Question

我一直试图阻止我的程序删除我的树视图的根节点，但是当我尝试这样做时，我的程序给了我一个＆＃34; java.lang.reflect.InvocationTargetException＆＃34;在编译期间，程序将无法启动。我不确定为什么它不会启动。

这是发生错误的TextFieldTreeCellImpl类：

private final class TextFieldTreeCellImpl extends TreeCell<String> {

    private TextField textField;
    private ContextMenu addMenu = new ContextMenu();


    public TextFieldTreeCellImpl() {
        MenuItem addMenuItem0 = new MenuItem("Add Folder");
        addMenu.getItems().add(addMenuItem0);
        addMenuItem0.setOnAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent t) {
                TreeItem<String> newFolder = 
                    new TreeItem<String>("New Folder",new ImageView(depIcon));
                        getTreeItem().getChildren().add(newFolder);
            }
        });

        MenuItem addMenuItem1 = new MenuItem("Delete");
        addMenu.getItems().add(addMenuItem1);

        addMenuItem1.setOnAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent t) {//There is not error when the if statement is in here
                        getTreeItem().getParent().getChildren().remove(getTreeItem());
                }
        });
        if(getTreeItem().getParent()==null){//The error is here-------------
             addMenuItem1.disableProperty().set(true);
        }
    }

    public void startEdit() {
        super.startEdit();

        if (textField == null) {
            createTextField();
        }
        setText(null);
        setGraphic(textField);
        textField.selectAll();
    }

    public void cancelEdit() {
        super.cancelEdit();

        setText((String) getItem());
        setGraphic(getTreeItem().getGraphic());
    }


    public void updateItem(String item, boolean empty) {
        super.updateItem(item, empty);

        if (empty) {
            setText(null);
            setGraphic(null);
        } else {
            if (isEditing()) {
                if (textField != null) {
                    textField.setText(getString());
                }
                setText(null);
                setGraphic(textField);
            } else {
                setText(getString());
                setGraphic(getTreeItem().getGraphic());
                    setContextMenu(addMenu);
            }
        }
    }

    private void createTextField() {
        textField = new TextField(getString());
        textField.setOnKeyReleased(new EventHandler<KeyEvent>() {

            public void handle(KeyEvent t) {
                if (t.getCode() == KeyCode.ENTER) {
                    commitEdit(textField.getText());
                } else if (t.getCode() == KeyCode.ESCAPE) {
                    cancelEdit();
                }
            }
        });  

    }

    private String getString() {
        return getItem() == null ? "" : getItem().toString();
    }
}
}

这是我得到的错误：

Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(Unknown Source)
at com.sun.javafx.application.LauncherImpl.launchApplication(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$147(Unknown Source)
at com.sun.javafx.application.LauncherImpl$$Lambda$48/128893786.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at application.CopyOfMain$TextFieldTreeCellImpl.<init>(CopyOfMain.java:82)
at application.CopyOfMain$1.call(CopyOfMain.java:48)
at application.CopyOfMain$1.call(CopyOfMain.java:1)
at com.sun.javafx.scene.control.skin.TreeViewSkin.createCell(Unknown Source)
at com.sun.javafx.scene.control.skin.TreeViewSkin.lambda$new$513(Unknown Source)
at com.sun.javafx.scene.control.skin.TreeViewSkin$$Lambda$115/979660402.call(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.getCell(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.getCellLength(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.computeViewportOffset(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.layoutChildren(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Scene.doLayoutPass(Unknown Source)
at javafx.scene.Scene.preferredSize(Unknown Source)
at javafx.scene.Scene.impl_preferredSize(Unknown Source)
at javafx.stage.Window$9.invalidated(Unknown Source)
at javafx.beans.property.BooleanPropertyBase.markInvalid(Unknown Source)
at javafx.beans.property.BooleanPropertyBase.set(Unknown Source)
at javafx.stage.Window.setShowing(Unknown Source)
at javafx.stage.Window.show(Unknown Source)
at javafx.stage.Stage.show(Unknown Source)
at application.CopyOfMain.start(CopyOfMain.java:54)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$153(Unknown Source)
at com.sun.javafx.application.LauncherImpl$$Lambda$57/1520696636.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$166(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$44/1051754451.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$164(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/1933975749.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$165(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$46/1775282465.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$141(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda$37/1109371569.run(Unknown Source)
... 1 more
Exception running application application.CopyOfMain

这是我的主类，虽然我不认为它是realavent：

public class Main extends Application {

private final Node rootIcon = 
    new ImageView(new Image(getClass().getResourceAsStream("folder.jpg")));
private final Image depIcon = 
    new Image(getClass().getResourceAsStream("folder.jpg"));

TreeItem<String> rootNode = 
    new TreeItem<String>("Resources", rootIcon);

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

public void start(Stage stage) {
    rootNode.setExpanded(true); 
    stage.setTitle("Tree View Sample");
    VBox box = new VBox();
    final Scene scene = new Scene(box, 400, 300);
    scene.setFill(Color.LIGHTGRAY);

    TreeView<String> treeView = new TreeView<String>(rootNode);
    treeView.setEditable(true);
    treeView.setCellFactory(new Callback<TreeView<String>,TreeCell<String>>(){
        public TreeCell<String> call(TreeView<String> p) {
            return new TextFieldTreeCellImpl();
        }
    });

    box.getChildren().add(treeView);
    stage.setScene(scene);
    stage.show();
}

我注意到的一件事是，如果我将if语句放在其中一个句柄方法中，则没有错误。

Answer 1

在构造TextFieldTreeCellImpl对象时，没有与TreeItem关联的对象。这通常在施工后不久发生，并在您的控制之外。无论如何，对getTreeItem()的调用正在返回null，因此被调用getParent()的链接会导致NPE。在处理程序中移动它时它起作用的原因是因为该代码仅在触发事件时被调用（即单击addMenuItem1），到那时，单元格中将填充treeItem。

我会为EventHandler的{{1}}事件添加另一个onShowing，并将检查并设置在其中。请参阅文档中的示例：ContextMenu Javadoc

如何测试树项是否是javafx中树视图的根节点？

1 个答案: