diff --git a/src/net/torvald/terrarum/Terrarum.kt b/src/net/torvald/terrarum/Terrarum.kt
index 07a549f09..23e187679 100644
--- a/src/net/torvald/terrarum/Terrarum.kt
+++ b/src/net/torvald/terrarum/Terrarum.kt
@@ -17,6 +17,7 @@ import net.torvald.terrarum.AppLoader.*
 import net.torvald.terrarum.gameactors.Actor
 import net.torvald.terrarum.gameactors.ActorID
 import net.torvald.terrarum.itemproperties.ItemCodex
+import net.torvald.terrarum.ui.UICanvas
 import net.torvald.terrarum.worlddrawer.CreateTileAtlas
 import net.torvald.terrarum.worlddrawer.WorldCamera
 import net.torvald.terrarumsansbitmap.gdx.GameFontBase
@@ -26,7 +27,6 @@ import java.io.File
 import java.io.PrintStream
 import kotlin.math.absoluteValue
 import kotlin.math.round
-import kotlin.math.roundToInt
 
 
 
@@ -578,3 +578,48 @@ fun printStackTrace(obj: Any, out: PrintStream = System.out) {
         }
     }
 }
+
+class UIContainer {
+    private val data = ArrayList<Any>()
+    fun add(vararg things: Any) {
+        things.forEach {
+            if (it is UICanvas || it is Id_UICanvasNullable)
+                data.add(it)
+            else throw IllegalArgumentException(it.javaClass.name) }
+    }
+
+    fun iterator() = object : Iterator<UICanvas?> {
+        private var cursor = 0
+
+        override fun hasNext() = cursor < data.size
+
+        override fun next(): UICanvas? {
+            val it = data[cursor]
+            // whatever the fucking reason when() does not work
+            if (it is UICanvas) {
+                cursor += 1
+                return it
+            }
+            else if (it is Id_UICanvasNullable) {
+                cursor += 1
+                return it.get()
+            }
+            else throw IllegalArgumentException("Unacceptable type ${it.javaClass.name}, instance of ${it.javaClass.superclass.name}")
+        }
+    }
+
+    fun forEach(operation: (UICanvas?) -> Unit) = iterator().forEach(operation)
+    fun countVisible(): Int {
+        var c = 0
+        forEach { if (it?.isVisible == true) c += 1 }
+        return c
+    }
+
+    fun contains(element: Any) = data.contains(element)
+
+    fun <T> map(transformation: (UICanvas?) -> T) = iterator().asSequence().map(transformation)
+}
+
+interface Id_UICanvasNullable {
+    fun get(): UICanvas?
+}
\ No newline at end of file
diff --git a/src/net/torvald/terrarum/TitleScreen.kt b/src/net/torvald/terrarum/TitleScreen.kt
index 3d8c47ca0..2abd0113a 100644
--- a/src/net/torvald/terrarum/TitleScreen.kt
+++ b/src/net/torvald/terrarum/TitleScreen.kt
@@ -114,7 +114,7 @@ class TitleScreen(batch: SpriteBatch) : IngameInstance(batch) {
     private val gradWhiteBottom = Color(0xd8d8d8ff.toInt())
 
 
-    val uiContainer = ArrayList<UICanvas?>()
+    val uiContainer = UIContainer()
     private lateinit var uiMenu: UICanvas
 
     private lateinit var worldFBO: FrameBuffer
@@ -242,7 +242,7 @@ class TitleScreen(batch: SpriteBatch) : IngameInstance(batch) {
 
 
         if (!demoWorld.layerTerrain.ptr.destroyed) { // FIXME q&d hack to circumvent the dangling pointer issue #26
-            IngameRenderer.invoke(gamePaused = false, uisToDraw = uiContainer)
+            IngameRenderer.invoke(gamePaused = false, uiContainer = uiContainer)
         }
         else {
             printdbgerr(this, "Demoworld is already been destroyed")
diff --git a/src/net/torvald/terrarum/gamecontroller/IngameController.kt b/src/net/torvald/terrarum/gamecontroller/IngameController.kt
index 2fa7d8198..50eaaacff 100644
--- a/src/net/torvald/terrarum/gamecontroller/IngameController.kt
+++ b/src/net/torvald/terrarum/gamecontroller/IngameController.kt
@@ -113,8 +113,8 @@ class IngameController(val terrarumIngame: TerrarumIngame) : InputAdapter() {
             }
         }
 
