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!

Answer 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

Xamarin form validation and ASP.Net WebAPI

1 个答案: