setter for initial page in PagedWidget

Author: brachy84

src/main/java/com/cleanroommc/modularui/widgets/PagedWidget.java

@@ -21,7 +21,7 @@ public class PagedWidget<W extends PagedWidget<W>> extends Widget<W> {
 
     @Override
     public void afterInit() {
-        setPage(0);
+        setPage(this.currentPageIndex);
     }
 
     /**
@@ -35,7 +35,7 @@ public W onPageChange(@Nullable IntConsumer onPageChange) {
 
     public void setPage(int page) {
         if (page < 0 || page >= this.pages.size()) {
-            throw new IndexOutOfBoundsException();
+            throw new IndexOutOfBoundsException("Setting page of " + this + " to " + page + " failed. Only values from 0 to " + (this.pages.size() - 1) + " are allowed.");
         }
         this.currentPageIndex = page;
         if (this.currentPage != null) {
@@ -80,6 +80,13 @@ public int getCurrentPageIndex() {
         return this.pages;
     }
 
+    public W initialPage(int page) {
+        if (!isValid()) {
+            this.currentPageIndex = page;
+        }
+        return getThis();
+    }
+
     public W addPage(IWidget widget) {
         this.pages.add(widget);
         widget.setEnabled(false);