simplified a structure of UIs a bit

src/net/torvald/terrarum/ui/UIItem.kt

@@ -28,19 +28,99 @@ abstract class UIItem(var parentUI: UICanvas) { // do not replace parentUI to UI
     open val mousePushed: Boolean
         get() = mouseUp && Gdx.input.isButtonPressed(Terrarum.getConfigInt("mouseprimary")!!)
 
-    abstract fun update(delta: Float)
+
+
+    // kind of listener implementation
+    var updateAction: ((Float) -> Unit)? = null
+    var keyDownAction: ((Int) -> Unit)? = null
+    var keyUpAction: ((Int) -> Unit)? = null
+    var mouseMovedAction: ((Int, Int) -> Unit)? = null
+    var touchDraggedAction: ((Int, Int, Int) -> Unit)? = null
+    var touchDownAction: ((Int, Int, Int, Int) -> Unit)? = null
+    var touchUpAction: ((Int, Int, Int, Int) -> Unit)? = null
+    var scrolledAction: ((Int) -> Unit)? = null
+
+    var clickOnceAction: ((Int, Int, Int) -> Unit)? = null
+    var clickOnceActionEngaged = false
+
+
+
+    open fun update(delta: Float) {
+        if (updateAction != null) {
+            updateAction!!.invoke(delta)
+        }
+    }
     abstract fun render(batch: SpriteBatch)
 
     // keyboard controlled
-    abstract fun keyDown(keycode: Int): Boolean
-    abstract fun keyUp(keycode: Int): Boolean
+    open fun keyDown(keycode: Int): Boolean {
+        if (keyDownAction != null) {
+            keyDownAction!!.invoke(keycode)
+            return true
+        }
+
+        return false
+    }
+    open fun keyUp(keycode: Int): Boolean {
+        if (keyUpAction != null) {
+            keyUpAction!!.invoke(keycode)
+            return true
+        }
+
+        return false
+    }
 
     // mouse controlled
-    abstract fun mouseMoved(screenX: Int, screenY: Int): Boolean
-    abstract fun touchDragged(screenX: Int, screenY: Int, pointer: Int): Boolean
-    abstract fun touchDown(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean
-    abstract fun touchUp(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean
-    abstract fun scrolled(amount: Int): Boolean
+    open fun mouseMoved(screenX: Int, screenY: Int): Boolean {
+        if (mouseMovedAction != null) {
+            mouseMovedAction!!.invoke(relativeMouseX, relativeMouseY)
+            return true
+        }
+
+        return false
+    }
+    open fun touchDragged(screenX: Int, screenY: Int, pointer: Int): Boolean {
+        if (touchDraggedAction != null) {
+            touchDraggedAction!!.invoke(relativeMouseX, relativeMouseY, pointer)
+            return true
+        }
+
+        return false
+    }
+    open fun touchDown(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {
+        var actionDone = false
+
+        if (touchDownAction != null) {
+            touchDownAction!!.invoke(relativeMouseX, relativeMouseY, pointer, button)
+            actionDone = true
+        }
+
+        if (!clickOnceActionEngaged && mouseUp) {
+            clickOnceAction!!.invoke(relativeMouseX, relativeMouseY, button)
+            actionDone = true
+        }
+
+        return actionDone
+    }
+    open fun touchUp(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {
+        clickOnceActionEngaged = false
+
+        if (touchUpAction != null) {
+            touchUpAction!!.invoke(relativeMouseX, relativeMouseY, pointer, button)
+            return true
+        }
+
+        return false
+    }
+    open fun scrolled(amount: Int): Boolean {
+        if (scrolledAction != null) {
+            scrolledAction!!.invoke(amount)
+            return true
+        }
+
+        return false
+    }
+
     abstract fun dispose()
 
 }