GetService<IMessageBoxService>() returned null.

Dear Support Team,

I readed online documentation of Data Editors (Lesson 1 ~ Lession 5 of [How To: Create a Registration Form]) and I also add the sample code as E4575 in my application project.
I tried to show validation fail error message dialogue, but application returned exception. It's because GetService<IMessageBoxService>() returned null. Could you tell me what's wrong and how to fix it?

The attach file is my sample code.

Thanks.

Hello Rinkin,

Thank you for providing the sample project. It is necessary to add the DXMessageBoxService service to the XAML code of the user controls to avoid this exception. Please try this and let me know your results.

XAML

</UserControl.Resources>  
<dxmvvm:Interaction.Behaviors>  
    <dx:DXMessageBoxService/>  
</dxmvvm:Interaction.Behaviors>  
<Grid>

需要添加上面的dxmvvm

<dxmvvm:Interaction.Behaviors>
                                <dxmvvm:EventToCommand EventName="SuggestionChosen"
                                                       Command="{Binding SuggestionChosenCommand}"
                                                       PassEventArgsToCommand="True" />
                            </dxmvvm:Interaction.Behaviors>

然后user model里面指定

public DelegateCommand<AutoSuggestEditSuggestionChosenEventArgs> SuggestionChosenCommand { get; set; }

UWP Binding to AutoSuggestBox in MVVM

InvokeCommandAction has a parameter named InputConverter which you can use to convert the event args to some other parameter that can be passed to your ViewModel.

First create a IValueConverter class to extract what you need from your event args like this:-

public class AutoSuggestQueryParameterConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
       {
          // cast value to whatever EventArgs class you are expecting here
          var args = (AutoSuggestBoxQuerySubmittedEventArgs)value;
          // return what you need from the args
          return (string)args.ChosenSuggestion;
       }
}

Then use that converter in your XAML like this:

<Page.Resources>
     <converters:AutoSuggestQueryParameterConverter x:Key="ArgsConverter" />
</Page.Resources>

<AutoSuggestBox Name="SearchAutoSuggestBox"
            PlaceholderText="Search by keywords"
            QueryIcon="Find">
    <interactivity:Interaction.Behaviors>
      <core:EventTriggerBehavior EventName="QuerySubmitted">
        <core:InvokeCommandAction 
              Command="{x:Bind ViewModel.SearchCommand}"
              InputConverter="{StaticResource ArgsConverter}" />
      </core:EventTriggerBehavior>
    </interactivity:Interaction.Behaviors>
</AutoSuggestBox>

Finally in your viewmodel change your command to accept a string as parameter. So you would have the following in your vm:

public DelegateCommand<string> SearchCommand { get; }

public MainPageViewModel()
{
    SearchCommand = new DelegateCommand<string>(ExecuteMethod);
}

private void ExecuteMethod(string o)
{
    // CODE HERE
}