JavaFX中的NullPointerException在TableView中初始化

Question

我有此控制器类用于在TableView中显示数据库查询，但是我在NullPointerException错误中出现了“
setCellValueFactory（new PropertyValueFactory”）

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);
    }
}

NullPointerExcepetion：

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

有什么办法吗？

Answer 1

控制器中的实例字段之一缺少@FXML注释。由于该字段是私有字段，因此FXML加载程序无法在加载过程中将控件引用注入到该字段中。这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。结果，当调用您的initialize方法时，该tbcNome字段包含一个null引用，从而导致异常。

要解决您的问题，您可能需要做的就是将@FXML注释添加到的实例字段声明中tbcNome。

您可能通过养成在类型声明中列出多个变量的习惯而鼓励了该错误，例如。private Button btAdicionar, btConsultar;。在我看来，这是一种不良习惯，会助长此类错误的发生。我建议您尝试采用每个实例字段都有其自己的类型声明语句的编码样式。