disable button instead of hiding, remove empty values before saving, update dialog result handling

Controls.LookupGrid/LookupControl2.vb

@@ -22,7 +22,6 @@ Public Class LookupControl2
             Return _SelectedValues
         End Get
         Set(value As List(Of String))
-            _SelectedValues = value
             UpdateSelectedValues(value)
         End Set
     End Property
@@ -31,19 +30,20 @@ Public Class LookupControl2
             Return _ReadOnly
         End Get
         Set(value As Boolean)
-            SetButtonVisibility(Not value)
+            SetFormButtonEnabled(Not value)
             _ReadOnly = value
         End Set
     End Property
 
     Private ReadOnly _LookupFormButton As EditorButton
 
+    Private Const TAG_DROPDOWN = "openDropdown"
     Private Const TAG_BUTTON_LOOKUP_FORM = "openLookupForm"
     Private Const TEXT_NO_RECORDS = "Keine Datensätze ausgewählt"
     Private Const TEXT_ONE_RECORD = "Ein Datensatz ausgewählt"
     Private Const TEXT_N_RECORDS = "{0} Datensätze ausgewählt"
 
-    Private _SelectedValues As List(Of String)
+    Private _SelectedValues As New List(Of String)
     Private _ReadOnly As Boolean = False
 
     Shared Sub New()
@@ -60,6 +60,7 @@ Public Class LookupControl2
             .Tag = TAG_BUTTON_LOOKUP_FORM
         }
 
+        Properties.Buttons.Item(0).Tag = TAG_DROPDOWN
         Properties.Buttons.AddRange({_LookupFormButton})
 
         AddHandler ButtonClick, AddressOf HandleButtonClick
@@ -67,13 +68,23 @@ Public Class LookupControl2
         AddHandler QueryPopUp, AddressOf HandleQueryPopup
     End Sub
 
-    Private Sub SetButtonVisibility(Visible As Boolean)
+    Private Sub SetFormButtonEnabled(Enabled As Boolean)
         Dim oButton As EditorButton = Properties.Buttons.
             Where(Function(b) b.Tag = TAG_BUTTON_LOOKUP_FORM).
             FirstOrDefault()
 
         If oButton IsNot Nothing Then
-            oButton.Visible = Visible
+            oButton.Enabled = Enabled
+        End If
+    End Sub
+
+    Private Sub SetDropdownButtonEnabled(Enabled As Boolean)
+        Dim oButton As EditorButton = Properties.Buttons.
+            Where(Function(b) b.Tag = TAG_DROPDOWN).
+            FirstOrDefault()
+
+        If oButton IsNot Nothing Then
+            oButton.Enabled = Enabled
         End If
     End Sub
 
@@ -106,14 +117,7 @@ Public Class LookupControl2
 
                     If oResult = Windows.Forms.DialogResult.OK Then
                         Dim oValues = oForm.SelectedValues
-
                         UpdateSelectedValues(oValues)
-                        SelectedValues = oValues
-                    ElseIf oResult = Windows.Forms.DialogResult.Cancel Then
-                        Dim oValues = New List(Of String)
-
-                        UpdateSelectedValues(oValues)
-                        SelectedValues = oValues
                     End If
                 End Using
         End Select
@@ -124,6 +128,8 @@ Public Class LookupControl2
             Exit Sub
         End If
 
+        Values.RemoveAll(Function(v) String.IsNullOrEmpty(v))
+
         If MultiSelect = True Then
             Properties.DataSource = Values
 
@@ -140,6 +146,8 @@ Public Class LookupControl2
             Text = Values.FirstOrDefault()
             EditValue = Nothing
         End If
+
+        _SelectedValues = Values
     End Sub
 
     Private Function GetLookupForm() As frmLookupGrid