angular version:

Angular CLI: 9.0.0-rc.7

Angular: 9.0.0-rc.7

I'm working with login but get an error:

browser console error:

formGroup expects a FormGroup instance. Please pass one in.

<div [formGroup]="myGroup">
  <input formControlName="firstName">
</div>

In your class:

this.myGroup = new FormGroup({
   firstName: new FormControl()
});

login.component.html

 <div class="card-body">
        <form [formGroup]="logincreteform" (ngSubmit)="onSubmit()">
              <div class="form-group">
                 <input type="text" formControlName="username" class="form-control" placeholder="Username" autocomplete="username" required>
              </div>

             <div class="form-group">
                   <input type="password" formControlName="password" class="form-control" placeholder="Password" autocomplete="current-password" required>
             </div>
            
             <button type="submit" class="btn btn-primary px-4">Login</button>
      </form>
</div>

login.component.ts

import { Component, OnInit,OnChanges, Input } from '@angular/core';
import { Router } from '@angular/router';
import { FormGroup, FormsModule, FormControl, ReactiveFormsModule, Validators} from "@angular/forms";

export class LoginComponent   {

    logincreteform : FormGroup;

    constructor(private router: Router) {
    }

    ngoninit() {
        this.logincreteform = new FormGroup({
            username: new FormControl(),
            password: new FormControl()
        });
    }
 
   onSubmit() {
        console.log(this.logincreteform);
        let username;
        let password ;
        if (username == 'abc' && password == '123') {
            this.router.navigate(['/register']);
        }
        else {
            console.log("error");
        }
    }
}

app.module.ts

import { FormsModule,ReactiveFormsModule } from '@angular/forms'; 
import { LoginComponent } from './views/login/login.component';
import { RegisterComponent } from './views/register/register.component';

@NgModule({
  imports: [
 
   ReactiveFormsModule,

  declarations: [
      LoginComponent,
      RegisterComponent
  ],
bootstrap: [ AppComponent ]
})
export class AppModule { }

and when I uncomment register page code:

then also give an error:

compiler.js:2531 Uncaught Error: Template parse errors:
No provider for ControlContainer ("
          <div class="card mx-4">
            <div class="card-body p-4">
              [ERROR ->]<form>
                <h1>Register</h1>
                <p class="text-muted">Create your account<"): ng:///AppModule/RegisterComponent.html@7:14

register.component.html

          <div class="card-body p-4">
              <form>
                <h1>Register</h1>
                <p class="text-muted">Create your account</p>
                <div class="form-group">
                        <input type="text" formControlName="username" class="form-control" placeholder="Username" autocomplete="username" required>
                </div>
               <div class="form-group">
                         <input type="text" formControlName="email" class="form-control" placeholder="Email" autocomplete="email" required>
               </div>
               <div class="form-group">
                     <input type="password" formControlName="password" class="form-control" placeholder="Password" autocomplete="new-password" required>
               </div>
                   <button type="button" class="btn btn-block btn-success">Create Account</button>
         </div>

register.component.ts

import { Component } from '@angular/core';

@Component({
  selector: 'app-dashboard',
  templateUrl: 'register.component.html'
})
export class RegisterComponent {

  constructor() { }

}

I want the simple login to enter username(abc) and password(123) then redirecting to the registration page?? what I m doing wrong?help.

You are missing formGroup in the register component. You need to add it in form tag the same as you did it in login component.

register.component.html

<div class="card-body p-4">
 <form [formGroup]="registerform" (ngSubmit)="onSubmit()>
   <h1>Register</h1>
   <p class="text-muted">Create your account</p>
   <div class="form-group">
      <input type="text" formControlName="username" class="form-control" placeholder="Username" autocomplete="username" required>
                </div>
               <div class="form-group">
                         <input type="text" formControlName="email" class="form-control" placeholder="Email" autocomplete="email" required>
               </div>
               <div class="form-group">
                     <input type="password" formControlName="password" class="form-control" placeholder="Password" autocomplete="new-password" required>
               </div>
                   <button type="button" class="btn btn-block btn-success">Create Account</button>
         </div>

you need add formGroup in you component.ts file as well.

`import { Component } from '@angular/core';
import { FormsModule,ReactiveFormsModule } from '@angular/forms'; 
@Component({
  selector: 'app-dashboard',
  templateUrl: 'register.component.html'
})
export class RegisterComponent {
registerform : FormGroup;
  constructor() { }

}`

now my issue is Solved.

login.component.cs

import { Component, OnInit } from '@angular/core';
import { Router } from '@angular/router';
import { FormGroup, FormControl, Validators, FormBuilder} from "@angular/forms";

@Component({
    selector: 'app-dashboard',
    templateUrl: 'login.component.html'
})

export class LoginComponent  {

    login: FormGroup;

    constructor(private frmbuilder: FormBuilder, public router:Router) {

        this.login = this.frmbuilder.group({
            username: [''],
            password: ['']

        });
    }

 onSubmit() {
        console.log(this.login);
        let username = this.login.get('username').value;
        let password = this.login.get('password').value;
        if (username == 'abc' && password == '123') {
            this.router.navigate(['/dashboard']);     //navigate when your criteria match then redirect dashboard page otherwise give an error.(Navigation)
        }
        else {
            console.log("error");
        }
    }

Do Not Forget this line in Html page

 <form [formGroup]="login" (ngSubmit)="onSubmit()">