MVVMCross how to use same events - xamarin.ios

Question

I have a View with 2 textbox and a button that call an action on a ViewModel to show another View; that what will show in it depends on values of 2 texbox.
For that reason before to call my ViewModel i want to check textbox values and if its are empty show a Dialog. Now to call my ViewModel i have add a binding like this:
this.AddBindings(new Dictionary<object, string>()
{
{ btnSearch, "TouchUpInside GoParameterizedCommand" },
});
as Swiss Binding. Now if i want to use same event to check if my textbox are valorized and don't call GoParameterizedCommand, how could i do?

Answer 1

You could bind all your controls to ViewModel properties like:
this.AddBindings(new Dictionary<object, string>()
{
{ btnSearch, "TouchUpInside GoCommand" },
{ text1, "Text MyText" },
{ switch1, "On MyOption" },
// ...
};
Then inside the GoCommand handler you could put whatever logic you need:
public ICommand GoCommand
{
get
{
return new MvxCommand(() => {
if (MyOption)
{
ShowViewModel<OptionViewModel>();
}
else
{
ShowViewModel<DetailViewModel>(new { text = MyText });
}
});
}
}
For showing a dialog - eg an error dialog - then this might be best done using a messenger - sending an error message from the viewmodel. There are a few questions on here about error handling - eg http://slodge.blogspot.co.uk/2012/05/one-pattern-for-error-handling-in.html - plenty of other options are available for giving the user a hint about what to do - eg you could bind the background colour of the text field to an IsMyTextValid property.