Windows drag-and-drop implementation

Drag-and-drop interfaces include

 

1. Register a window that supports drag-and-drop targets

Registerdragdrop (hwnd, idragtarget *);

Register the target window that supports drag and drop as a receiver and pass in the implemented idragtarget interface.

 

 

2. called when you need to start drag and drop

Dodragdrop (

Idataobject * pdataobject, // pointer to the Data Object

Idropsource * pdropsource, // pointer to the source

DWORD dwokeffect, // effects allowed by the source

DWORD * pdweffect // pointer to effects on the source

);

 

 

Dodragdrop enters the drag-and-drop loop, and calls the provided interfaces in turn.

 

A. the system calls idroptarget: dragenter when the drag and drop operation enters the target window.

Hresult dragenter (

Idataobject * pdataobject,

// Pointer to the interface of the source data

// Object

DWORD grfkeystate, // current state of keyboard modifier keys

Pointl PT, // current cursor coordinates

DWORD * pdweffect // pointer to the effect of the drag-and-drop

// Operation

);

 

This function provides the following dropeffectCode,

 

Dropeffect_none = 0,

Dropeffect_copy = 1,

Dropeffect_move = 2,

Dropeffect_link = 4,

Dropeffect_scroll = 0x80000000

Displays the current status of the drag.

 

 

Dodragdrop also calls idropsource: givefeedback to reflect the current display status.

Hresult givefeedback (

DWORD dweffect // effect of a drop operation, recently set status code

);

This function returns

E_invalidarg, e_unexpected, and e_outofmemory, dragdrop_s_usedefacurcursors or s_ OK

Show current icon

 

 

B. Call idroptarget: dragover when moving in the same window.

Hresult dragover (

DWORD grfkeystate, // current state of keyboard modifier keys

// Mk_control, mk_shift, mk_alt, mk_button, mk_lbutton, mk_mbutton, and mk_rbutton.

Pointl PT, // current cursor coordinates

DWORD * pdweffect // pointer to the effect of the drag-and-drop

// Operation

);

 

 

 

C. Call idroptarget: dragleave when leaving.

Hresult dragleave (void );

Return s_ OK.

 

 

 

If the status changes, idropsource: querycontinuedrag is called to determine the next action.

If s_ OK dodragdrop is returned, call idroptarget: dragover to continue the operation. Then call idropsource: givefeedback to reflect the icon.

If dragdrop_s_drop is returned, idroptarget: drop is called. This function returns a status code for source processing.

If dragdrop_s_cancel is returned, idroptarget: dragleave is called.