TimePicker now falls back to previous valid value

Changes made to force behavior of TimePicker to more closely follow the
behavior of the DatePicker control. When there is previously a good
value selected for the time and the user then enters an invalid time,
the time will fall back to the previous good value. The time parsing has
also been opened up to allow more formats.

Author: chris84948

MaterialDesignThemes.Wpf/TimePicker.cs

@@ -25,8 +25,9 @@ public class TimePicker : Control
 	    private Popup _popup;
 		private Button _dropDownButton;
 		private bool _disablePopupReopen;
+        private DateTime? _lastValidTime;
 
-		static TimePicker()
+        static TimePicker()
 		{
 			DefaultStyleKeyProperty.OverrideMetadata(typeof(TimePicker), new FrameworkPropertyMetadata(typeof(TimePicker)));
 		}
@@ -67,10 +68,11 @@ public string Text
 		private static void SelectedTimePropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
 		{
 			var timePicker = (TimePicker) dependencyObject;
-			timePicker.SetCurrentValue(TextProperty, timePicker.DateTimeToString(timePicker.SelectedTime));			
-		}
+			timePicker.SetCurrentValue(TextProperty, timePicker.DateTimeToString(timePicker.SelectedTime));		
+            timePicker._lastValidTime = timePicker.SelectedTime;
+        }
 
-		public DateTime? SelectedTime
+        public DateTime? SelectedTime
 		{
 			get { return (DateTime?) GetValue(SelectedTimeProperty); }
 			set { SetValue(SelectedTimeProperty, value); }
@@ -212,10 +214,36 @@ public override void OnApplyTemplate()
 
 		private void TextBoxOnLostFocus(object sender, RoutedEventArgs routedEventArgs)
 		{
-			SetSelectedTime();
-		}
+			if (_textBox == null) return;
+
+            if (!string.IsNullOrEmpty(_textBox.Text))
+            {
+                DateTime time;
+                if (IsTimeValid(_textBox.Text, out time))
+                    SetCurrentValue(SelectedTimeProperty, time);
+
+                else // Invalid time, jump back to previous good time
+                    SetInvalidTime();
+            }
+        }
+
+        private void SetInvalidTime()
+        {
+            if (_lastValidTime != null)
+            {
+                SetCurrentValue(SelectedTimeProperty, (DateTime)_lastValidTime);
+                _textBox.Text = SelectedTime.Value.ToString(SelectedTime.Value.Hour % 12 > 9 ? "hh:mm tt" : "h:mm tt");
+            }
+
+            else
+            {
+                SetCurrentValue(SelectedTimeProperty, null);
+                _textBox.Text = "";
+            }
 
-		private void TextBoxOnKeyDown(object sender, KeyEventArgs keyEventArgs)
+        }
+
+        private void TextBoxOnKeyDown(object sender, KeyEventArgs keyEventArgs)
 		{
 			keyEventArgs.Handled = ProcessKey(keyEventArgs) || keyEventArgs.Handled;
 		}
@@ -255,8 +283,9 @@ private bool ProcessKey(KeyEventArgs keyEventArgs)
 
 		private void TextBoxOnTextChanged(object sender, TextChangedEventArgs textChangedEventArgs)
 		{
-			SetCurrentValue(TextProperty, _textBox.Text);
-		}
+            if (_popup?.IsOpen == true)
+			    SetCurrentValue(TextProperty, _textBox.Text);
+        }
 
 		private void SetSelectedTime()
 		{
@@ -268,18 +297,24 @@ private void SetSelectedTime()
 			}
 		}
 
-		private static void ParseTime(string s, Action<DateTime> successContinuation)
+		private void ParseTime(string s, Action<DateTime> successContinuation)
 		{
 			var dtfi = CultureInfo.CurrentCulture.GetDateFormat();
 
 			DateTime time;
-			if (DateTime.TryParseExact(
-				s, new [] { dtfi.ShortTimePattern, dtfi.LongTimePattern }, 
-				CultureInfo.CurrentCulture, DateTimeStyles.None, out time))
+            if (IsTimeValid(s, out time))
 				successContinuation(time);
 		}
 
-		private string DateTimeToString(DateTime? d)
+        private bool IsTimeValid(string s, out DateTime time)
+        {
+            return DateTime.TryParse(s,
+                                     CultureInfo.CurrentCulture,
+                                     DateTimeStyles.AssumeLocal | DateTimeStyles.AllowWhiteSpaces,
+                                     out time);
+        }
+
+        private string DateTimeToString(DateTime? d)
 		{
 			return d.HasValue ? DateTimeToString(d.Value) : null;
 		}