-        terrarumIngame.uiContainer.forEach { it.keyDown(keycode) } // for KeyboardControlled UIcanvases
-
+        terrarumIngame.uiContainer.forEach { it?.keyDown(keycode) } // for KeyboardControlled UIcanvases
+        
         // Debug UIs
         if (keycode == Input.Keys.GRAVE) {
             terrarumIngame.consoleHandler.toggleOpening()
@@ -138,9 +138,8 @@ class IngameController(val terrarumIngame: TerrarumIngame) : InputAdapter() {
             terrarumIngame.uiQuickBar.setAsOpen()
         }
 
-        terrarumIngame.uiContainer.forEach { it.keyUp(keycode) } // for KeyboardControlled UIcanvases
-
-
+        terrarumIngame.uiContainer.forEach { it?.keyUp(keycode) } // for KeyboardControlled UIcanvases
+        
         // screenshot key
         if (keycode == Input.Keys.F12) f12Down = false
 
@@ -149,12 +148,12 @@ class IngameController(val terrarumIngame: TerrarumIngame) : InputAdapter() {
     }
 
     override fun keyTyped(character: Char): Boolean {
-        terrarumIngame.uiContainer.forEach { if (it.isVisible) it.keyTyped(character) }
+        terrarumIngame.uiContainer.forEach { if (it?.isVisible == true) it.keyTyped(character) }
         return true
     }
 
     override fun mouseMoved(screenX: Int, screenY: Int): Boolean {
-        terrarumIngame.uiContainer.forEach { it.mouseMoved(screenX, screenY) }
+        terrarumIngame.uiContainer.forEach { it?.mouseMoved(screenX, screenY) }
         return true
     }
 
@@ -162,7 +161,7 @@ class IngameController(val terrarumIngame: TerrarumIngame) : InputAdapter() {
         // don't separate Player from this! Physics will break, esp. airborne manoeuvre
         if (!terrarumIngame.paused) {
             // fire world click events; the event is defined as Ingame's (or any others') WorldClick event
-            if (terrarumIngame.uiContainer.map { if ((it.isOpening || it.isOpened) && it.mouseUp) 1 else 0 }.sum() == 0) { // no UI on the mouse, right?
+            if (terrarumIngame.uiContainer.map { if ((it?.isOpening == true || it?.isOpened == true) && it.mouseUp) 1 else 0 }.sum() == 0) { // no UI on the mouse, right?
 
                 if (
                         button == AppLoader.getConfigInt("config_mouseprimary") ||
@@ -181,8 +180,7 @@ class IngameController(val terrarumIngame: TerrarumIngame) : InputAdapter() {
             terrarumIngame.uiQuickBar.setAsOpen()
         }
 
-        terrarumIngame.uiContainer.forEach { it.touchUp(screenX, screenY, pointer, button) } // for MouseControlled UIcanvases
-
+        terrarumIngame.uiContainer.forEach { it?.touchUp(screenX, screenY, pointer, button) } // for MouseControlled UIcanvases
         return true
     }
 
@@ -197,18 +195,18 @@ class IngameController(val terrarumIngame: TerrarumIngame) : InputAdapter() {
             }
         }
 
-        terrarumIngame.uiContainer.forEach { it.scrolled(amount) }
+        terrarumIngame.uiContainer.forEach { it?.scrolled(amount) }
         return true
     }
 
     override fun touchDragged(screenX: Int, screenY: Int, pointer: Int): Boolean {
-        terrarumIngame.uiContainer.forEach { it.touchDragged(screenX, screenY, pointer) }
+        terrarumIngame.uiContainer.forEach { it?.touchDragged(screenX, screenY, pointer) }
         return true
     }
 
     override fun touchDown(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {
-        terrarumIngame.uiContainer.forEach { it.touchDown(screenX, screenY, pointer, button) }
-
+        terrarumIngame.uiContainer.forEach { it?.touchDown(screenX, screenY, pointer, button) }
+        
         // pie menu
         if (button == AppLoader.getConfigInt("config_mousequicksel")) {
             terrarumIngame.uiPieMenu.setAsOpen()
diff --git a/src/net/torvald/terrarum/modulebasegame/BuildingMaker.kt b/src/net/torvald/terrarum/modulebasegame/BuildingMaker.kt
index 8fad920b8..ef9e91f28 100644
--- a/src/net/torvald/terrarum/modulebasegame/BuildingMaker.kt
+++ b/src/net/torvald/terrarum/modulebasegame/BuildingMaker.kt
@@ -116,7 +116,7 @@ class BuildingMaker(batch: SpriteBatch) : IngameInstance(batch) {
     val uiPenMenu = UIBuildingMakerPenMenu(this)
 
 
-    val uiContainer = ArrayList<UICanvas?>()
+    val uiContainer = UIContainer()
 
     private val pensMustShowSelection = arrayOf(
             PENMODE_MARQUEE, PENMODE_MARQUEE_ERASE
@@ -392,7 +392,7 @@ class BuildingMaker(batch: SpriteBatch) : IngameInstance(batch) {
     private fun renderGame() {
         _testMarkerDrawCalls = 0L
 
-        IngameRenderer.invoke(false, actorsRenderOverlay = if (showSelection) actorsRenderOverlay + essentialOverlays else essentialOverlays, uisToDraw = uiContainer)
+        IngameRenderer.invoke(false, actorsRenderOverlay = if (showSelection) actorsRenderOverlay + essentialOverlays else essentialOverlays, uiContainer = uiContainer)
 
         AppLoader.setDebugTime("Test.MarkerDrawCalls", _testMarkerDrawCalls)
     }
diff --git a/src/net/torvald/terrarum/modulebasegame/IngameRenderer.kt b/src/net/torvald/terrarum/modulebasegame/IngameRenderer.kt
index 01da3f60e..91dd85acc 100644
--- a/src/net/torvald/terrarum/modulebasegame/IngameRenderer.kt
+++ b/src/net/torvald/terrarum/modulebasegame/IngameRenderer.kt
@@ -173,7 +173,7 @@ object IngameRenderer : Disposable {
             actorsRenderOverlay: List<ActorWithBody>? = null,
             particlesContainer : CircularArray<ParticleBase>? = null,
             player: ActorWithBody? = null,
-            uisToDraw: List<UICanvas?>? = null
+            uiContainer: UIContainer? = null
     ) {
         renderingActorsCount = (actorsRenderBehind?.size ?: 0) +
                                (actorsRenderMiddle?.size ?: 0) +
@@ -182,15 +182,9 @@ object IngameRenderer : Disposable {
                                (actorsRenderOverlay?.size ?: 0)
         //renderingParticleCount = particlesContainer?.size ?: 0
         //renderingParticleCount = (particlesContainer?.buffer?.map { (!it.flagDespawn).toInt() } ?: listOf(0)).sum()
-        renderingUIsCount = ((uisToDraw?.map { (it?.isVisible ?: false).toInt() }) ?: listOf(0)).sum()
-
+        renderingUIsCount = uiContainer?.countVisible() ?: 0
         val zoom = Terrarum.ingame?.screenZoom ?: 1f
 
-
-        if (uisToDraw != null) {
-            uiListToDraw = uisToDraw
-        }
-
         invokeInit()
 
         batch.color = Color.WHITE
@@ -331,7 +325,7 @@ object IngameRenderer : Disposable {
             batch.shader = null
             batch.color = Color.WHITE
 
