Fixes NumericUpDown text update issues

Fixes an issue where the NumericUpDown control was not properly updating the text in the TextBox when focus was lost after invalid input.
Adds a LostFocus event handler to update the textbox value.
Adds UI tests to verify that values are updated as expected.

Author: Keboo

src/MaterialDesignThemes.Wpf/UpDownBase.cs

@@ -201,7 +201,10 @@ public override void OnApplyTemplate()
         if (_decreaseButton != null)
             _decreaseButton.Click -= DecreaseButtonOnClick;
         if (_textBoxField != null)
+        {
             _textBoxField.TextChanged -= OnTextBoxTextChanged;
+            _textBoxField.LostFocus -= OnTextBoxLostFocus;
+        }
 
         base.OnApplyTemplate();
 
@@ -220,11 +223,20 @@ public override void OnApplyTemplate()
         if (_textBoxField != null)
         {
             _textBoxField.TextChanged += OnTextBoxTextChanged;
+            _textBoxField.LostFocus += OnTextBoxLostFocus;
             _textBoxField.Text = Value?.ToString();
         }
 
     }
 
+    private void OnTextBoxLostFocus(object sender, EventArgs e)
+    {
+        if (_textBoxField is { } textBoxField)
+        {
+            textBoxField.Text = Value?.ToString();
+        }
+    }
+
     private void OnTextBoxTextChanged(object sender, EventArgs e)
     {
         if (_textBoxField is { } textBoxField)
@@ -233,8 +245,6 @@ private void OnTextBoxTextChanged(object sender, EventArgs e)
             {
                 SetCurrentValue(ValueProperty, ClampValue(value));
             }
-            //NB: Because setting ValueProperty will coerce the value, we re-assign back to the textbox here.
-            textBoxField.Text = Value?.ToString();
         }
     }
 

tests/MaterialDesignThemes.UITests/WPF/UpDownControls/DecimalUpDownTests.cs

@@ -187,10 +187,10 @@ public async Task IncreaseButtonClickWhenTextIsAboveMaximum_DoesNotIncreaseValue
 
     [Theory]
     [Description("Issue 3781")]
-    [InlineData("30")]
-    [InlineData("abc")]
-    [InlineData("2a")]
-    public async Task LostFocusWhenTextIsInvalid_RevertsToOriginalValue(string inputText)
+    [InlineData("30", 2.5)]
+    [InlineData("abc", 2.5)]
+    [InlineData("2a", 2)]
+    public async Task LostFocusWhenTextIsInvalid_RevertsToOriginalValue(string inputText, decimal expectedValue)
     {
         await using var recorder = new TestRecorder(App);
 
@@ -209,8 +209,8 @@ public async Task LostFocusWhenTextIsInvalid_RevertsToOriginalValue(string input
         await textBox.SendKeyboardInput($"{ModifierKeys.Control}{Key.A}{ModifierKeys.None}{inputText}");
         await button.MoveKeyboardFocus();
 
-        Assert.Equal("2.5", await textBox.GetText());
-        Assert.Equal(2.5m, await decimalUpDown.GetValue());
+        Assert.Equal(expectedValue.ToString(), await textBox.GetText());
+        Assert.Equal(expectedValue, await decimalUpDown.GetValue());
 
         recorder.Success();
     }

tests/MaterialDesignThemes.UITests/WPF/UpDownControls/NumericUpDownTests.cs

@@ -1,4 +1,8 @@
-using System.ComponentModel;
+using System;
+using System.ComponentModel;
+using System.Windows.Controls;
+using System.Windows.Data;
+using Google.Protobuf.WellKnownTypes;
 using MaterialDesignThemes.UITests.Samples.UpDownControls;
 
 namespace MaterialDesignThemes.UITests.WPF.UpDownControls;
@@ -215,4 +219,74 @@ public async Task NumericUpDown_WhenValueEqualsMinimum_DisableButtons(int value,
 
         recorder.Success();
     }
+
+    [Fact]
+    [Description("Issue 3827")]
+    public async Task NumericUpDown_WhenBindingUpdateTriggerIsPropertyChanged_ItUpdatesBeforeLoosingFocus()
+    {
+        await using var recorder = new TestRecorder(App);
+        //Arrange
+        var numericUpDown = await LoadXaml<NumericUpDown>("""
+        <materialDesign:NumericUpDown Tag="{Binding Value, RelativeSource={RelativeSource Self}, UpdateSourceTrigger=PropertyChanged}" Maximum="10" Minimum="1" />
+        """);
+        
+        var textBox = await numericUpDown.GetElement<TextBox>("PART_TextBox");
+        //Act
+        await textBox.MoveKeyboardFocus();
+        await textBox.SendKeyboardInput($"{ModifierKeys.Control}{Key.A}{ModifierKeys.None}4");
+
+        //Act
+        object? tag = await numericUpDown.GetTag();
+
+        //Assert
+        Assert.Equal("4", tag?.ToString());
+
+        recorder.Success();
+    }
+
+    [Fact]
+    [Description("Issue 3827")]
+    public async Task NumericUpDown_WhenBindingUpdateTriggerIsLostFocus_ItDoesNotUpdateUntilItLoosesFocus()
+    {
+        await using var recorder = new TestRecorder(App);
+        //Arrange
+        var userControl = await LoadUserControl<BoundNumericUpDown>();
+        var numericUpDown = await userControl.GetElement<NumericUpDown>();
+        var buttonToFocus = await userControl.GetElement<Button>("btnToFocus");
+        await numericUpDown.SetValue(2);
+
+        static void SetBindingToLostFocus(NumericUpDown numericUpDown)
+        {
+            var binding = new Binding(nameof(NumericUpDown.Value))
+            {
+                Path = new(nameof(BoundNumericUpDownViewModel.Value)),
+                UpdateSourceTrigger = UpdateSourceTrigger.LostFocus
+            };
+            BindingOperations.SetBinding(numericUpDown, NumericUpDown.ValueProperty, binding);
+        }
+        await numericUpDown.RemoteExecute(SetBindingToLostFocus);
+
+        var textBox = await numericUpDown.GetElement<TextBox>("PART_TextBox");
+
+        static int GetViewModelValue(NumericUpDown numericUpDown)
+        {
+            return ((BoundNumericUpDownViewModel)numericUpDown.DataContext).Value;
+        }
+
+        //Act
+        await textBox.MoveKeyboardFocus();
+        await textBox.SendKeyboardInput($"{ModifierKeys.Control}{Key.A}{ModifierKeys.None}4");
+
+        //Act
+        int valueBeforeLostFocus = await numericUpDown.RemoteExecute(GetViewModelValue);
+        await textBox.SendKeyboardInput($"{Key.Tab}");
+        int valueAfterLostFocus = await numericUpDown.RemoteExecute(GetViewModelValue);
+
+
+        //Assert
+        Assert.Equal("2", valueBeforeLostFocus.ToString());
+        Assert.Equal("4", valueAfterLostFocus.ToString());
+
+        recorder.Success();
+    }
 }