Made the DragAndDropContainer::performExternalDragDropOfFiles() and ::performExternalDragDropOfText() methods asynchronous on Windows so that behaviour is consistent across all platforms and updated the documentation to reflect this

BREAKING-CHANGES.txt

@@ -6,7 +6,29 @@ Develop
 
 Change
 ------
-AudioProcessor::getTailLengthSeconds can now return infinity for VST/VST3/AU/AUv3
+DragAndDropContainer::performExternalDragDropOfFiles() and ::performExternalDragDropOfText() 
+are now asynchronous on Windows.
+
+Possible Issues
+---------------
+Code that previously relied on these operations being synchronous and blocking until 
+completion will no longer work as the methods will return immediately and run 
+asynchronously.
+
+Workaround
+----------
+Use the callback argument that has been added to these methods to register a lambda 
+that will be called when the operation has been completed.
+
+Rationale
+---------
+The behaviour of these methods is now consistent across all platforms and the method
+no longer blocks the message thread on Windows.
+
+
+Change
+------
+AudioProcessor::getTailLengthSeconds can now return infinity for VST/VST3/AU/AUv3.
 
 Possible Issues
 ---------------
@@ -20,7 +42,6 @@ a buffer.
 
 Rationale
 ---------
-
 Before this change there was no way for a JUCE plug-in to report an infinite tail time. 
 
 

modules/juce_gui_basics/mouse/juce_DragAndDropContainer.h

@@ -153,42 +153,46 @@ public:
 
 
     //==============================================================================
-    /** This performs a synchronous drag-and-drop of a set of files to some external
+    /** This performs an asynchronous drag-and-drop of a set of files to some external
         application.
 
         You can call this function in response to a mouseDrag callback, and it will
-        block, running its own internal message loop and tracking the mouse, while it
-        uses a native operating system drag-and-drop operation to move or copy some
+        use a native operating system drag-and-drop operation to move or copy some
         files to another application.
 
         @param files            a list of filenames to drag
         @param canMoveFiles     if true, the app that receives the files is allowed to move the files to a new location
                                 (if this is appropriate). If false, the receiver is expected to make a copy of them.
-        @param sourceComponent  Normally, JUCE will assume that the component under the mouse is the source component
+        @param sourceComponent  normally, JUCE will assume that the component under the mouse is the source component
                                 of the drag, but you can use this parameter to override this.
-        @returns                true if the files were successfully dropped somewhere, or false if it
-                                was interrupted
+        @param callback         an optional completion callback that will be called when the operation has ended.
+
+        @returns                true if the drag operation was successfully started, or false if it failed for some reason
+
         @see performExternalDragDropOfText
     */
     static bool performExternalDragDropOfFiles (const StringArray& files, bool canMoveFiles,
-                                                Component* sourceComponent = nullptr);
+                                                Component* sourceComponent = nullptr,
+                                                std::function<void()> callback = nullptr);
 
-    /** This performs a synchronous drag-and-drop of a block of text to some external
+    /** This performs an asynchronous drag-and-drop of a block of text to some external
         application.
 
         You can call this function in response to a mouseDrag callback, and it will
-        block, running its own internal message loop and tracking the mouse, while it
-        uses a native operating system drag-and-drop operation to move or copy some
+        use a native operating system drag-and-drop operation to move or copy some
         text to another application.
 
         @param text             the text to copy
         @param sourceComponent  Normally, JUCE will assume that the component under the mouse is the source component
                                 of the drag, but you can use this parameter to override this.
-        @returns                true if the text was successfully dropped somewhere, or false if it
-                                was interrupted
+        @param callback         an optional completion callback that will be called when the operation has ended.
+
+        @returns                true if the drag operation was successfully started, or false if it failed for some reason
+
         @see performExternalDragDropOfFiles
     */
-    static bool performExternalDragDropOfText (const String& text, Component* sourceComponent = nullptr);
+    static bool performExternalDragDropOfText (const String& text, Component* sourceComponent = nullptr,
+                                               std::function<void()> callback = nullptr);
 
 protected:
     /** Override this if you want to be able to perform an external drag of a set of files

modules/juce_gui_basics/mouse/juce_DragAndDropTarget.h

@@ -50,9 +50,7 @@ public:
     virtual ~DragAndDropTarget()  {}
 
     //==============================================================================
-    /** Contains details about the source of a drag-and-drop operation.
-        The contents of this
-    */
+    /** Contains details about the source of a drag-and-drop operation. */
     class JUCE_API  SourceDetails
     {
     public:

modules/juce_gui_basics/native/juce_android_Windowing.cpp

@@ -1077,13 +1077,16 @@ void MouseCursor::showInAllWindows() const  {}
 
 //==============================================================================
 bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& /*files*/, const bool /*canMove*/,
-                                                           Component* /*srcComp*/)
+                                                           Component* /*srcComp*/, std::function<void()> /*callback*/)
 {
+    jassertfalse;    // no such thing on Android!
     return false;
 }
 
-bool DragAndDropContainer::performExternalDragDropOfText (const String& /*text*/, Component* /*srcComp*/)
+bool DragAndDropContainer::performExternalDragDropOfText (const String& /*text*/, Component* /*srcComp*/,
+                                                          std::function<void()> /*callback*/)
 {
+    jassertfalse;    // no such thing on Android!
     return false;
 }
 

modules/juce_gui_basics/native/juce_ios_Windowing.mm

@@ -640,13 +640,13 @@ int JUCE_CALLTYPE NativeMessageBox::showYesNoBox (AlertWindow::AlertIconType /*i
 }
 
 //==============================================================================
-bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray&, bool, Component*)
+bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray&, bool, Component*, std::function<void()>)
 {
     jassertfalse;    // no such thing on iOS!
     return false;
 }
 
-bool DragAndDropContainer::performExternalDragDropOfText (const String&, Component*)
+bool DragAndDropContainer::performExternalDragDropOfText (const String&, Component*, std::function<void()>)
 {
     jassertfalse;    // no such thing on iOS!
     return false;

modules/juce_gui_basics/native/juce_linux_X11_Windowing.cpp

@@ -2471,15 +2471,15 @@ public:
         }
     }
 
-    bool externalDragTextInit (const String& text)
+    bool externalDragTextInit (const String& text, std::function<void()> cb)
     {
         if (dragState->dragging)
             return false;
 
-        return externalDragInit (true, text);
+        return externalDragInit (true, text, cb);
     }
 
-    bool externalDragFileInit (const StringArray& files, bool /*canMoveFiles*/)
+    bool externalDragFileInit (const StringArray& files, bool /*canMoveFiles*/, std::function<void()> cb)
     {
         if (dragState->dragging)
             return false;
@@ -2494,7 +2494,7 @@ public:
                 uriList.add ("file://" + f);
         }
 
-        return externalDragInit (false, uriList.joinIntoString ("\r\n"));
+        return externalDragInit (false, uriList.joinIntoString ("\r\n"), cb);
     }
 
     //==============================================================================
@@ -3183,6 +3183,7 @@ private:
         Rectangle<int> silentRect;
         String textOrFiles;
         Array<Atom> allowedTypes;
+        std::function<void()> completionCallback;
     };
 
     //==============================================================================
@@ -3624,7 +3625,7 @@ private:
         return externalFindDragTargetWindow (child);
     }
 
-    bool externalDragInit (bool isText, const String& textOrFiles)
+    bool externalDragInit (bool isText, const String& textOrFiles, std::function<void()> cb)
     {
         ScopedXLock xlock (display);
 
@@ -3632,6 +3633,7 @@ private:
         dragState->isText = isText;
         dragState->textOrFiles = textOrFiles;
         dragState->targetWindow = windowH;
+        dragState->completionCallback = cb;
 
         const int pointerGrabMask = Button1MotionMask | ButtonReleaseMask;
 
@@ -3664,6 +3666,9 @@ private:
             XUngrabPointer (display, CurrentTime);
         }
 
+        if (dragState->completionCallback != nullptr)
+            dragState->completionCallback();
+
         resetExternalDragState();
     }
 
@@ -4262,26 +4267,27 @@ static LinuxComponentPeer* getPeerForDragEvent (Component* sourceComp)
 }
 
 bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& files, bool canMoveFiles,
-                                                           Component* sourceComp)
+                                                           Component* sourceComp, std::function<void()> callback)
 {
     if (files.isEmpty())
         return false;
 
     if (auto* lp = getPeerForDragEvent (sourceComp))
-        return lp->externalDragFileInit (files, canMoveFiles);
+        return lp->externalDragFileInit (files, canMoveFiles, callback);
 
     // This method must be called in response to a component's mouseDown or mouseDrag event!
     jassertfalse;
     return false;
 }
 
-bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Component* sourceComp)
+bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Component* sourceComp,
+                                                          std::function<void()> callback)
 {
     if (text.isEmpty())
         return false;
 
     if (auto* lp = getPeerForDragEvent (sourceComp))
-        return lp->externalDragTextInit (text);
+        return lp->externalDragTextInit (text, callback);
 
     // This method must be called in response to a component's mouseDown or mouseDrag event!
     jassertfalse;

modules/juce_gui_basics/native/juce_mac_Windowing.mm

@@ -177,14 +177,22 @@ static NSView* getNSViewForDragEvent (Component* sourceComp)
     return nil;
 }
 
-struct TextDragDataProviderClass   : public ObjCClass<NSObject>
+struct NSDraggingSourceHelper   : public ObjCClass<NSObject<NSDraggingSource>>
 {
-    TextDragDataProviderClass()  : ObjCClass<NSObject> ("JUCE_NSTextDragDataProvider_")
+    NSDraggingSourceHelper() : ObjCClass<NSObject<NSDraggingSource>> ("JUCENSDraggingSourceHelper_")
     {
+        addIvar<std::function<void()>*> ("callback");
         addIvar<String*> ("text");
+        addIvar<NSDragOperation*> ("operation");
+
         addMethod (@selector (dealloc), dealloc, "v@:");
         addMethod (@selector (pasteboard:item:provideDataForType:), provideDataForType, "v@:@@@");
+
+        addMethod (@selector (draggingSession:sourceOperationMaskForDraggingContext:), sourceOperationMaskForDraggingContext, "c@:@@");
+        addMethod (@selector (draggingSession:endedAtPoint:operation:), draggingSessionEnded, "v@:@@@");
+
         addProtocol (@protocol (NSPasteboardItemDataProvider));
+
         registerClass();
     }
 
@@ -193,10 +201,23 @@ struct TextDragDataProviderClass   : public ObjCClass<NSObject>
         object_setInstanceVariable (self, "text", new String (text));
     }
 
+    static void setCompletionCallback (id self, std::function<void()> cb)
+    {
+        object_setInstanceVariable (self, "callback", new std::function<void()> (cb));
+    }
+
+    static void setDragOperation (id self, NSDragOperation op)
+    {
+        object_setInstanceVariable (self, "operation", new NSDragOperation (op));
+    }
+
 private:
     static void dealloc (id self, SEL)
     {
         delete getIvar<String*> (self, "text");
+        delete getIvar<std::function<void()>*> (self, "callback");
+        delete getIvar<NSDragOperation*> (self, "operation");
+
         sendSuperclassMessage (self, @selector (dealloc));
     }
 
@@ -207,9 +228,23 @@ private:
                 [sender setData: [juceStringToNS (*text) dataUsingEncoding: NSUTF8StringEncoding]
                         forType: NSPasteboardTypeString];
     }
+
+    static NSDragOperation sourceOperationMaskForDraggingContext (id self, SEL, NSDraggingSession*, NSDraggingContext)
+    {
+        return *getIvar<NSDragOperation*> (self, "operation");
+    }
+
+    static void draggingSessionEnded (id self, SEL, NSDraggingSession*, NSPoint, NSDragOperation)
+    {
+        if (auto* cb = getIvar<std::function<void()>*> (self, "callback"))
+            cb->operator()();
+    }
 };
 
-bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Component* sourceComponent)
+static NSDraggingSourceHelper draggingSourceHelper;
+
+bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Component* sourceComponent,
+                                                          std::function<void()> callback)
 {
     if (text.isEmpty())
         return false;
@@ -220,12 +255,15 @@ bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Co
         {
             if (auto* event = [[view window] currentEvent])
             {
-                static TextDragDataProviderClass dataProviderClass;
-                id delegate = [dataProviderClass.createInstance() init];
-                TextDragDataProviderClass::setText (delegate, text);
+                id helper = [draggingSourceHelper.createInstance() init];
+                NSDraggingSourceHelper::setText (helper, text);
+                NSDraggingSourceHelper::setDragOperation (helper, NSDragOperationCopy);
+
+                if (callback != nullptr)
+                    NSDraggingSourceHelper::setCompletionCallback (helper, callback);
 
                 auto* pasteboardItem = [[NSPasteboardItem new] autorelease];
-                [pasteboardItem setDataProvider: delegate
+                [pasteboardItem setDataProvider: helper
                                        forTypes: [NSArray arrayWithObjects: NSPasteboardTypeString, nil]];
 
                 auto* dragItem = [[[NSDraggingItem alloc] initWithPasteboardWriter: pasteboardItem] autorelease];
@@ -233,13 +271,15 @@ bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Co
                 NSImage* image = [[NSWorkspace sharedWorkspace] iconForFile: nsEmptyString()];
                 [dragItem setDraggingFrame: getDragRect (view, event) contents: image];
 
-                auto* draggingSession = [view beginDraggingSessionWithItems: [NSArray arrayWithObject: dragItem]
-                                                                      event: event
-                                                                     source: delegate];
+                if (auto* session = [view beginDraggingSessionWithItems: [NSArray arrayWithObject: dragItem]
+                                                                  event: event
+                                                                 source: helper])
+                {
+                    session.animatesToStartingPositionsOnCancelOrFail = YES;
+                    session.draggingFormation = NSDraggingFormationNone;
 
-                draggingSession.animatesToStartingPositionsOnCancelOrFail = YES;
-                draggingSession.draggingFormation = NSDraggingFormationNone;
-                return true;
+                    return true;
+                }
             }
         }
     }
@@ -247,24 +287,8 @@ bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Co
     return false;
 }
 
-struct NSDraggingSourceHelper   : public ObjCClass<NSObject<NSDraggingSource>>
-{
-    NSDraggingSourceHelper() : ObjCClass<NSObject<NSDraggingSource>> ("JUCENSDraggingSourceHelper_")
-    {
-        addMethod (@selector (draggingSession:sourceOperationMaskForDraggingContext:), sourceOperationMaskForDraggingContext, "c@:@@");
-        registerClass();
-    }
-
-    static NSDragOperation sourceOperationMaskForDraggingContext (id, SEL, NSDraggingSession*, NSDraggingContext)
-    {
-        return NSDragOperationCopy;
-    }
-};
-
-static NSDraggingSourceHelper draggingSourceHelper;
-
-bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& files, bool /*canMoveFiles*/,
-                                                           Component* sourceComponent)
+bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& files, bool canMoveFiles,
+                                                           Component* sourceComponent, std::function<void()> callback)
 {
     if (files.isEmpty())
         return false;
@@ -296,9 +320,16 @@ bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& fi
 
                 auto* helper = [draggingSourceHelper.createInstance() autorelease];
 
-                return [view beginDraggingSessionWithItems: dragItems
-                                                     event: event
-                                                    source: helper];
+                if (callback != nullptr)
+                    NSDraggingSourceHelper::setCompletionCallback (helper, callback);
+
+                NSDraggingSourceHelper::setDragOperation (helper, canMoveFiles ? NSDragOperationMove
+                                                                               : NSDragOperationCopy);
+
+                if (auto* session = [view beginDraggingSessionWithItems: dragItems
+                                                                  event: event
+                                                                 source: helper])
+                    return true;
             }
         }
     }

modules/juce_gui_basics/native/juce_win32_DragAndDrop.cpp

@@ -241,49 +241,112 @@ namespace DragAndDropHelpers
         return hDrop;
     }
 
-    bool performDragDrop (FORMATETC* const format, STGMEDIUM* const medium, const DWORD whatToDo)
+    struct DragAndDropJob   : public ThreadPoolJob
     {
-        auto source = new JuceDropSource();
-        auto data   = new JuceDataObject (source, format, medium);
+        DragAndDropJob (FORMATETC f, STGMEDIUM m, DWORD d, std::function<void()> cb)
+            : ThreadPoolJob ("DragAndDrop"),
+              format (f), medium (m), whatToDo (d),
+              completionCallback (cb)
+        {
+        }
 
