remove old observer before changing user

src/main/java/fr/insa/clavardator/ui/users/UserActiveIndicatorController.java

@@ -5,6 +5,7 @@ import javafx.fxml.FXML;
 import javafx.fxml.Initializable;
 import javafx.scene.shape.Circle;
 
+import java.beans.PropertyChangeEvent;
 import java.net.URL;
 import java.util.ResourceBundle;
 
@@ -12,21 +13,40 @@ public class UserActiveIndicatorController implements Initializable {
 
 	@FXML
 	private Circle circle;
+	private PeerUser user;
 
 	@Override
 	public void initialize(URL location, ResourceBundle resources) {
 
 	}
 
-	public void setUser(PeerUser user) {
+	private void updateState() {
-		circle.getStyleClass().clear();
+		if (user != null) {
-		if (user.isActive()) {
+			circle.getStyleClass().clear();
-			circle.getStyleClass().add("active-user-dot");
+			if (user.isActive()) {
-		} else {
+				circle.getStyleClass().add("active-user-dot");
-			circle.getStyleClass().add("inactive-user-dot");
+			} else {
+				circle.getStyleClass().add("inactive-user-dot");
+			}
 		}
 	}
 
+	private void onStateChange(PropertyChangeEvent propertyChangeEvent) {
+		if (propertyChangeEvent.getPropertyName().equals("state")) {
+			updateState();
+		}
+	}
+
+	public void setUser(PeerUser user) {
+		if (this.user != null) {
+			// remove old observer before setting new user
+			this.user.removeObserver(this::onStateChange);
+		}
+		this.user = user;
+		user.addObserver(this::onStateChange);
+		updateState();
+	}
+
 	public void setSize(double value) {
 		circle.setRadius(value);
 	}