我正在学习从TableView的选定行获取数据，并使用该数据预填充对话框。无论我在加载对话框时做什么，我在Controller.java中得到NullPointerException - ＆gt; showEditContactDialog（） - ＆GT; editController.setItem（item））。不知怎的，我无法将选定的数据传递给另一个类，并通过对话框显示它。感谢有人指出我正确的方向。这是代码：
Main.java：
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
import sample.datamodel.ContactData;
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage primaryStage) throws Exception{
Parent root = FXMLLoader.load(getClass().getResource("MainWindow.fxml"));
primaryStage.setTitle("Address Book");
primaryStage.setScene(new Scene(root, 1280, 500));
primaryStage.show();
}
@Override
public void stop(){
ContactData.getInstance().saveContacts();
}
}
Controller.java：
package sample;
@FXML
private TableView<Contact> tableView;
@FXML
private BorderPane mainBorderPane;
private Contact item;
public Controller() {
}
@FXML
public TableView<Contact> getTableView() {
return tableView;
}
@FXML
public void initialize(){
loadContacts();
tableView.setOnMouseClicked((MouseEvent event) -> {
if (event.getClickCount() > 0) {
item = tableView.getSelectionModel().getSelectedItem(); // *** get selection from TableView ***
}
});
}
@FXML
public void handleExit(){
ContactData.getInstance().saveContacts();
Platform.exit();
}
public void saveContacts() {
ContactData.getInstance().saveContacts();
}
public void loadContacts() {
ContactData.getInstance().loadContacts();
tableView.setItems(ContactData.getInstance().getContacts());
}
public void deleteContact(){
ContactData.getInstance().deleteContact(item);
}
public void showAddContactDialog(ActionEvent event) throws IOException {
Dialog<ButtonType> dialog = new Dialog<>();
dialog.initOwner(mainBorderPane.getScene().getWindow());
FXMLLoader fxmlLoader = new FXMLLoader();
fxmlLoader.setLocation(getClass().getResource("addContact.fxml"));
try{
dialog.getDialogPane().setContent(fxmlLoader.load());
}catch(IOException e){
System.out.println("Couldn't load the dialog");
e.printStackTrace();
return;
}
Optional<ButtonType> result = dialog.showAndWait();
if(result.isPresent()){
Dialog controller = fxmlLoader.getController();
}
}
public void showEditContactDialog() throws Exception {
Dialog<ButtonType> dialog = new Dialog<>();
dialog.initOwner(mainBorderPane.getScene().getWindow());
FXMLLoader fxmlLoader = new FXMLLoader();
fxmlLoader.setLocation(getClass().getResource("editContact.fxml"));
EditContactController editController = fxmlLoader.<EditContactController>getController();
editController.setItem(item); // ****** trying to pass "item" but get NullPointerException *********
try{
dialog.getDialogPane().setContent(fxmlLoader.load());
} catch (IOException e) {
System.out.println("Couldn't load the dialog");
e.printStackTrace();
return;
}
Optional<ButtonType> result = dialog.showAndWait();
}
}
EditContactController.java
package sample;
import javafx.fxml.FXML;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextField;
import javafx.stage.Stage;
import sample.datamodel.Contact;
public class EditContactController{
@FXML
private TextField fName;
@FXML
private TextField lName;
@FXML
private TextField pNumber;
@FXML
private TextArea nNotes;
@FXML
private javafx.scene.control.Button cancelButton;
@FXML
private Contact item;
public void setItem(Contact item) {
this.item = item;
}
@FXML
public void initialize(){
try {
fName.setText(item.getFirstName());
}catch(NullPointerException e) {
System.out.println("null point --> " + e.getMessage());
e.printStackTrace();
}
}
//@FXML
public void cancelButtonAction(){
// get a handle to the stage
Stage stage = (Stage) cancelButton.getScene().getWindow();
stage.close();
}
}
editContact.fxml：
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.RowConstraints?>
<?import javafx.scene.text.Font?>
<GridPane prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.121" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.EditContactController">
