Add StorageProvider actions

src/Avalonia.Xaml.Interactions/StorageProvider/Converters/StorageFileToReadStreamConverter.cs

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+using System;
+using System.Globalization;
+using Avalonia.Data;
+using Avalonia.Data.Converters;
+using Avalonia.Platform.Storage;
+
+namespace Avalonia.Xaml.Interactions.Core;
+
+/// <summary>
+/// Converts a <seealso cref="IStorageFile"/> to a read stream.
+/// </summary>
+public class StorageFileToReadStreamConverter : IValueConverter
+{
+    /// <summary>
+    /// Gets a static instance of <see cref="StorageFileToReadStreamConverter"/>.
+    /// </summary>
+    public static StorageFileToReadStreamConverter Instance { get; } = new ();
+
+    /// <inheritdoc />
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is IStorageFile storageFile)
+        {
+            return storageFile.OpenReadAsync();
+        }
+
+        return BindingOperations.DoNothing;
+    }
+
+    /// <inheritdoc />
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        return BindingOperations.DoNothing;
+    }
+}

src/Avalonia.Xaml.Interactions/StorageProvider/Converters/StorageFileToWriteStreamConverter.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Globalization;
+using Avalonia.Data;
+using Avalonia.Data.Converters;
+using Avalonia.Platform.Storage;
+
+namespace Avalonia.Xaml.Interactions.Core;
+
+/// <summary>
+/// Converts a <seealso cref="IStorageFile"/> to a path.
+/// </summary>
+public class StorageFileToWriteStreamConverter : IValueConverter
+{
+    /// <summary>
+    /// Gets a static instance of <see cref="StorageFileToWriteStreamConverter"/>.
+    /// </summary>
+    public static StorageFileToWriteStreamConverter Instance { get; } = new ();
+
+    /// <inheritdoc />
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is IStorageFile storageFile)
+        {
+            return storageFile.OpenWriteAsync();
+        }
+
+        return BindingOperations.DoNothing;
+    }
+
+    /// <inheritdoc />
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        return BindingOperations.DoNothing;
+    }
+}

src/Avalonia.Xaml.Interactions/StorageProvider/Converters/StorageItemToPathConverter.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Globalization;
+using Avalonia.Data;
+using Avalonia.Data.Converters;
+using Avalonia.Platform.Storage;
+
+namespace Avalonia.Xaml.Interactions.Core;
+
+/// <summary>
+/// Converts a <seealso cref="IStorageItem"/> to a path.
+/// </summary>
+public class StorageItemToPathConverter : IValueConverter
+{
+    /// <summary>
+    /// Gets a static instance of <see cref="StorageItemToPathConverter"/>.
+    /// </summary>
+    public static StorageItemToPathConverter Instance { get; } = new ();
+
+    /// <inheritdoc />
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is IStorageItem storageItem)
+        {
+            return storageItem.Path;
+        }
+
+        return BindingOperations.DoNothing;
+    }
+
+    /// <inheritdoc />
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        return BindingOperations.DoNothing;
+    }
+}

src/Avalonia.Xaml.Interactions/StorageProvider/Core/PickerActionBase.cs

@@ -0,0 +1,54 @@
+using Avalonia.Platform.Storage;
+
+namespace Avalonia.Xaml.Interactions.Core;
+
+/// <summary>
+/// Base class for picker actions.
+/// </summary>
+public abstract class PickerActionBase : InvokeCommandActionBase
+{
+    /// <summary>
+    /// Identifies the <seealso cref="Title"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<string?> TitleProperty =
+        AvaloniaProperty.Register<PickerActionBase, string?>(nameof(Title));
+
+    /// <summary>
+    /// Identifies the <seealso cref="SuggestedStartLocation"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<IStorageFolder?> SuggestedStartLocationProperty =
+        AvaloniaProperty.Register<PickerActionBase, IStorageFolder?>(nameof(SuggestedStartLocation));
+
+    /// <summary>
+    /// Identifies the <seealso cref="SuggestedFileName"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<string?> SuggestedFileNameProperty =
+        AvaloniaProperty.Register<PickerActionBase, string?>(nameof(SuggestedFileName));
+
+    /// <summary>
+    /// Gets or sets the text that appears in the title bar of a picker. This is an avalonia property.
+    /// </summary>
+    public string? Title
+    {
+        get => GetValue(TitleProperty);
+        set => SetValue(TitleProperty, value);
+    } 
+
+    /// <summary>
+    /// Gets or sets the initial location where the file open picker looks for files to present to the user. This is an avalonia property.
+    /// </summary>
+    public IStorageFolder? SuggestedStartLocation
+    {
+        get => GetValue(SuggestedStartLocationProperty);
+        set => SetValue(SuggestedStartLocationProperty, value);
+    } 
+
+    /// <summary>
+    /// Gets or sets the file name that the file picker suggests to the user. This is an avalonia property.
+    /// </summary>
+    public string? SuggestedFileName
+    {
+        get => GetValue(SuggestedFileNameProperty);
+        set => SetValue(SuggestedFileNameProperty, value);
+    } 
+}

