TvirtualStringTree之DragDrop

昨天在项目中需要做一个播放列表管理界面，播放列表中的结点本身要求可以拖动，并且要求播放列表能够支持从资源管理器上拖入FLV文件和播放列表文件。我继续使用了强大的TvirtualStringTree组件，但是在同时支持这两种拖动上犯了难，以前做的程序都是只支持其中一种拖动。

将TvirtualStringTree组件的dragMode属性设置为dmAutomatic，然后添加onDragOver事件，在事件处理函数中将Accept设置为true，然后运行，嗯很好，结点已经可以拖动了，而且拖动到结点的不同位置，光标处加亮形式是不一样的，也就是可以分别拖到结点正上方、和结点上面、和结点下面，做到这里我就知道结点是已经可以拖动的了。

然后开始处理文件的拖动，嗯，现成的有个TargetFileDrop组件，好的，拖到界面上去，目标设置为我使用的TvirtualStringTree组件，然后运行。砰……程序挂掉，弹出错误提示：“该窗口已经被注册为了拖放目标”。哇靠，不让我两个一起使用，我郁闷。然后仔细看看这个错误是OleException的一种，心里想我啥时候将TvirtualStringTree组件也注册为ole拖动对象了？看看TvirtualStringTree组件的属性，嗯，看见了属性TreeOptions.MiscOptions.toAcceptOleDrop默认是为true，原来是这个属性，想都不想直接改为false，然后运行。嗯，很好程序没挂。拖一个FLV到组件上面，等等，怎么拖动到指定结点，把鼠标移到任何地方都不加亮，这可真郁闷，因为我拖入文件要能够拖到指定的播放列表上去的。看来TargetFileDrop组件不合要求，pass。然后试一下拖动结点，唉？怎么也没加亮了？难道，难道是？对了，是TreeOptions.MiscOptions.toAcceptOleDrop属性的问题，还是改回true吧。嗯，可以有加亮了。

继续寻找拖入文件的方法，百度一下，嗯，有个方法是要将组件使用AcceptFileDrop函数注册成为能够接收文件拖放的组件?好方法，那来吧，照着说明添加上代码，然后运行，怎么发现怎么都执行不到消息处理代码里去，都直接执行到组件的OnDragDrop事件里了。唉，使用消息添加文件的方法，又失败……

继续看，嗯VB的Ole拖放？有么有delphi版本的？没有。没有怎么办，不管了，继续找。嗯，等等，ole拖放？怎么这么熟悉，向上看看toAcceptOleDrop属性，哇这个组件已经支持ole拖放了，看来还是去研究研究TvirtualStringTree的帮助文件吧。找到OnDragDrop事件的帮助文档，讲的不多，但是提到了

If you do not find CF_VIRTUALTREE then the operation has been initiated by another application, e.g. the Explorer (then you will find CF_HDROP or CF_SHELLIDLIST in formats) or Notepad (then you will get CF_TEXT and perhaps CF_UNICODETEXT) etc., depending on the data which is actually dropped.

嗯，看来是可以响应拖入文件的，而且帮助文件里还给了一个示范的代码（郁闷的是这个示范代码只处理 CF_VIRTUALTREE，其它的都没有），那照着搬一下。

procedure TTFrmPlayListMgr.vstPlayListMgrDragDrop(Sender: TBaseVirtualTree;
Source: TObject; DataObject: IDataObject; Formats: TFormatArray;
Shift: TShiftState; Pt: TPoint; var Effect: Integer; Mode: TDropMode);
var
I, J: Integer;
AttachMode: TVTNodeAttachMode;
Medium: TStgMedium;
Data: Pointer;
fomat: tagFORMATETC ;

DropHandle: HDROP;
path: string;
nFileCount: Integer;
nBufferLen: Integer;
lpszFile: LPSTR;
nCount : Cardinal;
begin
if Length(Formats) > 0 then
begin
// OLE drag'n drop
// If the native tree format is listed then use this and accept the drop, otherwise recject (ignore) it.
// It is recommend by Microsoft to order available clipboard formats in decreasing detail richness so
// the first best format which we can accept is usually the best format we can get at all.
for I := 0 to High(Formats) do
begin
if Formats[I] = CF_VIRTUALTREE then
begin
case Mode of
dmAbove:
AttachMode := amInsertBefore;
dmOnNode:
AttachMode := amAddChildLast;
dmBelow:
AttachMode := amInsertAfter;
else
if Assigned(Source) and (Source is TBaseVirtualTree) and (Sender <> Source) then
AttachMode := amInsertBefore
else
AttachMode := amNowhere;
end;
// in the case the drop target does an optimized move Effect is set to DROPEFFECT_NONE
// to indicate this also to the drag source (so the source doesn't need to take any further action)
Sender.ProcessDrop(DataObject, Sender.DropTargetNode, Effect, AttachMode);
Break;
end;
if Formats[i] = CF_HDROP then
begin
showMessage('CF_HDROP ');
end;
end
else
begin
// VCL drag'n drop, Effects contains by default both move and copy effect suggestion,
// as usual the application has to find out what operation is finally to do
Beep;
end;
end;

