add simple paged gui handler

src/main/java/com/songoda/core/gui/Gui.java

@@ -72,6 +72,10 @@ public class Gui {
         }
     }
 
+    public Gui(Gui parent) {
+        this.parent = parent;
+    }
+
     public Gui(int rows) {
         this.rows = Math.max(1, Math.min(6, rows));
     }
@@ -476,7 +480,8 @@ public class Gui {
                 updatePageNavigation();
 
                 // push new inventory to the view inventory
-                update();
+                // shouldn't be needed since adding inventory update to setItem
+                //update();
             }
         }
     }

src/main/java/com/songoda/core/gui/GuiUtils.java

@@ -91,6 +91,7 @@ public class GuiUtils {
     public static ItemStack createButtonItem(LegacyMaterials mat, String title, String... lore) {
         ItemStack item = mat.getItem();
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
@@ -98,18 +99,21 @@ public class GuiUtils {
                 meta.setLore(Collections.EMPTY_LIST);
             }
             item.setItemMeta(meta);
+        }
         return item;
     }
 
     public static ItemStack createButtonItem(ItemStack from, String title, String... lore) {
         ItemStack item = from.clone();
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
@@ -117,12 +121,14 @@ public class GuiUtils {
     public static ItemStack createButtonItem(LegacyMaterials mat, String title, List<String> lore) {
         ItemStack item = mat.getItem();
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
@@ -130,24 +136,28 @@ public class GuiUtils {
     public static ItemStack createButtonItem(ItemStack from, String title, List<String> lore) {
         ItemStack item = from.clone();
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
 
     public static ItemStack updateItem(ItemStack item, String title, String... lore) {
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
@@ -157,12 +167,14 @@ public class GuiUtils {
             item = matTo.getItem();
         }
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
@@ -172,24 +184,28 @@ public class GuiUtils {
             item = to.clone();
         }
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
 
     public static ItemStack updateItem(ItemStack item, String title, List<String> lore) {
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
@@ -199,12 +215,14 @@ public class GuiUtils {
             item = matTo.getItem();
         }
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }
@@ -214,12 +232,14 @@ public class GuiUtils {
             item = to.clone();
         }
         ItemMeta meta = item.getItemMeta();
+        if (meta != null) {
             meta.setDisplayName(title);
             if (lore != null) {
                 meta.setLore(getSafeLore(lore));
             } else {
                 meta.setLore(Collections.EMPTY_LIST);
             }
+        }
         item.setItemMeta(meta);
         return item;
     }