-            uiListToDraw.forEach {
+            uiContainer?.forEach {
                 it?.render(batch, camera)
             }
         }
diff --git a/src/net/torvald/terrarum/modulebasegame/TerrarumIngame.kt b/src/net/torvald/terrarum/modulebasegame/TerrarumIngame.kt
index ae72fb9c4..3e3254ef9 100644
--- a/src/net/torvald/terrarum/modulebasegame/TerrarumIngame.kt
+++ b/src/net/torvald/terrarum/modulebasegame/TerrarumIngame.kt
@@ -4,8 +4,8 @@ import com.badlogic.gdx.Gdx
 import com.badlogic.gdx.Input
 import com.badlogic.gdx.graphics.Camera
 import com.badlogic.gdx.graphics.g2d.SpriteBatch
+import com.badlogic.gdx.utils.GdxRuntimeException
 import net.torvald.EMDASH
-import net.torvald.UnsafeHelper
 import net.torvald.terrarum.*
 import net.torvald.terrarum.AppLoader.printdbg
 import net.torvald.terrarum.blockproperties.BlockPropUtil
@@ -62,7 +62,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
     //val actorContainerActive = ArrayList<Actor>(ACTORCONTAINER_INITIAL_SIZE)
     //val actorContainerInactive = ArrayList<Actor>(ACTORCONTAINER_INITIAL_SIZE)
     val particlesContainer = CircularArray<ParticleBase>(PARTICLES_MAX, true)
-    val uiContainer = ArrayList<UICanvas>()
+    val uiContainer = UIContainer()
 
     private val actorsRenderBehind = ArrayList<ActorWithBody>(ACTORCONTAINER_INITIAL_SIZE)
     private val actorsRenderMiddle = ArrayList<ActorWithBody>(ACTORCONTAINER_INITIAL_SIZE)
@@ -118,13 +118,20 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
      * This will not allow multiple fixture UIs from popping up (does not prevent them actually being open)
      * because UI updating and rendering is whitelist-operated
      */
-    var uiFixture: UICanvas? = null
+    private var uiFixture: UICanvas? = null
         set(value) {
             printdbg(this, "uiFixture change: $uiFixture -> $value")
             field?.let { it.setAsClose() }
             value?.let { uiFixturesHistory.add(it) }
             field = value
         }
+
+    val getUIFixture = object : Id_UICanvasNullable { // quick workaround for the type erasure (you can't use lambda...)
+        override fun get(): UICanvas? {
+            return uiFixture
+        }
+    }
+
     lateinit var uiInventoryContainer: UICanvas
     lateinit var uiVitalPrimary: UICanvas
     lateinit var uiVitalSecondary: UICanvas
@@ -361,7 +368,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
 
         // batch-process uiAliases
         // NOTE: UIs that should pause the game (e.g. Inventory) must have relevant codes ON THEIR SIDE
-        arrayListOf(
+        uiContainer.add(
                 // drawn first
                 //uiVitalPrimary,
                 //uiVitalSecondary,
@@ -373,13 +380,12 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
                 uiWatchTierOne,
                 UIScreenZoom(),
                 uiInventoryPlayer,
-                //uiInventoryContainer,
+                getUIFixture,
                 uiTooltip,
                 consoleHandler,
                 uiCheatMotherfuckerNootNoot
                 // drawn last
-        ).forEach { addUI(it) }
-
+        )
 
 
         ingameUpdateThread = ThreadIngameUpdate(this)
@@ -605,8 +611,13 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
         Gdx.graphics.setTitle(getCanonicalTitle())
 
         filterVisibleActors()
-        uiContainer.forEach { it.update(Gdx.graphics.rawDeltaTime) }
-        uiFixture?.update(Gdx.graphics.rawDeltaTime)
+        uiContainer.forEach {
+            when (it) {
+                is UICanvas -> it.update(Gdx.graphics.rawDeltaTime)
+                is Id_UICanvasNullable -> it.get()?.update(Gdx.graphics.rawDeltaTime)
+            }
+        }
+        //uiFixture?.update(Gdx.graphics.rawDeltaTime)
         // deal with the uiFixture being closed
         if (uiFixture?.isClosed == true) { uiFixture = null }
 
@@ -619,7 +630,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
                 visibleActorsRenderOverlay,
                 particlesContainer,
                 actorNowPlaying,
-                uiContainer + uiFixture
+                uiContainer// + uiFixture
         )
     }
 
@@ -828,7 +839,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
 
         if (actor.referenceID == theRealGamer.referenceID || actor.referenceID == 0x51621D) // do not delete this magic
             throw RuntimeException("Attempted to remove player.")
-        val indexToDelete = actorContainerActive.searchForIndex(actor.referenceID!!) { it.referenceID!! }
+        val indexToDelete = actorContainerActive.searchForIndex(actor.referenceID) { it.referenceID!! }
         if (indexToDelete != null) {
             printdbg(this, "Removing actor $actor")
             printStackTrace(this)
@@ -840,23 +851,23 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
             if (actor is ActorWithBody) {
                 when (actor.renderOrder) {
                     Actor.RenderOrder.BEHIND -> {
-                        val i = actorsRenderBehind.binarySearch(actor.referenceID!!)
+                        val i = actorsRenderBehind.binarySearch(actor.referenceID)
                         actorsRenderBehind.removeAt(i)
                     }
                     Actor.RenderOrder.MIDDLE -> {
-                        val i = actorsRenderMiddle.binarySearch(actor.referenceID!!)
+                        val i = actorsRenderMiddle.binarySearch(actor.referenceID)
                         actorsRenderMiddle.removeAt(i)
                     }
                     Actor.RenderOrder.MIDTOP -> {
-                        val i = actorsRenderMidTop.binarySearch(actor.referenceID!!)
+                        val i = actorsRenderMidTop.binarySearch(actor.referenceID)
                         actorsRenderMidTop.removeAt(i)
                     }
                     Actor.RenderOrder.FRONT  -> {
-                        val i = actorsRenderFront.binarySearch(actor.referenceID!!)
+                        val i = actorsRenderFront.binarySearch(actor.referenceID)
                         actorsRenderFront.removeAt(i)
                     }
                     Actor.RenderOrder.OVERLAY-> {
-                        val i = actorsRenderOverlay.binarySearch(actor.referenceID!!)
+                        val i = actorsRenderOverlay.binarySearch(actor.referenceID)
                         actorsRenderFront.removeAt(i)
                     }
                 }
@@ -864,7 +875,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
         }
     }
 
-    private fun ArrayList<*>.binarySearch(actor: Actor) = this.binarySearch(actor.referenceID!!)
+    private fun ArrayList<*>.binarySearch(actor: Actor) = this.binarySearch(actor.referenceID)
 
     private fun ArrayList<*>.binarySearch(ID: Int): Int {
         // code from collections/Collections.kt
@@ -892,7 +903,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
     override fun addNewActor(actor: Actor?) {
         if (actor == null) return
 
-        if (AppLoader.IS_DEVELOPMENT_BUILD && theGameHasActor(actor.referenceID!!)) {
+        if (AppLoader.IS_DEVELOPMENT_BUILD && theGameHasActor(actor.referenceID)) {
             throw Error("The actor $actor already exists in the game")
         }
         else {
@@ -924,8 +935,8 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
     }
 
     fun activateDormantActor(actor: Actor) {
-        if (AppLoader.IS_DEVELOPMENT_BUILD && !isInactive(actor.referenceID!!)) {
-            if (isActive(actor.referenceID!!))
+        if (AppLoader.IS_DEVELOPMENT_BUILD && !isInactive(actor.referenceID)) {
+            if (isActive(actor.referenceID))
                 throw Error("The actor $actor is already activated")
             else
                 throw Error("The actor $actor already exists in the game")
@@ -960,17 +971,6 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
         particlesContainer.appendHead(particle)
     }
 
-    fun addUI(ui: UICanvas) {
-        // check for exact duplicates
-        if (uiContainer.contains(ui)) {
-            throw IllegalArgumentException(
-                    "Exact copy of the UI already exists: The instance of ${ui.javaClass.simpleName}"
-            )
-        }
-
-        uiContainer.add(ui)
-    }
-
     private fun insertionSortLastElemAV(arr: ArrayList<ActorWithBody>) { // out-projection doesn't work, duh
         ReentrantLock().lock {
             var j = arr.lastIndex - 1
@@ -1003,7 +1003,7 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
     }
 
     override fun hide() {
-        uiContainer.forEach { it.handler.dispose() }
+        uiContainer.forEach { it?.handler?.dispose() }
     }
 
