When enabled allow the use of callbacks for controlling the drag and drop handling.
The user starts a drag and drop transfer by pressing the mouse button over the data (Windows and GTK: left button; Motif: middle button) which is referred to as the drag source. The data can be dropped in any location that has been registered as a drop target. The drop occurs when the user releases the mouse button. This can be done inside a control, from one control to another in the same dialog, in different dialogs of the same application, or between different applications (the other application does NOT need to be implemented with IUP).
In IUP, a drag and drop transfer can result in the data being moved or copied. A copy operation is enabled with the CTRL key pressed. A move operation is enabled with the SHIFT key pressed. A move operation will be possible only if the attribute DRAGSOURCEMOVE is Yes. When no key is pressed the default operation is copy when DRAGSOURCEMOVE=No and move when DRAGSOURCEMOVE=Yes. The user can cancel a drag at any time by pressing the ESCAPE key.
Steps to use the Drag & Drop support in an IUP application:
IupLabel, IupText, IupList, IupTree, IupCanvas and IupDialog.
DRAGCURSOR (non inheritable): name of an image to be used as cursor during drag. Use IupSetHandle or IupSetAttributeHandle to associate an image to a name. See also IupImage. (since 3.11)
DRAGSOURCE (non inheritable): Set up a control as a source for drag operations. Default: NO.
DRAGTYPES (non inheritable): A list of data types that are supported by the source. Accepts a string with one or more names separated by commas. See Notes bellow for a list of known names. Must be set.
DRAGSOURCEMOVE (non inheritable): Enables the move action. Default: NO (only copy is enabled).
DROPTARGET (non inheritable): Set up a control as a destination for drop operations. Default: NO.
DROPTYPES (non inheritable): A list of data types that are supported by the target. Accepts a string with one or more names separated by commas. See Notes bellow for a list of known names. Must be set.
DRAGBEGIN_CB: notifies source that drag started. It is called when the mouse starts a drag operation.
int function(Ihandle* ih, int x, int y) [in C]
elem:dragbegin_cb(x, y: number) -> (ret: number) [in Lua]
ih:
identifier of the element that activated the
event.
x, y: cursor position relative to the top-left
corner of the element.
Returns: If IUP_IGNORE is returned the drag is aborted.
DRAGDATASIZE_CB: request for size of drag data from source. It is called when the data is dropped, before the DRAGDATA_CB callback.
int function(Ihandle* ih, char* type) [in C]
elem:dragdatasize_cb(type: string) -> (ret: number) [in Lua]
ih:
identifier of the element that activated the
event.
type: type of the data. It is one of the registered
types in DRAGTYPES.
Returns: the size in bytes for the data. It will be used to allocate the buffer size for the data in transfer.
DRAGDATA_CB: request for drag data from source. It is called when the data is dropped.
int function(Ihandle* ih, char* type, void* data, int size) [in C]
elem:dragdata_cb(type: string, data: userdata size: number) -> (ret: number) [in Lua]
ih:
identifier of the element that activated the
event.
type: type of the data. It is one of the registered
types in DRAGTYPES.
data:
buffer to be filled by the application. In Lua is a light userdata. If your data
is a string you can use iup.CopyString2UserData(str, data,
size) to copy the string into the user data (since 3.27).
size: buffer size in
bytes.
The same value returned by DRAGDATASIZE_CB.
DRAGEND_CB: notifies source that drag is done. The only drag callback that is optional. It is called after the data has been dropped.
int function(Ihandle* ih, int action) [in C]
elem:dragend_cb(action: number) -> (ret: number) [in Lua]
ih:
identifier of the element that activated the
event.
action: action performed by the operation (1 = move,
0 = copy, -1 = drag failed or aborted)
If action is 1 it is responsibility of the application to remove the data from source.
DROPDATA_CB: source has sent target the requested data. It is called when the data is dropped. If both drag and drop would be in the same application it would be called after the DRAGDATA_CB callback.
int function(Ihandle* ih, char* type, void* data, int size, int x, int y) [in C]
elem:dropdata_cb(type: string, data: userdata, size, x, y: number) -> (ret: number) [in Lua]
ih:
identifier of the element that activated the
event.
type: type of the data. It is one of the registered
types in DROPTYPES.
data: content data received in the drop operation. In Lua
is a light userdata. If your data is a string you can use "str = iup.CopyUserData2String(data,
size)" to copy the user data into a string (since 3.27).
size: data size in bytes.
x, y: cursor position relative to the top-left
corner of the element.
DROPMOTION_CB: notifies destination about drag pointer motion. The only drop callback that is optional. It is called when the mouse moves over any valid drop site.
int function(Ihandle *ih, int x, int y, char *status); [in C] elem:dropmotion_cb(x, y: number, status: string) -> (ret: number) [in Lua]
ih: identifier of the element that activated
the event.
x, y: position in the canvas
where the event has occurred, in pixels.
status: status of
mouse buttons and certain keyboard keys at the moment the event was generated.
The same macros used for BUTTON_CB can
be used for this status.
Drag and Drop support can be set independently. A control can have drop without drag support and vice-versa.
Here are some common Drag&Drop types defined by existing applications: