38: Demo developed.

When run with 0.5.0 each click on "Show form" will add another
Validator/Check/TextField to the heap that will not be garbage collected
since it dependsOn the "global" property allowedModulus.

src/test/java/net/synedra/validatorfx/demo/WeakListenerDemo.java

@@ -0,0 +1,79 @@
+package net.synedra.validatorfx.demo;
+
+import javafx.application.Application;
+import javafx.beans.binding.Bindings;
+import javafx.beans.value.ObservableIntegerValue;
+import javafx.event.ActionEvent;
+import javafx.geometry.Insets;
+import javafx.geometry.Pos;
+import javafx.scene.Scene;
+import javafx.scene.control.Button;
+import javafx.scene.control.RadioButton;
+import javafx.scene.control.ToggleGroup;
+import javafx.scene.layout.GridPane;
+import javafx.stage.Stage;
+
+/** WeakListenerDemo shows why weak listeners are required in ValidatorFX.
+ * @author [email protected]
+ */
+public class WeakListenerDemo extends Application {
+
+	private WeakListenerDemoForm form;
+	private GridPane grid;
+	private RadioButton odd;
+	private RadioButton even;
+	private ToggleGroup togglegroup; // this contains the "global" property our check will depend on ...
+	private ObservableIntegerValue allowedModulus;
+
+	@Override
+	public void start(Stage primaryStage) throws Exception {
+		grid = createGrid();
+
+		Button showFormButton = new Button("Show form");
+		showFormButton.setOnAction(this::showNewForm);
+		grid.add(showFormButton, 0, 0);
+
+		togglegroup = new ToggleGroup();
+
+		odd = new RadioButton("Odd");
+		odd.setToggleGroup(togglegroup);
+		grid.add(odd, 1, 0);
+
+		even = new RadioButton("Even");
+		even.setToggleGroup(togglegroup);
+		grid.add(even, 2, 0);
+
+		togglegroup.selectToggle(odd);
+
+		allowedModulus = Bindings.createIntegerBinding(() -> {
+			return togglegroup.getSelectedToggle() == odd ? 1 : 0;
+		}, togglegroup.selectedToggleProperty());
+
+		Scene scene = new Scene(grid);		
+		primaryStage.setScene(scene);		
+		primaryStage.show();		
+	}
+
+	private void showNewForm(ActionEvent e) {
+		if (form != null) {
+			grid.getChildren().remove(form.getPresentation());
+		}
+		form = new WeakListenerDemoForm(allowedModulus);		
+		grid.add(form.getPresentation(), 0, 1, 2, 1);
+	}
+
+	private GridPane createGrid() {
+		GridPane grid = new GridPane();
+		grid.setAlignment(Pos.TOP_LEFT);
+		grid.setHgap(10);
+		grid.setVgap(10);
+		grid.setPadding(new Insets(25, 25, 25, 25));
+		grid.setMinSize(600, 400);
+		return grid;
+	}
+
+
+	public static void main(String[] args) {
+		launch();
+	}
+}

src/test/java/net/synedra/validatorfx/demo/WeakListenerDemoForm.java

@@ -0,0 +1,36 @@
+package net.synedra.validatorfx.demo;
+
+import javafx.beans.value.ObservableIntegerValue;
+import javafx.geometry.Insets;
+import javafx.scene.Node;
+import javafx.scene.control.TextField;
+import javafx.scene.layout.VBox;
+import net.synedra.validatorfx.Validator;
+
+/** This class simulates a (very simple) form that contains a validator and a check.
+ * The expectation is that if no reference to a WeakListenerDemoForm instance exists, it will be garbage collected.
+ */
+class WeakListenerDemoForm {
+	private Validator validator = new Validator();		
+	private TextField textField = new TextField();
+	WeakListenerDemoForm(ObservableIntegerValue allowedModulus) {
+		VBox.setMargin(textField, new Insets(5));
+		validator.createCheck()
+			.dependsOn("username", textField.textProperty())
+			.dependsOn("allowedModulus", allowedModulus)
+			.withMethod(c -> {
+				String userName = c.get("username");
+				int allowed = c.get("allowedModulus");
+				if (userName.length() % 2 != allowed) {
+					c.error("Please use " + (allowed == 0 ? "even" : "odd") + " number of letters.");
+				}
+			})
+			.decorates(textField)
+			.immediate();
+		;
+	}
+
+	Node getPresentation() {
+		return textField;
+	}
+}