When a configuration change is performed in Android (such as an orientation change), the current activity is destroyed and recreated with the updated configuration. The obvious downside of this is the loss of state in your application. However, Android provides a few ways of saving ui states. AndroidPages in coordination with the included library implement ViewModel and Saved instance state.
AndroidPages keeps the naming convetions of B4XPages for compatibility reasons, however, there are a few changes you need to make in existing B4A projects. Download the attatched library and extract the files in your additional libraries folder. Remove B4XPages and add AndroidPages in the libaries manager.
In the manifest editor, add:
B4X:
SetApplicationAttribute(android:theme, "@style/Theme.AppCompat.Light")In your Main class, remove:
B4X:
#SupportedOrientations: portraitAdd:
B4X:
#Extends: spavlyuk.viewmodel.AppCompatActivityAnd:
B4X:
Private Sub Activity_SaveInstanceState(OutState As Object)
B4XPages.Delegate.Activity_SaveInstanceState(OutState)
End SubThese changes will allow simple views (such as EditTexts) to automatically save and restore their state. For more complex views you can use either ViewModel or Saved instance state. In short, ViewModel should be used for complex or large data structures, while Saved instance state should be used for simple data structures. You can find more details in the link above.
ViewModel example:
Sub Class_Globals
' ...
Private Model As Map
End Sub
Public Sub SetImage(Value As Object)
Model.Put("ImageView1", Value)
ImageView1.SetBitmap(Value)
End Sub
Private Sub B4XPage_Created (Root1 As B4XView)
' ...
Model = ViewModelProvider.Get
If Model.ContainsKey("ImageView1") Then
ImageView1.SetBitmap(Model.Get("ImageView1"))
End If
End Sub
Saved instance state example:
Private Sub B4XPage_SaveInstanceState (OutState As Object)
OutState.As(JavaObject).RunMethod("putString", Array("AuthenticationToken", "123"))
End Sub
Private Sub B4XPage_RestoreInstanceState (SavedInstanceState As Object)
Dim AuthenticationToken As String = SavedInstanceState.As(JavaObject).RunMethod("getString", Array("AuthenticationToken"))
Log("Saved AuthenticationToken: " & AuthenticationToken)
End SubAttached you will also find a modified ThreePagesExample where some additional changes had to be made.