Merge pull request #4048 from puppetsw/TextBoxMask_bug_3279

TextBoxMask TextChanging fix for #3279

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI/Extensions/TextBox/TextBoxExtensions.Mask.Internals.cs

@@ -297,13 +297,18 @@ private static void Textbox_TextChanging(TextBox textbox, TextBoxTextChangingEve
             // case adding data at the end of the textbox
             if (oldSelectionStart >= oldText.Length && !isDeleteOrBackspace)
             {
-                textbox.Text = textbox.Text.Substring(0, oldText.Length);
-                if (oldText.Length >= 0)
+                // ignore change(s) if oldtext is a substring of new text value
+                if (textbox.Text.Contains(oldText))
                 {
-                    textbox.SelectionStart = oldText.Length;
-                }
+                    textbox.Text = oldText;
 
-                return;
+                    if (oldText.Length >= 0)
+                    {
+                        textbox.SelectionStart = oldText.Length;
+                    }
+
+                    return;
+                }
             }
 
             var textArray = oldText.ToCharArray();
@@ -323,6 +328,9 @@ private static void Textbox_TextChanging(TextBox textbox, TextBoxTextChangingEve
                 var displayText = textbox.GetValue(DefaultDisplayTextProperty) as string ?? string.Empty;
                 if (string.IsNullOrEmpty(textbox.Text))
                 {
+                    textbox.SetValue(OldTextProperty, displayText);
+                    textbox.SetValue(OldSelectionStartProperty, 0);
+                    textbox.SetValue(OldSelectionLengthProperty, 0);
                     textbox.Text = displayText;
                     return;
                 }
@@ -427,4 +435,4 @@ private static int GetSelectionStart(string mask, List<int> escapedChars, int se
             return selectionIndex;
         }
     }
-}
+}

UITests/UITests.Tests.Shared/Controls/TextBoxMaskTest.cs

@@ -46,5 +46,31 @@ public void TestTextBoxMaskBinding_Property()
 
             Verify.AreEqual(newValue, textBox.GetText());
         }
+
+        [TestMethod]
+        [TestPage("TextBoxMaskTestPage")]
+        public void TestTextBoxMaskBinding_TextChanging_RegressionCheck()
+        {
+            var initialValue = FindElement.ById<TextBlock>("InitialValueTextBlock").GetText();
+            var textBox = FindElement.ById<Edit>("TextBox");
+
+            Verify.AreEqual(initialValue, textBox.GetText());
+
+            var setEmptyButton = FindElement.ById<Button>("SetEmptyButton");
+
+            setEmptyButton.Click();
+            Wait.ForIdle();
+
+            // Previously, if the bound value of TextBox with a mask was set to an empty
+            // string. It would display the old values after text was entered by the user.
+            // PR #4048 should fix this issue.
+            textBox.SendKeys("0");
+
+            // The user entering "0" key at the start position of the TextBox would result
+            // in the following value prior to PR #4048.
+            const string incorrectValue = "02:50:59";
+
+            Verify.AreNotEqual(incorrectValue, textBox.GetText());
+        }
     }
 }

UITests/UITests.Tests.Shared/Controls/TextBoxMaskTestPage.xaml

@@ -12,6 +12,8 @@
             <RowDefinition Height="Auto" />
             <RowDefinition Height="10" />
             <RowDefinition Height="Auto" />
+            <RowDefinition Height="10" />
+            <RowDefinition Height="Auto" />
         </Grid.RowDefinitions>
         <Grid.ColumnDefinitions>
             <ColumnDefinition Width="Auto" />
@@ -43,5 +45,10 @@
                    Grid.Column="2"
                    HorizontalAlignment="Center"
                    Text="{x:Bind NewValue}" />
+        <Button x:Name="SetEmptyButton"
+                Grid.Row="4"
+                Grid.Column="0"
+                Click="SetEmptyButton_Click"
+                Content="Set Target Value Empty" />
     </Grid>
 </Page>

UITests/UITests.Tests.Shared/Controls/TextBoxMaskTestPage.xaml.cs

@@ -38,5 +38,11 @@ private void ChangeButton_Click(object sender, RoutedEventArgs e)
             Value = NEW_VALUE;
             Log.Comment("Value Changed to {0}", Value);
         }
+
+        private void SetEmptyButton_Click(object sender, RoutedEventArgs e)
+        {
+            Value = string.Empty;
+            Log.Comment("Value Changed to {0}", Value);
+        }
     }
 }