From 54c7110d9d02c0d48157e5075f5d08ece2b0b7ee Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 28 Mar 2021 11:16:33 +0200
Subject: [PATCH] LibCore: Add a way to install an event filter on a
 Core::Object

The event filter is consulted by Object::dispatch_event() and may
decide that the event should not be delivered to the target object.
---
 Userland/Libraries/LibCore/Object.cpp | 10 +++++++++-
 Userland/Libraries/LibCore/Object.h   |  5 ++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibCore/Object.cpp b/Userland/Libraries/LibCore/Object.cpp
index 854467a356..fc57e8be56 100644
--- a/Userland/Libraries/LibCore/Object.cpp
+++ b/Userland/Libraries/LibCore/Object.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -227,6 +227,9 @@ void Object::dispatch_event(Core::Event& e, Object* stay_within)
     VERIFY(!stay_within || stay_within == this || stay_within->is_ancestor_of(*this));
     auto* target = this;
     do {
+        // If there's an event filter on this target, ask if it wants to swallow this event.
+        if (target->m_event_filter && !target->m_event_filter(e))
+            return;
         target->event(e);
         target = target->parent();
         if (target == stay_within) {
@@ -262,4 +265,9 @@ void Object::register_property(const String& name, Function<JsonValue()> getter,
     m_properties.set(name, make<Property>(name, move(getter), move(setter)));
 }
 
+void Object::set_event_filter(Function<bool(Core::Event&)> filter)
+{
+    m_event_filter = move(filter);
+}
+
 }
diff --git a/Userland/Libraries/LibCore/Object.h b/Userland/Libraries/LibCore/Object.h
index 8554adb4fe..05a33d3f6d 100644
--- a/Userland/Libraries/LibCore/Object.h
+++ b/Userland/Libraries/LibCore/Object.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -113,6 +113,8 @@ public:
     void remove_child(Object&);
     void remove_all_children();
 
+    void set_event_filter(Function<bool(Core::Event&)>);
+
     void dump_tree(int indent = 0);
 
     void deferred_invoke(Function<void(Object&)>);
@@ -169,6 +171,7 @@ private:
     unsigned m_inspector_count { 0 };
     HashMap<String, NonnullOwnPtr<Property>> m_properties;
     NonnullRefPtrVector<Object> m_children;
+    Function<bool(Core::Event&)> m_event_filter;
 };
 
 }