Xamarin View with ViewModel and Behaviour

问题

I have a View which contains the userprofile of the current user. The view contains a viewmodel with a two-way binding to the single attributes like username or email adress. The view also has a behaviour, which validates the input and shows an error, of the input is not valid. Because of the two-way binding, the viewmodel updates the value even if the behavior says the input is wrong. I need to solve that.

My current approach is to use include the behavior in the viewmodel as a attribute. So I can access the attributes of the behavior in the setter of the attributes in the viewmodel. So I cant stop the update to the wrong inputs. But I can not get access the behavior from my viewmodel in the xaml of the view. Is that a way I can do it at all?

My next approach would be to pass the "isValid" attribute of the behavior to the viewmodel. But here again, I don't know how to do it, is it possible at all?

Last approach would be to create a command in the viewmodel, binding it to a new button in the userprofile, using a one-way binding and somehow pass the inputs from the view to the command and updateing the userprofile.

May be here is someone who can help me?

EDIT: I post some code:

This is a single entry with my behavior:

<Entry x:Name="phoneNumber" Text="{Binding TelephoneNum, Mode=TwoWay}">
    <Entry.Behaviors>
        <behaviors:TelNumBehavior x:Name="NumValidatorUser"/>
    </Entry.Behaviors>
</Entry>

The TelNumBehavior:

public class TelNumBehavior : Behavior<Entry>
{
...
public static readonly BindablePropertyKey IsVisiblePropertyKey = 
        BindableProperty.CreateReadOnly("IsVisible", typeof(bool), typeof(TelNumBehavior), false);
public static readonly BindableProperty IsVisibleProperty = IsVisiblePropertyKey.BindableProperty;

...
public bool IsVisible
{
    get { return (bool) this.GetValue(IsVisibleProperty); }
    set
      {
          this.SetValue(IsVisiblePropertyKey, value);
       }
    }
...
(OnAttachedTo, OnDetachingFrom)
...

private void bindable_TextChanged(object sender, TextChangedEventArgs e)
{
    Entry entry = sender as Entry;
    this.IsVisible = (entry.Text == "")
            ? true
            : (Regex.IsMatch(e.NewTextValue, mobileRegex) || Regex.IsMatch(e.NewTextValue, fixedLineRegex));
    entry.TextColor = this.IsVisible ? Color.Default : Color.Red;
}

To sum it up: I use that behavior for validation of some inputs. But the viewmodel does not know if the inputs are correct or not. And this is currently my problem. I dont know how to inform the viewmodel about the state of the inputs.

来源：https://stackoverflow.com/questions/52567801/xamarin-view-with-viewmodel-and-behaviour

标签

Xamarin

mvvm

viewmodel

behavior