Wrote up the event handling code for Haiku.

haiku/button.cpp

@@ -16,6 +16,17 @@ uiHaikuDefineControl(
 
 #define mButtonClicked 0x4E754E75
 
+static void onClicked(BMessage *msg)
+{
+	void *bb;
+	uiButton *b;
+
+	// TODO error check
+	msg->FindPointer(mControlField, &bb);
+	b = uiButton(bb);
+	(*(b->onClicked))(b, b->onClickedData);
+}
+
 static void defaultOnClicked(uiButton *b, void *data)
 {
 	// do nothing
@@ -40,10 +51,15 @@ void uiButtonOnClicked(uiButton *b, void (*f)(uiButton *b, void *data), void *da
 uiButton *uiNewButton(const char *text)
 {
 	uiButton *b;
+	BMessage *msg;
 
 	b = (uiButton *) uiNewControl(uiButtonType());
 
-	b->button = new BButton(text, new BMessage(mButtonClicked));
+	uiHaikuRegisterEventHandler(mButtonClicked, onClicked);
+	msg = new BMessage(mButtonClicked);
+	msg->AddPointer(mControlField, b);
+
+	b->button = new BButton(text, msg);
 
 	// TODO hook up events
 	uiButtonOnClicked(b, defaultOnClicked, NULL);

haiku/main.cpp

@@ -11,6 +11,7 @@ const char *uiInit(uiInitOptions *o)
 
 	options = *o;
 	// TODO properly set the MIME type
+	// TODO andlabs-libui?
 	app = new BApplication("application/x-vnd.andlabs.libui", &err);
 	if (err != B_NO_ERROR) {
 		delete app;

haiku/uipriv_haiku.hpp

@@ -18,3 +18,7 @@ extern void singleChildDestroy(struct singleChild *s);
 extern BLayoutItem *singleChildLayoutItem(struct singleChild *s);
 extern void singleChildUpdateState(struct singleChild *s);
 extern void singleChildSetMargined(struct singleChild *s, float inset);
+
+// TODO make this public?
+#define mControlField "libui_uiControl"
+// TODO write helper functions?

haiku/window.cpp

@@ -1,11 +1,15 @@
 // 18 november 2015
+#include <map>
 #include "uipriv_haiku.hpp"
+using namespace std;
 
 class libuiBWindow : public BWindow {
 public:
 	// C++11! Inherit constructors.
 	using BWindow::BWindow;
 
+	virtual void MessageReceived(BMessage *);
+
 	uiWindow *w;
 	virtual bool QuitRequested();
 };
@@ -31,6 +35,37 @@ uiHaikuDefineControlWithOnDestroy(
 	complain("attempt to use default CommitDestroy() code for uiWindow on Haiku");			// on destroy
 )
 
+static map<uint32, void (*)(BMessage *)> eventHandlers;
+typedef map<uint32, void (*)(BMessage *)>::const_iterator eventHandlerIter;
+
+void uiHaikuRegisterEventHandler(uint32 what, void (*handler)(BMessage *))
+{
+	eventHandlerIter iter;
+
+	// TODO decide a convention for libui internal messages
+	iter = eventHandlers.find(what);
+	if (iter == eventHandlers.end()) {		// new entry
+		eventHandlers[what] = handler;
+		return;
+	}
+	if (iter->second != handler)			// mismatch
+		complain("attempt to clobber BMessage::what 0x%08X in uiHaikuRegisterEventHandler()", what);
+}
+
+void libuiBWindow::MessageReceived(BMessage *msg)
+{
+	eventHandlerIter iter;
+
+	// handle registered events
+	iter = eventHandlers.find(msg->what);
+	if (iter != eventHandlers.end()) {
+		(*(iter->second))(msg);
+		return;
+	}
+	// no event found; defer to BWindow
+	this->BWindow::MessageReceived(msg);
+}
+
 bool libuiBWindow::QuitRequested()
 {
 	// manually destroy the window ourselves; don't let the default BWindow code do it directly

ui_haiku.hpp

@@ -57,6 +57,9 @@ _UI_EXTERN uintmax_t uiHaikuControlType(void);
 // Don't call it directly; use uiHaikuFinishNewControl() instead.
 _UI_EXTERN void uiHaikuFinishControl(uiControl *c);
 
+// TODO document this
+_UI_EXTERN void uiHaikuRegisterEventHandler(uint32 what, void (*handler)(BMessage *));
+
 // uiHaikuStrdupText() takes the given string and produces a copy of it suitable for being freed by uiFreeText().
 _UI_EXTERN char *uiHaikuStrdupText(const char *);