ISSUE:

Creating a ComboBox that has a sorted and filtered list and then changing the Predicate on the FilteredList causes "getSelectedItem" on the ComboBox to return null, but the visually selected item in the ComboBox itself remains the same.

If the selected item returns null, it would also be expected that the visual item is "nothing".

HOW TO REPRODUCE:

Run the test code below. Just press the button a few times and the error should present itself.

TEST CODE:

import java.util.Comparator;
import java.util.function.Predicate;

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.collections.transformation.FilteredList;
import javafx.collections.transformation.SortedList;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.control.TextArea;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.util.Callback;

public class ComboFilteredListPredicateNotUpdatingSelectedItem extends Application {

private FilteredList<ComboItem> _filteredList;

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

@Override
public void start(Stage primaryStage) throws Exception {
final ComboBox<ComboItem> combo = new ComboBox<>();

ObservableList<ComboItem> items = FXCollections.observableArrayList();
for (int i = 0; i < 10; i++) {
items.add(new ComboItem("Hello " + i));
}

SortedList<ComboItem> sorted = items.sorted(new Comparator<ComboItem>() {
@Override
public int compare(ComboItem o1, ComboItem o2) {
return o1.getText().compareTo(o2.getText());
}
});

_filteredList = sorted.filtered(getPredicate());
combo.setItems(_filteredList);
combo.getSelectionModel().select(0);

combo.setButtonCell(new ListCell<ComboItem>() {
@Override
protected void updateItem(ComboItem item, boolean empty) {
super.updateItem(item, empty);
setText(empty ? null : item.getText());
}
});
combo.setCellFactory(new Callback<ListView<ComboItem>, ListCell<ComboItem>>() {
@Override
public ListCell<ComboItem> call(ListView<ComboItem> param) {
return new ListCell<ComboItem>() {
@Override
protected void updateItem(ComboItem item, boolean empty) {
super.updateItem(item, empty);
setText(empty ? null : item.getText());
}
};
}
});

TextArea out = new TextArea();

combo.getSelectionModel().selectedItemProperty().addListener((prop, ov, nv) -> {
out.appendText("Selected item property changed to " + nv + "\n");
});

Label howTo = new Label("Press 'Change Filter' a few times, watch how the combo item you picked stays selected, but the printout says it's null");
howTo.setWrapText(true);

Button b = new Button("Change Filter");
b.setOnAction(e -> {
out.appendText("Selected Item Before: " + combo.getSelectionModel().getSelectedItem() + "\n");
_filteredList.setPredicate(getPredicate());
out.appendText("Selected Item After: " + combo.getSelectionModel().getSelectedItem() + "\n");
});

VBox content = new VBox(10);
content.setPadding(new Insets(20));
content.getChildren().addAll(howTo, combo, b, out);
Scene scene = new Scene(content, 600, 500);
primaryStage.setScene(scene);
primaryStage.show();
}

private Predicate<ComboItem> getPredicate() {
return new Predicate<ComboItem>() {
@Override
public boolean test(ComboItem t) {
return true;
}
};
}

public class ComboItem {
private StringProperty _textProperty;

public StringProperty textProperty() {
if (_textProperty == null) {
_textProperty = new SimpleStringProperty();
}

return _textProperty;
}

public void setText(String text) {
textProperty().set(text);
}

public String getText() {
return textProperty().get();
}

public ComboItem(String text) {
setText(text);
}

@Override
public String toString() {
return "ComboItem [_textProperty=" + getText() + "]";
}

}

}