Xamarin form validation and ASP.Net WebAPI

Question

I have a Xamarin.Form app, and I am consuming an ASP.Net Web WebAPI with Model State for validation in my internal models. If I got a "bad request" my API return this JSON object:

{
    message: 'The request is invalid.',
    modelState: {
        model.**Name**: [
            "The name is empty"
        ]
    }
  }

So, I want to simplify my work in the UI to read that result, my question are: How can I do to use this object for display the error in my UI? or Does Xamarin Form have any helper like to ASP.NET MVC Validator @Html.ValidationMessageFor(model => model.Name), it could display automatic the error in the UI?

Thanks!

Krishna · Accepted Answer · 2017-06-19 14:09:29Z

1

You can create behaviors for controls like the below one

public class EmailValidatorBehavior : Behavior<Entry>  
    {  
        const string emailRegex = @"^(?("")("".+?(?<!\\)""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" +  
            @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$";  


        protected override void OnAttachedTo(Entry bindable)  
        {  
            bindable.TextChanged += HandleTextChanged;  
            base.OnAttachedTo(bindable);  
        }  

        void HandleTextChanged(object sender, TextChangedEventArgs e)  
        {  
            bool IsValid = false;  
            IsValid = (Regex.IsMatch(e.NewTextValue, emailRegex, RegexOptions.IgnoreCase, TimeSpan.FromMilliseconds(250)));  
            ((Entry)sender).TextColor = IsValid ? Color.Default : Color.Red;  
        }  

        protected override void OnDetachingFrom(Entry bindable)  
        {  
            bindable.TextChanged -= HandleTextChanged;  
            base.OnDetachingFrom(bindable);  
        }  
    }

Use this behavior in XAML as below

Add namespace for your behavior

xmlns:local="clr-namespace:Mynamespace.Behaviors"

Add behavior to the entry

<Entry x:Name="txtEmail"  Placeholder="Enter Your Password" >  
      <Entry.Behaviors>  
        <local:EmailValidatorBehavior />  
      </Entry.Behaviors>  
    </Entry>

The above behavior will validate email and change the textbox color ro red if the email is not valid. Like that you can create more behaviours

edited Jun 19, 2017 at 14:09

answered Jun 19, 2017 at 13:58

Krishna

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2 Comments

Carlos Bolivar Over a year ago

Can you get me more information about this? What about of XAML?

Carlos Bolivar Over a year ago

Thank you for your answer! but I mean, I have a PLC with all model, for every model's property I have a data notations for validations in my web api. How can I do to use those validations in Xamarin Form with that validation in every model see this?

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