What's a good observable appendable base for a TextArea? - javafx

Question

I have a StringBuffer that is occasionally appended with new information.
In a separate module, I have a JavaFX TextArea that displays that StringBuffer.
Right now, I have to manually update the TextArea every time the underlying data is modified.
Is there something like an ObservableList (which I use for TableViews) that I can use as the back-end data for the TextArea instead, so I don't have to manually manage pushing the changes to the display?
I am not attached to using a StringBuffer. I'm glad to use any appendable data structure to hold text.

Answer 1

You can consider something simple like this:
import javafx.beans.binding.StringBinding;
public class ObservableStringBuffer extends StringBinding {
private final StringBuffer buffer = new StringBuffer() ;
#Override
protected String computeValue() {
return buffer.toString();
}
public void set(String content) {
buffer.replace(0, buffer.length(), content);
invalidate();
}
public void append(String text) {
buffer.append(text);
invalidate();
}
// wrap other StringBuffer methods as needed...
}
This enables easy coding for binding to a text area. You can simply do
TextArea textArea = new TextArea();
ObservableStringBuffer buffer = new ObservableStringBuffer();
textArea.textProperty().bind(buffer);
// ...
buffer.append("Hello world");
However, it's important to note here that you don't transfer the efficiency of the buffer API to the text area: the text area simply has a textProperty() representing its text, which can still only really be modified by set(...) and setValue(...). In other words, when you append to the buffer, you essentially end up with textArea.setText(textArea.getText() + "Hello world") (not textArea.appendText("Hello world"). If you're just looking for a clean API, then this should work for you; if you're looking for something efficient, you would have to "wire" the calls to appendText yourself, since that is simply not supported by the text area's textProperty().
Here's a SSCCE using the above class:
import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.Duration;
public class ObservableStringBufferTest extends Application {
private int counter ;
#Override
public void start(Stage primaryStage) {
ObservableStringBuffer buffer = new ObservableStringBuffer();
TextArea textArea = new TextArea();
textArea.setEditable(false);
textArea.textProperty().bind(buffer);
buffer.set("Item 0");
Timeline timeline = new Timeline(new KeyFrame(
Duration.seconds(1),
e -> buffer.append("\nItem "+(++counter))));
timeline.setCycleCount(Animation.INDEFINITE);
timeline.play();
primaryStage.setScene(new Scene(new StackPane(textArea)));
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}