JavaFX ListView selectedItemProperty 未触发 clearSelection(index)

Question

我将 JavaFX 用于我正在编写的应用程序的 GUI。我的 GUI 中有一个 ListView 和一个 Button。

我希望 ListView 在鼠标单击时保持多项选择，并且仅在再次单击时删除选择（这有效）。

我还需要验证是否已在 ListView 中选择了某些内容，如果未启用任何内容，则禁用该按钮（适用于选择但不适用于取消选择）。

这是我启用和禁用按钮的代码（这不起作用）：

//Binding used to enable and disable the button
    BooleanBinding validEntriesBinding = new BooleanBinding(){
        {
            super.bind(listView.getSelectionModel().selectedItemProperty());
        }
        @Override
        protected boolean computeValue() {
            log.info("No individual item selected? " + 
                    (listView.getSelectionModel().getSelectedItems().isEmpty()));
            log.info("Selected items: " + listView.getSelectionModel().getSelectedItems().toString());
            return (listView.getSelectionModel().getSelectedItems().isEmpty());
        }
    };

    button.disableProperty().bind(validEntriesBinding);

这是我用于捕获鼠标选择的代码（这是有效的，解决方案是根据 SO fabian 的回答开发的）：

//Example sourced from whosebug.com/questions/40900478/mimicking-ctrlclick-multiple-selection-in-listview-using-javafx
        //Answer by fabian
        //Must use MouseEvent.MOUSE_PRESSED and not MOUSE_CLICKED, otherwise the selection does not work
        listView.addEventFilter(MouseEvent.MOUSE_PRESSED, event -> {
            Node node = event.getPickResult().getIntersectedNode();

            while(node != null && node != listView && !(node instanceof ListCell)){
                node = node.getParent();
            }

            if(node instanceof ListCell){
                event.consume();
                listView.requestFocus();

                ListCell cell = (ListCell) node;
                if(!cell.isEmpty()){
                    if(cell.isSelected()){
                        log.info("Clear selection...");
                          listView.getSelectionModel().clearSelection(cell.getIndex());
                              log.info("Selection cleared");
                    }
                    else{
                          log.info("Selecting...");
                        listView.getSelectionModel().select(cell.getIndex());
                        log.info("Selected");
                    }
                }
                else{
                    log.warn("Cell is empty... cannot select");
                }
            }
            else{
                log.warn("Unable to handle event for " + node.getId() + " " + node.getClass());
            }
        });

这是我运行我的应用程序时的输出：

    //Before click, button disabled
    No individual item selected? true
    Selected items: []

    //First click selecting a cell, button enabled
    Selecting...
    No individual item selected? false
    Selected items: [SV124]
    Selected

    //Second click deselecting the first selected cell, button stays
    //enabled as the BooleanBinding never fires
    Clear selection...
    Selection cleared

为什么 BooleanBinding 没有在 listView.getSelectionModel().clearSelection(cell.getIndex()); 上触发？或者，更直接地说，为什么 listView.getSelectionModel().selectedItemProperty() 在选择为空时不触发？根据 Javadoc，它应该 return null 空的时候，所以不应该被捕获吗？

Answer 1

从列表视图的选择模型中删除选定的 index 似乎无法使 selectedItemProperty() 无效。（这似乎是一个错误。）

如果您绑定到 selectedIndexProperty 而不是 selectedItemProperty，它会起作用：

BooleanBinding validEntriesBinding = new BooleanBinding(){
    {
        super.bind(listView.getSelectionModel().selectedIndexProperty());
    }
    @Override
    protected boolean computeValue() {
        log.info("No individual item selected? " + 
                (listView.getSelectionModel().getSelectedItems().isEmpty()));
        log.info("Selected items: " + listView.getSelectionModel().getSelectedItems().toString());
        return (listView.getSelectionModel().getSelectedItems().isEmpty());
    }
};

也许，因为您启用了多项选择，所以无论如何最好绑定到所选项目的列表：

BooleanBinding validEntriesBinding = new BooleanBinding(){
    {
        super.bind(listView.getSelectionModel().getSelectedItems());
    }
    @Override
    protected boolean computeValue() {
        log.info("No individual item selected? " + 
                (listView.getSelectionModel().getSelectedItems().isEmpty()));
        log.info("Selected items: " + listView.getSelectionModel().getSelectedItems().toString());
        return (listView.getSelectionModel().getSelectedItems().isEmpty());
    }
};

注意如果把validEntriesBinding设为局部变量，容易出现accidental garbage collection。你应该把它改成一个字段：

private BooleanBinding validEntriesBinding ;

// ...

validEntriesBinding = new BooleanBinding(){
    {
        super.bind(listView.getSelectionModel().getSelectedItems());
    }
    @Override
    protected boolean computeValue() {
        log.info("No individual item selected? " + 
                (listView.getSelectionModel().getSelectedItems().isEmpty()));
        log.info("Selected items: " + listView.getSelectionModel().getSelectedItems().toString());
        return (listView.getSelectionModel().getSelectedItems().isEmpty());
    }
};

JavaFX ListView selectedItemProperty 未触发 clearSelection(index)

JavaFX ListView selectedItemProperty not firing on clearSelection(index)

java

user-interface

listview

javafx

multipleselection