Theme Editor: fixed preview of focused button in FlatDarkLaf (and probably other null value related issues)

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

@@ -928,6 +928,11 @@ public abstract class FlatLaf
 	 * Registers a UI defaults getter function that is invoked before the standard getter.
 	 * This allows using different UI defaults for special purposes
 	 * (e.g. using multiple themes at the same time).
+	 * <p>
+	 * The key is passed as parameter to the function.
+	 * If the function returns {@code null}, then the next registered function is invoked.
+	 * If all registered functions return {@code null}, then the current look and feel is asked.
+	 * If the function returns {@link #NULL_VALUE}, then the UI value becomes {@code null}.
 	 *
 	 * @see #unregisterUIDefaultsGetter(Function)
 	 * @see #runWithUIDefaultsGetter(Function, Runnable)
@@ -969,6 +974,25 @@ public abstract class FlatLaf
 	 * (e.g. using multiple themes at the same time).
 	 * If the current look and feel is not FlatLaf, then the getter is ignored and
 	 * the given runnable invoked.
+	 * <p>
+	 * The key is passed as parameter to the function.
+	 * If the function returns {@code null}, then the next registered function is invoked.
+	 * If all registered functions return {@code null}, then the current look and feel is asked.
+	 * If the function returns {@link #NULL_VALUE}, then the UI value becomes {@code null}.
+	 * <p>
+	 * Example:
+	 * <pre>{@code
+	 * // create secondary theme
+	 * UIDefaults darkDefaults = new FlatDarkLaf().getDefaults();
+	 *
+	 * // create panel using secondary theme
+	 * FlatLaf.runWithUIDefaultsGetter( key -> {
+	 *     Object value = darkDefaults.get( key );
+	 *     return (value != null) ? value : FlatLaf.NULL_VALUE;
+	 * }, () -> {
+	 *     // TODO create components that should use secondary theme here
+	 * } );
+	 * }</pre>
 	 *
 	 * @see #registerUIDefaultsGetter(Function)
 	 * @see #unregisterUIDefaultsGetter(Function)
@@ -987,6 +1011,17 @@ public abstract class FlatLaf
 			runnable.run();
 	}
 
+	/**
+	 * Special value returned by functions used in {@link #runWithUIDefaultsGetter(Function, Runnable)}
+	 * or {@link #registerUIDefaultsGetter(Function)} to indicate that the UI value should
+	 * become {@code null}.
+	 *
+	 * @see #runWithUIDefaultsGetter(Function, Runnable)
+	 * @see #registerUIDefaultsGetter(Function)
+	 * @since 1.6
+	 */
+	public static final Object NULL_VALUE = new Object();
+
 	//---- class FlatUIDefaults -----------------------------------------------
 
 	private class FlatUIDefaults
@@ -999,13 +1034,13 @@ public abstract class FlatLaf
 		@Override
 		public Object get( Object key ) {
 			Object value = getValue( key );
-			return (value != null) ? value : super.get( key );
+			return (value != null) ? (value != NULL_VALUE ? value : null) : super.get( key );
 		}
 
 		@Override
 		public Object get( Object key, Locale l ) {
 			Object value = getValue( key );
-			return (value != null) ? value : super.get( key, l );
+			return (value != null) ? (value != NULL_VALUE ? value : null) : super.get( key, l );
 		}
 
 		private Object getValue( Object key ) {

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemePreview.java

@@ -161,6 +161,17 @@ class FlatThemePreview
 			value = ((ActiveValue)value).createValue( null );
 
 //		System.out.println( key + " = " + value );
+
+		// If value is null and is a property that is defined in a core theme,
+		// then force the value to null.
+		// This is necessary for cases where the current application Laf defines a property
+		// but the edited theme does not (or has set the value explicitly to null).
+		// E.g. FlatLightLaf defines Button.focusedBackground, but in FlatDarkLaf
+		// it is not defined. Without this code, the preview for FlatDarkLaf would use
+		// Button.focusedBackground from FlatLightLaf if FlatLightLaf is the current application Laf.
+		if( value == null && FlatThemePropertiesBaseManager.getDefindedCoreKeys().contains( key ) )
+			return FlatLaf.NULL_VALUE;
+
 		return value;
 	}
 

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemePropertiesBaseManager.java

@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -47,7 +48,8 @@ class FlatThemePropertiesBaseManager
 	};
 
 	private final Map<String, MyBasePropertyProvider> providers = new HashMap<>();
-	private Map<String, Properties> coreThemes;
+	private static Map<String, Properties> coreThemes;
+	private static Set<String> definedCoreKeys;
 
 	FlatThemePropertiesSupport.BasePropertyProvider create( File file, FlatThemePropertiesSupport propertiesSupport ) {
 		String name = StringUtils.removeTrailing( file.getName(), ".properties" );
@@ -61,7 +63,31 @@ class FlatThemePropertiesBaseManager
 		providers.clear();
 	}
 
-	private void loadCoreThemes() {
+	static Set<String> getDefindedCoreKeys() {
+		if( definedCoreKeys != null )
+			return definedCoreKeys;
+
+		loadCoreThemes();
+
+		definedCoreKeys = new HashSet<>();
+		for( Properties properties : coreThemes.values() ) {
+			for( Object k : properties.keySet() ) {
+				String key = (String) k;
+				if( key.startsWith( "*." ) || key.startsWith( "@" ) )
+					continue;
+				if( key.startsWith( "[" ) ) {
+					int closeIndex = key.indexOf( ']' );
+					if( closeIndex < 0 )
+						continue;
+					key = key.substring( closeIndex + 1 );
+				}
+				definedCoreKeys.add( key );
+			}
+		}
+		return definedCoreKeys;
+	}
+
+	private static void loadCoreThemes() {
 		if( coreThemes != null )
 			return;