Fixed GetStringSize() is not consistent with actual string size in GraphicsView

src/Controls/tests/TestCases.HostApp/Issues/Issue18679.cs

@@ -0,0 +1,100 @@
+using Font = Microsoft.Maui.Graphics.Font;
+
+namespace Maui.Controls.Sample.Issues
+{
+    [Issue(IssueTracker.Github, 18679, "Canvas.GetStringSize() is not consistent with actual string size in GraphicsView", PlatformAffected.iOS | PlatformAffected.macOS)]
+    public class Issue18679 : TestContentPage
+    {
+        const string ShortText = "ShortText";
+        const string LongText = "CiaomondorowfdskleCiaomondorowfdsk";
+        const string MultiLineText = "HELLO, WORLD!\nCiao mondo row 2\nGuten tag!?àèìòù@";
+
+        protected override void Init()
+        {
+            var layout = new VerticalStackLayout
+            {
+                Spacing = 10,
+            };
+            var label = new Label
+            {
+                Text = "The drawn text should not overflow the bounding rectangle.",
+                FontSize = 16,
+                AutomationId = "18679DescriptionLabel",
+            };
+            layout.Add(label);
+
+            // Test Case 1: Single long line (basic case)
+            layout.Add(CreateDrawable("Test Case 1: Short text", ShortText));
+
+            // Test Case 2: Multi-line text
+            layout.Add(CreateDrawable("Test Case 2: Multi-line Text", MultiLineText));
+
+            // Test Case 3: Unicode/non-Latin text
+            layout.Add(CreateDrawable("Test Case 3: Long Text", LongText));
+
+            Content = layout;
+        }
+
+        private Border CreateDrawable(string testName, string text)
+        {
+            var graphicsView = new GraphicsView
+            {
+                HeightRequest = 150,
+                Drawable = new Issue18679_Drawable(text, testName)
+            };
+
+            return new Border
+            {
+                Content = graphicsView,
+                Stroke = Colors.LightGray,
+                StrokeThickness = 1,
+            };
+        }
+    }
+
+    public class Issue18679_Drawable : IDrawable
+    {
+        readonly string _text;
+        readonly string _label;
+        static readonly Font Font = Font.Default;
+        const int FontSize = 20;
+
+
+        public Issue18679_Drawable(string text, string label)
+        {
+            _text = text;
+            _label = label;
+        }
+
+        public void Draw(ICanvas canvas, RectF dirtyRect)
+        {
+            canvas.SaveState();
+
+            // Draw label
+            canvas.FontSize = 14;
+            canvas.Font = Font;
+            canvas.FontColor = Colors.Blue;
+            canvas.DrawString(_label, 10, 10, dirtyRect.Width - 20, 20,
+                HorizontalAlignment.Left, VerticalAlignment.Top);
+
+            // Set up for text measurement
+            canvas.FontSize = FontSize;
+            canvas.Font = Font;
+
+            // Get text size and create bounds
+            var stringSize = canvas.GetStringSize(_text, Font, FontSize);
+
+            // Draw the actual text first
+            canvas.FontColor = Colors.Black;
+            canvas.DrawString(_text, 2, 40, dirtyRect.Width, dirtyRect.Height,
+                HorizontalAlignment.Left, VerticalAlignment.Top);
+
+            // Draw the measured bounds rectangle
+            canvas.StrokeColor = Colors.Red;
+            canvas.StrokeSize = 1;
+            canvas.DrawRectangle(2, 40, stringSize.Width, stringSize.Height);
+
+            canvas.RestoreState();
+        }
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue18679.cs

@@ -0,0 +1,22 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue18679 : _IssuesUITest
+{
+    public Issue18679(TestDevice testDevice) : base(testDevice)
+    {
+    }
+
+    public override string Issue => "Canvas.GetStringSize() is not consistent with actual string size in GraphicsView";
+
+    [Test]
+    [Category(UITestCategories.GraphicsView)]
+    public void DrawTextWithinBounds()
+    {
+        App.WaitForElement("18679DescriptionLabel");
+        VerifyScreenshot();
+    }
+}

src/Graphics/src/Graphics/Platforms/Windows/PlatformStringSizeService.cs

@@ -23,28 +23,44 @@ public SizeF GetStringSize(string value, IFont font, float textSize)
 
