diff --git a/fpdfsdk/pwl/cpwl_caret.cpp b/fpdfsdk/pwl/cpwl_caret.cpp
index fe29388..47f7864 100644
--- a/fpdfsdk/pwl/cpwl_caret.cpp
+++ b/fpdfsdk/pwl/cpwl_caret.cpp
@@ -76,7 +76,7 @@
       return;
 
     m_pTimer.reset();
-    CPWL_Wnd::SetVisible(false);
+    (void)CPWL_Wnd::SetVisible(false);
     // Note, |this| may no longer be viable at this point. If more work needs
     // to be done, check the return value of SetVisible().
     return;
diff --git a/fpdfsdk/pwl/cpwl_combo_box.cpp b/fpdfsdk/pwl/cpwl_combo_box.cpp
index e3a144b..a691db1 100644
--- a/fpdfsdk/pwl/cpwl_combo_box.cpp
+++ b/fpdfsdk/pwl/cpwl_combo_box.cpp
@@ -277,7 +277,10 @@
   }
 
   if (m_pList) {
-    m_pList->SetVisible(false);
+    if (!m_pList->SetVisible(false)) {
+      m_pList = nullptr;  // Gone, dangling even.
+      return false;
+    }
     if (!this_observed) {
       return false;
     }
diff --git a/fpdfsdk/pwl/cpwl_edit.cpp b/fpdfsdk/pwl/cpwl_edit.cpp
index c3803bc..f079a2f 100644
--- a/fpdfsdk/pwl/cpwl_edit.cpp
+++ b/fpdfsdk/pwl/cpwl_edit.cpp
@@ -238,12 +238,15 @@
   ObservedPtr<CPWL_Edit> observed_ptr(this);
   CPWL_ScrollBar* pScroll = GetVScrollBar();
   if (pScroll && pScroll->IsVisible()) {
-    pScroll->SetVisible(false);
-    if (!observed_ptr)
+    if (!pScroll->SetVisible(false)) {
       return;
-
-    if (!Move(m_rcOldWindow, true, true))
+    }
+    if (!observed_ptr) {
       return;
+    }
+    if (!Move(m_rcOldWindow, true, true)) {
+      return;
+    }
   }
 
   m_pEditImpl->SelectNone();
diff --git a/fpdfsdk/pwl/cpwl_edit_impl.cpp b/fpdfsdk/pwl/cpwl_edit_impl.cpp
index 50e2c42..37ec306 100644
--- a/fpdfsdk/pwl/cpwl_edit_impl.cpp
+++ b/fpdfsdk/pwl/cpwl_edit_impl.cpp
@@ -1232,9 +1232,12 @@
       if (!m_bNotifyFlag) {
         AutoRestorer<bool> restorer(&m_bNotifyFlag);
         m_bNotifyFlag = true;
-        if (std::vector<CFX_FloatRect>* pRects = m_Refresh.GetRefreshRects()) {
-          for (auto& rect : *pRects)
-            m_pNotify->InvalidateRect(&rect);
+        std::vector<CFX_FloatRect>* pRects = m_Refresh.GetRefreshRects();
+        for (auto& rect : *pRects) {
+          if (!m_pNotify->InvalidateRect(&rect)) {
+            m_pNotify = nullptr;  // Gone, dangling even.
+            break;
+          }
         }
       }
     }
@@ -1302,7 +1305,9 @@
           AutoRestorer<bool> restorer(&m_bNotifyFlag);
           m_bNotifyFlag = true;
           CFX_FloatRect rcRefresh = VTToEdit(rcWord);
-          m_pNotify->InvalidateRect(&rcRefresh);
+          if (!m_pNotify->InvalidateRect(&rcRefresh)) {
+            m_pNotify = nullptr;  // Gone, dangling even.
+          }
         }
       }
     } else {
@@ -1316,7 +1321,9 @@
           AutoRestorer<bool> restorer(&m_bNotifyFlag);
           m_bNotifyFlag = true;
           CFX_FloatRect rcRefresh = VTToEdit(rcLine);
-          m_pNotify->InvalidateRect(&rcRefresh);
+          if (!m_pNotify->InvalidateRect(&rcRefresh)) {
+            m_pNotify = nullptr;  // Gone, dangling even.
+          }
         }
       }
 
diff --git a/fpdfsdk/pwl/cpwl_list_box.cpp b/fpdfsdk/pwl/cpwl_list_box.cpp
index e4874d5..5adb004 100644
--- a/fpdfsdk/pwl/cpwl_list_box.cpp
+++ b/fpdfsdk/pwl/cpwl_list_box.cpp
@@ -271,15 +271,13 @@
                           Info.fContentMax - Info.fContentMin) ||
       FXSYS_IsFloatEqual(Info.fPlateWidth,
                          Info.fContentMax - Info.fContentMin)) {
-    if (pScroll->IsVisible()) {
-      pScroll->SetVisible(false);
+    if (pScroll->IsVisible() && pScroll->SetVisible(false)) {
       RePosChildWnd();
     }
-  } else {
-    if (!pScroll->IsVisible()) {
-      pScroll->SetVisible(true);
-      RePosChildWnd();
-    }
+    return;
+  }
+  if (!pScroll->IsVisible() && pScroll->SetVisible(true)) {
+    RePosChildWnd();
   }
 }
 
