Xdnd drop 支持错误的实现
Xdnd drop support faulty implementation
我前段时间在VTK中实现了Xdnd drop支持实现。除了 Thunar 文件管理器外，它工作得很好。当时所有其他文件管理器都运行良好。我们当时通过 Thunar 错误消除了此限制。
我实现的功能很简单：
- 将应用程序的 window 设置为 XdndAware
- 收到位置消息并回复我们准备好接收
- 收到投递消息并请求选择
- 收到选择通知并恢复URI
- 将 URI 转换为我们可以使用的内容
没什么特别的，我什至没有接触列表类型。
快进几年，现在海豚用户无法将文件正确地放入我们的应用程序中。 URI 始终是 dolphin 启动后删除的第一个文件。重新启动我们的应用程序没有任何效果。 pcmanfm 完全没有错误。
这不是 dolphin 错误，文件可以从 dolphin 毫无问题地放到 blender 或 firefox 上。
所以我们的实现中肯定有一个错误，但我已经盯着代码看了一段时间，我尝试的一切都没有效果，除了完全破坏 Xdnd 支持。
以下是实施中有趣的部分：
//------------------------------------------------------------------------------
vtkXRenderWindowInteractor::vtkXRenderWindowInteractor()
{
this->Internal = new vtkXRenderWindowInteractorInternals;
this->DisplayId = nullptr;
this->WindowId = 0;
this->KillAtom = 0;
this->XdndSource = 0;
this->XdndPositionAtom = 0;
this->XdndDropAtom = 0;
this->XdndActionCopyAtom = 0;
this->XdndStatusAtom = 0;
this->XdndFinishedAtom = 0;
}
[...]
//------------------------------------------------------------------------------
void vtkXRenderWindowInteractor::Enable()
{
// avoid cycles of calling Initialize() and Enable()
if (this->Enabled)
{
return;
}
// Add the event handler to the system.
// If we change the types of events processed by this handler, then
// we need to change the Disable() routine to match. In order for Disable()
// to work properly, both the callback function AND the client data
// passed to XtAddEventHandler and XtRemoveEventHandler must MATCH
// PERFECTLY
XSelectInput(this->DisplayId, this->WindowId,
KeyPressMask | KeyReleaseMask | ButtonPressMask | ButtonReleaseMask | ExposureMask |
StructureNotifyMask | EnterWindowMask | LeaveWindowMask | PointerMotionHintMask |
PointerMotionMask);
// Setup for capturing the window deletion
this->KillAtom = XInternAtom(this->DisplayId, "WM_DELETE_WINDOW", False);
XSetWMProtocols(this->DisplayId, this->WindowId, &this->KillAtom, 1);
// Enable drag and drop
Atom xdndAwareAtom = XInternAtom(this->DisplayId, "XdndAware", False);
char xdndVersion = 5;
XChangeProperty(this->DisplayId, this->WindowId, xdndAwareAtom, XA_ATOM, 32, PropModeReplace,
(unsigned char*)&xdndVersion, 1);
this->XdndPositionAtom = XInternAtom(this->DisplayId, "XdndPosition", False);
this->XdndDropAtom = XInternAtom(this->DisplayId, "XdndDrop", False);
this->XdndActionCopyAtom = XInternAtom(this->DisplayId, "XdndActionCopy", False);
this->XdndStatusAtom = XInternAtom(this->DisplayId, "XdndStatus", False);
this->XdndFinishedAtom = XInternAtom(this->DisplayId, "XdndFinished", False);
this->Enabled = 1;
this->Modified();
}
[...]
//------------------------------------------------------------------------------
void vtkXRenderWindowInteractor::DispatchEvent(XEvent* event)
{
int xp, yp;
switch (event->type)
{
[...]
