HowTo: Using the ShowError method from Interop in Native Mobile applications

This method performs the equivalent of what is automatically done to display errors when a Composite command fails in a Native Mobile application.

Return value: Numeric(3).

When the action to be executed invokes a GeneXus object located on the server side—for example, an online Procedure object or Data Provider object—the returned value corresponds to the HTTP code returned by this call (for example, 404 or 500). If there is no response from the server, the &Err variable will have the value 1.

Parameters: none.

Samples

1) Sometimes it is necessary to use the Composite command to handle errors, but it is also necessary to implement something else. For example, suppose you have to solve a favorites toggle button in an online application.

The event can be defined as shown below:

Event “ToggleFavorites”
  Composite
     &IsFav = not &IsFav
     ProcSetFav(&IsFav) // The Procedure changes the style with dynamic properties to show the current state (if it is favorite or not). 
  EndComposite
EndEvent

The problem with this solution is that the appearance is changed but it is done after a round trip to the server, so the UX is not good. Besides, if the Procedure fails, the &IsFav value will have a wrong state.

Another solution could be:

Event “ToggleFav”
  Composite
     &IsFav = not &IsFav
     Control.Class = iif(&IsFav, !"FavClass”, !“FavClass”)
     ProcSetFav(&IsFav) // In this case the Procedure only saves the new favorite state
  EndComposite
EndEvent

This solution gives good UX feedback, but it has the same issues as the previous solution in the sense that if the Procedure fails, the &IsFav value will have a wrong state.

So, consider the following solution that uses the Interop.ShowError method:

Event “ToggleFav”
  Do ’ToogleIsFav’
  ProcSetFav(&IsFav) // // In this case the Procedure only saves the new favorite state
  if Interop.ShowError() <> 0
    Do ’ToogleIsFav’ // Restores the state before the Procedure failed
endif 
EndEvent 

Sub ’ToogleIsFav’ 
   &IsFav = not &IsFav 
   Control.Class = iif(&IsFav, !oFavClass”, !“FavClass”) 
EndSub

The Interop.ShowError() method is provided by GeneXus and does the same as is done automatically to display errors when Composite commands fail.

It solves the same as the following GeneXus code:

Sub “ShowError”

  if &err <> 0 and &err <> 2 // Error no Cancel
    if &errMsg.IsEmpty()
      msg(“GXM_ThereWasAnErrorExecutingAction”)
    else
      msg(&errMsg)
    endif
  endif
EndSub

In addition, to facilitate evaluations in If commands, the returned &Err variable is loaded.

2) The following code doesn't have a Composite command and shows the errors using the Interop.ShowError method:

Event 'InsertNewUser'
    &ErrorResult.SetEmpty()
    ProcNewUser(&UserInformation)
    &ErrorResult = Interop.ShowError()
    if &ErrorResult <> 0
        //Some code...
    Else
        msg("A new user was added successfully", nowait)
    EndIf
Endevent

Scope

Generators: Android, Apple

Availability

Since GeneXus 17 Upgrade 11.

See Also

Interop external object