Added support of drag events to back button in dialogs list.

Telegram/SourceFiles/history/view/history_view_top_bar_widget.cpp

@@ -14,6 +14,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "info/info_memento.h"
 #include "info/info_controller.h"
 #include "info/profile/info_profile_values.h"
+#include "storage/storage_media_prepare.h"
 #include "storage/storage_shared_media.h"
 #include "mainwidget.h"
 #include "mainwindow.h"
@@ -782,6 +783,7 @@ void TopBarWidget::setActiveChat(
 	updateOnlineDisplay();
 	updateControlsVisibility();
 	refreshUnreadBadge();
+	setupDragOnBackButton();
 }
 
 void TopBarWidget::handleEmojiInteractionSeen(const QString &emoticon) {
@@ -1444,6 +1446,45 @@ void TopBarWidget::updateInfoToggleActive() {
 	_infoToggle->setRippleColorOverride(rippleOverride);
 }
 
+void TopBarWidget::setupDragOnBackButton() {
+	_backLifetime.destroy();
+	if (_activeChat.section != Section::ChatsList) {
+		_back->setAcceptDrops(false);
+		return;
+	}
+	const auto lifetime = _backLifetime.make_state<rpl::lifetime>();
+	_back->setAcceptDrops(true);
+	_back->events(
+	) | rpl::filter([=](not_null<QEvent*> e) {
+		return e->type() == QEvent::DragEnter;
+	}) | rpl::start_with_next([=](not_null<QEvent*> e) {
+		using namespace Storage;
+		const auto d = static_cast<QDragEnterEvent*>(e.get());
+		const auto data = d->mimeData();
+		if (ComputeMimeDataState(data) == MimeDataState::None) {
+			return;
+		}
+		const auto timer = _backLifetime.make_state<base::Timer>([=] {
+			backClicked();
+		});
+		timer->callOnce(ChoosePeerByDragTimeout);
+		d->setDropAction(Qt::CopyAction);
+		d->accept();
+		_back->events(
+		) | rpl::filter([=](not_null<QEvent*> e) {
+			return e->type() == QEvent::DragMove
+				|| e->type() == QEvent::DragLeave;
+		}) | rpl::start_with_next([=](not_null<QEvent*> e) {
+			if (e->type() == QEvent::DragMove) {
+				timer->callOnce(ChoosePeerByDragTimeout);
+			} else if (e->type() == QEvent::DragLeave) {
+				timer->cancel();
+				lifetime->destroy();
+			}
+		}, *lifetime);
+	}, _backLifetime);
+}
+
 bool TopBarWidget::trackOnlineOf(not_null<PeerData*> user) const {
 	const auto peer = _activeChat.key.peer();
 	if (!peer || _activeChat.key.topic() || !user->isUser()) {

Telegram/SourceFiles/history/view/history_view_top_bar_widget.h

@@ -134,6 +134,7 @@ private:
 	void updateControlsGeometry();
 	void slideAnimationCallback();
 	void updateInfoToggleActive();
+	void setupDragOnBackButton();
 
 	void call();
 	void groupCall();
@@ -252,6 +253,8 @@ private:
 	rpl::event_stream<> _clearSelection;
 	rpl::event_stream<> _cancelChooseForReport;
 
+	rpl::lifetime _backLifetime;
+
 };
 
 } // namespace HistoryView