// Selection request for drag and drop has been delivered
case SelectionNotify:
{
// Sanity checks
if (!event->xselection.property || !this->XdndSource)
{
return;
}
// Recover the dropped file
char* data = nullptr;
Atom actualType;
int actualFormat;
unsigned long itemCount, bytesAfter;
XGetWindowProperty(this->DisplayId, event->xselection.requestor, event->xselection.property,
0, LONG_MAX, False, event->xselection.target, &actualType, &actualFormat, &itemCount,
&bytesAfter, (unsigned char**)&data);
// Conversion checks
if ((event->xselection.target != AnyPropertyType && actualType != event->xselection.target) ||
itemCount == 0)
{
return;
}
// Recover filepaths from uris and invoke DropFilesEvent
std::stringstream uris(data);
std::string uri, protocol, hostname, filePath;
std::string unused0, unused1, unused2, unused3;
vtkNew<vtkStringArray> filePaths;
while (std::getline(uris, uri, '\n'))
{
if (vtksys::SystemTools::ParseURL(
uri, protocol, unused0, unused1, hostname, unused3, filePath, true))
{
if (protocol == "file" && (hostname.empty() || hostname == "localhost"))
{
// The uris can be crlf delimited, remove ending \r if any
if (filePath.back() == '\r')
{
filePath.pop_back();
}
// The extracted filepath miss the first slash
filePath.insert(0, "/");
filePaths->InsertNextValue(filePath);
}
}
}
this->InvokeEvent(vtkCommand::DropFilesEvent, filePaths);
XFree(data);
// Inform the source the the drag and drop operation was sucessfull
XEvent reply;
memset(&reply, 0, sizeof(reply));
reply.type = ClientMessage;
reply.xclient.window = event->xclient.data.l[0];
reply.xclient.message_type = this->XdndFinishedAtom;
reply.xclient.format = 32;
reply.xclient.data.l[0] = this->WindowId;
reply.xclient.data.l[1] = itemCount;
reply.xclient.data.l[2] = this->XdndActionCopyAtom;
XSendEvent(this->DisplayId, this->XdndSource, False, NoEventMask, &reply);
XFlush(this->DisplayId);
this->XdndSource = 0;
}
break;
case ClientMessage:
{
if (event->xclient.message_type == this->XdndPositionAtom)
{
// Drag and drop event inside the window
// Recover the position
int xWindow, yWindow;
int xRoot = event->xclient.data.l[2] >> 16;
int yRoot = event->xclient.data.l[2] & 0xffff;
Window root = DefaultRootWindow(this->DisplayId);
Window child;
XTranslateCoordinates(
this->DisplayId, root, this->WindowId, xRoot, yRoot, &xWindow, &yWindow, &child);
// Convert it to VTK compatible location
double location[2];
location[0] = static_cast<double>(xWindow);
location[1] = static_cast<double>(this->Size[1] - yWindow - 1);
this->InvokeEvent(vtkCommand::UpdateDropLocationEvent, location);
// Reply that we are ready to copy the dragged data
XEvent reply;
memset(&reply, 0, sizeof(reply));
reply.type = ClientMessage;
reply.xclient.window = event->xclient.data.l[0];
reply.xclient.message_type = this->XdndStatusAtom;
reply.xclient.format = 32;
reply.xclient.data.l[0] = this->WindowId;
reply.xclient.data.l[1] = 1; // Always accept the dnd with no rectangle
reply.xclient.data.l[2] = 0; // Specify an empty rectangle
reply.xclient.data.l[3] = 0;
reply.xclient.data.l[4] = this->XdndActionCopyAtom;
XSendEvent(this->DisplayId, event->xclient.data.l[0], False, NoEventMask, &reply);
XFlush(this->DisplayId);
}
else if (event->xclient.message_type == this->XdndDropAtom)
{
// Item dropped in the window
// Store the source of the drag and drop
this->XdndSource = event->xclient.data.l[0];
// Ask for a conversion of the selection. This will trigger a SelectioNotify event later.
