Browser drag n drop target support

src/Browser/Avalonia.Browser/AvaloniaView.cs

@@ -106,6 +106,8 @@ namespace Avalonia.Browser
             InputHelper.SubscribePointerEvents(_containerElement, OnPointerMove, OnPointerDown, OnPointerUp,
                 OnPointerCancel, OnWheel);
 
+            InputHelper.SubscribeDropEvents(_containerElement, OnDragEvent);
+            
             var skiaOptions = AvaloniaLocator.Current.GetService<SkiaOptions>();
 
             _dpi = DomHelper.ObserveDpi(OnDpiChanged);
@@ -293,6 +295,59 @@ namespace Avalonia.Browser
             return modifiers;
         }
 
+        public bool OnDragEvent(JSObject args)
+        {
+            var eventType = args?.GetPropertyAsString("type") switch
+            {
+                "dragenter" => RawDragEventType.DragEnter,
+                "dragover" => RawDragEventType.DragOver,
+                "dragleave" => RawDragEventType.DragLeave,
+                "drop" => RawDragEventType.Drop,
+                _ => (RawDragEventType)(int)-1
+            };
+            var dataObject = args?.GetPropertyAsJSObject("dataTransfer");
+            if (args is null || eventType < 0 || dataObject is null)
+            {
+                return false;
+            }
+
+            // If file is dropped, we need storage js to be referenced.
+            // TODO: restructure JS files, so it's not needed.
+            _ = AvaloniaModule.ImportStorage();
+
+            var position = new Point(args.GetPropertyAsDouble("offsetX"), args.GetPropertyAsDouble("offsetY"));
+            var modifiers = GetModifiers(args);
+
+            var effectAllowedStr = dataObject.GetPropertyAsString("effectAllowed") ?? "none";
+            var effectAllowed = DragDropEffects.None;
+            if (effectAllowedStr.Contains("copy", StringComparison.OrdinalIgnoreCase))
+            {
+                effectAllowed |= DragDropEffects.Copy;
+            }
+            if (effectAllowedStr.Contains("link", StringComparison.OrdinalIgnoreCase))
+            {
+                effectAllowed |= DragDropEffects.Link;
+            }
+            if (effectAllowedStr.Contains("move", StringComparison.OrdinalIgnoreCase))
+            {
+                effectAllowed |= DragDropEffects.Move;
+            }
+            if (effectAllowedStr.Equals("all", StringComparison.OrdinalIgnoreCase))
+            {
+                effectAllowed |= DragDropEffects.Move | DragDropEffects.Copy | DragDropEffects.Link;
+            }
+            if (effectAllowed == DragDropEffects.None)
+            {
+                return false;
+            }
+
+            var dropEffect = _topLevelImpl.RawDragEvent(eventType, position, modifiers, new BrowserDataObject(dataObject), effectAllowed);
+            dataObject.SetProperty("dropEffect", dropEffect.ToString().ToLowerInvariant());
+
+            return eventType is RawDragEventType.Drop or RawDragEventType.DragOver
+                   && dropEffect != DragDropEffects.None;
+        }
+        
         private bool OnKeyDown (string code, string key, int modifier)
         {
             var handled = _topLevelImpl.RawKeyboardEvent(RawKeyEventType.KeyDown, code, key, (RawInputModifiers)modifier);

