Question

我正在使用JavaFX作为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在鼠标点击时保持多项选择，并且只在再次点击时删除选择（这样可行）。

我还需要验证ListView中是否已选择某些内容，并在未启用任何内容时禁用该按钮（适用于选择但不取消选择）。

这是按钮启用和禁用的代码（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);

以下是我捕获鼠标选择的代码（这是有效的，解决方案是从this SO 回答fabian开发的）：

//Example sourced from stackoverflow.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());
            }
        });

以下是我运行应用程序时的输出结果：

    //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不会触发listView.getSelectionModel().clearSelection(cell.getIndex());？或者，更直接地说，为什么listView.getSelectionModel().selectedItemProperty()在选择为空时不会触发？根据Javadoc，它应该在空时返回null，所以不应该被捕获？

Answer 1

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

如果您绑定到selectedIndexProperty而不是selectedItemProperty：

，则此功能正常

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，因为您启用了多个选择，所以最好还是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());
    }
};

请注意，如果您将validEntriesBinding设为局部变量，则很容易accidental garbage collection。你应该把它变成一个字段：

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未在clearSelection上触发（索引）

1 个答案: