Don't show wxDatePickerCtrl as being disabled when it isn't in wxOSX.

Use setDrawsBackground: to fix the background colour and adjust the text
colour whenever the control is enabled or disabled.

Closes #16807.

(this is a backport of 9bedba0bf3 from master)

docs/changes.txt

@@ -640,6 +640,7 @@ wxOSX:
 - Fix handling of "Cancel" button in wxSearchCtrl (John Roberts).
 - Generate correct events for WXK_NUMPAD_ENTER (John Roberts).
 - Fix handling of WXK_NUMPAD_ENTER in wxTextCtrl (John Roberts).
+- Don't show wxDatePickerCtrl as being disabled when it isn't (John Roberts).
 - Generate wxEVT_TEXT_ENTER for wxTE_PASSWORD controls too (mj_smoker).
 - Send wxIconizeEvent when a window is iconized/restore (Rob Krakora).
 - Use correct colour for disabled wxStaticText (sbrowne).

src/osx/cocoa/datetimectrl.mm

@@ -128,6 +128,26 @@ public:
         }
     }
 
+    virtual void Enable(bool enable = true)
+    {
+        wxNSDatePicker* const nsdatePicker = View();
+
+        [nsdatePicker setEnabled: enable];
+
+        if ( enable )
+        {
+            wxWindow* const wxpeer = GetWXPeer();
+            if ( wxpeer )
+                [nsdatePicker setTextColor: wxpeer->GetForegroundColour().OSXGetNSColor()];
+            else
+                [nsdatePicker setTextColor: [NSColor controlTextColor]];
+        }
+        else
+        {
+            [nsdatePicker setTextColor: [NSColor disabledControlTextColor]];
+        }
+    }
+
 private:
     wxNSDatePicker* View() const
     {
@@ -170,6 +190,9 @@ wxDateTimeWidgetImpl::CreateDateTimePicker(wxDateTimePickerCtrl* wxpeer,
 
     [v setDatePickerStyle: NSTextFieldAndStepperDatePickerStyle];
 
+    // Avoid a disabled looking transparent background for the text cells.
+    [v setDrawsBackground: YES];
+
     if ( dt.IsValid() )
     {
         [v setDateValue: NSDateFromWX(dt)];