@@ -287,8 +285,8 @@
   SetScrollPosition(fy);
 }
 
-void CPWL_ListBox::OnInvalidateRect(const CFX_FloatRect& rect) {
-  InvalidateRect(&rect);
+bool CPWL_ListBox::OnInvalidateRect(const CFX_FloatRect& rect) {
+  return InvalidateRect(&rect);
 }
 
 void CPWL_ListBox::Select(int32_t nItemIndex) {
diff --git a/fpdfsdk/pwl/cpwl_list_box.h b/fpdfsdk/pwl/cpwl_list_box.h
index 49d9363..5ee56b0 100644
--- a/fpdfsdk/pwl/cpwl_list_box.h
+++ b/fpdfsdk/pwl/cpwl_list_box.h
@@ -52,7 +52,7 @@
                         float fSmallStep,
                         float fBigStep) override;
   void OnSetScrollPosY(float fy) override;
-  void OnInvalidateRect(const CFX_FloatRect& pRect) override;
+  [[nodiscard]] bool OnInvalidateRect(const CFX_FloatRect& pRect) override;
 
   bool OnNotifySelectionChanged(bool bKeyDown, Mask<FWL_EVENTFLAG> nFlag);
 
diff --git a/fpdfsdk/pwl/cpwl_list_ctrl.cpp b/fpdfsdk/pwl/cpwl_list_ctrl.cpp
index 046e772..d7e3b15 100644
--- a/fpdfsdk/pwl/cpwl_list_ctrl.cpp
+++ b/fpdfsdk/pwl/cpwl_list_ctrl.cpp
@@ -356,26 +356,30 @@
 }
 
 void CPWL_ListCtrl::InvalidateItem(int32_t nItemIndex) {
-  if (m_pNotify) {
-    if (nItemIndex == -1) {
-      if (!m_bNotifyFlag) {
-        m_bNotifyFlag = true;
-        CFX_FloatRect rcRefresh = m_rcPlate;
-        m_pNotify->OnInvalidateRect(rcRefresh);
-        m_bNotifyFlag = false;
+  if (!m_pNotify) {
+    return;
+  }
+  if (nItemIndex == -1) {
+    if (!m_bNotifyFlag) {
+      m_bNotifyFlag = true;
+      CFX_FloatRect rcRefresh = m_rcPlate;
+      if (!m_pNotify->OnInvalidateRect(rcRefresh)) {
+        m_pNotify = nullptr;  // Gone, dangling even.
       }
-    } else {
-      if (!m_bNotifyFlag) {
-        m_bNotifyFlag = true;
-        CFX_FloatRect rcRefresh = GetItemRect(nItemIndex);
-        rcRefresh.left -= 1.0f;
-        rcRefresh.right += 1.0f;
-        rcRefresh.bottom -= 1.0f;
-        rcRefresh.top += 1.0f;
-
-        m_pNotify->OnInvalidateRect(rcRefresh);
-        m_bNotifyFlag = false;
+      m_bNotifyFlag = false;
+    }
+  } else {
+    if (!m_bNotifyFlag) {
+      m_bNotifyFlag = true;
+      CFX_FloatRect rcRefresh = GetItemRect(nItemIndex);
+      rcRefresh.left -= 1.0f;
+      rcRefresh.right += 1.0f;
+      rcRefresh.bottom -= 1.0f;
+      rcRefresh.top += 1.0f;
+      if (!m_pNotify->OnInvalidateRect(rcRefresh)) {
+        m_pNotify = nullptr;  // Gone, dangling even.
       }
+      m_bNotifyFlag = false;
     }
   }
 }
diff --git a/fpdfsdk/pwl/cpwl_list_ctrl.h b/fpdfsdk/pwl/cpwl_list_ctrl.h
index 3f36354..c278b81 100644
--- a/fpdfsdk/pwl/cpwl_list_ctrl.h
+++ b/fpdfsdk/pwl/cpwl_list_ctrl.h
@@ -31,7 +31,9 @@
                                   float fSmallStep,
                                   float fBigStep) = 0;
     virtual void OnSetScrollPosY(float fy) = 0;
-    virtual void OnInvalidateRect(const CFX_FloatRect& rect) = 0;
+
+    // Returns true if `this` is still allocated.
+    [[nodiscard]] virtual bool OnInvalidateRect(const CFX_FloatRect& rect) = 0;
   };
 
