diff --git a/src/buffer/vec.rs b/src/buffer/vec.rs
index 76dc062..04d893e 100644
--- a/src/buffer/vec.rs
+++ b/src/buffer/vec.rs
@@ -75,7 +75,7 @@ pub struct VecBuffer<T>
 where
     T: Clone + Send + Sync + 'static,
 {
-    data: Arc<RwLock<Vec<T>>>,
+    pub data: Arc<RwLock<Vec<T>>>,
     port: InnerViewPort<RwLock<Vec<T>>>
 }
 
@@ -103,6 +103,7 @@ where
     }
 
     pub fn attach_to(&self, port: OuterViewPort< dyn ListView<T> >) -> Arc<RwLock<VecBufferTarget<T>>> {
+        self.port.0.update_hooks.write().unwrap().clear();
         self.port.0.add_update_hook(Arc::new(port.0.clone()));
 
         let target = Arc::new(RwLock::new(
diff --git a/src/projection/map_list.rs b/src/projection/map_list.rs
index 61eb380..7b055ea 100644
--- a/src/projection/map_list.rs
+++ b/src/projection/map_list.rs
@@ -88,14 +88,14 @@ where
         let old_len = self.len();
         self.src_view = view;
         let new_len = self.len();
-        /* ????
-        if let Some(len) = old_len {
-            self.cast.notify_each(0..len);
+
+/* required ? */
+        self.cast.notify(&ListDiff::Clear);
+/*
+        for idx in 0..self.len().unwrap_or(0) {
+            self.cast.notify(&ListDiff::Insert{ idx, val: self.get(&idx).unwrap() });
         }
-        if let Some(len) = new_len {
-            self.cast.notify_each(0..len);
-        }
-        */
+*/
     }
 
     fn notify(&mut self, msg: &ListDiff<SrcItem>) {
diff --git a/src/projection/map_sequence.rs b/src/projection/map_sequence.rs
index c745f1e..e2d1583 100644
--- a/src/projection/map_sequence.rs
+++ b/src/projection/map_sequence.rs
@@ -81,11 +81,9 @@ where
         self.src_view = view;
         let new_len = self.len();
 
-        if let Some(len) = old_len {
-            self.cast.notify_each(0..len);
-        }
-        if let Some(len) = new_len {
-            self.cast.notify_each(0..len);
+        if let Some(old_len) = old_len {
+            let new_len = new_len.unwrap_or(0);
+            self.cast.notify_each(0..std::cmp::max(old_len, new_len));
         }
     }
 
diff --git a/src/projection/projection_helper.rs b/src/projection/projection_helper.rs
index ac533b6..b6b91f0 100644
--- a/src/projection/projection_helper.rs
+++ b/src/projection/projection_helper.rs
@@ -71,6 +71,10 @@ where
         port.get_view_arc()
     }
 
+    /*
+        TODO: new_list_arg()
+    */
+
     pub fn new_index_arg<Key: Clone + Send + Sync + 'static, Item: 'static>(
         &mut self,
         arg_key: ArgKey,
diff --git a/src/view/port.rs b/src/view/port.rs
index 6b4b13a..a6e0ce7 100644
--- a/src/view/port.rs
+++ b/src/view/port.rs
@@ -38,7 +38,7 @@ where
     }
 
     pub fn set_view(&self, view: Option<Arc<V>>) {
-        let mut v = self.view.write().unwrap();        
+        let mut v = self.view.write().unwrap();
         *v = view.clone();
         self.cast.write().unwrap().reset(view);
     }
@@ -49,15 +49,12 @@ where
 
     pub fn add_observer(&self, observer: Arc<RwLock<dyn Observer<V>>>) {
         self.update();
-        self.cast
-            .write()
-            .unwrap()
-            .add_observer(Arc::downgrade(&observer));
 
-        observer
-            .write()
-            .unwrap()
-            .reset(self.view.read().unwrap().clone());
+        let mut obs = observer.write().unwrap();
+        let mut cst = self.cast.write().unwrap();
+
+        obs.reset(self.view.read().unwrap().clone());
+        cst.add_observer(Arc::downgrade(&observer));
     }
 
     pub fn add_update_hook(&self, hook_cast: Arc<dyn UpdateTask>) {
@@ -112,8 +109,9 @@ where V::Msg: Clone
         let keepalive = Arc::new(RwLock::new( self.inner() ));
 
         other_port.update(); // todo: required?
-        other_port.add_observer( keepalive.clone() );
         self.update_hooks.write().unwrap().clear();
+        other_port.add_observer( keepalive.clone() );
+        self.set_view( other_port.view.read().unwrap().clone() );
         self.add_update_hook( Arc::new(other_port) );
         self.update();
         keepalive
@@ -129,7 +127,7 @@ impl<V: View + ?Sized + 'static> Observer<V> for InnerViewPort<V> where V::Msg:
     fn reset(&mut self, new_view: Option<Arc<V>>) {
          self.set_view(new_view);
     }
- 
+
     fn notify(&mut self, msg: &V::Msg) {
          self.0.cast.write().unwrap().notify(msg);
     }
@@ -374,4 +372,3 @@ where
 }
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
-