I tried the dialog class, but using the theme Holo.light, the text color is same as background.
It seems very strange that B4A not implement a native class for file selection.
Dim cc As ContentChooser
cc.Initialize("cc")
cc.Show("*/*","Open File")
but
B4X:
Sub cc_Result (Success As Boolean, Dir As String, FileName As String)
Dim nameFile As String 'in Globals
Dim pathDir As String 'in Globals
If Success = True Then
nameFile = FileName
pathDir = Dir
End If
End Sub