TextField和属性之间的JavaFX绑定

Question

If you create a binding between a JavaFX TextField and a property, then this binding is invalidated on every keystroke, which causes a change to the text.

If you have a chain of bindings the default behavior could cause problems, because in the middle of the editing values may be not valid.

Ok, I know I could create an uni-directional binding from the property to the textfield and register a change listener to get informed when the cursor leaves the field and update the property manually if necessary.

Is there an easy, elegant way to change this behavior so that the binding is only invalidated when the editing is complete, eg when the cursor leaves the field?

Thanks

Answer 1

I think you've pretty much described the only way to do it. Here's about the cleanest way I can see to implement it (using Java 8, though it's easy enough to convert the lambdas back to be JavaFX 2.2 compatible if you need):

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.binding.StringBinding;
import javafx.event.ActionEvent;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

    public class CommitBoundTextField extends Application {

        @Override
        public void start(Stage primaryStage) {
            TextField tf1 = new TextField();
            createCommitBinding(tf1).addListener((obs, oldText, newText) -> 
                System.out.printf("Text 1 changed from \"%s\" to \"%s\"%n", oldText, newText));
            TextField tf2 = new TextField();
            createCommitBinding(tf2).addListener((obs, oldText, newText) -> 
                System.out.printf("Text 2 changed from \"%s\" to \"%s\"%n", oldText, newText));
            VBox root = new VBox(5, tf1, tf2);
            Scene scene = new Scene(root, 250, 100);
            primaryStage.setScene(scene);
            primaryStage.show();
        }

        private StringBinding createCommitBinding(TextField textField) {
            StringBinding binding = Bindings.createStringBinding(() -> textField.getText());
            textField.addEventHandler(ActionEvent.ACTION, evt -> binding.invalidate());
            textField.focusedProperty().addListener((obs, wasFocused, isFocused)-> {
                if (! isFocused) binding.invalidate();
            });
            return binding ;
        }

        public static void main(String[] args) {
            launch(args);
        }
    }