How to bind ComboBox to a list in JavaFX? - list

Question

My application periodically adds Strings to a List using a Thread. I want to add those strings to a ComboBox as soon as they get added to the List. Is there anyway to bind a ComboBox to a List?
My Code:
static final int max = 20;
List<String> ips = new ArrayList<String>();
public void getIP() throws UnknownHostException {
Task task = new Task<Void>() {
#Override
public Void call() throws UnknownHostException {
InetAddress localhost = InetAddress.getLocalHost();
byte[] ip = localhost.getAddress();
for (int i = 10; i <= max; i++) {
if (isCancelled()) {
break;
}
try {
ip[3] = (byte) i;
InetAddress address = InetAddress.getByAddress(ip);
if (address.isReachable(100)) {
//============================== Populating List ===============//
ips.add(address.getHostName());
}
} catch (Exception e) {
System.err.println(e);
}
updateProgress(i, max);
}
return null;
}
};
//============================== Bind ComboBox to List Code here ===============//
indicator.progressProperty().bind(task.progressProperty());
new Thread(task).start();
}

Answer 1

No there is no way to bind a simple list, since it's not observable. Even with a ObservableList, there would be the problem of the updates coming from a different thread.
You could however use a synchronized list and use the value property to pass the current size, which would allow you to add the items via listener.
Example
This uses a ListView instead of a ComboBox, since the results are visible without user interaction, but you could also use targetList = comboBox.getItems().
#Override
public void start(Stage primaryStage) {
ListView<String> listView = new ListView<>();
List<String> targetList = listView.getItems();
final List<String> ips = Collections.synchronizedList(new ArrayList<>());
Task<Integer> task = new Task<Integer>() {
#Override
protected Integer call() throws Exception {
Random random = new Random();
int size;
for (size = 0; size < 100; size++) {
ips.add(Integer.toString(size));
updateValue(size);
Thread.sleep(random.nextInt(500));
}
return size;
}
};
task.valueProperty().addListener((observable, oldValue, newValue) -> {
// add values not yet in the target list.
for (int i = targetList.size(), newSize = newValue; i < newSize; i++) {
targetList.add(ips.get(i));
}
});
new Thread(task).start();
Scene scene = new Scene(listView);
primaryStage.setScene(scene);
primaryStage.show();
}
It would be a bit simpler though to simply post the updates on the ui thread using Platform.runLater though:
ips = comboBox.getItems();
Task task = new Task<Void>() {
#Override
public Void call() throws UnknownHostException {
InetAddress localhost = InetAddress.getLocalHost();
byte[] ip = localhost.getAddress();
for (int i = 10; i <= max; i++) {
if (isCancelled()) {
break;
}
try {
ip[3] = (byte) i;
InetAddress address = InetAddress.getByAddress(ip);
if (address.isReachable(100)) {
//============================== Populating List ===============//
final String hostName = address.getHostName();
// do update on application thread
Platform.runLater(() -> ips.add(hostName));
}
} catch (Exception e) {
System.err.println(e);
}
updateProgress(i, max);
}
return null;
}
};

Answer 2

i suggest you to do the following:
change
List<String> ips = new ArrayList<String>();
to
final ObservableList<String> ips = FXCollections.observableArrayList();
change:
Task task = new Task<Void>()
to
Task<ObservableList<String> task = new Task<>(){
#Override
public ObservableList<String> call() throws UnknownHostException {
...
return ips;
}
};
comboBox.itemsProperty().bind(task.valueProperty());