 
@@ -1063,15 +1063,17 @@ open class TerrarumIngame(batch: SpriteBatch) : IngameInstance(batch) {
         actorsRenderOverlay.forEach { it.dispose() }
 
         uiContainer.forEach {
-            it.handler.dispose()
-            it.dispose()
+            it?.handler?.dispose()
+            it?.dispose()
         }
         uiFixturesHistory.forEach {
-            it.handler.dispose()
-            it.dispose()
+            try {
+                it.handler.dispose()
+                it.dispose()
+            }
+            catch (e: GdxRuntimeException) {}
         }
 
         super.dispose()
     }
-
 }
diff --git a/src/net/torvald/terrarum/modulebasegame/gameactors/FixtureStorageChest.kt b/src/net/torvald/terrarum/modulebasegame/gameactors/FixtureStorageChest.kt
index 742902215..a411c7cdc 100644
--- a/src/net/torvald/terrarum/modulebasegame/gameactors/FixtureStorageChest.kt
+++ b/src/net/torvald/terrarum/modulebasegame/gameactors/FixtureStorageChest.kt
@@ -44,9 +44,7 @@ internal object UIStorageChest : UICanvas(), HasInventory {
     override var height = 512
     override var openCloseTime: Second = 0.0f
 
-    private val negotiator = object : InventoryNegotiator {
-        override fun getItemFilter(): List<String> = listOf(CAT_ALL)
-
+    private val negotiator = object : InventoryNegotiator() {
         override fun accept(item: GameItem, amount: Int) {
             TODO("Not yet implemented")
         }
@@ -66,32 +64,38 @@ internal object UIStorageChest : UICanvas(), HasInventory {
         TODO("Not yet implemented")
     }
 
+    private lateinit var catBar: UIItemInventoryCatBar
+
+    private lateinit var itemList: UIItemInventoryItemGrid
+
     init {
+        catBar = UIItemInventoryCatBar(
+                this,
+                100,
+                50,
+                500,
+                500,
+                { itemList.rebuild(catBar.catIconsMeaning[catBar.selectedIcon]) },
+                false
+        )
+        itemList = UIItemInventoryItemGrid(
+                this,
+                catBar,
+                Terrarum.ingame!!.actorNowPlaying!!.inventory, // just for a placeholder...
+                100,
+                100,
+                4, 5,
+                drawScrollOnRightside = true,
+                drawWallet = true,
+                listRebuildFun = { itemListUpdate() }
+    )
+
         handler.allowESCtoClose = true
+
+        addUIitem(catBar)
+        addUIitem(itemList)
     }
 
-    private val catBar = UIItemInventoryCatBar(
-            this,
-            100,
-            50,
-            500,
-            500,
-            {},
-            false
-    )
-
-    private val itemList = UIItemInventoryItemGrid(
-            this,
-            catBar,
-            Terrarum.ingame!!.actorNowPlaying!!.inventory, // just for a placeholder...
-            100,
-            100,
-            4, 5,
-            drawScrollOnRightside = true,
-            drawWallet = true,
-            listRebuildFun = { itemListUpdate() }
-    )
-
     private fun itemListUpdate() {
         itemList.rebuild(catBar.catIconsMeaning[catBar.selectedIcon])
     }
@@ -104,6 +108,7 @@ internal object UIStorageChest : UICanvas(), HasInventory {
     override fun renderUI(batch: SpriteBatch, camera: Camera) {
         batch.color = Color.WHITE
 
+        catBar.render(batch, camera)
         itemList.render(batch, camera)
     }
 
diff --git a/src/net/torvald/terrarum/modulebasegame/ui/InventoryNegotiator.kt b/src/net/torvald/terrarum/modulebasegame/ui/InventoryNegotiator.kt
index 718e3893e..bc927ee7e 100644
--- a/src/net/torvald/terrarum/modulebasegame/ui/InventoryNegotiator.kt
+++ b/src/net/torvald/terrarum/modulebasegame/ui/InventoryNegotiator.kt
@@ -1,15 +1,16 @@
 package net.torvald.terrarum.modulebasegame.ui
 
