GUI Background

src/main/java/de/studiocode/invui/InvUI.java

@@ -17,27 +17,21 @@ public class InvUI implements Listener {
     private static InvUI instance;
     
     private final List<Runnable> disableHandlers = new ArrayList<>();
-    private Plugin plugin;
+    private final Plugin plugin;
+    
+    public InvUI() {
+        plugin = ReflectionUtils.getFieldValue(PLUGIN_CLASS_LOADER_PLUGIN_FIELD, getClass().getClassLoader());
+        Bukkit.getPluginManager().registerEvents(this, plugin);
+    }
     
     public static InvUI getInstance() {
         return instance == null ? instance = new InvUI() : instance;
     }
     
     public Plugin getPlugin() {
-        if (plugin == null) {
-            System.out.println("[InvUI] Retrieving plugin from PluginClassLoader... This may cause issues!");
-            setPlugin(ReflectionUtils.getFieldValue(PLUGIN_CLASS_LOADER_PLUGIN_FIELD, getClass().getClassLoader()));
-        }
         return plugin;
     }
     
-    public void setPlugin(Plugin plugin) {
-        if (this.plugin != null)
-            throw new IllegalStateException("The plugin is already set!");
-        this.plugin = plugin;
-        Bukkit.getPluginManager().registerEvents(this, plugin);
-    }
-    
     public void addDisableHandler(Runnable runnable) {
         disableHandlers.add(runnable);
     }

src/main/java/de/studiocode/invui/gui/GUI.java

@@ -5,6 +5,7 @@ import de.studiocode.invui.gui.builder.GUIBuilder;
 import de.studiocode.invui.gui.impl.*;
 import de.studiocode.invui.gui.structure.Structure;
 import de.studiocode.invui.item.Item;
+import de.studiocode.invui.item.ItemBuilder;
 import de.studiocode.invui.virtualinventory.VirtualInventory;
 import de.studiocode.invui.window.Window;
 import org.bukkit.entity.Player;
@@ -163,6 +164,21 @@ public interface GUI extends GUIParent {
      */
     void addItems(@NotNull Item... items);
     
+    /**
+     * Sets the {@link ItemBuilder} that will be used if nothing else
+     * is placed on a slot.
+     * @param itemBuilder The {@link ItemBuilder}
+     */
+    void setBackground(@Nullable ItemBuilder itemBuilder);
+    
+    /**
+     * Gets the {@link ItemBuilder} that will used if nothing else
+     * is placed on a slot.
+     * 
+     * @return The {@link ItemBuilder}
+     */
+    ItemBuilder getBackground();
+    
     /**
      * Removes an {@link Item} by its coordinates.
      *

src/main/java/de/studiocode/invui/gui/impl/IndexedGUI.java

@@ -9,6 +9,7 @@ import de.studiocode.invui.gui.SlotElement.LinkedSlotElement;
 import de.studiocode.invui.gui.SlotElement.VISlotElement;
 import de.studiocode.invui.gui.structure.Structure;
 import de.studiocode.invui.item.Item;
+import de.studiocode.invui.item.ItemBuilder;
 import de.studiocode.invui.util.ArrayUtils;
 import de.studiocode.invui.virtualinventory.VirtualInventory;
 import de.studiocode.invui.virtualinventory.event.ItemUpdateEvent;
@@ -37,6 +38,8 @@ abstract class IndexedGUI implements GUI {
     private SlotElement[] animationElements;
     private Animation animation;
     
+    private ItemBuilder background;
+    
     public IndexedGUI(int size) {
         this.size = size;
         slotElements = new SlotElement[size];
@@ -397,6 +400,16 @@ abstract class IndexedGUI implements GUI {
         return null;
     }
     
+    @Override
+    public void setBackground(ItemBuilder itemBuilder) {
+        this.background = itemBuilder;
+    }
+    
+    @Override
+    public ItemBuilder getBackground() {
+        return background;
+    }
+    
     @Override
     public void remove(int index) {
         setSlotElement(index, null);

src/main/java/de/studiocode/invui/window/impl/BaseWindow.java

@@ -7,6 +7,7 @@ import de.studiocode.invui.gui.SlotElement;
 import de.studiocode.invui.gui.SlotElement.ItemSlotElement;
 import de.studiocode.invui.gui.SlotElement.VISlotElement;
 import de.studiocode.invui.item.Item;
+import de.studiocode.invui.item.ItemBuilder;
 import de.studiocode.invui.util.ArrayUtils;
 import de.studiocode.invui.util.Pair;
 import de.studiocode.invui.virtualinventory.VirtualInventory;
@@ -46,7 +47,11 @@ public abstract class BaseWindow implements Window {
     
     protected void redrawItem(int index, SlotElement element, boolean setItem) {
         // put ItemStack in inventory
-        ItemStack itemStack = element == null ? null : element.getItemStack(viewerUUID);
+        ItemStack itemStack;
+        if (element == null) {
+            ItemBuilder background = getGuiAt(index).getFirst().getBackground();
+            itemStack = background == null ? null : background.buildFor(viewerUUID);
+        } else itemStack = element.getItemStack(viewerUUID);
         setInvItem(index, itemStack);
         
         if (setItem) {

src/main/java/de/studiocode/invui/window/impl/merged/MergedWindow.java

@@ -35,14 +35,14 @@ public abstract class MergedWindow extends BaseWindow {
     protected void initUpperItems() {
         for (int i = 0; i < upperInventory.getSize(); i++) {
             SlotElement element = getSlotElement(i);
-            if (element != null) redrawItem(i, element, true);
+            redrawItem(i, element, true);
         }
     }
     
     private void initPlayerItems() {
         for (int i = upperInventory.getSize(); i < upperInventory.getSize() + 36; i++) {
             SlotElement element = getSlotElement(i);
-            if (element != null) redrawItem(i, element, true);
+            redrawItem(i, element, true);
         }
     }
     

src/main/java/de/studiocode/invui/window/impl/single/SingleWindow.java

@@ -36,7 +36,7 @@ public abstract class SingleWindow extends BaseWindow {
     protected void initItems() {
         for (int i = 0; i < size; i++) {
             SlotElement element = gui.getSlotElement(i);
-            if (element != null) redrawItem(i, element, true);
+            redrawItem(i, element, true);
         }
     }