Start using WeakPtr for some of the WindowManager window pointers.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/560405667e9

AK/WeakPtr.h

@@ -11,11 +11,28 @@ public:
     WeakPtr() { }
     WeakPtr(std::nullptr_t) { }
 
+    template<typename U>
+    WeakPtr& operator=(WeakPtr<U>&& other)
+    {
+        m_link = reinterpret_cast<WeakLink<T>*>(other.leakLink());
+        return *this;
+    }
+
     operator bool() const { return ptr(); }
 
     T* ptr() { return m_link ? m_link->ptr() : nullptr; }
     const T* ptr() const { return m_link ? m_link->ptr() : nullptr; }
+
+    T* operator->() { return ptr(); }
+    const T* operator->() const { return ptr(); }
+
+    T& operator*() { return *ptr(); }
+    const T& operator*() const { return *ptr(); }
+
     bool isNull() const { return !m_link || !m_link->ptr(); }
+    void clear() { m_link = nullptr; }
+
+    WeakLink<T>* leakLink() { return m_link.leakRef(); }
 
 private:
     WeakPtr(RetainPtr<WeakLink<T>>&& link) : m_link(std::move(link)) { }
@@ -27,7 +44,7 @@ template<typename T>
 inline WeakPtr<T> Weakable<T>::makeWeakPtr()
 {
     if (!m_link)
-        m_link = adopt(*new WeakLink<T>(*this));
+        m_link = adopt(*new WeakLink<T>(static_cast<T&>(*this)));
     return WeakPtr<T>(m_link.copyRef());
 }
 

AK/Weakable.h

@@ -2,6 +2,7 @@
 
 #include "Assertions.h"
 #include "Retainable.h"
+#include "RetainPtr.h"
 
 namespace AK {
 
@@ -16,8 +17,8 @@ public:
     const T* ptr() const { return static_cast<const T*>(m_ptr); }
 
 private:
-    explicit WeakLink(Weakable<T>& weakable) : m_ptr(&weakable) { }
-    Weakable<T>* m_ptr;
+    explicit WeakLink(T& weakable) : m_ptr(&weakable) { }
+    T* m_ptr;
 };
 
 template<typename T>

Widgets/Object.h

@@ -1,11 +1,12 @@
 #pragma once
 
 #include <AK/Vector.h>
+#include <AK/Weakable.h>
 
 class Event;
 class TimerEvent;
 
-class Object {
+class Object : public Weakable<Object> {
 public:
     Object(Object* parent = nullptr);
     virtual ~Object();

Widgets/WindowManager.cpp

@@ -96,7 +96,7 @@ void WindowManager::paintWindowFrame(Window& window)
         m_lastDragRect = Rect();
     }
 
-    if (m_dragWindow == &window) {
+    if (m_dragWindow.ptr() == &window) {
         p.xorRect(outerRect, Color::Red);
         m_lastDragRect = outerRect;
         return;
@@ -138,7 +138,7 @@ void WindowManager::handleTitleBarMouseEvent(Window& window, MouseEvent& event)
 {
     if (event.type() == Event::MouseDown) {
         printf("[WM] Begin dragging Window{%p}\n", &window);
-        m_dragWindow = &window;
+        m_dragWindow = window.makeWeakPtr();;
         m_dragOrigin = event.position();
         m_dragWindowOrigin = window.position();
         m_dragStartRect = outerRectForWindow(window);
@@ -180,7 +180,7 @@ void WindowManager::processMouseEvent(MouseEvent& event)
 {
     if (event.type() == Event::MouseUp) {
         if (m_dragWindow) {
-            printf("[WM] Finish dragging Window{%p}\n", m_dragWindow);
+            printf("[WM] Finish dragging Window{%p}\n", m_dragWindow.ptr());
             m_dragWindow->setIsBeingDragged(false);
             m_dragEndRect = outerRectForWindow(*m_dragWindow);
             m_dragWindow = nullptr;

Widgets/WindowManager.h

@@ -4,6 +4,7 @@
 #include "Rect.h"
 #include "Color.h"
 #include <AK/HashTable.h>
+#include <AK/WeakPtr.h>
 
 class MouseEvent;
 class PaintEvent;
@@ -41,7 +42,8 @@ private:
     HashTable<Window*> m_windows;
     Widget* m_rootWidget { nullptr };
 
-    Window* m_dragWindow { nullptr };
+    WeakPtr<Window> m_dragWindow;
+
     Point m_dragOrigin;
     Point m_dragWindowOrigin;
     Rect m_lastDragRect;