src/Browser/Avalonia.Browser/BrowserDataObject.cs

@@ -0,0 +1,91 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices.JavaScript;
+using Avalonia.Browser.Interop;
+using Avalonia.Browser.Storage;
+using Avalonia.Input;
+using Avalonia.Platform.Storage;
+
+namespace Avalonia.Browser;
+
+internal class BrowserDataObject : IDataObject
+{
+    private readonly JSObject _dataObject;
+
+    public BrowserDataObject(JSObject dataObject)
+    {
+        _dataObject = dataObject;
+    }
+    
+    public IEnumerable<string> GetDataFormats()
+    {
+        var types = new HashSet<string>(_dataObject.GetPropertyAsStringArray("types"));
+        var dataFormats = new HashSet<string>(types.Count);
+
+        foreach (var type in types)
+        {
+            if (type.StartsWith("text/", StringComparison.Ordinal))
+            {
+                dataFormats.Add(DataFormats.Text);
+            }
+            else if (type.Equals("Files", StringComparison.Ordinal))
+            {
+                dataFormats.Add(DataFormats.Files);
+            }
+            dataFormats.Add(type);
+        }
+
+        // If drag'n'drop an image from the another web page, if won't add "Files" to the supported types, but only a "text/uri-list".
+        // With "text/uri-list" browser can add actual file as well.
+        var filesCount = _dataObject.GetPropertyAsJSObject("files")?.GetPropertyAsInt32("count");
+        if (filesCount > 0)
+        {
+            dataFormats.Add(DataFormats.Files);
+        }
+
+        return dataFormats;
+    }
+
+    public bool Contains(string dataFormat)
+    {
+        return GetDataFormats().Contains(dataFormat);
+    }
+
+    public object? Get(string dataFormat)
+    {
+        if (dataFormat == DataFormats.Files)
+        {
+            var files = _dataObject.GetPropertyAsJSObject("files");
+            if (files is not null)
+            {
+                return StorageHelper.FilesToItemsArray(files)
+                    .Select(reference => reference.GetPropertyAsString("kind") switch
+                    {
+                        "directory" => (IStorageItem)new JSStorageFolder(reference),
+                        "file" => new JSStorageFile(reference),
+                        _ => null
+                    })
+                    .Where(i => i is not null)
+                    .ToArray()!;
+            }
+
+            return null;
+        }
+
+        if (dataFormat == DataFormats.Text)
+        {
+            if (_dataObject.CallMethodString("getData", "text/plain") is { Length :> 0 } textData)
+            {
+                return textData;
+            }
+        }
+
+        if (_dataObject.CallMethodString("getData", dataFormat) is { Length: > 0 } data)
+        {
+            return data;
+        }
+
+        return null;
+    }
+}

src/Browser/Avalonia.Browser/BrowserTopLevelImpl.cs

@@ -164,6 +164,15 @@ namespace Avalonia.Browser
 
             return false;
         }
+        
+        public DragDropEffects RawDragEvent(RawDragEventType eventType, Point position, RawInputModifiers modifiers, BrowserDataObject dataObject, DragDropEffects dropEffect)
+        {
+            var device = AvaloniaLocator.Current.GetRequiredService<IDragDropDevice>();
+            var eventArgs = new RawDragEvent(device, eventType, _inputRoot!, position, dataObject, dropEffect, modifiers);
+            Console.WriteLine($"{eventArgs.Location} {eventArgs.Effects} {eventArgs.Type} {eventArgs.KeyModifiers}");
+            Input?.Invoke(eventArgs);
+            return eventArgs.Effects;
+        }
 
         public void Dispose()
         {

src/Browser/Avalonia.Browser/ClipboardImpl.cs

@@ -24,6 +24,6 @@ namespace Avalonia.Browser
 
         public Task<string[]> GetFormatsAsync() => Task.FromResult(Array.Empty<string>());
 
-        public Task<object?> GetDataAsync(string format) => Task.FromResult<object?>(new());
+        public Task<object?> GetDataAsync(string format) => Task.FromResult<object?>(null);
     }
 }

src/Browser/Avalonia.Browser/Interop/AvaloniaModule.cs

@@ -1,24 +1,29 @@
-using System.Runtime.InteropServices.JavaScript;
+using System;
+using System.Runtime.InteropServices.JavaScript;
 using System.Threading.Tasks;
 
 namespace Avalonia.Browser.Interop;
 
 internal static partial class AvaloniaModule
 {
-    public const string MainModuleName = "avalonia";
-    public const string StorageModuleName = "storage";
-
-    public static Task ImportMain()
+    private static readonly Lazy<Task> s_importMain = new(() =>
     {
         var options = AvaloniaLocator.Current.GetService<BrowserPlatformOptions>() ?? new BrowserPlatformOptions();
         return JSHost.ImportAsync(MainModuleName, options.FrameworkAssetPathResolver!("avalonia.js"));
-    }
+    });
 
-    public static Task ImportStorage()
+    private static readonly Lazy<Task> s_importStorage = new(() =>
     {
         var options = AvaloniaLocator.Current.GetService<BrowserPlatformOptions>() ?? new BrowserPlatformOptions();
         return JSHost.ImportAsync(StorageModuleName, options.FrameworkAssetPathResolver!("storage.js"));
-    }
+    });
+
+    public const string MainModuleName = "avalonia";
+    public const string StorageModuleName = "storage";
+
+    public static Task ImportMain() => s_importMain.Value;
+
+    public static Task ImportStorage() => s_importStorage.Value;
 
