o_19mgorv9t13a3ko71fev19l81mqa.pdf

the problem (Please enter your name).
I can check to see whether the model binder was able to assign a value to a property by using the
ModelState.IsValidField property. I do this for the Date property to make sure that the model binder was able
to parse the value the user submitted; there is no point performing additional checks or reporting additional errors if no value could
be parsed from the request data.
After I have validated all the properties in the model object, I read the ModelState.IsValid property to see whether
there were errors. This method returns true if I called the Model.State.AddModelError method during the
checks or if the model binder had any problems creating the Appointment object:
...
if (ModelState.IsValid) {
// statements to store new Appointment in a
// repository would go here in a real project
return View("Completed", appt);
} else {
return View();
}
...
I know I have a valid Appointment object if there are no problems reported by the IsValid property and I can render
the Completed.cshtml view (and, in a real project, store the Appointment object in the repository). If the
IsValue property returns false, then I know that I have a problem, which I deal with by calling the View method to
render the default view.
Displaying Validation Errors to the User
It may seem odd to deal with a validation error by calling the View method, but the templated view helpers that I used to
generate input elements in the MakeBooking.cshtml view check the view model for validation errors.
The helpers add a CSS class called input-validation-error to the input elements if an error has been
reported for the corresponding properties, which is why I added these CSS styles to the layout when I created the example
project:
...
.input-validation-error { border: 2px solid #f00; background-color: #fee;
}
input[type="checkbox"].input-validation-error { outline: 2px solid #f00; }
...
The first style creates the effect of setting a red border and a pink background on any element for which there is an error. The
second style applies a red border to checkbox elements. These elements are hard to style and usually require special attention. You
can test the explicit validation approach by starting the application, navigating to the /Home/MakeBooking URL, and
clicking the Make Booking button without entering any data in the form. The result is shown in Figure 25-2.
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