Atom xdndSelectionAtom = XInternAtom(this->DisplayId, "XdndSelection", False);
XConvertSelection(this->DisplayId, xdndSelectionAtom,
XInternAtom(this->DisplayId, "UTF8_STRING", False), xdndSelectionAtom, this->WindowId,
CurrentTime);
}
else if (static_cast<Atom>(event->xclient.data.l[0]) == this->KillAtom)
{
this->ExitCallback();
}
}
break;
}
}
[...]
和header：
#include "vtkRenderWindowInteractor.h"
#include "vtkRenderingUIModule.h" // For export macro
#include <X11/Xlib.h> // Needed for X types in the public interface
class vtkCallbackCommand;
class vtkXRenderWindowInteractorInternals;
class VTKRENDERINGUI_EXPORT vtkXRenderWindowInteractor : public vtkRenderWindowInteractor
{
public:
static vtkXRenderWindowInteractor* New();
vtkTypeMacro(vtkXRenderWindowInteractor, vtkRenderWindowInteractor);
void PrintSelf(ostream& os, vtkIndent indent) override;
/**
* Initializes the event handlers without an XtAppContext. This is
* good for when you don't have a user interface, but you still
* want to have mouse interaction.
*/
void Initialize() override;
/**
* Break the event loop on 'q','e' keypress. Want more ???
*/
void TerminateApp() override;
/**
* Run the event loop and return. This is provided so that you can
* implement your own event loop but yet use the vtk event handling as
* well.
*/
void ProcessEvents() override;
///@{
/**
* Enable/Disable interactions. By default interactors are enabled when
* initialized. Initialize() must be called prior to enabling/disabling
* interaction. These methods are used when a window/widget is being
* shared by multiple renderers and interactors. This allows a "modal"
* display where one interactor is active when its data is to be displayed
* and all other interactors associated with the widget are disabled
* when their data is not displayed.
*/
void Enable() override;
void Disable() override;
///@}
/**
* Update the Size data member and set the associated RenderWindow's
* size.
*/
void UpdateSize(int, int) override;
/**
* Re-defines virtual function to get mouse position by querying X-server.
*/
void GetMousePosition(int* x, int* y) override;
void DispatchEvent(XEvent*);
protected:
vtkXRenderWindowInteractor();
~vtkXRenderWindowInteractor() override;
/**
* Update the Size data member and set the associated RenderWindow's
* size but do not resize the XWindow.
*/
void UpdateSizeNoXResize(int, int);
// Using static here to avoid destroying context when many apps are open:
static int NumAppInitialized;
Display* DisplayId;
Window WindowId;
Atom KillAtom;
int PositionBeforeStereo[2];
vtkXRenderWindowInteractorInternals* Internal;
// Drag and drop related
Window XdndSource;
Atom XdndPositionAtom;
Atom XdndDropAtom;
Atom XdndActionCopyAtom;
Atom XdndStatusAtom;
Atom XdndFinishedAtom;
///@{
/**
* X-specific internal timer methods. See the superclass for detailed
* documentation.
*/
int InternalCreateTimer(int timerId, int timerType, unsigned long duration) override;
int InternalDestroyTimer(int platformTimerId) override;
///@}
void FireTimers();
/**
* This will start up the X event loop and never return. If you
* call this method it will loop processing X events until the
* application is exited.
