Standard: DataAnnotation Validation in Xamarin.Forms

[PKYADAV]

Hi Team,

I have class library in .net Standard 2.0 with EntityFrameworkCore. I have created class with Custom DataAnnotation as below:

Model Definition

```C#
public class UserLogin : NotificationObject
{
[DbRequired]
[Display(Name = "USER NAME", Prompt = "ENTER USER NAME")]
public string User_Name
{
get { return GetValue(() => User_Name); }
set { SetValue(() => User_Name, value); }
}

    [Display(Name = "PASSWORD", Prompt = "ENTER PASSWORD")]
    [DataType(DataType.Password)]
    [DbRequired]
    public string User_Password
    {
        get { return GetValue(() => User_Password); }
        set { SetValue(() => User_Password, value); }
    }
}

```

But this data annotation validation is working in Asp.Net Core and WPF. But we want to use the same in Xamarin.Forms for Android & iOS and UWP. Is it possible or any workaround? As I heard that in .net Standard you need write once and can be reuse in all other environment

[terrajobst]

@divega any idea why this wouldn't work? It should just work in Xamarin too, no?

[divega]

@PKYADAV what is DbRequiredAttribute? Is that your own custom validation attribute? What do you mean exactly with the data annotation validation not working? Please provide a precise descriptions of expected and actual behaviors and any exceptions. A small repro project would be ideal.

[PKYADAV]

Hi @divega,

Yes, DbRequiredAttribute is custom validation attribute and it is working in WPF, ASP.NET CORE and Blazor but not in xamarin.forms.

Below image is our target, write class library in .net Standard, class library will be decorated with Validation Attribute and re-use the same in all application:

Please suggest / guide us.

I have already posted the same on StackOverflow and Xamarin Forums.

Thanks !!

[divega]

@PKYADAV, thanks for answering my first question. Please also answer this part:

What do you mean exactly with the data annotation validation not working? Please provide a precise descriptions of expected and actual behaviors and any exceptions. A small repro project would be ideal.

I ask this because (among other reasons) I want to understand if you are invoking ValidateObject() directly or expecting this to happen automatically. One of the technologies mentioned in your first post, ASP.NET Core, implements validation based on data annotations, but others like EF Core don’t.

As I said, a repro would be ideal.

[PKYADAV]

@divega sorry for delay in response as my notification was off and couldn't get notified.

Again sorry for your question as I didn't get your question that what exactly you want to know from my side .
Request to elaborate once again please !!

[PureWeen]

@PKYADAV Xamarin.Forms doesn't have SDK support for INotifyDataErrorInfo at this point

https://github.com/xamarin/Xamarin.Forms/issues/5524

So you would need to wire this up yourself.

https://www.codeproject.com/Articles/1274851/Xamarin-Forms-Validations-Made-Simple

[kevin-mueller]

You might want to check out this library I wrote: https://www.nuget.org/packages/Xamarin.AttributeValidation/

It allows you to validate your UI by simply putting Attributes above your properties in the ViewModel. That's it. Nothing more to do. Just like you do in ASP.NET Core. The Validation Messages are automatically shown in the form of a little floating text bubble, hovering over the entry. Very similar to the native Android Validation.

For an example, or a detailed explanation, check out the repository: https://github.com/kevin-mueller/Xamarin.AttributeValidation