运行然后拖入文件，嗯有提示了，证明是能够执行到ShowMessage的地方，但是从哪里去找拖入的文件名呢？看参数说明，是可以从DataObject里找到数据，但是鬼知道怎么获取数据啊，百度没有，google没有，唉，看TDropFIletarget自己的源码是怎么处理DataOjbect的，从上面的代码看到DataObject参数传给方法ProcessDrop再传到GetTreeFromDataObject，然后，嗯，有处理代码了。

function TBaseVirtualTree.GetTreeFromDataObject(const DataObject: IDataObject): TBaseVirtualTree;

// Returns the owner/sender of the given data object by means of a special clipboard format
// or nil if the sender is in another process or no virtual tree at all.

var
Medium: TStgMedium;
Data: PVTReference;

begin
Result := nil;
if Assigned(DataObject) then
begin
StandardOLEFormat.cfFormat := CF_VTREFERENCE;
if DataObject.GetData(StandardOLEFormat, Medium) = S_OK then
begin
Data := GlobalLock(Medium.hGlobal);
if Assigned(Data) then
begin
if Data.Process = GetCurrentProcessID then
Result := Data.Tree;
GlobalUnlock(Medium.hGlobal);
end;
ReleaseStgMedium(Medium);
end;
end;
end;

嗯，照着做吧，但问题只有一个对应着cfFormat = CF_HDROP的数据是什么格式？对GlobaLock返回的指针我怎么处理。结果没有一个地方有说明，MSDN、delphi的Windows SDK帮助文档上对CF_HDROP都没有说明，使用百度对CF_HDROP进行搜索，发现只有对剪切板的一些操作的示范代码，再回去研究下OleDrop的原理，正是将数据存到剪切板中。那么，把对剪切板的操作的代码移植到程序中，好了，一个成功的OnDragDrop事件处理函数出来了。

procedure TTFrmPlayListMgr.vstPlayListMgrDragDrop(Sender: TBaseVirtualTree;
Source: TObject; DataObject: IDataObject; Formats: TFormatArray;
Shift: TShiftState; Pt: TPoint; var Effect: Integer; Mode: TDropMode);
var
I, J: Integer;
AttachMode: TVTNodeAttachMode;
Medium: TStgMedium;
Data: Pointer;
fomat: tagFORMATETC ;

DropHandle: HDROP;
path: string;
nFileCount: Integer;
nBufferLen: Integer;
lpszFile: LPSTR;
nCount : Cardinal;
begin
if Length(Formats) > 0 then
begin
// OLE drag'n drop
// If the native tree format is listed then use this and accept the drop, otherwise recject (ignore) it.
// It is recommend by Microsoft to order available clipboard formats in decreasing detail richness so
// the first best format which we can accept is usually the best format we can get at all.
for I := 0 to High(Formats) do
begin
if Formats[I] = CF_VIRTUALTREE then
begin
case Mode of
dmAbove:
AttachMode := amInsertBefore;
dmOnNode:
AttachMode := amAddChildLast;
dmBelow:
AttachMode := amInsertAfter;
else
if Assigned(Source) and (Source is TBaseVirtualTree) and (Sender <> Source) then
AttachMode := amInsertBefore
else
AttachMode := amNowhere;
end;
// in the case the drop target does an optimized move Effect is set to DROPEFFECT_NONE
// to indicate this also to the drag source (so the source doesn't need to take any further action)
Sender.ProcessDrop(DataObject, Sender.DropTargetNode, Effect, AttachMode);
Break;
end;
if Formats[i] = CF_HDROP then
begin
if Assigned(DataObject) then
begin

// Format must later be set.
fomat.cfFormat:= CF_HDROP;
// No specific target device to render on.
fomat.ptd:= nil;
// Normal content to render.
fomat.dwAspect:= DVASPECT_CONTENT;
// No specific page of multipage data (we don't use multipage data by default).
fomat.lindex:= -1;
// Acceptable storage formats are IStream and global memory. The first is preferred.
fomat.tymed:= TYMED_ISTREAM or TYMED_HGLOBAL;

//fomat.cfFormat := CF_HDROP;
if DataObject.GetData(fomat, Medium) = S_OK then
begin
Data := GlobalLock(Medium.hGlobal);
if Assigned(Data) then
begin
DropHandle := Integer(Data);
nFileCount := DragQueryFile(DropHandle, Cardinal(-1),nil,0);
for J := 0 to nFileCount - 1 do
begin
nBufferLen := DragQueryFile(DropHandle,j,nil,0);
// lpszFile := LPSTR(GlobalAlloc(GPTR,nBufferLen+1));
// nCount := DragQueryFile(DropHandle,i,lpszFile,nBufferLen+1);
lpszFile := LPSTR(GlobalAlloc(GPTR,255));
nCount := DragQueryFile(DropHandle,j,lpszFile,255);
//FIXme operation   about   lpszFile
path := lpszFile;
ShowMessage(path);
GlobalFree(Cardinal(lpszFile));
end;

GlobalUnlock(Medium.hGlobal);
end;
ReleaseStgMedium(Medium);
end;
end;
end;
end;
end
else
begin
// VCL drag'n drop, Effects contains by default both move and copy effect suggestion,
// as usual the application has to find out what operation is finally to do
Beep;
end;
end;

然后运行，拖入一个文件，OK，文件全路径弹出来了。搞定了这一步，下面的就是一个程序逻辑问题了，嘿嘿。