src/main/java/com/songoda/core/gui/SimplePagedGui.java

@@ -0,0 +1,166 @@
+package com.songoda.core.gui;
+
+import com.songoda.core.compatibility.LegacyMaterials;
+import static com.songoda.core.gui.Gui.trimTitle;
+import com.songoda.core.gui.events.GuiClickEvent;
+import com.songoda.core.gui.methods.Clickable;
+import java.util.Map;
+import org.bukkit.Bukkit;
+import org.bukkit.ChatColor;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.ClickType;
+import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.ItemStack;
+
+/**
+ * Paged GUI for when you aren't going to be making too many pages
+ *
+ * @since 2019-08-31
+ * @author jascotty2
+ */
+public class SimplePagedGui extends Gui {
+
+    protected boolean useHeader;
+    private int rowsPerPage, maxCellSlot;
+    protected ItemStack headerBackItem;
+    protected ItemStack footerBackItem;
+    final int nextPageIndex = -4, prevPageIndex = -6;
+
+    public SimplePagedGui() {
+        this(null);
+    }
+
+    public SimplePagedGui(Gui parent) {
+        super(parent);
+
+        nextPage = GuiUtils.createButtonItem(LegacyMaterials.ARROW, "Next Page");
+        prevPage = GuiUtils.createButtonItem(LegacyMaterials.ARROW, "Previous Page");
+    }
+
+    public SimplePagedGui setUseHeader(boolean useHeader) {
+        this.useHeader = useHeader;
+        return this;
+    }
+
+    public SimplePagedGui setNextPage(ItemStack item) {
+        nextPage = item;
+        return this;
+    }
+
+    public SimplePagedGui setPrevPage(ItemStack item) {
+        prevPage = item;
+        return this;
+    }
+
+    @Override
+    public void nextPage() {
+        if (page < pages) {
+            ++page;
+            showPage();
+        }
+    }
+
+    @Override
+    public void prevPage() {
+        if (page > 1) {
+            --page;
+            showPage();
+        }
+    }
+
+    public void showPage() {
+        int startCell = useHeader ? 9 : 0;
+        int cellIndex = startCell + (page - 1) * (rowsPerPage * 9);
+
+        for (int i = startCell; i < (rows - 1) * 9; ++i) {
+            final ItemStack item = cellItems.get(cellIndex++);
+            inventory.setItem(i, item != null ? item : blankItem);
+        }
+        // page markers
+        updatePageNavigation();
+    }
+
+    @Override
+    protected void updatePageNavigation() {
+        if (page > 1) {
+            inventory.setItem((rows * 9) - 6, prevPage);
+            this.setButton(prevPageIndex, prevPage, ClickType.LEFT, (event) -> this.prevPage());
+        } else {
+            inventory.setItem((rows * 9) - 6, footerBackItem != null ? footerBackItem : blankItem);
+            this.setItem(prevPageIndex, null);
+            this.clearActions(prevPageIndex);
+        }
+        if (pages > 1 && page != pages) {
+            inventory.setItem((rows * 9) - 4, nextPage);
+            this.setButton(nextPageIndex, nextPage, ClickType.LEFT, (event) -> this.nextPage());
+        } else {
+            inventory.setItem((rows * 9) - 4, footerBackItem != null ? footerBackItem : blankItem);
+            this.setItem(nextPageIndex, null);
+            this.clearActions(nextPageIndex);
+        }
+    }
+
+    @Override
+    protected Inventory generateInventory(GuiManager manager) {
+        // calculate pages here
+        rowsPerPage = useHeader ? 4 : 5;
+        maxCellSlot = this.cellItems.isEmpty() ? 0 : this.cellItems.keySet().stream().max(Integer::compare).get();
+        int maxRows = (int) Math.ceil(maxCellSlot / 9.);
+        pages = (int) Math.ceil(maxRows / rowsPerPage);
+        page = 1;
+        this.setRows(maxRows + 1);
+
+        // create inventory view
+        final int cells = rows * 9;
+        inventory = Bukkit.getServer().createInventory(new GuiHolder(manager, this), cells,
+                title == null ? "" : trimTitle(ChatColor.translateAlternateColorCodes('&', title)));
+
+        // populate initial inventory
+        if (useHeader) {
+            for (int i = 0; i < 9; ++i) {
+                final ItemStack item = cellItems.get(i);
+                inventory.setItem(i, item != null ? item : (headerBackItem != null ? headerBackItem : blankItem));
+            }
+        }
+        for (int i = useHeader ? 9 : 0; i < cells - 9; ++i) {
+            final ItemStack item = cellItems.get(i);
+            inventory.setItem(i, item != null ? item : blankItem);
+        }
+
+        // last row is dedicated to pagation
+        for (int i = cells - 9; i < cells; ++i) {
+            inventory.setItem(i, footerBackItem != null ? footerBackItem : blankItem);
+        }
+        updatePageNavigation();
+
+        return inventory;
+    }
+
+    @Override
+    protected boolean onClick(GuiManager manager, Player player, Inventory inventory, InventoryClickEvent event) {
+        int cell = event.getSlot();
+        Map<ClickType, Clickable> conditionals;
+
+        if (useHeader && cell < 9) {
+            conditionals = conditionalButtons.get(cell);
+        } else if (cell >= (rows - 1) * 9) {
+            // footer row
+            conditionals = conditionalButtons.get(cell - (rows * 9));
+        } else {
+            int startCell = useHeader ? 9 : 0;
+            int cellIndex = startCell + (page - 1) * rowsPerPage;
+            conditionals = conditionalButtons.get(cellIndex);
+        }
+
+        Clickable button;
+        if (conditionals != null
+                && ((button = conditionals.get(event.getClick())) != null || (button = conditionals.get(null)) != null)) {
+            button.onClick(new GuiClickEvent(manager, this, player, event, cell, true));
+        } else {
+            // no event for this button
+            return false;
+        }
+        return true;
+    }
+}