我有以下代码:
package pl.javastart.youtufy.controller;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.application.Platform;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.Node;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ToggleButton;
import javafx.scene.web.WebEngine;
import javafx.stage.Stage;
public class ConnectionErrorController implements Initializable {
@FXML
private Label infoLabel;
@FXML
private Button tryButton;
@FXML
private Button exitButton;
@Override
public void initialize(URL location, ResourceBundle resources) {
MainController mc = new MainController();
infoLabel.setText("Connection lost, please try again");
tryButton.setText("try again");
exitButton.setText("exit");
tryButton.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
WebEngine webEngine = mc.getContentPaneController().getVideoWebView().getEngine(); // 1
ToggleButton playButton = mc.getControlPaneController().getPlayButton(); // 2
Node source = (Node) event.getSource();
Stage stage = (Stage) source.getScene().getWindow();
if (mc.testInet()) {
stage.close();
mc.play(webEngine, playButton);
} else {
stage.close();
MainController.exist = false;
}
}
});
exitButton.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
Platform.exit();
}
});
}
}
我正在尝试从MainController中的控制器使用WebEngine和ToggleButton对象(我在MainController中为它们生成了getter和setter):
public class MainController implements Initializable {
@FXML
private ContentPaneController contentPaneController;
@FXML
private ControlPaneController controlPaneController;
@FXML
private MenuPaneController menuPaneController;
@FXML
private SearchPaneController searchPaneController;
private Youtube youtubeInstance;
public static boolean exist = false;
public ControlPaneController getControlPaneController() {
return controlPaneController;
}
public void setControlPaneController(ControlPaneController controlPaneController) {
this.controlPaneController = controlPaneController;
}
public ContentPaneController getContentPaneController() {
return contentPaneController;
}
public void setContentPaneController(ContentPaneController contentPaneController) {
this.contentPaneController = contentPaneController;
}
但是它仍然返回NullPointerException。当我尝试仅对ConnectionErrorController中的控制器进行引用时,我遇到了同样的问题。如何从ConnectionErrorController中的控制器正确引用ToggleButton i WebEngine对象?
问候
最佳答案
您正在使用“手动”创建控制器实例
MainController mc = new MainController();
@FXML
带注释的字段由FXMLLoader
在为您创建控制器(作为加载FXML文件的过程的一部分)时初始化。由于您创建的控制器不是FXMLLoader
创建的控制器实例,因此其@FXML
注释字段未初始化(即它们为null),因此会出现空指针异常。在调用
FXMLLoader
之后,通过在getController()
实例上调用FXMLLoader
可以获得对load()
创建的控制器的引用。如果要一个控制器与另一个控制器通信,则通过在第二个控制器中定义适当的方法,将对一个控制器的引用传递给另一个控制器:
public class ConnectionErrorController implements Initializable {
private MainController mainController ;
public void setMainController(MainController mainController) {
this.mainController = mainController ;
}
// ...
@Override
public void initialize(URL location, ResourceBundle resources) {
infoLabel.setText("Connection lost, please try again");
tryButton.setText("try again");
exitButton.setText("exit");
tryButton.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
WebEngine webEngine = mainController.getContentPaneController().getVideoWebView().getEngine(); // 1
ToggleButton playButton = mainController.getControlPaneController().getPlayButton(); // 2
if (mainController.testInet()) {
mainController.play(webEngine, playButton);
} else {
// obviously you can now do something better than the "public static field hack" here:
MainController.exist = false;
}
tryButton.getScene().getWindow().hide();
}
});
// ...
}
}
假设您正在
MainController
中的方法中加载第二个fxml文件,则可以执行以下操作:public class MainController {
// ...
public void showConnectionErrorWindow(String fileName) {
FXMLLoader loader = new FXMLLoader(getClass().getResource("path/to/ConnectionError.fxml"));
Parent root = loader.load();
ConnectionErrorController connectionErrorController = loader.getController();
connectionErrorController.setMainController(this);
Scene scene = new Scene(root);
Stage stage = new Stage();
// etc...
}
// ...
}
请注意,有很多更优雅的方法可以解决此问题,例如,将
ConnectionErrorController
传递给回调函数(以lambda表达式的形式)以处理对play(...)
的调用,这可以避免ConnectionErrorController
之间的紧密耦合。 >和MainController
。但是,由于您似乎不熟悉Java,因此这种更简单的方法可能更适合。有关将值传递给控制器的更多信息,请参见Passing Parameters JavaFX FXML。
关于java - javafx在适当的Controller类中使用MainController或其他Controller中的对象,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/43710971/