Fixes disposal of temporary file on iOS

Ensures temporary directory used by the file picker is
always removed after the file selection is made, regardless
of success or failure. Also improves error handling when
a view controller cannot be retrieved.

Fixes CommunityToolkit#2460

Author: VladislavAntonyuk

src/CommunityToolkit.Maui.Core/Essentials/FileSaver/FileSaverImplementation.macios.cs

@@ -10,7 +10,6 @@ public sealed partial class FileSaverImplementation : IFileSaver, IDisposable
 {
 	UIDocumentPickerViewController? documentPickerViewController;
 	TaskCompletionSource<string>? taskCompetedSource;
-	NSUrl? tempDirectoryPath;
 
 	/// <inheritdoc />
 	public void Dispose()
@@ -22,38 +21,45 @@ async Task<string> InternalSaveAsync(string initialPath, string fileName, Stream
 	{
 		cancellationToken.ThrowIfCancellationRequested();
 		var fileManager = NSFileManager.DefaultManager;
-		tempDirectoryPath = fileManager.GetTemporaryDirectory().Append(Guid.NewGuid().ToString(), true);
+		var tempDirectoryPath = fileManager.GetTemporaryDirectory().Append(Guid.NewGuid().ToString(), true);
 		var isDirectoryCreated = fileManager.CreateDirectory(tempDirectoryPath, true, null, out var error);
 		if (!isDirectoryCreated)
 		{
 			throw new FileSaveException(error?.LocalizedDescription ?? "Unable to create temp directory.");
 		}
 
 		var fileUrl = tempDirectoryPath.Append(fileName, false);
-		await WriteStream(stream, fileUrl.Path ?? throw new Exception("Path cannot be null."), progress, cancellationToken);
+		try
+		{
+			await WriteStream(stream, fileUrl.Path ?? throw new Exception("Path cannot be null."), progress, cancellationToken);
 
-		cancellationToken.ThrowIfCancellationRequested();
-		taskCompetedSource?.TrySetCanceled(CancellationToken.None);
-		var tcs = taskCompetedSource = new(cancellationToken);
+			cancellationToken.ThrowIfCancellationRequested();
+			taskCompetedSource?.TrySetCanceled(CancellationToken.None);
+			var tcs = taskCompetedSource = new(cancellationToken);
 
-		documentPickerViewController = new([fileUrl], true)
-		{
-			DirectoryUrl = NSUrl.FromString(initialPath)
-		};
-		documentPickerViewController.DidPickDocumentAtUrls += DocumentPickerViewControllerOnDidPickDocumentAtUrls;
-		documentPickerViewController.WasCancelled += DocumentPickerViewControllerOnWasCancelled;
+			documentPickerViewController = new([fileUrl], true)
+			{
+				DirectoryUrl = NSUrl.FromString(initialPath)
+			};
+			documentPickerViewController.DidPickDocumentAtUrls += DocumentPickerViewControllerOnDidPickDocumentAtUrls;
+			documentPickerViewController.WasCancelled += DocumentPickerViewControllerOnWasCancelled;
 
-		var currentViewController = Platform.GetCurrentUIViewController();
-		if (currentViewController is not null)
-		{
-			currentViewController.PresentViewController(documentPickerViewController, true, null);
+			var currentViewController = Platform.GetCurrentUIViewController();
+			if (currentViewController is not null)
+			{
+				currentViewController.PresentViewController(documentPickerViewController, true, null);
+			}
+			else
+			{
+				throw new FileSaveException("Unable to get a window where to present the file saver UI.");
+			}
+
+			return await tcs.Task.WaitAsync(cancellationToken).ConfigureAwait(false);
 		}
-		else
+		finally
 		{
-			throw new FileSaveException("Unable to get a window where to present the file saver UI.");
+			fileManager.Remove(tempDirectoryPath, out _);
 		}
-
-		return await tcs.Task.WaitAsync(cancellationToken).ConfigureAwait(false);
 	}
 
 	Task<string> InternalSaveAsync(string fileName, Stream stream, IProgress<double>? progress, CancellationToken cancellationToken)
@@ -64,7 +70,6 @@ Task<string> InternalSaveAsync(string fileName, Stream stream, IProgress<double>
 	void DocumentPickerViewControllerOnWasCancelled(object? sender, EventArgs e)
 	{
 		taskCompetedSource?.TrySetException(new FileSaveException("Operation cancelled."));
-		CleanupTempDirectory();
 		InternalDispose();
 	}
 
@@ -76,19 +81,9 @@ void DocumentPickerViewControllerOnDidPickDocumentAtUrls(object? sender, UIDocum
 		}
 		finally
 		{
-			CleanupTempDirectory();
 			InternalDispose();
 		}
 	}
-	
-	void CleanupTempDirectory()
-	{
-		if (tempDirectoryPath is not null)
-		{
-			var fileManager = NSFileManager.DefaultManager;
-			fileManager.Remove(tempDirectoryPath, out var _);
-		}
-	}
 
 
 	void InternalDispose()