-        DWORD effect;
-        auto res = DoDragDrop (data, source, whatToDo, &effect);
+        JobStatus runJob() override
+        {
+            OleInitialize (0);
 
-        data->Release();
-        source->Release();
+            auto source = new JuceDropSource();
+            auto data = new JuceDataObject (source, &format, &medium);
 
-        return res == DRAGDROP_S_DROP;
-    }
+            DWORD effect;
+            DoDragDrop (data, source, whatToDo, &effect);
+
+            data->Release();
+            source->Release();
+
+            if (completionCallback != nullptr)
+                MessageManager::callAsync (completionCallback);
+
+            return jobHasFinished;
+        }
+
+        FORMATETC format;
+        STGMEDIUM medium;
+        DWORD whatToDo;
+
+        std::function<void()> completionCallback;
+    };
+
+    class ThreadPoolHolder   : private DeletedAtShutdown
+    {
+    public:
+        ThreadPoolHolder() = default;
+
+        ~ThreadPoolHolder()
+        {
+            // Wait forever if there's a job running. The user needs to cancel the transfer
+            // in the GUI.
+            pool.removeAllJobs (true, -1);
+
+            clearSingletonInstance();
+        }
+
+        juce_DeclareSingleton_SingleThreaded (ThreadPoolHolder, true)
+
+        // We need to make sure we don't do simultaneous text and file drag and drops,
+        // so use a pool that can only run a single job.
+        ThreadPool pool { 1 };
+    };
+
+    juce_ImplementSingleton_SingleThreaded (ThreadPoolHolder)
 }
 
 //==============================================================================
-bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& files, const bool canMove, Component*)
+bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& files, const bool canMove,
+                                                           Component*, std::function<void()> callback)
 {
+    if (files.isEmpty())
+        return false;
+
     FORMATETC format = { CF_HDROP, 0, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
     STGMEDIUM medium = { TYMED_HGLOBAL, { 0 }, 0 };
 
     medium.hGlobal = DragAndDropHelpers::createHDrop (files);
 
-    return DragAndDropHelpers::performDragDrop (&format, &medium, canMove ? (DWORD) (DROPEFFECT_COPY | DROPEFFECT_MOVE)
-                                                                          : (DWORD) DROPEFFECT_COPY);
+    auto& pool = DragAndDropHelpers::ThreadPoolHolder::getInstance()->pool;
+    pool.addJob (new DragAndDropHelpers::DragAndDropJob (format, medium,
+                                                         canMove ? (DROPEFFECT_COPY | DROPEFFECT_MOVE) : DROPEFFECT_COPY,
+                                                         callback),
+                true);
+
+    return true;
 }
 
-bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Component*)
+bool DragAndDropContainer::performExternalDragDropOfText (const String& text, Component*, std::function<void()> callback)
 {
+    if (text.isEmpty())
+        return false;
+
     FORMATETC format = { CF_TEXT, 0, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
     STGMEDIUM medium = { TYMED_HGLOBAL, { 0 }, 0 };
 
     auto numBytes = CharPointer_UTF16::getBytesRequiredFor (text.getCharPointer());
 
     medium.hGlobal = GlobalAlloc (GMEM_MOVEABLE | GMEM_ZEROINIT, numBytes + 2);
-    WCHAR* const data = static_cast<WCHAR*> (GlobalLock (medium.hGlobal));
+    auto* data = static_cast<WCHAR*> (GlobalLock (medium.hGlobal));
 
-    text.copyToUTF16 (data, numBytes);
+    text.copyToUTF16 (data, numBytes + 2);
     format.cfFormat = CF_UNICODETEXT;
 
     GlobalUnlock (medium.hGlobal);
 
-    return DragAndDropHelpers::performDragDrop (&format, &medium, DROPEFFECT_COPY | DROPEFFECT_MOVE);
+    auto& pool = DragAndDropHelpers::ThreadPoolHolder::getInstance()->pool;
+    pool.addJob (new DragAndDropHelpers::DragAndDropJob (format,
+                                                        medium,
+                                                        DROPEFFECT_COPY | DROPEFFECT_MOVE,
+                                                        callback),
+                 true);
+
+    return true;
 }
 
 } // namespace juce