*/
void StartEventLoop() override;
private:
vtkXRenderWindowInteractor(const vtkXRenderWindowInteractor&) = delete;
void operator=(const vtkXRenderWindowInteractor&) = delete;
};
#endif
完整的文件可以在这里看到：
https://gitlab.kitware.com/vtk/vtk/-/blob/master/Rendering/UI/vtkXRenderWindowInteractor.cxx
你可以按照我的思路和调试在这里：
https://gitlab.kitware.com/f3d/f3d/-/issues/228
要测试这段代码，一个简单的方法是使用 F3D，它正在使用拖放的文件，但一个简单的 VTK 应用程序也应该可以工作：
https://gitlab.kitware.com/f3d/f3d
当前的 Dolphin 问题
根据一些测试，问题出在处理 SelectionNotify 事件时准备和发送 XdndFinished ClientMessage 回拖放源。
而不是：
reply.xclient.window = event->xclient.data.l[0];
该行应该是：
reply.xclient.window = this->XdndSource;
这会将 XClientMessageEvent window 成员与 XSendEvent 的目标 window 参数对齐。这可能是一个简单的复制粘贴错误，因为 xclient 对 SelectionNotify 事件类型无效。 window 的实际值很可能之前没有被检查过，但最近已更改，因此出现错误。
spec 很好地涵盖了这一点，还提出了一些其他需要考虑的事项：
- 对于
data.l[1]：“如果当前目标接受放置并成功执行接受的放置操作，则设置位 0。（版本 5 中的新功能）”，因此使用 itemCount 作为值只要计数是偶数 ，技术上就会不正确
- 如果
XdndPosition 的处理不需要实际跟踪当前位置的位置（即，如果您只是将整个 window 用作放置目标），您可能能够发送 XdndStatus 以响应 XdndEnter 消息
上一个 Thunar 问题
进一步调查，我对 Thunar 的前一个问题进行了一些故障排除，归结为代码处理 XdndDrop 假设传入数据的格式可以转换为 UTF8_STRING. GLFW 的 diff 处理几乎完全相同的问题。
如果在处理 XdndEnter 消息时，通过 xclient.data.l[4] 检查 xclient.data.l[2] 的值，您可以看到 Dolphin 报告支持以下格式：
text/uri-listtext/x-moz-urltext/plain
而 Thunar 仅支持以下内容：
text/uri-list
最简单的解决方案是：
- 处理时跟踪支持的格式
XdndEnter
- 在处理
XdndDrop 时将此格式提供给 XConvertSelection（而不是 UTF8_STRING）
- 在处理
SelectionNotify 事件时适当处理格式
为了更完整，如果在XdndEnter消息上设置了xclient.data.l[1]的位0，您应该得到拖放源的XdndTypeList 属性 window 并以此为基础选择格式，而不是邮件本身包含的格式。
我前段时间在VTK中实现了Xdnd drop支持实现。除了 Thunar 文件管理器外，它工作得很好。当时所有其他文件管理器都运行良好。我们当时通过 Thunar 错误消除了此限制。
我实现的功能很简单：
- 将应用程序的 window 设置为 XdndAware
- 收到位置消息并回复我们准备好接收
- 收到投递消息并请求选择
- 收到选择通知并恢复URI
- 将 URI 转换为我们可以使用的内容
没什么特别的，我什至没有接触列表类型。
快进几年，现在海豚用户无法将文件正确地放入我们的应用程序中。 URI 始终是 dolphin 启动后删除的第一个文件。重新启动我们的应用程序没有任何效果。 pcmanfm 完全没有错误。
这不是 dolphin 错误，文件可以从 dolphin 毫无问题地放到 blender 或 firefox 上。
所以我们的实现中肯定有一个错误，但我已经盯着代码看了一段时间，我尝试的一切都没有效果，除了完全破坏 Xdnd 支持。
以下是实施中有趣的部分：
//------------------------------------------------------------------------------
vtkXRenderWindowInteractor::vtkXRenderWindowInteractor()
{
this->Internal = new vtkXRenderWindowInteractorInternals;
this->DisplayId = nullptr;
this->WindowId = 0;
this->KillAtom = 0;
this->XdndSource = 0;
this->XdndPositionAtom = 0;
this->XdndDropAtom = 0;
this->XdndActionCopyAtom = 0;
this->XdndStatusAtom = 0;
this->XdndFinishedAtom = 0;
}
[...]
//------------------------------------------------------------------------------
void vtkXRenderWindowInteractor::Enable()
{
// avoid cycles of calling Initialize() and Enable()
if (this->Enabled)
{
return;
}
// Add the event handler to the system.
