button>
</form>

1.3 Form verification

• required Required Fill in the field
• minlength The minimum length of the field
• maxlength The maximum length of the field
• pattern Verify the regular expression, for example ：pattern="\d" Match a value

<form #f="ngForm" (submit)="onSubmit(f)">
  <input type="text" name="username" ngModel required pattern="\d" />
  <button>提交</button>
</form>

export class AppComponent {
  onSubmit(form: NgForm) {
    // 查看表单整体是否验证通过
    console.log(form.valid)
  }
}

<!-- 表单整体未通过验证时禁用提交表单 -->
<button type="submit" [disabled]="f.invalid">提交</button>

Display the error message when the form item fails in the component template

<form #f="ngForm" (submit)="onSubmit(f)">
  <input #username="ngModel" />
  <div *ngIf="username.touched && !username.valid && username.errors">
    <div *ngIf="username.errors.required">请填写用户名</div>
    <div *ngIf="username.errors.pattern">不符合正则规则</div>
  </div>
</form>

The specified form item is not passed Style when passing validation

input.ng-touched.ng-invalid {
  border: 2px solid red;
}

2. Model-driven

2.1 Overview

of the form The control logic is written in the component class, which gives you more control over the validation logic and is suitable for complex form types.

In a model-driven form, the form field needs to be an instance of the

FormControl class. The instance object can verify the value in the form field, whether the value has been modified, etc.

A group of form fields constitutes the entire form. The entire form needs to be an instance of the

FormGroup class, which can perform overall validation on the form

• FormControl: A form item in the form group

• FormGroup: Form group, the form is at least Is a FormGroup

• ##FormArray

  : used for complex forms, you can dynamically add form items or form groups, during form validation, ## One item in #FormArray failed, and the whole failed

2.2 Get started quickly

IntroductionReactiveFormsModule

import { ReactiveFormsModule } from "@angular/forms"

@NgModule({
  imports: [ReactiveFormsModule]
})
export class AppModule {}

Create in the component classFormGroup

Form control object

import { FormControl, FormGroup } from "@angular/forms"

export class AppComponent {
  contactForm: FormGroup = new FormGroup({
    name: new FormControl(),
    phone: new FormControl()
  })
}

Associate the form in the component template

<form [formGroup]="contactForm" (submit)="onSubmit()">
  <input type="text" formControlName="name" />
  <input type="text" formControlName="phone" />
  <button>提交</button>
</form>

Get the form value

export class AppComponent {
  onSubmit() {
    console.log(this.contactForm.value)
  }
}

Set the form default value

contactForm: FormGroup = new FormGroup({
  name: new FormControl("默认值"),
  phone: new FormControl(15888888888)
})

Form grouping

contactForm: FormGroup = new FormGroup({
  fullName: new FormGroup({
    firstName: new FormControl(),
    lastName: new FormControl()
  }),
  phone: new FormControl()
})

<form [formGroup]="contactForm" (submit)="onSubmit()">
  <div formGroupName="fullName">
    <input type="text" formControlName="firstName" />
    <input type="text" formControlName="lastName" />
  </div>
  <input type="text" formControlName="phone" />
  <button>提交</button>
</form>

onSubmit() {
  console.log(this.contactForm.value.name.username)
  console.log(this.contactForm.get(["name", "username"])?.value)
}

2.3

FormArray

Requirement: Display a group by default on the page Contact information, you can add more contact information groups by clicking the button

import { Component, OnInit } from "@angular/core"
import { FormArray, FormControl, FormGroup } from "@angular/forms"
@Component({
  selector: "app-root",
  templateUrl: "./app.component.html",
  styles: []
})
export class AppComponent implements OnInit {
  // 表单
  contactForm: FormGroup = new FormGroup({
    contacts: new FormArray([])
  })

  get contacts() {
    return this.contactForm.get("contacts") as FormArray
  }

  // 添加联系方式
  addContact() {
    // 联系方式
    const myContact: FormGroup = new FormGroup({
      name: new FormControl(),
      address: new FormControl(),
      phone: new FormControl()
    })
    // 向联系方式数组中添加联系方式
    this.contacts.push(myContact)
  }

  // 删除联系方式
  removeContact(i: number) {
    this.contacts.removeAt(i)
  }

  ngOnInit() {
    // 添加默认的联系方式
    this.addContact()
  }

  onSubmit() {
    console.log(this.contactForm.value)
  }
}

<form [formGroup]="contactForm" (submit)="onSubmit()">
  <div formArrayName="contacts">
    <div
      *ngFor="let contact of contacts.controls; let i = index"
      [formGroupName]="i"
    >
      <input type="text" formControlName="name" />
      <input type="text" formControlName="address" />
      <input type="text" formControlName="phone" />
      <button (click)="removeContact(i)">删除联系方式</button>
    </div>
  </div>
  <button (click)="addContact()">添加联系方式</button>
  <button>提交</button>
</form>

2.4 Built-in form validator

Use the validation rules provided by the built-in validator to validate the form fields

import { FormControl, FormGroup, Validators } from "@angular/forms"

contactForm: FormGroup = new FormGroup({
  name: new FormControl("默认值", [
    Validators.required,
    Validators.minLength(2)
  ])
})

