Bug 200297 – [GTK] Cannot disable drag-and-drop functionality with gtk_drag_source_set()/gtk_drag_source_unset() inside a WebKitWebView

• Status: NEW
• Component: WebKitGTK

[Jussi]

Hello,

I'm trying to disable drag-and-drop functionality in a gtkmm project where I'm using WebKitGTK to render HTML pages. After creating the webview and creating a gtkmm widget out of it, as shown here:

mWebView = WEBKIT_WEB_VIEW(webkit_web_view_new_with_context(mWebContext));
auto webWidget = Gtk::manage(Glib::wrap(GTK_WIDGET(mWebView)));
mBrowserContainer.pack_start(*webWidget, Gtk::PACK_EXPAND_WIDGET);

I try to disable the drag-and-drop functionality with the respective gtkmm widget class member functions:

webWidget->drag_source_unset();
webWidget->drag_dest_unset();

The "drag_dest_unset()" works as expected (https://developer.gnome.org/gtkmm/stable/classGtk_1_1Widget.html#a0940c95059601a152db59a2fc99a2ed3), but the "drag_source_unset()" doesn't seem to have any effect; I can still drag links and text out from the WebView.

I also tried to disable the dragging with a more "hacky" way, by calling drag_source_set()

webWidget->drag_source_set(std::vector<Gtk::TargetEntry>({ Gtk::TargetEntry("STRING", Gtk::TargetFlags::TARGET_SAME_WIDGET, 0) }));

This should create a custom Gtk::TargetEntry list which is allowed to copy data from the widget. However, after setting this drag_source_set(), the program aborts because an assert fails in the webkitWebViewBaseDragEnd(GtkWidget* widget, GdkDragContext* context) function inside WebKitWebViewBase.cpp (https://trac.webkit.org/browser/webkit/releases/WebKitGTK/webkit-2.25.1/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp#L1281). Seems like calling "drag_source_set()" on a WebView nullifies some internal structure (WebKitWebViewBasePrivate->dragAndDropHandler).

I also tried to connect the webWidget->signal_drag_begin() signal to a function where I would call gdk_drag_abort() for the Gdk::DragContext, but it does not seem to work on all systems.

What is the proper way to disable WebView's DnD functionality from the code, if I don't compile the whole WebKitGTK library from source without the "ENABLE(DRAG_SUPPORT)" macro?

[Jussi]

It seems like the same thing has been asked before, and the resolution to the "bug" last time was to make WebView widget honour the gtk-dnd-drag-threshold setting which can be set inside the widget's GtkSettings struct.

The old bug can be found from: https://bugs.webkit.org/show_bug.cgi?id=64459

At least I cannot get it working with following code:

Glib::RefPtr<Gtk::Settings> settings = webWidget->get_settings();
settings->property_gtk_dnd_drag_threshold() = 100000;

[Michael Catanzaro]

(In reply to Jussi from comment #0)
> This should create a custom Gtk::TargetEntry list which is allowed to copy
> data from the widget. However, after setting this drag_source_set(), the
> program aborts because an assert fails in the
> webkitWebViewBaseDragEnd(GtkWidget* widget, GdkDragContext* context)
> function inside WebKitWebViewBase.cpp
> (https://trac.webkit.org/browser/webkit/releases/WebKitGTK/webkit-2.25.1/
> Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp#L1281). Seems like
> calling "drag_source_set()" on a WebView nullifies some internal structure
> (WebKitWebViewBasePrivate->dragAndDropHandler).

Good bug report... I guess we didn't consider that applications could use these functions. Of course using GTK public APIs shouldn't cause WebKit to crash, so we'll need to reconsider these assertions.

(In reply to Jussi from comment #1)
> It seems like the same thing has been asked before, and the resolution to
> the "bug" last time was to make WebView widget honour the
> gtk-dnd-drag-threshold setting which can be set inside the widget's
> GtkSettings struct.
> 
> The old bug can be found from: https://bugs.webkit.org/show_bug.cgi?id=64459
> 
> At least I cannot get it working with following code:
> 
> Glib::RefPtr<Gtk::Settings> settings = webWidget->get_settings();
> settings->property_gtk_dnd_drag_threshold() = 100000;

Well that old patch was never committed. The bug is still open.

[Jussi]

(In reply to Michael Catanzaro from comment #2)
> (In reply to Jussi from comment #0)
> > This should create a custom Gtk::TargetEntry list which is allowed to copy
> > data from the widget. However, after setting this drag_source_set(), the
> > program aborts because an assert fails in the
> > webkitWebViewBaseDragEnd(GtkWidget* widget, GdkDragContext* context)
> > function inside WebKitWebViewBase.cpp
> > (https://trac.webkit.org/browser/webkit/releases/WebKitGTK/webkit-2.25.1/
> > Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp#L1281). Seems like
> > calling "drag_source_set()" on a WebView nullifies some internal structure
> > (WebKitWebViewBasePrivate->dragAndDropHandler).
> 
> Good bug report... I guess we didn't consider that applications could use
> these functions. Of course using GTK public APIs shouldn't cause WebKit to
> crash, so we'll need to reconsider these assertions.
> 

Thanks, I was wondering whether this is a bug at all.. :-) Well, meanwhile I've come around the problem by just running the javascript code "document.addEventListener(\"dragstart\", function(evt) { evt.preventDefault(); });" after a page has loaded inside a WebView. But I would like to have a "proper" solution for the dragging issue.

> (In reply to Jussi from comment #1)
> > It seems like the same thing has been asked before, and the resolution to
> > the "bug" last time was to make WebView widget honour the
> > gtk-dnd-drag-threshold setting which can be set inside the widget's
> > GtkSettings struct.
> > 
> > The old bug can be found from: https://bugs.webkit.org/show_bug.cgi?id=64459
> > 
> > At least I cannot get it working with following code:
> > 
> > Glib::RefPtr<Gtk::Settings> settings = webWidget->get_settings();
> > settings->property_gtk_dnd_drag_threshold() = 100000;
> 
> Well that old patch was never committed. The bug is still open.

Oh, my bad. It just came up when I was searching web for others having similar problems.