How to Validate & Display Error Message - Angular2 Material Design?

问题

I have this input:

<form #f="ngForm" name="productForm">
     <md-input [(ngModel)]="product.price" name="price" required="true" placeholder="Price (USD)"></md-input>
     <div ng-messages="productForm.price.$error" role="alert">
         <div ng-message-exp="['required']">
              Price is required
          </div>
     </div>
</form>

But the message Price is required doesn't show up.

How should I properly format the error message?

The ng-invalid class appears when the price input is empty:

When I fill in something:

Angular injects ng-valid class in it.

I want is to have the style similar to angular1 md design that looks like this:

回答1:

Hopefully this will be added as angular2-material evolves, but currently the way to mimic this is to set the dividerColor and use the MD-HINT directive. example:

<md-input placeholder="Email address"
    #email="ngModel"
    name="email"
    type="text"
    fullWidth={true}
    [(ngModel)]="model.email"
    required
    email
    dividerColor="{{ !email.valid ? 'warn' : 'primary' }}">
    <md-hint [hidden]="email.pristine || email.valid">
        <span [hidden]="email.errors?.required || !email.errors?.email">
            This doesn't appear to be a valid email address.
        </span>
        <span [hidden]="!email.errors?.required">Email address is required.</span>
    </md-hint>
</md-input>

回答2:

Validation messages can now be inserted with Angular Material version 2.0.0 onward. Check the documentation here.

<form class="example-form">
  <mat-form-field class="example-full-width">
    <input matInput placeholder="Email" [formControl]="emailFormControl">
    <mat-error *ngIf="emailFormControl.hasError('pattern')">
      Please enter a valid email address
    </mat-error>
    <mat-error *ngIf="emailFormControl.hasError('required')">
      Email is <strong>required</strong>
    </mat-error>
  </mat-form-field>
</form>

来源：https://stackoverflow.com/questions/39019430/how-to-validate-display-error-message-angular2-material-design