Enhance howto-drag-and-drop example program.

Refer to discussion if fltk.general, thread "Drag and drop issue"
in August September 2017.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12432 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

1 files changed, 74 insertions, 10 deletions

diff --git a/examples/howto-drag-and-drop.cxx b/examples/howto-drag-and-drop.cxx
index 5b1c1f4f7..98829c39c 100644
--- a/examples/howto-drag-and-drop.cxx
+++ b/examples/howto-drag-and-drop.cxx
@@ -1,14 +1,17 @@
 //
 // "$Id$"
 //
-//     A simple demo of drag+drop with FLTK. 
-//     Originally from erco's cheat sheet, permission by author.
-//     Inspired by Michael Sephton's original example posted on fltk.general.
+// A simple demo of 'drag and drop' with FLTK.
+// Originally from erco's cheat sheet, permission by author.
+// Inspired by Michael Sephton's original example posted on fltk.general.
 //
-//     When you run the program, just drag the red square over
-//     to the green square to show a 'drag and drop' sequence.
+// When you run the program, just drag the red square over
+// to the green square to show a 'drag and drop' sequence.
 //
-// Copyright 1998-2010 by Bill Spitzak and others.
+// You can also drag and drop text from another application over
+// to the green square to show a 'drag and drop' sequence.
+//
+// Copyright 1998-2017 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -25,6 +28,7 @@
 #include <FL/Fl.H>
 #include <FL/Fl_Window.H>
 #include <FL/Fl_Box.H>
+#include <FL/fl_ask.H> // fl_message()
 
 // SIMPLE SENDER CLASS
 class Sender : public Fl_Box {
@@ -52,29 +56,89 @@ public:
 };
 // SIMPLE RECEIVER CLASS
 class Receiver : public Fl_Box {
+  int dnd_inside;
+  char *dnd_text;
 public:
   // Ctor
   Receiver(int x,int y,int w,int h) : Fl_Box(x,y,w,h) {
     box(FL_FLAT_BOX); color(10); label("..to\nhere");
+    dnd_inside = 0;
+    dnd_text = 0;
   }
   // Receiver event handler
   int handle(int event) {
     int ret = Fl_Box::handle(event);
+    int len;
     switch ( event ) {
-      case FL_DND_ENTER:          // return(1) for these events to 'accept' dnd
-      case FL_DND_DRAG:
-      case FL_DND_RELEASE:
+      case FL_DND_ENTER:	// return(1) for this event to 'accept' dnd
+	label("ENTER");		// visible only if you stop the mouse at the widget's border
+	fprintf(stderr, "FL_DND_ENTER\n");
+	dnd_inside = 1;		// status: inside the widget, accept drop
+	ret = 1;
+	break;
+      case FL_DND_DRAG:		// return(1) for this event to 'accept' dnd
+	label("drop\nhere");
+	fprintf(stderr, "FL_DND_DRAG\n");
 	ret = 1;
 	break;
+      case FL_DND_RELEASE:	// return(1) for this event to 'accept' the payload (drop)
+	fprintf(stderr, "FL_DND_RELEASE\n");
+	if (dnd_inside) {
+	  ret = 1;		// return(1) and expect FL_PASTE event to follow
+	  label("RELEASE");
+	} else {
+	  ret = 0;		// return(0) to reject the DND payload (drop)
+	  label("DND\nREJECTED!");
+	}
+	break;
       case FL_PASTE:              // handle actual drop (paste) operation
-	label(Fl::event_text());
+	fprintf(stderr, "FL_PASTE\n");
+	copy_label(Fl::event_text());
 	fprintf(stderr, "Pasted '%s'\n", Fl::event_text());
+
+	// Don't pop up dialog windows in FL_DND_* or FL_PASTE event handling
+	// resulting from DND operations. This may hang or even crash the
+	// application on *some* platforms. Use a short timer to delay the
+	// message display after the event processing is completed.
+
+	delete[] dnd_text;	// don't leak (just in case)
+	dnd_text = 0;
+
+	len = Fl::event_length();
+	if (len && Fl::event_text()) {
+	  dnd_text = new char[len + 1];
+	  memcpy(dnd_text, Fl::event_text(), len);
+	  dnd_text[len] = '\0';
+	  Fl::add_timeout(0.001, timer_cb, this); // delay message popup
+	}
 	ret = 1;
 	break;
+      case FL_DND_LEAVE:	// not strictly necessary to return(1) for this event
+	label("..to\nhere");	// reset label
+	fprintf(stderr, "FL_DND_LEAVE\n");
+	dnd_inside = 0;		// status: mouse is outside, don't accept drop
+	ret = 1;		// return(1) anyway..
+	break;
     }
     return(ret);
   }
+
+  // static timer callback
+  static void timer_cb(void *data) {
+    Receiver *r = (Receiver *)data;
+    r->dnd_cb();
+  }
+
+  // dnd (FL_PASTE) popup method
+  void dnd_cb() {
+    if (dnd_text) {
+      fl_message("%s", dnd_text);
+      delete[] dnd_text;
+      dnd_text = 0;
+    }
+  }
 };
+
 int main(int argc, char **argv) {
   // Create sender window and widget
   Fl_Window win_a(0,0,200,100,"Sender");