// If we change the types of events processed by this handler, then
// we need to change the Disable() routine to match. In order for Disable()
// to work properly, both the callback function AND the client data
// passed to XtAddEventHandler and XtRemoveEventHandler must MATCH
// PERFECTLY
XSelectInput(this->DisplayId, this->WindowId,
KeyPressMask | KeyReleaseMask | ButtonPressMask | ButtonReleaseMask | ExposureMask |
StructureNotifyMask | EnterWindowMask | LeaveWindowMask | PointerMotionHintMask |
PointerMotionMask);
// Setup for capturing the window deletion
this->KillAtom = XInternAtom(this->DisplayId, "WM_DELETE_WINDOW", False);
XSetWMProtocols(this->DisplayId, this->WindowId, &this->KillAtom, 1);
// Enable drag and drop
Atom xdndAwareAtom = XInternAtom(this->DisplayId, "XdndAware", False);
char xdndVersion = 5;
XChangeProperty(this->DisplayId, this->WindowId, xdndAwareAtom, XA_ATOM, 32, PropModeReplace,
(unsigned char*)&xdndVersion, 1);
this->XdndPositionAtom = XInternAtom(this->DisplayId, "XdndPosition", False);
this->XdndDropAtom = XInternAtom(this->DisplayId, "XdndDrop", False);
this->XdndActionCopyAtom = XInternAtom(this->DisplayId, "XdndActionCopy", False);
this->XdndStatusAtom = XInternAtom(this->DisplayId, "XdndStatus", False);
this->XdndFinishedAtom = XInternAtom(this->DisplayId, "XdndFinished", False);
this->Enabled = 1;
this->Modified();
}
[...]
//------------------------------------------------------------------------------
void vtkXRenderWindowInteractor::DispatchEvent(XEvent* event)
{
int xp, yp;
switch (event->type)
{
[...]
// Selection request for drag and drop has been delivered
case SelectionNotify:
{
// Sanity checks
if (!event->xselection.property || !this->XdndSource)
{
return;
}
// Recover the dropped file
char* data = nullptr;
Atom actualType;
int actualFormat;
unsigned long itemCount, bytesAfter;
XGetWindowProperty(this->DisplayId, event->xselection.requestor, event->xselection.property,
0, LONG_MAX, False, event->xselection.target, &actualType, &actualFormat, &itemCount,
&bytesAfter, (unsigned char**)&data);
// Conversion checks
if ((event->xselection.target != AnyPropertyType && actualType != event->xselection.target) ||
itemCount == 0)
{
return;
}
// Recover filepaths from uris and invoke DropFilesEvent
std::stringstream uris(data);
std::string uri, protocol, hostname, filePath;
std::string unused0, unused1, unused2, unused3;
vtkNew<vtkStringArray> filePaths;
while (std::getline(uris, uri, '\n'))
{
if (vtksys::SystemTools::ParseURL(
uri, protocol, unused0, unused1, hostname, unused3, filePath, true))
{
if (protocol == "file" && (hostname.empty() || hostname == "localhost"))
{
// The uris can be crlf delimited, remove ending \r if any
if (filePath.back() == '\r')
{
filePath.pop_back();
}
// The extracted filepath miss the first slash
filePath.insert(0, "/");
filePaths->InsertNextValue(filePath);
}
}
}
this->InvokeEvent(vtkCommand::DropFilesEvent, filePaths);
XFree(data);
// Inform the source the the drag and drop operation was sucessfull
XEvent reply;
memset(&reply, 0, sizeof(reply));
reply.type = ClientMessage;
reply.xclient.window = event->xclient.data.l[0];
reply.xclient.message_type = this->XdndFinishedAtom;
reply.xclient.format = 32;
reply.xclient.data.l[0] = this->WindowId;
reply.xclient.data.l[1] = itemCount;
reply.xclient.data.l[2] = this->XdndActionCopyAtom;
XSendEvent(this->DisplayId, this->XdndSource, False, NoEventMask, &reply);
XFlush(this->DisplayId);
this->XdndSource = 0;
}
break;
case ClientMessage:
{
if (event->xclient.message_type == this->XdndPositionAtom)
