feat: Provide Intent access for Android pickers

doc/articles/features/windows-storage-pickers.md

@@ -352,6 +352,19 @@ The `SuggestedStartLocation` property has no effect on certain Android devices,
 
 The `FileSavePicker` API, which uses `ACTION_CREATE_DOCUMENT` on Android, has various limitations. To allow for the best possible compatibility across different Android versions, you should always add your file type extension to `FileTypeChoices`, and, if possible, provide only one such file type. In addition, if the `SuggestedFileName` or the user-typed file name matches an existing file, the resulting file will be renamed with `(1)` in the name, e.g., `test.txt` will become `test (1).txt` and the existing file will not be overwritten. However, if the user explicitly taps an existing file in the file browser, the system will show a dialog allowing the app to overwrite the existing file. This inconsistent behavior is caused by Android itself, so there is, unfortunately, no way to work around it from our side. See [this issue](https://issuetracker.google.com/issues/37136466) for more information.
 
+If you want to have further influence on the pickers and, for example, create permanent access to the file for the `FileOpenPicker` (flag with GrantPersistableUriPermission), you can do this with the `FilePickerHelper`.
+
+```csharp
+FileOpenPicker fileOpenPicker = new FileOpenPicker
+{
+    SuggestedStartLocation = PickerLocationId.ComputerFolder
+};
+var intent = new Android.Content.Intent(Android.Content.Intent.ActionOpenDocument);
+intent.AddFlags(Android.Content.ActivityFlags.GrantPersistableUriPermission);
+FilePickerHelper.RegisterOnBeforeStartActivity(fileOpenPicker, intent);
+var result = await fileOpenPicker.PickSingleFileAsync();
+```
+
 ## iOS
 
 iOS does not offer a built-in `FileSavePicker` experience. Luckily, it is possible to implement this functionality, for example, using a combination of a `FolderPicker` and `ContentDialog`.

src/Uno.UWP/Storage/Pickers/FileOpenPicker.Android.cs

@@ -21,6 +21,7 @@ public partial class FileOpenPicker
 		private const string AnyWildcard = "*/*";
 		private const string ImageWildcard = "image/*";
 		private const string VideoWildcard = "video/*";
+		private ActivityFlags _activityFlags;
 
 		internal static bool TryHandleIntent(Intent intent, Result resultCode)
 		{
@@ -73,11 +74,22 @@ Intent GetIntent()
 					// apps related to Photos and Videos to be suggested on the picker.
 					var intent = new Intent(Intent.ActionGetContent);
 					intent.AddCategory(Intent.CategoryOpenable);
+					// additional flags are added
+					if (_activityFlags != 0)
+					{
+						intent.AddFlags(_activityFlags);
+					}
 
 					return intent;
 				}
+				var openDocumentIntent = new Intent(Intent.ActionOpenDocument);
+				// additional flags are added
+				if (_activityFlags != 0)
+				{
+					openDocumentIntent.AddFlags(_activityFlags);
+				}
 
-				return new Intent(Intent.ActionOpenDocument);
+				return openDocumentIntent;
 			}
 
 			var intent = GetIntent();
@@ -234,5 +246,8 @@ private string GetMimeType()
 
 			return mimeTypes.ToArray();
 		}
+
+		internal void RegisterOnBeforeStartActivity(Intent intent)
+			=> _activityFlags = intent.Flags;
 	}
 }

src/Uno.UWP/Storage/Pickers/FilePickerHelper.Android.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Android.App;
+using Android.Content;
+
+namespace Windows.Storage.Pickers
+{
+	/// <summary>
+	/// Enables the user to extend the flags of the used intent
+	/// </summary>
+	public static class FilePickerHelper
+	{
+		public static void RegisterOnBeforeStartActivity(FileOpenPicker picker, Intent intent)
+		   => picker.RegisterOnBeforeStartActivity(intent);
+
+		public static void RegisterOnBeforeStartActivity(FileSavePicker picker, Intent intent)
+			=> picker.RegisterOnBeforeStartActivity(intent);
+	}
+}

src/Uno.UWP/Storage/Pickers/FileSavePicker.Android.cs

@@ -18,6 +18,7 @@ public partial class FileSavePicker
 {
 	private const string XmlCorrectMimeToActionCreateDocument = "application/xhtml+xml";
 	private const string XmlIncorrectMimeToActionCreateDocument = "application/xml";
+	private ActivityFlags _activityFlags;
 
 	private async Task<StorageFile?> PickSaveFileTaskAsync(CancellationToken token)
 	{
@@ -30,6 +31,11 @@ public partial class FileSavePicker
 
 		var intent = new Intent(action);
 		intent.AddCategory(Intent.CategoryOpenable);
+		// additional flags are added
+		if (_activityFlags != 0)
+		{
+			intent.AddFlags(_activityFlags);
+		}
 		var mimeTypes = GetMimeTypes();
 		this.AdjustInvalidMimeTypes(mimeTypes);
 
@@ -109,4 +115,7 @@ private string[] GetMimeTypes()
 		AdjustInvalidMimeTypes(mimes);
 		return mimes ?? Array.Empty<string>();
 	}
+
+	internal void RegisterOnBeforeStartActivity(Intent intent)
+		=> _activityFlags = intent.Flags;
 }