diff --git a/README.md b/README.md
index ce90255d..02a2f431 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,8 @@ Dlang UI
 
 GUI for D programming language, written in D.
 
+Alpha stage of development.
+
 * Crossplatform (Win32 and Linux are supported in current version)
 * Mostly inspired by Android UI API (layouts, styles, two phase layout, ...)
 * Supports highly customizable UI themes and styles
@@ -13,6 +15,24 @@ GUI for D programming language, written in D.
 * Almost ready for 2D games development
 * Goal: provide set of widgets suitable for building of IDE.
 
+Widgets
+-------
+
+Currently implemented widgets:
+
+* TextWidget - simple static text (TODO: implement multiline formatting)
+* ImageWidget - static image
+* Button - simple button with text label
+* ImageButton - image only button
+* TextImageButton - button with icon and label
+* CheckBox - check button with label
+* RadioButton - radio button with label
+* VSpacer - vertical spacer - just an empty widget with layoutHeight == FILL_PARENT, to fill vertical space in layouts
+* HSpacer - horizontal spacer - just an empty widget with layoutWidth == FILL_PARENT, to fill horizontal space in layouts
+* ScrollBar - scroll bar
+
+Layouts
+-------
 
 Win32 builds
 ------------
diff --git a/src/dlangui/core/signals.d b/src/dlangui/core/signals.d
index 9bdbfdf8..d9713d33 100644
--- a/src/dlangui/core/signals.d
+++ b/src/dlangui/core/signals.d
@@ -177,7 +177,8 @@ struct Signal(T1) if (is(T1 == interface) && __traits(allMembers, T1).length ==
     /// replace all previously assigned listeners with new one (if null passed, remove all listeners)
     final void opAssign(slot_t listener) {
         _listeners.clear();
-        _listeners ~= listener;
+		if (listener !is null)
+			_listeners ~= listener;
     }
     /// call all listeners; for signals having non-void return type, stop iterating when first return value is nonzero
     static if (is (return_t == void)) {
@@ -225,9 +226,11 @@ struct Signal(RETURN_T, T1...)
     final bool assigned() {
         return _listeners.length > 0;
     }
+    /// replace all previously assigned listeners with new one (if null passed, remove all listeners)
     final void opAssign(slot_t listener) {
         _listeners.clear();
-        _listeners ~= listener;
+		if (listener !is null)
+			_listeners ~= listener;
     }
     /// call all listeners; for signals having non-void return type, stop iterating when first return value is nonzero
     static if (is (RETURN_T == void)) {
diff --git a/src/dlangui/widgets/controls.d b/src/dlangui/widgets/controls.d
index 51bbee49..3a2620f5 100644
--- a/src/dlangui/widgets/controls.d
+++ b/src/dlangui/widgets/controls.d
@@ -112,7 +112,7 @@ class TextWidget : Widget {
     }
 }
 
-/// image widget
+/// static image widget
 class ImageWidget : Widget {
 
     protected string _drawableId;
@@ -339,11 +339,8 @@ class AbstractSlider : WidgetGroup {
         super(ID);
     }
 
-    protected bool delegate(AbstractSlider source, ScrollEvent event) _onScrollEventListener;
-    /// scroll event listener
-    @property bool delegate(AbstractSlider source, ScrollEvent event) onScrollEventListener() const { return _onScrollEventListener; }
-    /// sets new scroll event listener
-    @property AbstractSlider onScrollEventListener(bool delegate(AbstractSlider source, ScrollEvent event) listener) { _onScrollEventListener = listener; return this; }
+    /// scroll event listeners
+    Signal!OnScrollHandler onScrollEventListener;
 
     /// returns slider position
     @property int position() const { return _position; }
@@ -383,10 +380,10 @@ class AbstractSlider : WidgetGroup {
     }
 
     protected bool sendScrollEvent(ScrollAction action, int position) {
-        if (_onScrollEventListener is null)
+        if (!onScrollEventListener.assigned)
             return false;
         ScrollEvent event = new ScrollEvent(action, _minValue, _maxValue, _pageSize, position);
-        bool res = _onScrollEventListener(this, event);
+        bool res = onScrollEventListener(this, event);
         if (event.positionChanged) {
             _position = event.position;
             if (_position > _maxValue)