Minor changes in drag_and_drop example

The most important change here is clearing the data from the
windowData about types that weren't dropped in the last action, to
avoid mixing dropped data from previous actions and only show the last
dropped data.

examples/drag_and_drop.cpp

@@ -65,12 +65,20 @@ class DragTarget : public os::DragTarget {
     if (ev.acceptDrop()) {
       if (ev.dataProvider()->contains(os::DragDataItemType::Paths))
         windowData.paths = ev.dataProvider()->getPaths();
+      else
+        windowData.paths.clear();
+
 #if CLIP_ENABLE_IMAGE
       if (ev.dataProvider()->contains(os::DragDataItemType::Image))
         windowData.image = ev.dataProvider()->getImage();
+      else
+        windowData.image.reset();
 #endif
+
       if (ev.dataProvider()->contains(os::DragDataItemType::Url))
         windowData.url = ev.dataProvider()->getUrl();
+      else
+        windowData.url.clear();
     }
 
     redraw_window(ev.target());
@@ -167,7 +175,7 @@ static os::WindowRef create_window(os::DragTarget& dragTarget)
 
   os::WindowRef newWindow = os::instance()->makeWindow(spec);
   newWindow->setCursor(os::NativeCursor::Arrow);
-  newWindow->setTitle("Drag & Drop example");
+  newWindow->setTitle("Drag & Drop");
   newWindow->setDragTarget(&dragTarget);
 
   windowData.dropZone = gfx::Rect(spec.frame().w-64-12, 12, 64, 64);
@@ -196,6 +204,14 @@ int app_main(int argc, char* argv[])
 
     switch (ev.type()) {
 
+      case os::Event::KeyDown:
+        switch (ev.scancode()) {
+          case os::kKeyEsc:
+            running = false;
+            break;
+        }
+        break;
+
       case os::Event::CloseApp:
       case os::Event::CloseWindow:
         running = false;