我刚刚启动Java并使用Fx获取一些GUI,但在尝试替换我的scenecontent时我得到一个空指针异常。 在主要的加载Login.fxml没有任何问题,但当我点击按钮切换到另一个fxml我得到错误。
主要:
package application;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ResourceBundle;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.fxml.JavaFXBuilderFactory;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;
public class Main extends Application {
private Stage stage;
@Override
public void start(Stage primaryStage) {
Parent root;
try {
root = FXMLLoader.load(getClass().getResource("Login.fxml"));
} catch (IOException e) {
e.printStackTrace();
return;
}
Scene scene = new Scene(root);
primaryStage.setScene(scene);
primaryStage.sizeToScene();
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
private void gotoMainView() {
try {
MainViewController profile = (MainViewController) replaceSceneContent("MainView.fxml");
profile.setApp(this);
} catch (Exception ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
void Userlogin()
{
gotoMainView();
}
private void gotoLogin() {
try {
LoginController login = (LoginController) replaceSceneContent("Login.fxml");
login.setApp(this);
} catch (Exception ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
private Initializable replaceSceneContent(String fxml) throws Exception {
FXMLLoader loader = new FXMLLoader();
InputStream in = Main.class.getResourceAsStream(fxml);
loader.setBuilderFactory(new JavaFXBuilderFactory());
loader.setLocation(Main.class.getResource(fxml));
AnchorPane page;
try {
page = (AnchorPane) loader.load(in);
} finally {
in.close();
}
Scene scene = new Scene(page, 800, 600);
stage.setScene(scene);
stage.sizeToScene();
return (Initializable) loader.getController();
}
}
Logincontroller类:
package application;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import javafx.scene.layout.AnchorPane;
public class LoginController extends AnchorPane implements Initializable {
@FXML
static private Button btntext;
@FXML
static private TextField loginusr;
@FXML
static private PasswordField loginpwd;
private Main application;
public void setApp(Main application){
this.application = application;
}
@Override
public void initialize(URL location, ResourceBundle resources) {
btntext.setOnAction(new EventHandler<ActionEvent>() {
@Override public void handle(ActionEvent e) {
System.out.println(loginusr.getText());
System.out.println(loginpwd.getText());
application.Userlogin();
}
});
}
错误发生在:
application.Userlogin();
非常感谢提前
答案 0 :(得分:0)
加载FXML后立即调用initialize()
方法。看看here
initialize()
之前调用setApp(Main application)
。此时,application
对象尚未初始化且为null
!
这意味着在{/ p>调用initialize()
方法
MainViewController profile = (MainViewController) replaceSceneContent("MainView.fxml");
而在application
内使用的initialize()
对象在此行之后被实例化,当您使用时
profile.setApp(this);
因此,当您在application.Userlogin();
内尝试代码initalize()
时,在执行时application is null
!