+import net.torvald.terrarum.UIItemInventoryCatBar.Companion.CAT_ALL
 import net.torvald.terrarum.gameitem.GameItem
 
 /**
  * Created by minjaesong on 2021-03-12.
  */
-interface InventoryNegotiator {
+abstract class InventoryNegotiator {
     /** Retrieve item filter to be used to show only the acceptable items when player's own inventory is being displayed */
-    fun getItemFilter(): List<String> // GameItem.Category
+    open fun getItemFilter(): List<String> = listOf(CAT_ALL) // GameItem.Category
     /** Accepts item from the player and pass it to right inventory (object), slot (UI), etc... */
-    fun accept(item: GameItem, amount: Int = 1)
+    abstract fun accept(item: GameItem, amount: Int = 1)
     /** Rejects item and perhaps returns it back to the player, or make explosion, etc... */
-    fun reject(item: GameItem, amount: Int = 1)
+    abstract fun reject(item: GameItem, amount: Int = 1)
 }
\ No newline at end of file
diff --git a/src/net/torvald/terrarum/modulebasegame/ui/UIItemInventoryItemGrid.kt b/src/net/torvald/terrarum/modulebasegame/ui/UIItemInventoryItemGrid.kt
index 635314b4e..9540473f6 100644
--- a/src/net/torvald/terrarum/modulebasegame/ui/UIItemInventoryItemGrid.kt
+++ b/src/net/torvald/terrarum/modulebasegame/ui/UIItemInventoryItemGrid.kt
@@ -221,6 +221,8 @@ class UIItemInventoryItemGrid(
             gridModeButtons[1].highlighted = false
             itemPage = 0
             rebuild(currentFilter)
+
+            println("ItemGridMode 0 touchdown")
         }
         gridModeButtons[1].touchDownListener = { _, _, _, _ ->
             isCompactMode = true
@@ -228,6 +230,8 @@ class UIItemInventoryItemGrid(
             gridModeButtons[1].highlighted = true
             itemPage = 0
             rebuild(currentFilter)
+
+            println("ItemGridMode 1 touchdown")
         }
 
         scrollUpButton.clickOnceListener = { _, _, _ ->
diff --git a/src/net/torvald/terrarum/ui/UICanvas.kt b/src/net/torvald/terrarum/ui/UICanvas.kt
index a05be8a26..f63e256df 100644
--- a/src/net/torvald/terrarum/ui/UICanvas.kt
+++ b/src/net/torvald/terrarum/ui/UICanvas.kt
@@ -65,10 +65,6 @@ abstract class UICanvas(
      */
     val handler = UIHandler(toggleKeyLiteral, toggleButtonLiteral, customPositioning, doNotWarnConstant)
 
-    init {
-
-    }
-
     /**
      * In milliseconds
      *
@@ -285,6 +281,9 @@ abstract class UICanvas(
 
     // end of handler func aliases
 
+    init {
+        if (uiItems.isEmpty()) println("UICanvas '${this.javaClass.name}' has no UIItem registered, just so you know...")
+    }
 
     companion object {
         const val OPENCLOSE_GENERIC = 0.2f
diff --git a/src/net/torvald/terrarum/ui/UIItem.kt b/src/net/torvald/terrarum/ui/UIItem.kt
index 67d201985..c4dbf0eb2 100644
--- a/src/net/torvald/terrarum/ui/UIItem.kt
+++ b/src/net/torvald/terrarum/ui/UIItem.kt
@@ -193,6 +193,8 @@ abstract class UIItem(var parentUI: UICanvas, val initialX: Int, val initialY: I
         return false
     }
     open fun touchDown(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {
+        println("uiitem ${this.javaClass.name} touchdown")
+
         var actionDone = false
 
         if (parentUI.isVisible) {