Get whether the entire form has passed verification

onSubmit() {
  console.log(this.contactForm.valid)
}

<!-- 表单整体未验证通过时禁用表单按钮 -->
<button [disabled]="contactForm.invalid">提交</button>

Display the error message when verification passes in the component template

get name() {
  return this.contactForm.get("name")!
}

<form [formGroup]="contactForm" (submit)="onSubmit()">
  <input type="text" formControlName="name" />
  <div *ngIf="name.touched && name.invalid && name.errors">
    <div *ngIf="name.errors.required">请填写姓名</div>
    <div *ngIf="name.errors.maxlength">
      姓名长度不能大于
      {{ name.errors.maxlength.requiredLength }} 实际填写长度为
      {{ name.errors.maxlength.actualLength }}
    </div>
  </div>
</form>

2.5 Custom synchronization form validator

The type of custom validator is

TypeScript
• Class
  The class contains specific verification methods, which must The validation method for the static method

• has a parameter
control
• of type

  AbstractControl. In fact, it is the type of the instance object of the FormControl class

  If the verification is successful, return
null

• If the verification fails, return the object. The attribute in the object is the verification identification, and the value is
true
• , which indicates that the verification failed.
  The return value of the verification method is
ValidationErrors | null

• import { AbstractControl, ValidationErrors } from "@angular/forms"
  
  export class NameValidators {
    // 字段值中不能包含空格
    static cannotContainSpace(control: AbstractControl): ValidationErrors | null {
      // 验证未通过
      if (/\s/.test(control.value)) return { cannotContainSpace: true }
      // 验证通过
      return null
    }
  }

  import { NameValidators } from "./Name.validators"
  
  contactForm: FormGroup = new FormGroup({
    name: new FormControl("", [
      Validators.required,
      NameValidators.cannotContainSpace
    ])
  })

  <div *ngIf="name.touched && name.invalid && name.errors">
    <div *ngIf="name.errors.cannotContainSpace">姓名中不能包含空格</div>
  </div>

2.6 Custom asynchronous form validator

import { AbstractControl, ValidationErrors } from "@angular/forms"

export class NameValidators {
  static shouldBeUnique(control: AbstractControl): Promise<ValidationErrors | null> {
    return new Promise(resolve => {
      if (control.value == "admin") {
         resolve({ shouldBeUnique: true })
       } else {
         resolve(null)
       }
    })
  }
}

contactForm: FormGroup = new FormGroup({
    name: new FormControl(
      "",
      [
        Validators.required
      ],
      NameValidators.shouldBeUnique
    )
 })

<div *ngIf="name.touched && name.invalid && name.errors">
  <div *ngIf="name.errors.shouldBeUnique">用户名重复</div>
</div>
<div *ngIf="name.pending">正在检测姓名是否重复</div>

2.7

FormBuilder

Shortcut to create a form.

this.fb.control
• : Form item

this.fb.group
• : Form group, the form is at least one

  FormGroup

this.fb.array
• : used for complex forms, you can dynamically add form items or forms Group, during form validation, one item in

  FormArray failed, and the whole failed

2.8 Exercise

Get the selected value in a set of check boxes

<form [formGroup]="form" (submit)="onSubmit()">
  <label *ngFor="let item of Data">
    <input type="checkbox" [value]="item.value" (change)="onChange($event)" />
    {{ item.name }}
  </label>
  <button>提交</button>
</form>

import { Component } from "@angular/core"
import { FormArray, FormBuilder, FormGroup } from "@angular/forms"
interface Data {
  name: string
  value: string
}
@Component({
  selector: "app-checkbox",
  templateUrl: "./checkbox.component.html",
  styles: []
})
export class CheckboxComponent {
  Data: Array<Data> = [
    { name: "Pear", value: "pear" },
    { name: "Plum", value: "plum" },
    { name: "Kiwi", value: "kiwi" },
    { name: "Apple", value: "apple" },
    { name: "Lime", value: "lime" }
  ]
  form: FormGroup

  constructor(private fb: FormBuilder) {
    this.form = this.fb.group({
      checkArray: this.fb.array([])
    })
  }

  onChange(event: Event) {
    const target = event.target as HTMLInputElement
    const checked = target.checked
    const value = target.value
    const checkArray = this.form.get("checkArray") as FormArray

    if (checked) {
      checkArray.push(this.fb.control(value))
    } else {
      const index = checkArray.controls.findIndex(
        control => control.value === value
      )
      checkArray.removeAt(index)
    }
  }

  onSubmit() {
    console.log(this.form.value)
  }
}

Get the selected value in the radio button

export class AppComponent {
  form: FormGroup

  constructor(public fb: FormBuilder) {
    this.form = this.fb.group({ gender: "" })
  }

  onSubmit() {
    console.log(this.form.value)
  }
}

<form [formGroup]="form" (submit)="onSubmit()">
  <input type="radio" value="male" formControlName="gender" /> Male
  <input type="radio" value="female" formControlName="gender" /> Female
  <button type="submit">Submit</button>
</form>

2.9  其他

• patchValue：设置表单控件的值（可以设置全部，也可以设置其中某一个，其他不受影响）

• setValue：设置表单控件的值 (设置全部，不能排除任何一个)

• valueChanges：当表单控件的值发生变化时被触发的事件

• reset：表单内容置空

• updateValueAndValidity：对指定输入框 取消校验

validateForm: FormGroup; 

this.validateForm.get('cpwd').updateValueAndValidity();

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