   CPWL_ListCtrl();
diff --git a/fpdfsdk/pwl/cpwl_scroll_bar.cpp b/fpdfsdk/pwl/cpwl_scroll_bar.cpp
index 1483191..da98ee9 100644
--- a/fpdfsdk/pwl/cpwl_scroll_bar.cpp
+++ b/fpdfsdk/pwl/cpwl_scroll_bar.cpp
@@ -338,7 +338,7 @@
   m_sData.SetClientWidth(fClientWidth);
 
   if (FXSYS_IsFloatSmaller(m_sData.ScrollRange.GetWidth(), 0.0f)) {
-    m_pPosButton->SetVisible(false);
+    (void)m_pPosButton->SetVisible(false);
     // Note, |this| may no longer be viable at this point. If more work needs
     // to be done, check this_observed.
     return;
@@ -348,7 +348,7 @@
     return;
   }
 
-  MovePosButton(true);
+  (void)MovePosButton(true);
   // Note, |this| may no longer be viable at this point. If more work needs
   // to be done, check the return value of MovePosButton().
 }
@@ -357,7 +357,7 @@
   float fOldPos = m_sData.fScrollPos;
   m_sData.SetPos(fPos);
   if (!FXSYS_IsFloatEqual(m_sData.fScrollPos, fOldPos)) {
-    MovePosButton(true);
+    (void)MovePosButton(true);
     // Note, |this| may no longer be viable at this point. If more work needs
     // to be done, check the return value of MovePosButton().
   }
diff --git a/fpdfsdk/pwl/cpwl_scroll_bar.h b/fpdfsdk/pwl/cpwl_scroll_bar.h
index 6cca8fb..91e7c29 100644
--- a/fpdfsdk/pwl/cpwl_scroll_bar.h
+++ b/fpdfsdk/pwl/cpwl_scroll_bar.h
@@ -124,7 +124,7 @@
   void SetScrollPos(float fPos);
 
   // Returns |true| iff this instance is still allocated.
-  bool MovePosButton(bool bRefresh);
+  [[nodiscard]] bool MovePosButton(bool bRefresh);
   void SetScrollStep(float fBigStep, float fSmallStep);
   void NotifyScrollWindow();
   CFX_FloatRect GetScrollArea() const;
diff --git a/fpdfsdk/pwl/cpwl_wnd.cpp b/fpdfsdk/pwl/cpwl_wnd.cpp
index 2716fde..8d14656 100644
--- a/fpdfsdk/pwl/cpwl_wnd.cpp
+++ b/fpdfsdk/pwl/cpwl_wnd.cpp
@@ -557,7 +557,9 @@
 
   ObservedPtr<CPWL_Wnd> this_observed(this);
   for (const auto& pChild : m_Children) {
-    pChild->SetVisible(bVisible);
+    if (!pChild->SetVisible(bVisible)) {
+      return false;
+    }
     if (!this_observed) {
       return false;
     }
diff --git a/fpdfsdk/pwl/cpwl_wnd.h b/fpdfsdk/pwl/cpwl_wnd.h
index 752fed1..eb22934 100644
--- a/fpdfsdk/pwl/cpwl_wnd.h
+++ b/fpdfsdk/pwl/cpwl_wnd.h
@@ -138,7 +138,7 @@
   virtual ~CPWL_Wnd();
 
   // Returns |true| iff this instance is still allocated.
-  virtual bool InvalidateRect(const CFX_FloatRect* pRect);
+  [[nodiscard]] virtual bool InvalidateRect(const CFX_FloatRect* pRect);
 
   virtual bool OnKeyDown(FWL_VKEYCODE nKeyCode, Mask<FWL_EVENTFLAG> nFlag);
   virtual bool OnChar(uint16_t nChar, Mask<FWL_EVENTFLAG> nFlag);
@@ -165,7 +165,7 @@
   virtual void SetCursor();
 
   // Returns |true| iff this instance is still allocated.
-  virtual bool SetVisible(bool bVisible);
+  [[nodiscard]] virtual bool SetVisible(bool bVisible);
   virtual void SetFontSize(float fFontSize);
   virtual float GetFontSize() const;
 
@@ -224,7 +224,7 @@
   virtual void CreateChildWnd(const CreateParams& cp);
 
   // Returns |true| iff this instance is still allocated.
-  virtual bool RePosChildWnd();
+  [[nodiscard]] virtual bool RePosChildWnd();
 
   virtual void DrawThisAppearance(CFX_RenderDevice* pDevice,
                                   const CFX_Matrix& mtUser2Device);
@@ -248,8 +248,8 @@
   CPWL_ScrollBar* GetVScrollBar() const;
 
   // Returns |true| iff this instance is still allocated.
-  bool InvalidateRectMove(const CFX_FloatRect& rcOld,
-                          const CFX_FloatRect& rcNew);
+  [[nodiscard]] bool InvalidateRectMove(const CFX_FloatRect& rcOld,
+                                        const CFX_FloatRect& rcNew);
 
   void SetCapture();
   void ReleaseCapture();