UndoManager emits events when state changes

src/UndoManager.cpp

@@ -38,6 +38,10 @@ UndoManager
 
 #include <unordered_set>
 
+wxDEFINE_EVENT(EVT_UNDO_PUSHED, wxCommandEvent);
+wxDEFINE_EVENT(EVT_UNDO_MODIFIED, wxCommandEvent);
+wxDEFINE_EVENT(EVT_UNDO_RESET, wxCommandEvent);
+
 using ConstBlockFilePtr = const BlockFile*;
 using Set = std::unordered_set<ConstBlockFilePtr>;
 
@@ -245,6 +249,9 @@ void UndoManager::ModifyState(const TrackList * l,
 
    stack[current]->state.selectedRegion = selectedRegion;
    SonifyEndModifyState();
+
+   // wxWidgets will own the event object
+   QueueEvent( safenew wxCommandEvent{ EVT_UNDO_MODIFIED } );
 }
 
 void UndoManager::PushState(const TrackList * l,
@@ -298,6 +305,9 @@ void UndoManager::PushState(const TrackList * l,
    }
 
    lastAction = longDescription;
+
+   // wxWidgets will own the event object
+   QueueEvent( safenew wxCommandEvent{ EVT_UNDO_PUSHED } );
 }
 
 void UndoManager::SetStateTo(unsigned int n, const Consumer &consumer)
@@ -312,6 +322,9 @@ void UndoManager::SetStateTo(unsigned int n, const Consumer &consumer)
    mayConsolidate = false;
 
    consumer( stack[current]->state );
+
+   // wxWidgets will own the event object
+   QueueEvent( safenew wxCommandEvent{ EVT_UNDO_RESET } );
 }
 
 void UndoManager::Undo(const Consumer &consumer)
@@ -324,6 +337,9 @@ void UndoManager::Undo(const Consumer &consumer)
    mayConsolidate = false;
 
    consumer( stack[current]->state );
+
+   // wxWidgets will own the event object
+   QueueEvent( safenew wxCommandEvent{ EVT_UNDO_RESET } );
 }
 
 void UndoManager::Redo(const Consumer &consumer)
@@ -349,6 +365,9 @@ void UndoManager::Redo(const Consumer &consumer)
    mayConsolidate = false;
 
    consumer( stack[current]->state );
+
+   // wxWidgets will own the event object
+   QueueEvent( safenew wxCommandEvent{ EVT_UNDO_RESET } );
 }
 
 bool UndoManager::UnsavedChanges()

src/UndoManager.h

@@ -51,10 +51,24 @@
 
 #include "MemoryX.h"
 #include <vector>
+#include <wx/event.h>
 #include <wx/string.h>
 #include "ondemand/ODTaskThread.h"
 #include "SelectedRegion.h"
 
+// Events emitted by UndoManager for the use of listeners
+
+// Project state did not change, but a new state was copied into Undo history
+// and any redo states were lost
+wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API, EVT_UNDO_PUSHED, wxCommandEvent);
+
+// Project state did not change, but current state was modified in Undo history
+wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API, EVT_UNDO_MODIFIED, wxCommandEvent);
+
+// Project state changed because of undo or redo or rollback; undo manager
+// contents did not change other than the pointer to current state
+wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API, EVT_UNDO_RESET, wxCommandEvent);
+
 class Tags;
 class Track;
 class TrackList;
@@ -90,7 +104,7 @@ inline UndoPush operator | (UndoPush a, UndoPush b)
 inline UndoPush operator & (UndoPush a, UndoPush b)
 { return static_cast<UndoPush>(static_cast<int>(a) & static_cast<int>(b)); }
 
-class AUDACITY_DLL_API UndoManager {
+class AUDACITY_DLL_API UndoManager : public wxEvtHandler {
  public:
    UndoManager();
    ~UndoManager();
@@ -118,7 +132,8 @@ class AUDACITY_DLL_API UndoManager {
    wxLongLong_t GetLongDescription(unsigned int n, wxString *desc, wxString *size);
    void SetLongDescription(unsigned int n, const wxString &desc);
 
-   // These functions accept a callback that uses the state
+   // These functions accept a callback that uses the state,
+   // and then they emit EVT_UNDO_RESET when that has finished.
    using Consumer = std::function< void( const UndoState & ) >;
    void SetStateTo(unsigned int n, const Consumer &consumer);
    void Undo(const Consumer &consumer);