add on detach

example/layers/ui_layer/ui_layer.cpp

@@ -11,6 +11,12 @@ namespace example
     hack::log()("on_attach");
   }
 
+  void ui_layer::on_detach() 
+  {
+    VE::DISCONNECT(this);
+    hack::log()("on_detach");
+  }
+
   void ui_layer::render()
   {
     ImGui::SetNextWindowPos(m_pos);

example/layers/ui_layer_double/ui_layer_double.cpp

@@ -11,6 +11,12 @@ namespace example
     hack::log()("on_attach");
   }
 
+  void ui_layer_double::on_detach() 
+  {
+    VE::DISCONNECT(this);
+    hack::log()("on_detach");
+  }
+
   void ui_layer_double::render()
   {
     ImGui::SetNextWindowPos(ImVec2{ 10.f, 10.f });

src/layer/layer.hpp

@@ -16,6 +16,7 @@ namespace VE
 
     public:
       virtual void on_attach() {};
+      virtual void on_detach() {};
       virtual void render() {};
       virtual void update() {};
       virtual void on_event(event e) {};

src/utils/define.hpp

@@ -6,6 +6,7 @@
 #define VE_OVERIDE()\
   public:\
     void on_attach() override;\
+    void on_detach() override;\
     void render() override;\
     void update() override;\
     void on_event(VE::event e) override