     [JSImport("Caniuse.isMobile", AvaloniaModule.MainModuleName)]
     public static partial bool IsMobile();

src/Browser/Avalonia.Browser/Interop/GeneralHelpers.cs

@@ -0,0 +1,22 @@
+using System.Runtime.InteropServices.JavaScript;
+
+namespace Avalonia.Browser.Interop;
+
+internal static partial class GeneralHelpers
+{
+    [JSImport("GeneralHelpers.itemsArrayAt", AvaloniaModule.MainModuleName)]
+    public static partial JSObject[] ItemsArrayAt(JSObject jsObject, string key);
+    public static JSObject[] GetPropertyAsJSObjectArray(this JSObject jsObject, string key) => ItemsArrayAt(jsObject, key);
+    
+    [JSImport("GeneralHelpers.itemsArrayAt", AvaloniaModule.MainModuleName)]
+    public static partial string[] ItemsArrayAtAsStrings(JSObject jsObject, string key);
+    public static string[] GetPropertyAsStringArray(this JSObject jsObject, string key) => ItemsArrayAtAsStrings(jsObject, key);
+    
+    [JSImport("GeneralHelpers.callMethod", AvaloniaModule.MainModuleName)]
+    public static partial string IntCallMethodString(JSObject jsObject, string name);
+    [JSImport("GeneralHelpers.callMethod", AvaloniaModule.MainModuleName)]
+    public static partial string IntCallMethodStringString(JSObject jsObject, string name, string arg1);
+
+    public static string CallMethodString(this JSObject jsObject, string name) => IntCallMethodString(jsObject, name);
+    public static string CallMethodString(this JSObject jsObject, string name, string arg1) => IntCallMethodStringString(jsObject, name, arg1);
+}

src/Browser/Avalonia.Browser/Interop/InputHelper.cs

@@ -43,13 +43,16 @@ internal static partial class InputHelper
         [JSMarshalAs<JSType.Function<JSType.Object, JSType.Boolean>>]
         Func<JSObject, bool> wheel);
 
-
     [JSImport("InputHelper.subscribeInputEvents", AvaloniaModule.MainModuleName)]
     public static partial void SubscribeInputEvents(
         JSObject htmlElement,
         [JSMarshalAs<JSType.Function<JSType.String, JSType.Boolean>>]
         Func<string, bool> input);
 
+    [JSImport("InputHelper.subscribeDropEvents", AvaloniaModule.MainModuleName)]
+    public static partial void SubscribeDropEvents(JSObject containerElement,
+        [JSMarshalAs<JSType.Function<JSType.Object, JSType.Boolean>>] Func<JSObject, bool> dragEvent);
+    
     [JSImport("InputHelper.getCoalescedEvents", AvaloniaModule.MainModuleName)]
     [return: JSMarshalAs<JSType.Array<JSType.Object>>]
     public static partial JSObject[] GetCoalescedEvents(JSObject pointerEvent);

src/Browser/Avalonia.Browser/Interop/StorageHelper.cs

@@ -46,6 +46,9 @@ internal static partial class StorageHelper
 
     [JSImport("StorageItems.itemsArray", AvaloniaModule.StorageModuleName)]
     public static partial JSObject[] ItemsArray(JSObject item);
+    
+    [JSImport("StorageItems.filesToItemsArray", AvaloniaModule.StorageModuleName)]
+    public static partial JSObject[] FilesToItemsArray(JSObject item);
 
     [JSImport("StorageProvider.createAcceptType", AvaloniaModule.StorageModuleName)]
     public static partial JSObject CreateAcceptType(string description, string[] mimeTypes, string[]? extensions);

src/Browser/Avalonia.Browser/Storage/BrowserStorageProvider.cs

@@ -1,10 +1,8 @@
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices.JavaScript;
-using System.Runtime.Versioning;
 using System.Threading.Tasks;
 using Avalonia.Browser.Interop;
 using Avalonia.Platform.Storage;
@@ -18,15 +16,13 @@ internal class BrowserStorageProvider : IStorageProvider
     internal const string PickerCancelMessage = "The user aborted a request";
     internal const string NoPermissionsMessage = "Permissions denied";
 
