how to show validate message in form in angular 2?

问题

I am trying to show validate message in form in angular 2 ? I am getting this error

Cannot read property 'hasError' of undefined

I added these lines

 <div *ngIf="username.hasError('required') && username.touched" 
           class="error-box"> username is required</div>    
       <div *ngIf="username.hasError('minlength') && username.touched" 
           class="error-box"> Minimum password length is 8!</div>

here is my code https://plnkr.co/edit/slhySWT0mJXkloGK1kfO?p=preview

回答1:

This should do what you want:

<ion-input type="text" ngControl="username" #username="ngForm"></ion-input>

 <div *ngIf="username.errors?.required && username.touched" 
           class="error-box"> username is required</div>    
       <div *ngIf="username.errors?.minlength && username.touched" 
           class="error-box"> Minimum password length is 8!</div>

Plunker example

来源：https://stackoverflow.com/questions/37428715/how-to-show-validate-message-in-form-in-angular-2