JavaFX中的java NullPointerException在TableView中初始化

Question

我有一个用于在TableView中显示数据库查询的控制器类，但我有一个“setCellValueFactory（new PropertyValueFactory）”的NullPointerException错误

package aplicativo;

import java.net.URL;
import java.util.ResourceBundle;

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.TextField;
import javafx.scene.control.cell.PropertyValueFactory;

public class Controle implements Initializable{
    @FXML
    private TextField txtCampo,txtCampo2;
    @FXML
    private Button btAdicionar,btConsultar;
    @FXML
    private TableView<Pessoa> tabValues;
    @FXML
    private TableColumn<Pessoa, Integer> tbcCod;
    private TableColumn<Pessoa, String>tbcNome;
    ObservableList<Pessoa> List = FXCollections.observableArrayList();
    @FXML
    private void btAdd(){
        insertBD a = new insertBD(txtCampo.getText());
        consultaBD b = new consultaBD();
        List = b.consultaTudo();
        tabValues.setItems(List);
        txtCampo.clear();
    }
    @FXML

    private void btCons(){
        String tx = txtCampo2.getText();
        if(tx.isEmpty()){

        }else{
        consultaBD a = new consultaBD();
        a.consultaParecido(tx, "nome");
        txtCampo2.clear();
        }
    }
    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {

        // TODO Auto-generated method stub
        tbcCod.setCellValueFactory(new PropertyValueFactory<Pessoa, Integer>("cod"));
        tbcNome.setCellValueFactory(new PropertyValueFactory<Pessoa, String>("nome"));
        tabValues.setItems(List);
        tabValues.getColumns().addAll(tbcCod,tbcNome);
    }
}

NullPointerException：

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$152(Unknown Source)
    at com.sun.javafx.application.LauncherImpl$$Lambda$50/1645995473.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: javafx.fxml.LoadException: 
/C:/Users/lucas/workspace/BDFX/bin/aplicativo/Tela.fxml

    at javafx.fxml.FXMLLoader.constructLoadException(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
    at javafx.fxml.FXMLLoader.load(Unknown Source)
    at aplicativo.Main.start(Main.java:13)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$159(Unknown Source)
    at com.sun.javafx.application.LauncherImpl$$Lambda$53/1031257736.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda$45/186276003.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$null$170(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda$48/1529876784.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda$47/237061348.run(Unknown Source)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$145(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$$Lambda$36/2117255219.run(Unknown Source)
    ... 1 more
Caused by: java.lang.NullPointerException
    at aplicativo.Controle.initialize(Controle.java:52)
    ... 23 more
Exception running application aplicativo.Main

有解决办法吗

Answer 1

控制器中的一个实例字段缺少@FXML注释。由于该字段是私有的，FXML加载程序在加载期间无法将控件引用注入该字段。以下是您的实例字段声明：

@FXML
private TextField txtCampo,txtCampo2;

@FXML
private Button btAdicionar,btConsultar;

@FXML
private TableView<Pessoa> tabValues;

@FXML
private TableColumn<Pessoa, Integer> tbcCod;

private TableColumn<Pessoa, String>tbcNome;

请注意，最后一个字段tbcNome没有注释。因此，当调用initialize方法时，tbcNome字段包含一个null引用，从而导致异常

要解决问题，您可能需要做的只是将@FXML注释添加到tbcNome的实例字段声明中

您可能已经养成了在类型声明中列出多个变量的习惯，例如private Button btAdicionar, btConsultar;，从而助长了这个错误。在我看来，这是一个坏习惯，可能会鼓励像这样的错误发生。我建议您尝试采用编码风格，其中每个实例字段都有自己的类型声明语句