Tree on macOS: fixed Left and Right keys to collapse or expand nodes

CHANGELOG.md

@@ -8,6 +8,8 @@ FlatLaf Change Log
 - TabbedPane: In scroll-tab-layout, the cropped line is now hidden. (issue #40)
 - Tree: UI default value `Tree.textBackground` now has a valid color and is no
   longer `null`.
+- Tree on macOS: Fixed <kbd>Left</kbd> and <kbd>Right</kbd> keys to collapse or
+  expand nodes.
 - Button and ToggleButton: Support per component minimum height (set client
   property `JComponent.minimumHeight` to an integer). (issue #44)
 - Button and ToggleButton: Do not apply minimum width if button border was

flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java

@@ -34,12 +34,15 @@ import java.util.function.Consumer;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.swing.AbstractButton;
+import javax.swing.InputMap;
 import javax.swing.JLabel;
 import javax.swing.JTabbedPane;
+import javax.swing.KeyStroke;
 import javax.swing.LookAndFeel;
 import javax.swing.PopupFactory;
 import javax.swing.SwingUtilities;
 import javax.swing.UIDefaults;
+import javax.swing.UIDefaults.LazyValue;
 import javax.swing.UIManager;
 import javax.swing.UnsupportedLookAndFeelException;
 import javax.swing.plaf.ColorUIResource;
@@ -231,6 +234,7 @@ public abstract class FlatLaf
 
 		initFonts( defaults );
 		initIconColors( defaults, isDark() );
+		initInputMaps( defaults );
 
 		// load defaults from properties
 		List<Class<?>> lafClassesForDefaultsLoading = getLafClassesForDefaultsLoading();
@@ -337,6 +341,40 @@ public abstract class FlatLaf
 		defaults.put( "Objects.BlackText",      new ColorUIResource( 0x231F20 ) );
 	}
 
+	private void initInputMaps( UIDefaults defaults ) {
+		if( SystemInfo.IS_MAC ) {
+			// AquaLookAndFeel (the base for UI defaults on macOS) uses special
+			// action keys (e.g. "aquaExpandNode") for its macOS typical tree node
+			// expanding/collapsing, which are not available in FlatLaf.
+			// --> map the keys back to default Java actions
+			modifyInputMap( defaults, "Tree.focusInputMap",
+				         "RIGHT", "selectChild",
+				      "KP_RIGHT", "selectChild",
+				          "LEFT", "selectParent",
+				       "KP_LEFT", "selectParent",
+				   "shift RIGHT", null,
+				"shift KP_RIGHT", null,
+				    "shift LEFT", null,
+				 "shift KP_LEFT", null,
+				     "ctrl LEFT", null,
+				  "ctrl KP_LEFT", null,
+				    "ctrl RIGHT", null,
+				 "ctrl KP_RIGHT", null
+			);
+			defaults.put( "Tree.focusInputMap.RightToLeft", new UIDefaults.LazyInputMap( new Object[] {
+	                     "RIGHT", "selectParent",
+	                  "KP_RIGHT", "selectParent",
+	                      "LEFT", "selectChild",
+	                   "KP_LEFT", "selectChild"
+			} ) );
+		}
+	}
+
+	private void modifyInputMap( UIDefaults defaults, String key, Object... bindings ) {
+		// Note: not using `defaults.get(key)` here because this would resolve the lazy value
+		defaults.put( key, new LazyModifyInputMap( defaults.remove( key ), bindings ) );
+	}
+
 	private static void reSetLookAndFeel() {
 		EventQueue.invokeLater( () -> {
 			LookAndFeel lookAndFeel = UIManager.getLookAndFeel();
@@ -445,4 +483,38 @@ public abstract class FlatLaf
 
 		return false;
 	}
+
+	//---- class LazyModifyInputMap -------------------------------------------
+
+	private static class LazyModifyInputMap
+		implements LazyValue
+	{
+		private final Object baseInputMap;
+		private final Object[] bindings;
+
+		public LazyModifyInputMap( Object baseInputMap, Object[] bindings ) {
+			this.baseInputMap = baseInputMap;
+			this.bindings = bindings;
+		}
+
+		@Override
+		public Object createValue( UIDefaults table ) {
+			// get base input map
+			InputMap inputMap = (baseInputMap instanceof LazyValue)
+				? (InputMap) ((LazyValue)baseInputMap).createValue( table )
+				: (InputMap) baseInputMap;
+
+			// modify input map (replace or remove)
+			for( int i = 0; i < bindings.length; i += 2 ) {
+				KeyStroke keyStroke = KeyStroke.getKeyStroke( (String) bindings[i] );
+				if( bindings[i + 1] != null )
+					inputMap.put( keyStroke, bindings[i + 1] );
+				else
+					inputMap.remove( keyStroke );
+			}
+
+			return inputMap;
+		}
+
+	}
 }