A list of basic values is filtered by a (changing) predicate. The FilteredList
is mapped to TreeItem
s and this resulting list is then used as the root TreeItem
s children.
When a selection was made on the TreeTableView
and afterwards the predicate changes, accessing the selected items results in a NullPointerException
.
It seems to me that items contained in the change are null
. Is there a design flaw in this coarse concept?
This does not happen for the classes TreeView
and ListView
.
I tried to produce a MCVE using https://github.com/TomasMikula/EasyBind for the mapping:
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.fxmisc.easybind.EasyBind;
import javafx.application.Application;
import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.beans.binding.Bindings;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.collections.transformation.FilteredList;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.Spinner;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeTableColumn;
import javafx.scene.control.TreeTableView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class App extends Application {
// fields protect bound lists from GC
private ObservableList<DataItem> itemizedDataPool;
private FilteredList<Data> filteredDataPool;
private ObservableList<Data> selectedData;
static class Data {
final int value;
public Data(int value) {
this.value = value;
}
}
static class DataItem extends TreeItem<Data> {
final Data data;
public DataItem(Data data) {
this.data = data;
}
}
@Override
public void start(Stage primaryStage) throws IOException {
List<Data> dataPool = new ArrayList<Data>();
for (int i = 1; i < 20; i++) {
dataPool.add(new Data(i));
}
filteredDataPool = new FilteredList<>(FXCollections.observableArrayList(dataPool));
TreeTableView<Data> listView = createTreeTableView();
Spinner<?> lowerBoundSelector = createLowerBoundFilter();
Label sumLabel = createSummarizingLabel(listView.getSelectionModel().getSelectedItems());
Parent root = new VBox(listView, lowerBoundSelector, sumLabel);
Scene scene = new Scene(root, 768, 480);
primaryStage.setScene(scene);
primaryStage.show();
}
private TreeTableView<Data> createTreeTableView() {
itemizedDataPool = EasyBind.map(filteredDataPool, DataItem::new);
TreeItem<Data> itemRoot = new TreeItem<>();
Bindings.bindContent(itemRoot.getChildren(), itemizedDataPool);
TreeTableView<Data> listView = new TreeTableView<>(itemRoot);
listView.setShowRoot(false);
itemRoot.setExpanded(true);
listView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
listView.getColumns().add(new TreeTableColumn<>("Data"));
return listView;
}
private Label createSummarizingLabel(ObservableList<TreeItem<Data>> selectedItems) {
Label sumLabel = new Label();
selectedData = EasyBind.map(selectedItems, (TreeItem<Data> t) -> ((DataItem) t).data);
selectedData.addListener(new InvalidationListener() {
@Override
public void invalidated(Observable observable) {
int sum = 0;
for (Data d : selectedData) {
sum += d.value;
}
sumLabel.setText("Sum: " + sum);
}
});
return sumLabel;
}
private Spinner<Integer> createLowerBoundFilter() {
Spinner<Integer> lowerBoundSelector = new Spinner<>(0, 20, 0, 1);
lowerBoundSelector.valueProperty().addListener(new InvalidationListener() {
@Override
public void invalidated(Observable observable) {
filteredDataPool.setPredicate(t -> t.value > lowerBoundSelector.getValue());
}
});
return lowerBoundSelector;
}
public static void main(String[] args) {
launch(args);
}
}
TreeTableView
uses TreeTableViewArrayListSelectionModel
, which extends MultipleSelectionModelBase
, which uses ReadOnlyUnbackedObservableList
, which uses (and contains) SelectionListIterator
, which has a broken implementation for its method nextIndex
.
Thanks to fabian for pointing that out. He also filed a bug report ( http://bugs.java.com/bugdatabase/view_bug.do?bug_id=8145887 ).
Using a buffer in between could provide an effective workaround for the problem above. I tried several approaches. setAll
on selection invalidation and Bindings.bindContent
do not work . In both cases I received null
values in the list. The straightforward "solution" is to simply filter the null
s out. This leads to the inefficient but apparently effective code below.
// [...]
TreeTableView<Data> listView = createTreeTableView();
selectionBuffer = FXCollections.observableArrayList();
listView.getSelectionModel().getSelectedItems().addListener(new InvalidationListener() {
@Override
public void invalidated(Observable observable) {
selectionBuffer.clear();
for (TreeItem<Data> t : listView.getSelectionModel().getSelectedItems()) {
if (t != null) {
selectionBuffer.add(t);
}
}
}
});
// [...]
Using selectionBuffer
instead of listView.getSelectionModel().getSelectedItems()
should now compensate the implementation problem in nextIndex
.
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