Angular learning talks about two types of forms

This article will take you to understand the forms in angular and learn about the two types of forms: template-driven and model-driven. I hope it will be helpful to everyone!

In Angular, there are two types of forms, namely template driven and model driven. [Recommended related tutorials: "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

1), introduce the dependent module FormsModule

import { FormsModule } from "@angular/forms"

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

2), convert the DOM form to ngForm

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

3), declare the form field as ngModel

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

4), get the form field value

import { NgForm } from "@angular/forms"

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

5), 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>

import { NgForm } from "@angular/forms"

export class AppComponent {
 onSubmit(form: NgForm) {
   console.log(form.value) // {contact: {phone: ''}, user:{username: ''}}
 }
}

1.3 Form validation

##required Required fields
• minlength Minimum field length
• maxlength Maximum field length
• pattern validation regular example: pattern="\d" matches 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>

Specify the style when the form item fails validation.

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

2. Model driven

2.1 Overview

## of the form #Control logic

Written in the component class, it has more control over the verification 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 overall validate the form.

FormControl: a form item in the form group
FormGroup: form group, the form is at least A FormGroup
FormArray: used for complex forms, which can dynamically add form items or form groups. During form validation, if one item in the FormArray fails, the entire form fails.

2.2 Get started quickly1), introduce ReactiveFormsModule

import { ReactiveFormsModule } from "@angular/forms"

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

2), in the component Create a FormGroup form control object in the class

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

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

3), 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>

4), get the form value

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

5), and set the form default value

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

6), 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 FormArrayRequirement: Display a set of contact information on the page by default , you can add more contact 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 validator1), 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)
  ])
})

2), Get whether the entire form has passed the 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>

3), and display the error message when the verification has passed 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 Customize the synchronization form Validator

The type of custom validator is TypeScript class
The class contains specific verification methods, verification The method must be a static method
The verification 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, null will be returned.
If the verification fails, the object and the properties in the object will be returned. It is the verification identifier, and the value is true, indicating 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"
import { Observable } from "rxjs"

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 FormBuilderCreate the form

A shortcut.

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 form groups during form validation , one item in FormArray failed, and the whole failed.

  import { FormBuilder, FormGroup, Validators } from "@angular/forms"
  
  export class AppComponent {
    contactForm: FormGroup
    constructor(private fb: FormBuilder) {
      this.contactForm = this.fb.group({
        fullName: this.fb.group({
          firstName: ["", [Validators.required]],
          lastName: [""]
        }),
        phone: []
      })
    }
  }

2.8 Monitoring changes in form values

实际工作中，我们常常需要根据某个表单值得变化而进行相应的处理，一般可以使用ngModalChange或者表单来实现

2.8.1 ngModalChange

<div>
  <input type="text" [(ngModal)]="name" (ngModalChange)="nameChange()" />
</div>

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

export class AppComponent {
  public name = 'a';
  public nameChange() {
  }
}

angular官方并不建议使用ngModalChange。

2.8.2 表单控制

<div [formGroup]="contactForm">
  <input type="text" formControlName="name" />
</div>

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

export class AppComponent {
  contactForm: FormGroup = new FormGroup({
    name: new FormControl()
  })
	
	ngOnInt() {
		this.contactForm.get("name").valueChanges.subscribe(data => {
			console.log(data);
		}
	}
}

2.9 练习

1）、获取一组复选框中选中的值

<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)
  }
}

2）、获取单选框中选中的值

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>

2.10 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

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