-    private readonly Lazy<Task> _lazyModule = new(() => AvaloniaModule.ImportStorage());
-
     public bool CanOpen => true;
     public bool CanSave => StorageHelper.HasNativeFilePicker();
     public bool CanPickFolder => true;
 
     public async Task<IReadOnlyList<IStorageFile>> OpenFilePickerAsync(FilePickerOpenOptions options)
     {
-        await _lazyModule.Value;
+        await AvaloniaModule.ImportStorage();
         var startIn = (options.SuggestedStartLocation as JSStorageItem)?.FileHandle;
 
         var (types, excludeAll) = ConvertFileTypes(options.FileTypeFilter);
@@ -60,7 +56,7 @@ internal class BrowserStorageProvider : IStorageProvider
 
     public async Task<IStorageFile?> SaveFilePickerAsync(FilePickerSaveOptions options)
     {
-        await _lazyModule.Value;
+        await AvaloniaModule.ImportStorage();
         var startIn = (options.SuggestedStartLocation as JSStorageItem)?.FileHandle;
 
         var (types, excludeAll) = ConvertFileTypes(options.FileTypeChoices);
@@ -88,7 +84,7 @@ internal class BrowserStorageProvider : IStorageProvider
 
     public async Task<IReadOnlyList<IStorageFolder>> OpenFolderPickerAsync(FolderPickerOpenOptions options)
     {
-        await _lazyModule.Value;
+        await AvaloniaModule.ImportStorage();
         var startIn = (options.SuggestedStartLocation as JSStorageItem)?.FileHandle;
 
         try
@@ -104,14 +100,14 @@ internal class BrowserStorageProvider : IStorageProvider
 
     public async Task<IStorageBookmarkFile?> OpenFileBookmarkAsync(string bookmark)
     {
-        await _lazyModule.Value;
+        await AvaloniaModule.ImportStorage();
         var item = await StorageHelper.OpenBookmark(bookmark);
         return item is not null ? new JSStorageFile(item) : null;
     }
 
     public async Task<IStorageBookmarkFolder?> OpenFolderBookmarkAsync(string bookmark)
     {
-        await _lazyModule.Value;
+        await AvaloniaModule.ImportStorage();
         var item = await StorageHelper.OpenBookmark(bookmark);
         return item is not null ? new JSStorageFolder(item) : null;
     }
@@ -128,7 +124,7 @@ internal class BrowserStorageProvider : IStorageProvider
 
     public async Task<IStorageFolder?> TryGetWellKnownFolderAsync(WellKnownFolder wellKnownFolder)
     {
-        await _lazyModule.Value;
+        await AvaloniaModule.ImportStorage();
         var directory = StorageHelper.CreateWellKnownDirectory(wellKnownFolder switch
         {
             WellKnownFolder.Desktop => "desktop",

src/Browser/Avalonia.Browser/webapp/modules/avalonia.ts

@@ -5,6 +5,7 @@ import { Caniuse } from "./avalonia/caniuse";
 import { StreamHelper } from "./avalonia/stream";
 import { NativeControlHost } from "./avalonia/nativeControlHost";
 import { NavigationHelper } from "./avalonia/navigationHelper";
+import { GeneralHelpers } from "./avalonia/generalHelpers";
 
 export {
     Caniuse,
@@ -15,5 +16,6 @@ export {
     AvaloniaDOM,
     StreamHelper,
     NativeControlHost,
-    NavigationHelper
+    NavigationHelper,
+    GeneralHelpers
 };

src/Browser/Avalonia.Browser/webapp/modules/avalonia/generalHelpers.ts

@@ -0,0 +1,19 @@
+export class GeneralHelpers {
+    public static itemsArrayAt(instance: any, key: string): any[] {
+        const items = instance[key];
+        if (!items) {
+            return [];
+        }
+
+        const retItems = [];
+        for (let i = 0; i < items.length; i++) {
+            retItems[i] = items[i];
+        }
+        return retItems;
+    }
+
+    public static callMethod(instance: any, name: string /*, args */): any {
+        const args = Array.prototype.slice.call(arguments, 2);
+        return instance[name].apply(instance, args);
+    }
+}

src/Browser/Avalonia.Browser/webapp/modules/avalonia/input.ts

@@ -174,6 +174,28 @@ export class InputHelper {
         };
     }
 
+    public static subscribeDropEvents(
+        element: HTMLInputElement,
+        dragEvent: (args: any) => boolean
+    ) {
+        const dragHandler = (args: Event) => {
+            if (dragEvent(args as any)) {
+                args.preventDefault();
+            }
+        };
+        element.addEventListener("dragover", dragHandler);
+        element.addEventListener("dragenter", dragHandler);
+        element.addEventListener("dragleave", dragHandler);
+        element.addEventListener("drop", dragHandler);
+
+        return () => {
+            element.removeEventListener("dragover", dragHandler);
+            element.removeEventListener("dragenter", dragHandler);
+            element.removeEventListener("dragleave", dragHandler);
+            element.removeEventListener("drop", dragHandler);
+        };
+    }
+
     public static getCoalescedEvents(pointerEvent: PointerEvent): PointerEvent[] {
         return pointerEvent.getCoalescedEvents();
     }

