Add caching of current item expansion status to recover it next time

Issue-ref: 4352
Issue-URL: af3#4352



Signed-off-by: Sebastian Bergemann <bergemann@fortiss.org>

org.fortiss.tooling.kernel.ui/src/org/fortiss/tooling/kernel/ui/internal/views/.ratings

 DoubleClick.java a94d27299814a93b0d8914050a5da7378a7eccd1 GREEN
 GenericNewMenu.java 7e0dd435cb5ca6d4b486235ec17eef3e5c7aa5f6 GREEN
 LinkWithEditorPartListener.java c5ab74424378e7b158a805c4dd14fc03c8abeded GREEN
-ModelElementsView.java ea9b92e2b538a71275a19561633ae53cc5b397a5 YELLOW
+ModelElementsView.java a271d0785ed0943f8d600ca8ffa50a21804c0739 YELLOW
 NavigatorNewMenu.java a35e391960d1dacbe7f77982e53e1891e9382d5a GREEN
 NavigatorTreeContentComparator.java d9f1354cfdff78b104b28887d2397e5ca0e9755b GREEN
 NavigatorTreeContentProvider.java 8162138aab09b2cf833cf5f90ff6ab1fc3edc4d8 GREEN

org.fortiss.tooling.kernel.ui/src/org/fortiss/tooling/kernel/ui/internal/views/ModelElementsView.java

@@ -20,6 +20,8 @@ import static java.util.Collections.emptyList;
 import static org.fortiss.tooling.kernel.service.IPrototypeService.PROTOTYPE_DATA_FORMAT;
 
 import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Set;
 
 import org.conqat.ide.commons.ui.ui.EmptyPartListener;
@@ -55,20 +57,31 @@ import javafx.scene.layout.BorderPane;
  * @author hoelzl
  */
 public final class ModelElementsView extends FXViewPart {
+
 	/** A dummy object serving as hidden root element of the tree view. */
 	private static final Object DUMMY_ROOT = new Object();
+
 	/** The tree-table viewer. */
 	private DynamicTreeViewer<Object> treeViewer;
+
 	/** The filter text field if filtering is enabled in content provider. */
 	private TextField filterWidget;
+
 	/** Current active {@link ExtendableMultiPageEditor}. */
 	private ExtendableMultiPageEditor activeBindingEditor = null;
+
 	/** Stores the editor activation listener. */
 	private EditorActivationListener editorActivationListener = new EditorActivationListener();
+
 	/** The container object used. */
 	private EObject containerObject = null;
+
 	/** The prototypes supported by the current editor. */
 	private Set<Prototype> supportedBaseClasses = new IdentityHashSet<Prototype>();
+
+	/** Cached expansion status of each contained prototype category. */
+	private Map<PrototypeCategory, Boolean> prototypeCategoryExpansionCache = new HashMap<>();
+
 	/** Listener for reacting to changes of the embedded editor. */
 	private final ExtendableMultiPageEditorPageChangeListener bindingEditorPageChangeListener =
 			new ExtendableMultiPageEditorPageChangeListener() {
@@ -126,10 +139,40 @@ public final class ModelElementsView extends FXViewPart {
 			containerObject = null;
 		}
 
+		cacheCurrentItemExpansionStatus();
+
 		treeViewer.update();
+
 		expandCorrectItems();
 	}
 
+	/**
+	 * Goes through the current active {@link TreeItem}s and stores/caches their current expansion
+	 * status, i.e., whether they are expanded as item or not.
+	 */
+	private void cacheCurrentItemExpansionStatus() {
+		TreeItem<Object> rootItem = treeViewer.getControl().getRoot();
+		for(TreeItem<Object> topLevelItem : rootItem.getChildren()) {
+			cacheItemExpansionStatusOfItemAndChildrenRecursively(topLevelItem);
+		}
+	}
+
+	/**
+	 * Stores/caches the current expansion status of the given {@link TreeItem}, i.e., whether they
+	 * are expanded as item or not, and does the same recursively for all of its (possible)
+	 * children.
+	 */
+	private void cacheItemExpansionStatusOfItemAndChildrenRecursively(TreeItem<Object> item) {
+		Object itemObject = item.getValue();
+		if(itemObject instanceof PrototypeCategory) {
+			PrototypeCategory category = (PrototypeCategory)itemObject;
+			prototypeCategoryExpansionCache.put(category, item.isExpanded());
+			for(TreeItem<Object> childItem : item.getChildren()) {
+				cacheItemExpansionStatusOfItemAndChildrenRecursively(childItem);
+			}
+		}
+	}
+
 	/**
 	 * Expands the {@link TreeItem}s that should be expanded due to their (prototype) attribute (if
 	 * they should be expanded by default) or because they were already manually expanded by the
@@ -153,7 +196,12 @@ public final class ModelElementsView extends FXViewPart {
 		Object itemObject = item.getValue();
 		if(itemObject instanceof PrototypeCategory) {
 			PrototypeCategory category = (PrototypeCategory)itemObject;
-			if(category.getExpandedByDefaultStatus()) {
+			// Try getting previous/cached status before checking default one.
+			Boolean shouldBeExpanded = prototypeCategoryExpansionCache.get(category);
+			if(shouldBeExpanded == null) {
+				shouldBeExpanded = category.getExpandedByDefaultStatus();
+			}
+			if(shouldBeExpanded) {
 				// Expand this category (must also be set for all its direct children, otherwise the
 				// children will not show up in the expansion).
 				treeViewer.expandItem(item);