{
// Drag and drop event inside the window
// Recover the position
int xWindow, yWindow;
int xRoot = event->xclient.data.l[2] >> 16;
int yRoot = event->xclient.data.l[2] & 0xffff;
Window root = DefaultRootWindow(this->DisplayId);
Window child;
XTranslateCoordinates(
this->DisplayId, root, this->WindowId, xRoot, yRoot, &xWindow, &yWindow, &child);
// Convert it to VTK compatible location
double location[2];
location[0] = static_cast<double>(xWindow);
location[1] = static_cast<double>(this->Size[1] - yWindow - 1);
this->InvokeEvent(vtkCommand::UpdateDropLocationEvent, location);
// Reply that we are ready to copy the dragged data
XEvent reply;
memset(&reply, 0, sizeof(reply));
reply.type = ClientMessage;
reply.xclient.window = event->xclient.data.l[0];
reply.xclient.message_type = this->XdndStatusAtom;
reply.xclient.format = 32;
reply.xclient.data.l[0] = this->WindowId;
reply.xclient.data.l[1] = 1; // Always accept the dnd with no rectangle
reply.xclient.data.l[2] = 0; // Specify an empty rectangle
reply.xclient.data.l[3] = 0;
reply.xclient.data.l[4] = this->XdndActionCopyAtom;
XSendEvent(this->DisplayId, event->xclient.data.l[0], False, NoEventMask, &reply);
XFlush(this->DisplayId);
}
else if (event->xclient.message_type == this->XdndDropAtom)
{
// Item dropped in the window
// Store the source of the drag and drop
this->XdndSource = event->xclient.data.l[0];
// Ask for a conversion of the selection. This will trigger a SelectioNotify event later.
Atom xdndSelectionAtom = XInternAtom(this->DisplayId, "XdndSelection", False);
XConvertSelection(this->DisplayId, xdndSelectionAtom,
XInternAtom(this->DisplayId, "UTF8_STRING", False), xdndSelectionAtom, this->WindowId,
CurrentTime);
}
else if (static_cast<Atom>(event->xclient.data.l[0]) == this->KillAtom)
{
this->ExitCallback();
}
}
break;
}
}
[...]
和header：
#include "vtkRenderWindowInteractor.h"
#include "vtkRenderingUIModule.h" // For export macro
#include <X11/Xlib.h> // Needed for X types in the public interface
class vtkCallbackCommand;
class vtkXRenderWindowInteractorInternals;
class VTKRENDERINGUI_EXPORT vtkXRenderWindowInteractor : public vtkRenderWindowInteractor
{
public:
static vtkXRenderWindowInteractor* New();
vtkTypeMacro(vtkXRenderWindowInteractor, vtkRenderWindowInteractor);
void PrintSelf(ostream& os, vtkIndent indent) override;
/**
* Initializes the event handlers without an XtAppContext. This is
* good for when you don't have a user interface, but you still
* want to have mouse interaction.
*/
void Initialize() override;
/**
* Break the event loop on 'q','e' keypress. Want more ???
*/
void TerminateApp() override;
/**
* Run the event loop and return. This is provided so that you can
* implement your own event loop but yet use the vtk event handling as
* well.
*/
void ProcessEvents() override;
///@{
/**
* Enable/Disable interactions. By default interactors are enabled when
* initialized. Initialize() must be called prior to enabling/disabling
* interaction. These methods are used when a window/widget is being
* shared by multiple renderers and interactors. This allows a "modal"
* display where one interactor is active when its data is to be displayed
* and all other interactors associated with the widget are disabled
* when their data is not displayed.
*/
void Enable() override;
void Disable() override;
///@}
/**
* Update the Size data member and set the associated RenderWindow's
* size.
*/
void UpdateSize(int, int) override;
/**
* Re-defines virtual function to get mouse position by querying X-server.
