JavaFX : TableView inside Dialog has duplicate items - duplicates

Question

I have an issue with my TableView and its items. I have created a small Dialog window to display warnings about my app, and inside the Dialog I have a TableView which displays the name of the warning and some information about it upon clicking on a button.
I have created a WarningUtil class (Singleton pattern) just to open / close the Dialog. The relevant code follows.
The constructor of the WarningUtil class (called once only) :
private WarningUtil(RootCtrl rootCtrl) {
this.rootCtrl = rootCtrl;
warnings = new HashMap<>();
setupWarningCallbacks(); // not relevant
setupTable();
setupColumns(); // not relevant
setupDialog();
}
The function managing the construction of the Dialog :
private void setupTable() {
// create the content pane
content = new AnchorPane(); // class variable - reference needed for further uses
content.setPrefSize(480, 240);
// create the root nodes of the view (table + 2 columns)
warningTable = new TableView<>(); // class variable - reference needed for further uses
warnDescriptionCol = new PTableColumn<>(); // class variable - reference needed for further uses
warnDetailsCol = new PTableColumn<>(); // class variable - reference needed for further uses
// settings anchors to keep the ration between dialog <-> table
AnchorPane.setBottomAnchor(warningTable, 15.0);
AnchorPane.setTopAnchor(warningTable, 15.0);
AnchorPane.setLeftAnchor(warningTable, 15.0);
AnchorPane.setRightAnchor(warningTable, 15.0);
// setting up the columns
warnDescriptionCol.setText(i18n("label.desc"));
warnDetailsCol.setText(i18n("label.details"));
warnDescriptionCol.setPercentageWidth(0.7);
warnDetailsCol.setPercentageWidth(0.3);
warnDescriptionCol.setResizable(false);
warnDetailsCol.setResizable(false);
// adding nodes to containers
warningTable.getColumns().addAll(warnDescriptionCol, warnDetailsCol);
content.getChildren().add(warningTable);
}
The function used to create the Dialog and set the content :
private void setupDialog() {
// creation and saving of the dialog in a variable reused later
warningDialog = DialogFactory.getInstance(rootCtrl.getPrimaryStage()).createWarningDialog();
warningDialog.getDialogPane().setContent(content);
warningDialog.getDialogPane().getScene().getWindow().sizeToScene();
}
// The DialogFactory function creating the dialog
public Dialog createWarningDialog(){
CustomDialog dialog = new CustomDialog(rootStage);
dialog.setTitle(i18n("warning.description"));
ButtonType cancelBt = new ButtonType(i18n("button.close"), ButtonData.OK_DONE);
dialog.getDialogPane().getButtonTypes().add(cancelBt);
return dialog.setupLayout();
}
The Main class is in charge of loading the warnings (stored in a .json file and deserialized upon starting the app). For now, the file only contains one entry.
When I click on my Warning button, the following function is called :
public void showWarnings() {
warningTable.getItems().clear(); // BP
warningTable.setItems(FXCollections.observableArrayList(warnings.values()));
warningDialog.showAndWait();
}
What happens is the following : When I have only one entry in my .json file, the first time I click on the button, only one warning is shown. If I click a second time, a second entry appears (the same) which should not be possible because of the following reasons :
Logic constraint : warnings.values() comes from an HashMap where the key is the type of the warning (WarningType class) > Not possible to have two identical keys
Debugging : When I set a breakpoint at "//BP", I clearly see that the warningTable has one item, and after clear the number of items is zero
Debugging : Still with the same breakpoint, I also check that warnings.values() has only one item, which is the case
After five clicks on the button, the Dialog clearly shows something is bugging.
More surprisingly, when I add a second warning (different from the first one, another type), the problem does not occur : No duplicates, warnings are correctly displayed and no matter how many times I open the window.
My question is : Could that be that the way I am creating this warning dialog leads to uncommon errors ? If so, why isn't it the case with two warnings ?
EDIT Include of the cellFactories / cellValueFactories
private void setupColumns() {
warnDescriptionCol.setCellFactory(new Callback<TableColumn<CustomWarning, String>, TableCell<CustomWarning, String>>() {
#Override
public TableCell<CustomWarning, String> call(TableColumn<CustomWarning, String> param) {
TableCell<CustomWarning, String> cell = new TableCell<CustomWarning, String>() {
#Override
protected void updateItem(String item, boolean empty) {
super.updateItem(item, empty);
if (item != null) {
Label label = new Label(item);
setGraphic(label);
}
}
};
return cell;
}
});
warnDetailsCol.setCellFactory(new Callback<TableColumn<CustomWarning, CustomWarning>, TableCell<CustomWarning, CustomWarning>>() {
#Override
public TableCell<CustomWarning, CustomWarning> call(TableColumn<CustomWarning, CustomWarning> param) {
TableCell<CustomWarning, CustomWarning> cell = new TableCell<CustomWarning, CustomWarning>() {
#Override
protected void updateItem(CustomWarning item, boolean empty) {
super.updateItem(item, empty);
if (item != null) {
Button button = new Button(i18n("button.view"));
button.getStyleClass().add("save");
button.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
showWarning(item);
}
});
setGraphic(button);
}
}
};
return cell;
}
});
warnDescriptionCol.setCellValueFactory(new Callback<TableColumn.CellDataFeatures<CustomWarning, String>, ObservableValue<String>>() {
TableViewObjectWrapper<CustomWarning, String> wrapper = new TableViewObjectWrapper<CustomWarning, String>() {
#Override
public String getData() {
return getModel().getTitle();
}
};
#Override
public ObservableValue<String> call(TableColumn.CellDataFeatures<CustomWarning, String> param) {
return new ReadOnlyObjectWrapper<>(wrapper.setModel(param.getValue()).getData());
}
});
warnDetailsCol.setCellValueFactory(new Callback<TableColumn.CellDataFeatures<CustomWarning, CustomWarning>, ObservableValue<CustomWarning>>() {
TableViewObjectWrapper<CustomWarning, CustomWarning> wrapper = new TableViewObjectWrapper<CustomWarning, CustomWarning>() {
#Override
public CustomWarning getData() {
return getModel();
}
};
#Override
public ObservableValue<CustomWarning> call(TableColumn.CellDataFeatures<CustomWarning, CustomWarning> param) {
return new ReadOnlyObjectWrapper<>(wrapper.setModel(param.getValue()).getData());
}
});
}

Answer 1

You have to clear your cells in the cell factory if the cell is empty, as explained in the documentation:
It is very important that subclasses of Cell override the updateItem method properly, as failure to do so will lead to issues such as blank cells or cells with unexpected content appearing within them. Here is an example of how to properly override the updateItem method:
protected void updateItem(T item, boolean empty) {
super.updateItem(item, empty);
if (empty || item == null) {
setText(null);
setGraphic(null);
} else {
setText(item.toString());
}
}
Note in this code sample two important points:
We call the super.updateItem(T, boolean) method. If this is not done, the item and empty properties are not correctly set, and you are likely to end up with graphical issues.
We test for the empty condition, and if true, we set the text and graphic properties to null. If we do not do this, it is almost guaranteed that end users will see graphical artifacts in cells unexpectedly.
Since the cells are reused, you have to clear the graphic if it has become empty, not just set it if it's not.