src/Browser/Avalonia.Browser/webapp/modules/storage/storageItem.ts

@@ -3,8 +3,9 @@ import { FileSystemFileHandle, FileSystemDirectoryHandle, FileSystemWritableFile
 import { Caniuse } from "../avalonia";
 
 export class StorageItem {
-    constructor(
+    private constructor(
         public handle?: FileSystemFileHandle | FileSystemDirectoryHandle,
+        private readonly file?: File,
         private readonly bookmarkId?: string,
         public wellKnownType?: WellKnownDirectory
     ) {
@@ -14,6 +15,9 @@ export class StorageItem {
         if (this.handle) {
             return this.handle.name;
         }
+        if (this.file) {
+            return this.file.name;
+        }
         return this.wellKnownType ?? "";
     }
 
@@ -21,14 +25,29 @@ export class StorageItem {
         if (this.handle) {
             return this.handle.kind;
         }
+        if (this.file) {
+            return "file";
+        }
         return "directory";
     }
 
+    public static createFromHandle(handle: FileSystemFileHandle | FileSystemDirectoryHandle, bookmarkId?: string) {
+        return new StorageItem(handle, undefined, bookmarkId, undefined);
+    }
+
+    public static createFromFile(file: File) {
+        return new StorageItem(undefined, file, undefined, undefined);
+    }
+
     public static createWellKnownDirectory(type: WellKnownDirectory) {
-        return new StorageItem(undefined, undefined, type);
+        return new StorageItem(undefined, undefined, undefined, type);
     }
 
     public static async openRead(item: StorageItem): Promise<Blob> {
+        if (item.file) {
+            return item.file;
+        }
+
         if (!item.handle || item.kind !== "file") {
             throw new Error("StorageItem is not a file");
         }
@@ -41,7 +60,7 @@ export class StorageItem {
 
     public static async openWrite(item: StorageItem): Promise<FileSystemWritableFileStream> {
         if (!item.handle || item.kind !== "file") {
-            throw new Error("StorageItem is not a file");
+            throw new Error("StorageItem is not a writeable file");
         }
 
         await item.verityPermissions("readwrite");
@@ -52,8 +71,9 @@ export class StorageItem {
     public static async getProperties(item: StorageItem): Promise<{ Size: number; LastModified: number; Type: string } | null> {
         // getFile can fail with an exception depending if we use polyfill with a save file dialog or not.
         try {
-            const file = item.handle instanceof FileSystemFileHandle &&
-                await item.handle.getFile();
+            const file = item.handle && "getFile" in item.handle
+                ? await item.handle.getFile()
+                : item.file;
 
             if (!file) {
                 return null;
@@ -144,4 +164,16 @@ export class StorageItems {
     public static itemsArray(instance: StorageItems): StorageItem[] {
         return instance.items;
     }
+
+    public static filesToItemsArray(files: File[]): StorageItem[] {
+        if (!files) {
+            return [];
+        }
+
+        const retItems = [];
+        for (let i = 0; i < files.length; i++) {
+            retItems[i] = StorageItem.createFromFile(files[i]);
+        }
+        return retItems;
+    }
 }

src/Browser/Avalonia.Browser/webapp/modules/storage/storageProvider.ts

@@ -19,7 +19,7 @@ export class StorageProvider {
         };
 
         const handle = await showDirectoryPicker(options as any);
-        return new StorageItem(handle);
+        return StorageItem.createFromHandle(handle);
     }
 
     public static async openFileDialog(
@@ -33,7 +33,7 @@ export class StorageProvider {
         };
 
         const handles = await showOpenFilePicker(options);
-        return new StorageItems(handles.map((handle: FileSystemFileHandle) => new StorageItem(handle)));
+        return new StorageItems(handles.map((handle: FileSystemFileHandle) => StorageItem.createFromHandle(handle)));
     }
 
     public static async saveFileDialog(
@@ -48,14 +48,14 @@ export class StorageProvider {
 
         // Always prefer native save file picker, as polyfill solutions are not reliable.
         const handle = await (globalThis as any).showSaveFilePicker(options);
-        return new StorageItem(handle);
+        return StorageItem.createFromHandle(handle);
     }
 
     public static async openBookmark(key: string): Promise<StorageItem | null> {
         const connection = await avaloniaDb.connect();
         try {
             const handle = await connection.get(fileBookmarksStore, key);
-            return handle && new StorageItem(handle, key);
+            return handle && StorageItem.createFromHandle(handle, key);
         } finally {
             connection.close();
         }