*/
void GetMousePosition(int* x, int* y) override;
void DispatchEvent(XEvent*);
protected:
vtkXRenderWindowInteractor();
~vtkXRenderWindowInteractor() override;
/**
* Update the Size data member and set the associated RenderWindow's
* size but do not resize the XWindow.
*/
void UpdateSizeNoXResize(int, int);
// Using static here to avoid destroying context when many apps are open:
static int NumAppInitialized;
Display* DisplayId;
Window WindowId;
Atom KillAtom;
int PositionBeforeStereo[2];
vtkXRenderWindowInteractorInternals* Internal;
// Drag and drop related
Window XdndSource;
Atom XdndPositionAtom;
Atom XdndDropAtom;
Atom XdndActionCopyAtom;
Atom XdndStatusAtom;
Atom XdndFinishedAtom;
///@{
/**
* X-specific internal timer methods. See the superclass for detailed
* documentation.
*/
int InternalCreateTimer(int timerId, int timerType, unsigned long duration) override;
int InternalDestroyTimer(int platformTimerId) override;
///@}
void FireTimers();
/**
* This will start up the X event loop and never return. If you
* call this method it will loop processing X events until the
* application is exited.
*/
void StartEventLoop() override;
private:
vtkXRenderWindowInteractor(const vtkXRenderWindowInteractor&) = delete;
void operator=(const vtkXRenderWindowInteractor&) = delete;
};
#endif
完整的文件可以在这里看到： https://gitlab.kitware.com/vtk/vtk/-/blob/master/Rendering/UI/vtkXRenderWindowInteractor.cxx
你可以按照我的思路和调试在这里： https://gitlab.kitware.com/f3d/f3d/-/issues/228
要测试这段代码，一个简单的方法是使用 F3D，它正在使用拖放的文件，但一个简单的 VTK 应用程序也应该可以工作： https://gitlab.kitware.com/f3d/f3d
当前的 Dolphin 问题
根据一些测试，问题出在处理 SelectionNotify 事件时准备和发送 XdndFinished ClientMessage 回拖放源。
而不是：
reply.xclient.window = event->xclient.data.l[0];
该行应该是：
reply.xclient.window = this->XdndSource;
这会将 XClientMessageEvent window 成员与 XSendEvent 的目标 window 参数对齐。这可能是一个简单的复制粘贴错误，因为 xclient 对 SelectionNotify 事件类型无效。 window 的实际值很可能之前没有被检查过，但最近已更改，因此出现错误。
spec 很好地涵盖了这一点，还提出了一些其他需要考虑的事项：
- 对于
data.l[1]：“如果当前目标接受放置并成功执行接受的放置操作，则设置位 0。（版本 5 中的新功能）”，因此使用itemCount作为值只要计数是偶数 ，技术上就会不正确
- 如果
XdndPosition的处理不需要实际跟踪当前位置的位置（即，如果您只是将整个 window 用作放置目标），您可能能够发送XdndStatus以响应XdndEnter消息
上一个 Thunar 问题
进一步调查，我对 Thunar 的前一个问题进行了一些故障排除，归结为代码处理 XdndDrop 假设传入数据的格式可以转换为 UTF8_STRING. GLFW 的 diff 处理几乎完全相同的问题。
如果在处理 XdndEnter 消息时，通过 xclient.data.l[4] 检查 xclient.data.l[2] 的值，您可以看到 Dolphin 报告支持以下格式：
text/uri-listtext/x-moz-urltext/plain
而 Thunar 仅支持以下内容：
text/uri-list
最简单的解决方案是：
- 处理时跟踪支持的格式
XdndEnter - 在处理
XdndDrop时将此格式提供给XConvertSelection（而不是UTF8_STRING） - 在处理
SelectionNotify事件时适当处理格式
为了更完整，如果在XdndEnter消息上设置了xclient.data.l[1]的位0，您应该得到拖放源的XdndTypeList 属性 window 并以此为基础选择格式，而不是邮件本身包含的格式。