我正在JavaFX中构建一个小编辑器应用程序，我正在使用FXML文件和控制器。我有几个FXML文件（每个文件都有相应的控制器）。我要做的就是从'root'fxml（包含MenuBar）处理'open file'操作，然后将该文件传递给另一个控制器，该控制器应该“解析”它然后显示它在指定的TextArea。但我得到一个NullPointerException，我无法理解。调试也没有帮助我。
以下是我的一些代码：
首先，来自我的RootLayout.fxml的方法，其中包含用于打开文件的菜单项：
@FXML
private void handleOpen() {
fileChooser = new FileChooser();
fileChooser.setInitialDirectory(new File("."));
extFilter1 = new FileChooser.ExtensionFilter("XML Documents (*.xml)", "*.xml");
extFilter2 = new FileChooser.ExtensionFilter("All Files", "*.*");
fileChooser.getExtensionFilters().addAll(extFilter1, extFilter2);
xmlFile = fileChooser.showOpenDialog(mainApp.getPrimaryStage());
if(xmlFile != null) {
EditorOverviewController controller = new EditorOverviewController();
try {
controller.loadXmlFile(xmlFile);
} catch (IOException ex) {
Logger.getLogger(RootLayoutController.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
现在是另一个控制器中的loadXmlFile方法：
public void loadXmlFile(File file) throws IOException {
StringBuilder sb = new StringBuilder();
try (FileInputStream fis = new FileInputStream(file);
BufferedInputStream bis = new BufferedInputStream(fis)) {
while (bis.available() > 0) {
sb.append((char) bis.read());
}
} catch (Exception e) {
e.printStackTrace();
}
try {
sourceEditor.setText(sb.toString());
} catch (Exception ex) {
Logger.getLogger(RootLayoutController.class.getName()).log(Level.SEVERE, null, ex);
}
}
其中sourceEditor是我的fx:id文本区域，在控制器顶部正常注释：
@FXML
private TextArea sourceEditor;
我在NullPointer得到了这个：
java.lang.NullPointerException
at mainApp.view.EditorOverviewController.loadXmlFile(EditorOverviewController.java:103)
at uimlbuddy.view.RootLayoutController.handleOpen(RootLayoutController.java:81)
关于我究竟做错了什么的任何线索？提前谢谢！
更新
我正在加载我的fxml文件并在我的MainApp类中获取这样的控制器：
@Override
public void start(Stage primaryStage) {
this.primaryStage = primaryStage;
primaryStage.getIcons().add(new Image("/assets/app_icon.png"));
initRootLayout();
showEditorOverview();
}
/**
* Initializes the root layout.
*/
private void initRootLayout() {
try {
// Load root layout from fxml file.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(MainApp.class.getResource("view/RootLayout.fxml"));
rootLayout = (BorderPane) loader.load();
// Show the scene containing the root layout.
Scene scene = new Scene(rootLayout);
primaryStage.setScene(scene);
// Give the controller access to the main app.
RootLayoutController controller = loader.getController();
controller.setMainApp(this);
primaryStage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Shows the editor overview with all panels inside the root layout.
*/
private void showEditorOverview() {
try {
// Load person overview.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(MainApp.class.getResource("view/EditorOverview.fxml"));
AnchorPane editorOverview = (AnchorPane) loader.load();
// Set editor overview into the center of root layout.
rootLayout.setCenter(editorOverview);
EditorOverviewController controller = loader.getController();
controller.setMainApp(this);
} catch (IOException e) {
e.printStackTrace();
}
}
然后在每个控制器中我都有这个方法setMainApp来给自己一个引用：
/**
* Is called by the main application to give a reference back to itself.
*
* @param mainApp
*/
public void setMainApp(MainApp mainApp) {
this.mainApp= mainApp;
}
答案 0 :(得分：2)
在RootLayoutController中公开一个属性（我假设这是带有handleOpen()方法的控制器）来保存所选文件：
public class RootLayoutController {
private final ObjectProperty<File> selectedFile = new SimpleObjectProperty<>(this, "selectedFile");
public final ObjectProperty<File> selectedFileProperty() {
return selectedFile ;
}
public final File getSelectedFile() {
return selectedFile.get();
}
public final void setSelectedFile(File file) {
this.selectedFile.set(file);
}
@FXML
private void handleOpen() {
fileChooser = new FileChooser();
fileChooser.setInitialDirectory(new File("."));
extFilter1 = new FileChooser.ExtensionFilter("XML Documents (*.xml)", "*.xml");
extFilter2 = new FileChooser.ExtensionFilter("All Files", "*.*");
fileChooser.getExtensionFilters().addAll(extFilter1, extFilter2);
xmlFile = fileChooser.showOpenDialog(mainApp.getPrimaryStage());
if (xmlFile != null) {
setSelectedFile(xmlFile);
}
}
// ...
}
然后在您的主应用程序中，您可以观察该属性并在其更改时更新另一个控制器：
private void initRootLayout() {
try {
// Load root layout from fxml file.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(MainApp.class.getResource("view/RootLayout.fxml"));
rootLayout = (BorderPane) loader.load();
// Show the scene containing the root layout.
Scene scene = new Scene(rootLayout);
primaryStage.setScene(scene);
// Give the controller access to the main app.
RootLayoutController controller = loader.getController();
// really should not need this ugly coupling from your controllers back to the app
// controller.setMainApp(this);
controller.selectedFileProperty().addListener((obs, oldFile, newFile) -> {
if (newFile != null) {
editorOverviewController.loadXmlFile(newFile);
}
}
primaryStage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
您显然需要editorOverviewController成为主应用中的实例字段，可以使用showEditorOverview方法进行初始化：
public class MainApp extends Application {
private EditorOverviewController editorOverviewController ;
@Override
public void start(Stage primaryStage) throws Exception {
// as before ...
}
private void initRootLayout() {
// as above ...
}
private void showEditorOverview() {
try {
// Load person overview.
FXMLLoader loader = new FXMLLoader();
loader.setLocation(MainApp.class.getResource("view/EditorOverview.fxml"));
AnchorPane editorOverview = (AnchorPane) loader.load();
// Set editor overview into the center of root layout.
rootLayout.setCenter(editorOverview);
// note subtle change here:
this.editorOverviewController = loader.getController();
// again, should not need this:
// controller.setMainApp(this);
} catch (IOException e) {
e.printStackTrace();
}
}
}
答案 1 :(得分：1)
您必须加载第二个FXML，然后从中提取控制器。使用：
FXMLoader loader = new FXMLoader(path to your fxml);
loader.load();
EditorOverviewController controller = (EditorOverviewController)loader.getController();