List, Table and Tree: added colors for drag-and-drop

- added "enable drag and drop" checkbox to Demo on "Data Components" tab
- support copying UI default values lazy

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

@@ -32,6 +32,7 @@ import java.util.ServiceLoader;
 import java.util.function.Function;
 import java.util.logging.Level;
 import javax.swing.UIDefaults;
+import javax.swing.UIManager;
 import javax.swing.UIDefaults.ActiveValue;
 import javax.swing.UIDefaults.LazyValue;
 import javax.swing.plaf.ColorUIResource;
@@ -227,6 +228,15 @@ class UIDefaultsLoader
 			case "true":	return true;
 		}
 
+		// check for function "lazy"
+		//     Syntax: lazy(uiKey)
+		if( value.startsWith( "lazy(" ) && value.endsWith( ")" ) ) {
+			String uiKey = value.substring( 5, value.length() - 1 ).trim();
+			return (LazyValue) t -> {
+				return lazyUIManagerGet( uiKey );
+			};
+		}
+
 		ValueType valueType = ValueType.UNKNOWN;
 
 		// check whether value type is specified in the value
@@ -281,7 +291,7 @@ class UIDefaultsLoader
 			case UNKNOWN:
 			default:
 				// colors
-				ColorUIResource color = parseColorOrFunction( value, resolver, false );
+				Object color = parseColorOrFunction( value, resolver, false );
 				if( color != null )
 					return color;
 
@@ -301,7 +311,7 @@ class UIDefaultsLoader
 			List<String> parts = split( value, ',' );
 			Insets insets = parseInsets( value );
 			ColorUIResource lineColor = (parts.size() == 5)
-				? parseColorOrFunction( resolver.apply( parts.get( 4 ) ), resolver, true )
+				? (ColorUIResource) parseColorOrFunction( resolver.apply( parts.get( 4 ) ), resolver, true )
 				: null;
 
 			return (LazyValue) t -> {
@@ -377,7 +387,7 @@ class UIDefaultsLoader
 		}
 	}
 
-	private static ColorUIResource parseColorOrFunction( String value, Function<String, String> resolver, boolean reportError ) {
+	private static Object parseColorOrFunction( String value, Function<String, String> resolver, boolean reportError ) {
 		if( value.endsWith( ")" ) )
 			return parseColorFunctions( value, resolver, reportError );
 
@@ -447,7 +457,7 @@ class UIDefaultsLoader
 			: (((n >> 8) & 0xffffff) | ((n & 0xff) << 24)); // move alpha from lowest to highest byte
 	}
 
-	private static ColorUIResource parseColorFunctions( String value, Function<String, String> resolver, boolean reportError ) {
+	private static Object parseColorFunctions( String value, Function<String, String> resolver, boolean reportError ) {
 		int paramsStart = value.indexOf( '(' );
 		if( paramsStart < 0 ) {
 			if( reportError )
@@ -511,9 +521,9 @@ class UIDefaultsLoader
 	 * Syntax: lighten([color,]amount[,options]) or darken([color,]amount[,options])
 	 *   - color: a color (e.g. #f00) or a color function
 	 *   - amount: percentage 0-100%
-	 *   - options: [relative] [autoInverse]
+	 *   - options: [relative] [autoInverse] [lazy]
 	 */
-	private static ColorUIResource parseColorLightenOrDarken( boolean lighten, List<String> params,
+	private static Object parseColorLightenOrDarken( boolean lighten, List<String> params,
 		Function<String, String> resolver, boolean reportError )
 	{
 		boolean isDerived = params.get( 0 ).endsWith( "%" );
@@ -522,11 +532,13 @@ class UIDefaultsLoader
 		int amount = parsePercentage( params.get( nextParam++ ) );
 		boolean relative = false;
 		boolean autoInverse = false;
+		boolean lazy = false;
 
 		if( params.size() > nextParam ) {
 			String options = params.get( nextParam++ );
 			relative = options.contains( "relative" );
 			autoInverse = options.contains( "autoInverse" );
+			lazy = options.contains( "lazy" );
 		}
 
 		ColorFunctions.ColorFunction function = lighten
@@ -536,7 +548,16 @@ class UIDefaultsLoader
 		if( isDerived )
 			return new DerivedColor( function );
 
-		ColorUIResource color = parseColorOrFunction( resolver.apply( colorStr ), resolver, reportError );
+		if( lazy ) {
+			return (LazyValue) t -> {
+				Object color = lazyUIManagerGet( colorStr );
+				return (color instanceof Color)
+					? new ColorUIResource( ColorFunctions.applyFunctions( (Color) color, function ) )
+					: null;
+			};
+		}
+
+		ColorUIResource color = (ColorUIResource) parseColorOrFunction( resolver.apply( colorStr ), resolver, reportError );
 		return new ColorUIResource( ColorFunctions.applyFunctions( color, function ) );
 	}
 
@@ -618,4 +639,21 @@ class UIDefaultsLoader
 
 		return strs;
 	}
+
+	/**
+	 * For use in LazyValue to get value for given key from UIManager and report error
+	 * if not found. If key is prefixed by '?', then no error is reported.
+	 */
+	private static Object lazyUIManagerGet( String uiKey ) {
+		boolean optional = false;
+		if( uiKey.startsWith( OPTIONAL_PREFIX ) ) {
+			uiKey = uiKey.substring( OPTIONAL_PREFIX.length() );
+			optional = true;
+		}
+
+		Object value = UIManager.get( uiKey );
+		if( value == null && !optional )
+			FlatLaf.LOG.log( Level.SEVERE, "FlatLaf: '" + uiKey + "' not found in UI defaults." );
+		return value;
+	}
 }

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatDarkLaf.properties

@@ -35,6 +35,12 @@
 @buttonHoverBackground=lighten(3%,autoInverse)
 @buttonPressedBackground=lighten(6%,autoInverse)
 
+# Drop (use lazy colors for IntelliJ platform themes, which usually do not specify these colors)
+@dropCellBackground=darken(List.selectionBackground,10%,lazy)
+@dropCellForeground=lazy(List.selectionForeground)
+@dropLineColor=lighten(List.selectionBackground,10%,lazy)
+@dropLineShortColor=lighten(List.selectionBackground,30%,lazy)
+
 
 #---- globals ----
 

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLaf.properties

@@ -203,6 +203,9 @@ List.focusCellHighlightBorder=com.formdev.flatlaf.ui.FlatListCellBorder$Focused
 List.focusSelectedCellHighlightBorder=com.formdev.flatlaf.ui.FlatListCellBorder$Selected
 List.selectionInactiveBackground=@selectionInactiveBackground
 List.selectionInactiveForeground=@selectionInactiveForeground
+List.dropCellBackground=@dropCellBackground
+List.dropCellForeground=@dropCellForeground
+List.dropLineColor=@dropLineColor
 
 
 #---- Menu ----
@@ -376,6 +379,10 @@ Table.cellNoFocusBorder=2,3,2,3
 Table.focusSelectedCellHighlightBorder=2,3,2,3,@cellFocusColor
 Table.selectionInactiveBackground=@selectionInactiveBackground
 Table.selectionInactiveForeground=@selectionInactiveForeground
+Table.dropCellBackground=@dropCellBackground
+Table.dropCellForeground=@dropCellForeground
+Table.dropLineColor=@dropLineColor
+Table.dropLineShortColor=@dropLineShortColor
 
 
 #---- TableHeader ----
@@ -455,6 +462,9 @@ Tree.selectionInactiveBackground=@selectionInactiveBackground
 Tree.selectionInactiveForeground=@selectionInactiveForeground
 Tree.textBackground=null
 Tree.selectionBorderColor=@cellFocusColor
+Tree.dropCellBackground=@dropCellBackground
+Tree.dropCellForeground=@dropCellForeground
+Tree.dropLineColor=@dropLineColor
 Tree.rendererMargins=1,2,1,2
 Tree.wideSelection=true
 Tree.paintLines=false

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLightLaf.properties

@@ -35,6 +35,12 @@
 @buttonHoverBackground=darken(3%,autoInverse)
 @buttonPressedBackground=darken(10%,autoInverse)
 
+# Drop (use lazy colors for IntelliJ platform themes, which usually do not specify these colors)
+@dropCellBackground=lighten(List.selectionBackground,10%,lazy)
+@dropCellForeground=lazy(List.selectionForeground)
+@dropLineColor=lighten(List.selectionBackground,20%,lazy)
+@dropLineShortColor=darken(List.selectionBackground,20%,lazy)
+
 
 #---- globals ----