<HBox GridPane.columnSpan="2">
<Label text="Edit contact">
<font>
<Font name="System Bold" size="17.0" />
</font>
<padding>
<Insets bottom="10.0" left="10.0" />
</padding></Label>
</HBox>
<Label text="First Name" GridPane.columnIndex="0" GridPane.hgrow="ALWAYS" GridPane.rowIndex="1">
<GridPane.margin>
<Insets left="10.0" />
</GridPane.margin>
<padding>
<Insets bottom="5.0" />
</padding></Label>
<Label text="Last Name" GridPane.columnIndex="0" GridPane.rowIndex="2">
<GridPane.margin>
<Insets bottom="5.0" left="10.0" />
</GridPane.margin></Label>
<Label text="Phone number" GridPane.columnIndex="0" GridPane.rowIndex="3">
<GridPane.margin>
<Insets bottom="5.0" left="10.0" />
</GridPane.margin></Label>
<Label text="Notes" GridPane.columnIndex="0" GridPane.rowIndex="4">
<GridPane.margin>
<Insets bottom="5.0" left="10.0" />
</GridPane.margin></Label>
<TextField fx:id="fName" GridPane.columnIndex="1" GridPane.rowIndex="1">
<GridPane.margin>
<Insets bottom="5.0" />
</GridPane.margin></TextField>
<TextField fx:id="lName" GridPane.columnIndex="1" GridPane.rowIndex="2">
<GridPane.margin>
<Insets bottom="5.0" />
</GridPane.margin></TextField>
<TextField fx:id="pNumber" GridPane.columnIndex="1" GridPane.rowIndex="3">
<GridPane.margin>
<Insets bottom="5.0" />
</GridPane.margin></TextField>
<TextArea fx:id="nNotes" GridPane.columnIndex="1" GridPane.rowIndex="4">
<GridPane.margin>
<Insets bottom="5.0" />
</GridPane.margin></TextArea>
<HBox alignment="TOP_RIGHT" spacing="5.0" GridPane.columnIndex="1" GridPane.rowIndex="5">
<Button text="Edit">
<opaqueInsets>
<Insets />
</opaqueInsets></Button>
<Button fx:id="cancelButton" cancelButton="true" onAction="#cancelButtonAction" text="Cancel" />
<opaqueInsets>
<Insets />
</opaqueInsets>
<GridPane.margin>
<Insets />
</GridPane.margin>
<padding>
<Insets bottom="5.0" left="5.0" right="5.0" />
</padding>
</HBox>
<columnConstraints>
<ColumnConstraints maxWidth="288.0" minWidth="22.0" prefWidth="129.0" />
<ColumnConstraints maxWidth="578.0" minWidth="312.0" prefWidth="471.0" />
</columnConstraints>
<rowConstraints>
<RowConstraints />
<RowConstraints />
<RowConstraints />
<RowConstraints />
<RowConstraints />
<RowConstraints />
</rowConstraints>
<padding>
<Insets left="5.0" right="5.0" top="5.0" />
</padding>
<opaqueInsets>
<Insets />
</opaqueInsets>
</GridPane>
堆栈：
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:394)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:432)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
... 48 more
Caused by: java.lang.NullPointerException
at sample.Controller.showEditContactDialog(Controller.java:105)
... 58 more
答案 0 :(得分：0)
您的控制器类在FXML文件中指定，因此FXMLLoader在读取该文件之前无法实例化它。这意味着控制器仅在调用load()期间创建，并且在此之前调用fxmlLoader.getController()将返回null。
因此，您需要移动检索控制器的代码并对其进行操作，以便在调用load()后执行：
public void showEditContactDialog() throws Exception {
Dialog<ButtonType> dialog = new Dialog<>();
dialog.initOwner(mainBorderPane.getScene().getWindow());
FXMLLoader fxmlLoader = new FXMLLoader();
fxmlLoader.setLocation(getClass().getResource("editContact.fxml"));
try {
Parent dialogContent = fxmlLoader.load();
EditContactController editController = fxmlLoader.<EditContactController>getController();
editController.setItem(item);
dialog.getDialogPane().setContent(dialogContent);
} catch (IOException e) {
System.out.println("Couldn't load the dialog");
e.printStackTrace();
return;
}
Optional<ButtonType> result = dialog.showAndWait();
}
在调用initialize()期间，还会调用控制器中的FXMLLoader.load()方法。因此，由于这些更改，现在在initialize()上调用setItem(...)之前调用EditContactController。因此，您需要将依赖于initialize()方法中的项目的代码移动到setItem()方法：
public void setItem(Contact item) {
this.item = item;
fName.setText(item.getFirstName());
}
@FXML
public void initialize(){
}