macOS: Refactor NSView subclass implementation

Cargo.toml

@@ -70,8 +70,9 @@ uuid = { version = "0.8", features = ["v4"], optional = true }
 
 [target.'cfg(target_os="macos")'.dependencies]
 objc2 = "0.6.4"
-objc2-core-foundation = { version = "0.3.2", default-features = false, features = ["std", "CFString", "CFUUID"] }
-objc2-foundation = { version = "0.3.2", default-features = false, features = ["std", "NSEnumerator"] }
+objc2-core-foundation = { version = "0.3.2", default-features = false, features = ["std", "CFString", "CFUUID", "block2", "objc2"] }
+block2 = "0.6.2"
+objc2-foundation = { version = "0.3.2", default-features = false, features = ["std", "NSEnumerator", "block2", "NSOperation"] }
 objc2-app-kit = { version = "0.3.2", default-features = false, features = [
     "NSApplication",
     "NSDragging",

src/macos/mod.rs

@@ -2,39 +2,4 @@ mod keyboard;
 mod view;
 mod window;
 
-use objc2::rc::Retained;
-use objc2::Message;
-use std::cell::RefCell;
 pub use window::*;
-
-pub struct RetainedCell<T> {
-    inner: RefCell<Option<Retained<T>>>,
-}
-
-impl<T> RetainedCell<T> {
-    pub const fn empty() -> Self {
-        RetainedCell { inner: RefCell::new(None) }
-    }
-
-    pub const fn new(value: Retained<T>) -> Self {
-        RetainedCell { inner: RefCell::new(Some(value)) }
-    }
-
-    pub const fn with(value: Option<Retained<T>>) -> Self {
-        RetainedCell { inner: RefCell::new(value) }
-    }
-
-    pub fn take(&self) -> Option<Retained<T>> {
-        self.inner.borrow_mut().take()
-    }
-}
-
-impl<T: Message> RetainedCell<T> {
-    pub fn get(&self) -> Option<Retained<T>> {
-        (*self.inner.borrow()).as_ref().map(|inner| inner.retain())
-    }
-
-    pub fn set(&self, value: Retained<T>) {
-        self.inner.replace(Some(value));
-    }
-}