Optimize Apple camera session startup

ZXing.Net.MAUI.Tests/CameraManagerTests.cs

@@ -98,4 +98,40 @@ public void ContainsReferenceReturnsTrueOnlyForSameInstance()
 		Assert.True(CameraManager.ContainsReference(items, shared));
 		Assert.False(CameraManager.ContainsReference(items, sameValueDifferentInstance));
 	}
+
+	[Fact]
+	public void RequiresCameraConfigurationSkipsAnAlreadyAppliedConfiguration()
+	{
+		CameraResolutionSelectorDelegate selector = availableResolutions => availableResolutions.FirstOrDefault();
+		var configuration = new CameraConfiguration(CameraLocation.Rear, "rear-camera", selector);
+
+		Assert.False(CameraManager.RequiresCameraConfiguration(configuration, configuration, hasInput: true, hasOutput: true));
+	}
+
+	[Fact]
+	public void RequiresCameraConfigurationReconfiguresWhenStateOrSessionGraphChanges()
+	{
+		CameraResolutionSelectorDelegate selector = availableResolutions => availableResolutions.FirstOrDefault();
+		CameraResolutionSelectorDelegate otherSelector = availableResolutions => availableResolutions.LastOrDefault();
+		var configuration = new CameraConfiguration(CameraLocation.Rear, "rear-camera", selector);
+
+		Assert.True(CameraManager.RequiresCameraConfiguration(null, configuration, hasInput: true, hasOutput: true));
+		Assert.True(CameraManager.RequiresCameraConfiguration(configuration, configuration, hasInput: false, hasOutput: true));
+		Assert.True(CameraManager.RequiresCameraConfiguration(configuration, configuration, hasInput: true, hasOutput: false));
+		Assert.True(CameraManager.RequiresCameraConfiguration(
+			configuration,
+			new CameraConfiguration(CameraLocation.Front, "front-camera", selector),
+			hasInput: true,
+			hasOutput: true));
+		Assert.True(CameraManager.RequiresCameraConfiguration(
+			configuration,
+			new CameraConfiguration(CameraLocation.Rear, "other-rear-camera", selector),
+			hasInput: true,
+			hasOutput: true));
+		Assert.True(CameraManager.RequiresCameraConfiguration(
+			configuration,
+			new CameraConfiguration(CameraLocation.Rear, "rear-camera", otherSelector),
+			hasInput: true,
+			hasOutput: true));
+	}
 }

ZXing.Net.MAUI/Apple/CameraManager.ios.maccatalyst.cs

@@ -46,6 +46,8 @@ public static partial bool IsSupported
 		AVCaptureVideoPreviewLayer videoPreviewLayer;
 		CaptureDelegate captureDelegate;
 		DispatchQueue dispatchQueue;
+		CameraConfiguration? appliedConfiguration;
+		bool isConnected;
 		Dictionary<NSString, MSize> Resolutions => new()
 		{
 			{ AVCaptureSession.Preset352x288, new MSize(352, 288) },
@@ -73,7 +75,10 @@ public NativePlatformCameraPreviewView CreateNativeView()
 
 		public void Connect()
 		{
-			UpdateCamera(startIfStopped: true);
+			if (isConnected)
+				return;
+
+			isConnected = true;
 			view?.StartObservingOrientationChanges();
 
 			if (videoDataOutput == null)
@@ -106,27 +111,41 @@ public void Connect()
 				videoDataOutput.SetSampleBufferDelegate(captureDelegate, dispatchQueue);
 			}
 
-			captureSession.AddOutput(videoDataOutput);
+			UpdateCamera(startIfStopped: true);
 		}
 
 		public void UpdateCamera()
 			=> UpdateCamera(startIfStopped: false);
 
 		void UpdateCamera(bool startIfStopped)
 		{
-			if (captureSession != null)
+			if (captureSession != null && isConnected)
 			{
-				var wasRunning = captureSession.Running;
-				if (wasRunning)
-					captureSession.StopRunning();
+				var configuration = Configuration;
+				var hasInput = ContainsReference(captureSession.Inputs, captureInput);
+				var hasOutput = ContainsReference(captureSession.Outputs, videoDataOutput);
+
+				if (!RequiresCameraConfiguration(appliedConfiguration, configuration, hasInput, hasOutput))
+				{
+					if (startIfStopped && !captureSession.Running)
+						captureSession.StartRunning();
+
+					ApplyZoomFactor();
+					return;
+				}
 
 				captureSession.BeginConfiguration();
 				try
 				{
+					if (!hasOutput)
+						captureSession.AddOutput(videoDataOutput);
+
 					// Cleanup old input
-					if (captureInput != null && captureSession.Inputs.Length > 0 && captureSession.Inputs.Contains(captureInput))
+					if (captureInput != null)
 					{
-						captureSession.RemoveInput(captureInput);
+						if (hasInput)
+							captureSession.RemoveInput(captureInput);
+
 						captureInput.Dispose();
 						captureInput = null;
 					}
@@ -207,6 +226,7 @@ void UpdateCamera(bool startIfStopped)
 
 					captureSession.AddInput(captureInput);
 					ApplySelectedResolution();
+					appliedConfiguration = configuration;
 
 #if IOS
 					// Enable multitasking camera access for iPadOS Windowed Apps mode
@@ -224,7 +244,7 @@ void UpdateCamera(bool startIfStopped)
 					captureSession.CommitConfiguration();
 				}
 
-				if (wasRunning || startIfStopped)
+				if (startIfStopped && !captureSession.Running)
 					captureSession.StartRunning();
 
 				ApplyZoomFactor();
@@ -316,6 +336,7 @@ public Task<IReadOnlyList<CameraInfo>> GetAvailableCameras()
 
 		public void Disconnect()
 		{
+			isConnected = false;
 			view?.StopObservingOrientationChanges();
 
 			if (captureSession != null)
@@ -342,6 +363,8 @@ public void Disconnect()
 					captureDevice.Dispose();
 					captureDevice = null;
 				}
+
+				appliedConfiguration = null;
 			}
 		}
 

ZXing.Net.MAUI/CameraManager.cs

@@ -26,6 +26,8 @@ public CameraManager(IMauiContext context, CameraLocation cameraLocation)
 		public float ZoomFactor { get; private set; }
 
 		protected CameraManagerOptions Options => options;
+		internal CameraConfiguration Configuration
+			=> new(CameraLocation, SelectedCamera?.DeviceId, Options.CameraResolutionSelector);
 
 		/// <summary>
 		/// Gets a value indicating whether barcode scanning is supported on this device.
@@ -81,6 +83,13 @@ internal static bool ContainsReference<T>(IReadOnlyCollection<T> items, object i
 			return false;
 		}
 
+		internal static bool RequiresCameraConfiguration(
+			CameraConfiguration? appliedConfiguration,
+			CameraConfiguration configuration,
+			bool hasInput,
+			bool hasOutput)
+			=> !hasInput || !hasOutput || appliedConfiguration != configuration;
+
 		public void UpdateZoomFactor(float zoomFactor)
 		{
 			if (float.IsNaN(zoomFactor))
@@ -98,4 +107,9 @@ public static async Task<bool> CheckPermissions()
 		private static partial bool ShouldApplyPlatformCameraOptions(CameraManagerOptions currentOptions, CameraManagerOptions nextOptions);
 		partial void ApplyZoomFactor();
 	}
+
+	internal readonly record struct CameraConfiguration(
+		CameraLocation CameraLocation,
+		string SelectedCameraDeviceId,
+		CameraResolutionSelectorDelegate CameraResolutionSelector);
 }