[C] avoid NRE on null GesturRecognizer (#25029)

- fixes #24900

Co-authored-by: Stephane Delcroix <[email protected]>

Author: github-actions[bot]

src/Controls/src/Core/View/View.cs

@@ -101,9 +101,11 @@ void AddItems(IList newItems)
 					foreach (IElementDefinition item in newItems)
 					{
 						var gestureRecognizer = item as IGestureRecognizer;
-						ValidateGesture(gestureRecognizer);
-						item.Parent = this;
-						GestureController.CompositeGestureRecognizers.Add(gestureRecognizer);
+						if (ValidateGesture(gestureRecognizer))
+						{
+							item.Parent = this;
+							GestureController.CompositeGestureRecognizers.Add(gestureRecognizer);
+						}
 					}
 				}
 
@@ -266,12 +268,13 @@ static void MarginPropertyChanged(BindableObject bindable, object oldValue, obje
 			((View)bindable).InvalidateMeasureInternal(InvalidationTrigger.MarginChanged);
 		}
 
-		void ValidateGesture(IGestureRecognizer gesture)
+		bool ValidateGesture(IGestureRecognizer gesture)
 		{
 			if (gesture == null)
-				return;
+				return false;
 			if (gesture is PinchGestureRecognizer && _gestureRecognizers.GetGesturesFor<PinchGestureRecognizer>().Count() > 1)
 				throw new InvalidOperationException($"Only one {nameof(PinchGestureRecognizer)} per view is allowed");
+			return true;
 		}
 
 #nullable enable

src/Controls/tests/Xaml.UnitTests/Issues/Maui24900.xaml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:local="clr-namespace:Microsoft.Maui.Controls.Xaml.UnitTests"
+             x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Maui24900">
+    <Border>
+        <Border.GestureRecognizers>
+            <OnPlatform x:TypeArguments="GestureRecognizer">
+                <OnPlatform.Platforms>
+                    <On Platform="Android">
+                        <TapGestureRecognizer Tapped="Header_Tapped" />
+                    </On>
+                    <!-- <On Platform="WinUI">
+                        <TapGestureRecognizer Tapped="Header_Tapped" />
+                    </On> -->
+                </OnPlatform.Platforms>
+            </OnPlatform>
+        </Border.GestureRecognizers>
+    </Border>
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Issues/Maui24900.xaml.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Globalization;
+using System.Linq;
+using Microsoft.Maui.ApplicationModel;
+using Microsoft.Maui.Controls.Core.UnitTests;
+using Microsoft.Maui.Controls.Shapes;
+using Microsoft.Maui.Devices;
+using Microsoft.Maui.Dispatching;
+
+using Microsoft.Maui.Graphics;
+using Microsoft.Maui.UnitTests;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+public partial class Maui24900 : ContentPage
+{
+    public Maui24900()
+    {
+        InitializeComponent();
+    }
+
+    public Maui24900(bool useCompiledXaml)
+    {
+        //this stub will be replaced at compile time
+    }
+
+    void Header_Tapped(object sender, TappedEventArgs e)
+    {
+
+    }
+
+    [TestFixture]
+    class Test
+    {
+        MockDeviceInfo mockDeviceInfo;
+
+        [SetUp]
+        public void Setup()
+        {
+            Application.SetCurrentApplication(new MockApplication());
+            DeviceInfo.SetCurrent(mockDeviceInfo = new MockDeviceInfo());
+            DispatcherProvider.SetCurrent(new DispatcherProviderStub());
+        }
+
+
+        [TearDown] public void TearDown()
+        {
+            AppInfo.SetCurrent(null);
+            DeviceInfo.SetCurrent(null);
+        }
+
+        [Test]
+        public void OnPlatformDownNotThrow([Values(false, true)] bool useCompiledXaml)
+        {
+            mockDeviceInfo.Platform = DevicePlatform.WinUI;
+            Assert.DoesNotThrow(()=>  new Maui24900(useCompiledXaml));
+
+
+
+        }
+    }
+}