src/Avalonia.Xaml.Interactions/StorageProvider/OpenFilePickerAction.cs

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+using System.Threading.Tasks;
+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+
+namespace Avalonia.Xaml.Interactions.Core;
+
+/// <summary>
+/// An action that will open a file picker dialog.
+/// </summary>
+public class OpenFilePickerAction : PickerActionBase
+{
+    /// <summary>
+    /// Identifies the <seealso cref="AllowMultiple"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<bool> AllowMultipleProperty =
+        AvaloniaProperty.Register<OpenFilePickerAction, bool>(nameof(AllowMultiple));
+
+    /// <summary>
+    /// Identifies the <seealso cref="FileTypeFilter"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<string?> FileTypeFilterProperty =
+        AvaloniaProperty.Register<OpenFilePickerAction, string?>(nameof(FileTypeFilter));
+
+    /// <summary>
+    /// Gets or sets an option indicating whether open picker allows users to select multiple files. This is an avalonia property.
+    /// </summary>
+    public bool AllowMultiple
+    {
+        get => GetValue(AllowMultipleProperty);
+        set => SetValue(AllowMultipleProperty, value);
+    }
+
+    /// <summary>
+    /// Gets or sets the collection of file types that the file open picker displays. This is an avalonia property.
+    /// </summary>
+    public string? FileTypeFilter
+    {
+        get => GetValue(FileTypeFilterProperty);
+        set => SetValue(FileTypeFilterProperty, value);
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="OpenFilePickerAction"/> class.
+    /// </summary>
+    public OpenFilePickerAction()
+    {
+        PassEventArgsToCommand = true;
+    }
+
+    /// <summary>
+    /// Executes the action.
+    /// </summary>
+    /// <param name="sender">The <see cref="object"/> that is passed to the action by the behavior. Generally this is <seealso cref="Avalonia.Xaml.Interactivity.IBehavior.AssociatedObject"/> or a target object.</param>
+    /// <param name="parameter">The value of this parameter is determined by the caller.</param>
+    /// <returns>True if the command is successfully executed; else false.</returns>
+    public override object Execute(object? sender, object? parameter)
+    {
+        if (sender is not Visual visual)
+        {
+            return false;
+        }
+
+        Dispatcher.UIThread.InvokeAsync(async () => await OpenFilePickerAsync(visual));
+
+        return true; 
+    }
+
+    private async Task OpenFilePickerAsync(Visual visual)
+    {
+        if (IsEnabled != true || Command is null)
+        {
+            return;
+        }
+
+        var storageProvider = (visual.GetVisualRoot() as TopLevel)?.StorageProvider;
+        if (storageProvider is null)
+        {
+            return;
+        }
+
+        var files = await storageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
+        {
+            Title = Title,
+            SuggestedStartLocation = SuggestedStartLocation,
+            SuggestedFileName = SuggestedFileName,
+            AllowMultiple = AllowMultiple,
+            FileTypeFilter = FileTypeFilter is not null 
+                ? FileFilterParser.ConvertToFilePickerFileType(FileTypeFilter) 
+                : null
+        });
+
+        if (files.Count <= 0)
+        {
+            return;
+        }
+
+        var resolvedParameter = ResolveParameter(files);
+
+        if (!Command.CanExecute(resolvedParameter))
+        {
+            return;
+        }
+
+        Command.Execute(resolvedParameter);
+    }
+}

src/Avalonia.Xaml.Interactions/StorageProvider/OpenFolderPickerAction.cs

@@ -0,0 +1,90 @@
+using System.Threading.Tasks;
+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+
+namespace Avalonia.Xaml.Interactions.Core;
+
+/// <summary>
+/// An action that will open a folder picker dialog.
+/// </summary>
+public class OpenFolderPickerAction : PickerActionBase
+{
+    /// <summary>
+    /// Identifies the <seealso cref="AllowMultiple"/> avalonia property.
+    /// </summary>
+    public static readonly StyledProperty<bool> AllowMultipleProperty =
+        AvaloniaProperty.Register<OpenFolderPickerAction, bool>(nameof(AllowMultiple));
+
+    /// <summary>
+    /// Gets or sets an option indicating whether open picker allows users to select multiple folders. This is an avalonia property.
+    /// </summary>
+    public bool AllowMultiple
+    {
+        get => GetValue(AllowMultipleProperty);
+        set => SetValue(AllowMultipleProperty, value);
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="OpenFolderPickerAction"/> class.
+    /// </summary>
+    public OpenFolderPickerAction()
+    {
+        PassEventArgsToCommand = true;
+    }
+
+    /// <summary>
+    /// Executes the action.
+    /// </summary>
+    /// <param name="sender">The <see cref="object"/> that is passed to the action by the behavior. Generally this is <seealso cref="Avalonia.Xaml.Interactivity.IBehavior.AssociatedObject"/> or a target object.</param>
+    /// <param name="parameter">The value of this parameter is determined by the caller.</param>
+    /// <returns>True if the command is successfully executed; else false.</returns>
+    public override object Execute(object? sender, object? parameter)
+    {
+        if (sender is not Visual visual)
+        {
+            return false;
+        }
+
+        Dispatcher.UIThread.InvokeAsync(async () => await OpenFolderPickerAsync(visual));
+
+        return true; 
+    }
+
+    private async Task OpenFolderPickerAsync(Visual visual)
+    {
+        if (IsEnabled != true || Command is null)
+        {
+            return;
+        }
+
+        var storageProvider = (visual.GetVisualRoot() as TopLevel)?.StorageProvider;
+        if (storageProvider is null)
+        {
+            return;
+        }
+
+        var folders = await storageProvider.OpenFolderPickerAsync(new FolderPickerOpenOptions
+        {
+            Title = Title,
+            SuggestedStartLocation = SuggestedStartLocation,
+            SuggestedFileName = SuggestedFileName,
+            AllowMultiple = AllowMultiple
+        });
+
+        if (folders.Count <= 0)
+        {
+            return;
+        }
+
+        var resolvedParameter = ResolveParameter(folders);
+
+        if (!Command.CanExecute(resolvedParameter))
+        {
+            return;
+        }
+
+        Command.Execute(resolvedParameter);
+    }
+}