Question

I have a label and a textfield and it will display two different values.

if(a != null && b == null) {
   return "a"; 
}
else if(a == null && b != null) {
   return "b"; 
}

The logic is quite simple, but how to fit this in xaml and mvvm-pattern? I have a viewmodel and a view (xaml-ui). The code should propably be placed in the viewmodel.

Answer 1

Youe mean to say…. you want to diplay a for first condition and b for second condition ??

if Thats true…

then ..

Make a property with Property chnaged notification in your ViewModel

Code inside your ViewModel

public void ValidationFunction
{
    if(a != null && b == null) 
    {
          TextToDisplay ="a";
    }
    else if(a == null && b != null) 
    {
          TextToDisplay ="b";
    }
    else
    {
          TextToDisplay= string.Empty;
    } 
}

Binding in XAML

<TextBlock Text={Binding Path=TextToDisplay}/> 

Dont forget to implement INotifyPropertyChanged in Setter of property.

Call the validation function when required.