Fix ImageSize unit switching to Percent - set width/height to 100%

Co-authored-by: yeelam-gordon <73506701+yeelam-gordon@users.noreply.github.com>

src/settings-ui/Settings.UI.Library/ImageSize.cs

@@ -32,12 +32,12 @@ public partial class ImageSize : INotifyPropertyChanged, IHasId
 
     public ImageSize(int id = 0, string name = "", ResizeFit fit = ResizeFit.Fit, double width = 0, double height = 0, ResizeUnit unit = ResizeUnit.Pixel)
     {
-        Id = id;
-        Name = name;
-        Fit = fit;
-        Width = width;
-        Height = height;
-        Unit = unit;
+        _id = id;
+        _name = name;
+        _fit = fit;
+        _width = width < 0 || double.IsNaN(width) ? 0 : width;
+        _height = height < 0 || double.IsNaN(height) ? 0 : height;
+        _unit = unit;
     }
 
     private int _id;
@@ -105,8 +105,16 @@ public partial class ImageSize : INotifyPropertyChanged, IHasId
         get => _unit;
         set
         {
+            var previousUnit = _unit;
             if (SetProperty(ref _unit, value))
             {
+                // When switching to Percent unit, set width and height to 100 (representing 100%)
+                if (value == ResizeUnit.Percent && previousUnit != ResizeUnit.Percent)
+                {
+                    Width = 100.0;
+                    Height = 100.0;
+                }
+                
                 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsHeightUsed)));
             }
         }

src/settings-ui/Settings.UI.UnitTests/ModelsTests/ImageSizeTests.cs

@@ -0,0 +1,67 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.PowerToys.Settings.UI.Library;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Microsoft.PowerToys.Settings.UI.UnitTests.ModelsTests
+{
+    [TestClass]
+    public class ImageSizeTests
+    {
+        [TestMethod]
+        public void WhenUnitChangesToPercent_WidthShouldBeSetTo100()
+        {
+            // Arrange
+            var imageSize = new ImageSize(1, "Test", ResizeFit.Fit, 854, 480, ResizeUnit.Pixel);
+            
+            // Act
+            imageSize.Unit = ResizeUnit.Percent;
+            
+            // Assert
+            Assert.AreEqual(100.0, imageSize.Width, "Width should be set to 100 when switching to Percent unit");
+        }
+        
+        [TestMethod]
+        public void WhenUnitChangesToPercent_HeightShouldBeSetTo100()
+        {
+            // Arrange
+            var imageSize = new ImageSize(1, "Test", ResizeFit.Stretch, 854, 480, ResizeUnit.Pixel);
+            
+            // Act
+            imageSize.Unit = ResizeUnit.Percent;
+            
+            // Assert
+            Assert.AreEqual(100.0, imageSize.Height, "Height should be set to 100 when switching to Percent unit");
+        }
+        
+        [TestMethod]
+        public void WhenUnitChangesFromPercentToPixel_ValuesShouldNotChange()
+        {
+            // Arrange
+            var imageSize = new ImageSize(1, "Test", ResizeFit.Fit, 50, 75, ResizeUnit.Percent);
+            
+            // Act
+            imageSize.Unit = ResizeUnit.Pixel;
+            
+            // Assert
+            Assert.AreEqual(50.0, imageSize.Width, "Width should remain unchanged when switching from Percent to other units");
+            Assert.AreEqual(75.0, imageSize.Height, "Height should remain unchanged when switching from Percent to other units");
+        }
+        
+        [TestMethod]
+        public void WhenUnitRemainsPercent_ValuesShouldNotChange()
+        {
+            // Arrange
+            var imageSize = new ImageSize(1, "Test", ResizeFit.Fit, 75, 60, ResizeUnit.Percent);
+            
+            // Act
+            imageSize.Unit = ResizeUnit.Percent;
+            
+            // Assert
+            Assert.AreEqual(75.0, imageSize.Width, "Width should remain unchanged when unit stays as Percent");
+            Assert.AreEqual(60.0, imageSize.Height, "Height should remain unchanged when unit stays as Percent");
+        }
+    }
+}