Scenario lifecycle methods

- Add ScenarioContext which knows about View and start/stop
  runnable methods.
- Change Catalog to rely on ScenarioContext and call
  start/stop on an appropriate moment.
- Still keep Scenario.build() around so that we have time
  to refactor in favour of ScenarioContext.buildContext()
  or whatever build() method in it should be.
- Fixes #1004

spring-shell-samples/spring-shell-sample-catalog/src/main/java/org/springframework/shell/samples/catalog/Catalog.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 the original author or authors.
+ * Copyright 2023-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -43,7 +43,6 @@ import org.springframework.shell.component.view.control.MenuView.MenuItem;
 import org.springframework.shell.component.view.control.MenuView.MenuItemCheckStyle;
 import org.springframework.shell.component.view.control.StatusBarView;
 import org.springframework.shell.component.view.control.StatusBarView.StatusItem;
-import org.springframework.shell.component.view.control.View;
 import org.springframework.shell.component.view.control.cell.AbstractListCell;
 import org.springframework.shell.component.view.event.EventLoop;
 import org.springframework.shell.component.view.event.KeyEvent;
@@ -56,6 +55,7 @@ import org.springframework.shell.geom.HorizontalAlign;
 import org.springframework.shell.geom.Rectangle;
 import org.springframework.shell.geom.VerticalAlign;
 import org.springframework.shell.samples.catalog.scenario.Scenario;
+import org.springframework.shell.samples.catalog.scenario.Scenario.ScenarioContext;
 import org.springframework.shell.samples.catalog.scenario.ScenarioComponent;
 import org.springframework.shell.style.ThemeResolver;
 import org.springframework.util.ObjectUtils;
@@ -78,7 +78,7 @@ public class Catalog {
 
 	// mapping from category name to scenarios(can belong to multiple categories)
 	private final Map<String, List<ScenarioData>> categoryMap = new TreeMap<>();
-	private View currentScenarioView = null;
+	private ScenarioContext currentScenarioContext = null;
 	private TerminalUI ui;
 	private ListView<String> categories;
 	private ListView<ScenarioData> scenarios;
@@ -130,8 +130,9 @@ public class Catalog {
 		eventLoop.onDestroy(eventLoop.keyEvents()
 			.doOnNext(m -> {
 				if (m.getPlainKey() == Key.q && m.hasCtrl()) {
-					if (currentScenarioView != null) {
+					if (currentScenarioContext != null) {
-						currentScenarioView = null;
+						currentScenarioContext.stop();
+						currentScenarioContext = null;
 						ui.setRoot(app, true);
 						ui.setFocus(categories);
 					}
@@ -172,13 +173,11 @@ public class Catalog {
 		// handle event when scenario is chosen
 		eventLoop.onDestroy(eventLoop.viewEvents(LISTVIEW_SCENARIO_TYPEREF, scenarios)
 			.subscribe(event -> {
-				View view = event.args().item().scenario().configure(ui).build();
+				ScenarioContext context = event.args().item().scenario().configure(ui).buildContext();
-				ui.configure(view);
+				ui.configure(context.view());
-				// View view = event.args().item().scenario()
+				component.setRoot(context.view(), true);
-				// 	.configure(ui, eventLoop, themeResolver, activeThemeName)
+				context.start();
-				// 	.build();
+				currentScenarioContext = context;
-				component.setRoot(view, true);
-				currentScenarioView = view;
 			}));
 
 

spring-shell-samples/spring-shell-sample-catalog/src/main/java/org/springframework/shell/samples/catalog/scenario/AbstractScenario.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 the original author or authors.
+ * Copyright 2023-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -54,6 +54,11 @@ public abstract class AbstractScenario implements Scenario {
 		return ui;
 	}
 
+	@Override
+	public View build() {
+		throw new UnsupportedOperationException("Need to implement via 'buildContext'");
+	}
+
 	@Override
 	public Scenario configure(TerminalUI ui) {
 		this.ui = ui;

spring-shell-samples/spring-shell-sample-catalog/src/main/java/org/springframework/shell/samples/catalog/scenario/Scenario.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 the original author or authors.
+ * Copyright 2023-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,8 +15,10 @@
  */
 package org.springframework.shell.samples.catalog.scenario;
 
+import org.springframework.lang.Nullable;
 import org.springframework.shell.component.view.TerminalUI;
 import org.springframework.shell.component.view.control.View;
+import org.springframework.shell.samples.catalog.Catalog;
 
 /**
  * {@link Scenario} participates in a catalog showcase.
@@ -28,17 +30,29 @@ public interface Scenario {
 	// Common category names
 	public static final String CATEGORY_ALL = "All Scenarios";
 	public static final String CATEGORY_LISTVIEW = "ListView";
+	public static final String CATEGORY_PROGRESSVIEW = "ProgressView";
 	public static final String CATEGORY_BOXVIEW = "BoxView";
 	public static final String CATEGORY_LAYOUT = "Layout";
 	public static final String CATEGORY_OTHER = "Other";
 
 	/**
-	 * Build a {@link View} to be shown with a scenario.
+	 * Build a {@link View} to be shown with a scenario. Prefer {@link #buildContext()}
+	 * as this method will be deprecated and renamed.
 	 *
 	 * @return view of a scenario
+	 * @see #buildContext()
 	 */
 	View build();
 
+	/**
+	 * Build a {@link ScenarioContext} wrapping needed view and lifecycle methods.
+	 *
+	 * @return a scenario context
+	 */
+	default ScenarioContext buildContext() {
+		return ScenarioContext.of(build());
+	}
+
 	/**
 	 * Configure scenario.
 	 *
@@ -47,4 +61,78 @@ public interface Scenario {
 	 */
 	Scenario configure(TerminalUI ui);
 
+	/**
+	 * Context represents a build {@code View} and lifecycle methods called by a
+	 * catalog app.
+	 *
+	 * For simple {@link View} without any need for lifecycle methods, just call
+	 * {@link #of(View)}.
+	 */
+	public interface ScenarioContext {
+
+		/**
+		 * Get a view represented by a {@link Scenario}.
+		 *
+		 * @return a scenario view
+		 */
+		View view();
+
+		/**
+		 * Called by a {@link Catalog} when its ready to show a {@link View} build from
+		 * a {@link Scenario}.
+		 */
+		void start();
+
+		/**
+		 * Called by a {@link Catalog} when its ready to discard a {@link View} build from
+		 * a {@link Scenario}.
+		 */
+		void stop();
+
+		/**
+		 * Utility method to build a {@code ScenarioContext} of {@link View} without
+		 * lifecycle callbacks.
+		 *
+		 * @param view the main view
+		 * @return a scenario context
+		 */
+		public static ScenarioContext of(View view) {
+			return of(view, null, null);
+		}
+
+		/**
+		 * Utility method to build a {@code ScenarioContext}.
+		 *
+		 * @param view the main view
+		 * @param start the start callback
+		 * @param stop the stop callback
+		 * @return a scenario context
+		 */
+		public static ScenarioContext of(View view, @Nullable Runnable start, @Nullable Runnable stop) {
+			return new ScenarioContext() {
+
+				@Override
+				public View view() {
+					return view;
+				}
+
+				@Override
+				public void start() {
+					if (start != null) {
+						start.run();
+					}
+				}
+
+				@Override
+				public void stop() {
+					if (stop != null) {
+						stop.run();
+					}
+				}
+
+			};
+		}
+
+	}
+
 }