 		public SizeF GetStringSize(string value, IFont font, float textSize, HorizontalAlignment horizontalAlignment, VerticalAlignment verticalAlignment)
 		{
-			var format = font.ToCanvasTextFormat(textSize);
-			format.WordWrapping = CanvasWordWrapping.NoWrap;
-
-			var device = CanvasDevice.GetSharedDevice();
-			var textLayout = new CanvasTextLayout(device, value, format, 0.0f, 0.0f);
-			textLayout.VerticalAlignment = verticalAlignment switch
-			{
-				VerticalAlignment.Top => CanvasVerticalAlignment.Top,
-				VerticalAlignment.Center => CanvasVerticalAlignment.Center,
-				VerticalAlignment.Bottom => CanvasVerticalAlignment.Bottom,
-				_ => CanvasVerticalAlignment.Top
-			};
-			textLayout.HorizontalAlignment = horizontalAlignment switch
-			{
-				HorizontalAlignment.Left => CanvasHorizontalAlignment.Left,
-				HorizontalAlignment.Center => CanvasHorizontalAlignment.Center,
-				HorizontalAlignment.Right => CanvasHorizontalAlignment.Right,
-				HorizontalAlignment.Justified => CanvasHorizontalAlignment.Justified,
-				_ => CanvasHorizontalAlignment.Left,
-			};
-
-			return new SizeF((float)textLayout.DrawBounds.Width, (float)textLayout.DrawBounds.Height);
-		}
+            if (string.IsNullOrEmpty(value) || font is null || textSize <= 0)
+            {
+                return SizeF.Zero;
+            }
+
+            var format = font.ToCanvasTextFormat(textSize);
+            format.WordWrapping = CanvasWordWrapping.NoWrap;
+
+            var device = CanvasDevice.GetSharedDevice();
+
+            using (var textLayout = new CanvasTextLayout(device, value, format, float.MaxValue, float.MaxValue))
+            {
+                textLayout.VerticalAlignment = verticalAlignment switch
+                {
+                    VerticalAlignment.Top => CanvasVerticalAlignment.Top,
+                    VerticalAlignment.Center => CanvasVerticalAlignment.Center,
+                    VerticalAlignment.Bottom => CanvasVerticalAlignment.Bottom,
+                    _ => CanvasVerticalAlignment.Top
+                };
+                textLayout.HorizontalAlignment = horizontalAlignment switch
+                {
+                    HorizontalAlignment.Left => CanvasHorizontalAlignment.Left,
+                    HorizontalAlignment.Center => CanvasHorizontalAlignment.Center,
+                    HorizontalAlignment.Right => CanvasHorizontalAlignment.Right,
+                    HorizontalAlignment.Justified => CanvasHorizontalAlignment.Justified,
+                    _ => CanvasHorizontalAlignment.Left,
+                };
+
+                var bounds = textLayout.LayoutBounds;
+
+                // If LayoutBounds is empty, fallback to DrawBounds
+                if (bounds.Width <= 0 || bounds.Height <= 0)
+                {
+                    bounds = textLayout.DrawBounds;
+                }
+
+                return new SizeF((float)bounds.Width, (float)bounds.Height);
+            }
+        }
 	}
-}
+}

src/Graphics/src/Graphics/Platforms/iOS/PlatformStringSizeService.cs

@@ -1,5 +1,6 @@
 using System;
 using CoreGraphics;
+using CoreText;
 using Foundation;
 using UIKit;
 
@@ -10,19 +11,26 @@ public partial class PlatformStringSizeService : IStringSizeService
 		public SizeF GetStringSize(string value, IFont font, float fontSize)
 		{
 			if (string.IsNullOrEmpty(value))
+			{
 				return new SizeF();
+			}
 
-			var nsString = new NSString(value);
-			var uiFont = font?.ToPlatformFont(fontSize) ?? FontExtensions.GetDefaultPlatformFont();
+			var attributes = new CTStringAttributes();
+			attributes.Font = font?.ToCTFont(fontSize) ?? FontExtensions.GetDefaultCTFont(fontSize);
 
-			CGSize size = nsString.GetBoundingRect(
-				CGSize.Empty,
-				NSStringDrawingOptions.UsesLineFragmentOrigin,
-				new UIStringAttributes { Font = uiFont },
-				null).Size;
+			var attributedString = new NSAttributedString(value, attributes);
+			var framesetter = new CTFramesetter(attributedString);
 
-			uiFont.Dispose();
-			return new SizeF((float)size.Width, (float)size.Height);
+			// Get suggested frame size with unlimited constraints
+			var measuredSize = framesetter.SuggestFrameSize(
+				new NSRange(0, 0),
+				null,
+				new CGSize(float.MaxValue, float.MaxValue),
+				out _);
+
+			framesetter.Dispose();
+			attributedString.Dispose();
+			return new SizeF((float)measuredSize.Width, (float)measuredSize.Height);
 		}
 	}
-}
+}