JavaFX中的NullPointerException在TableView中初始化

Question

我有這個控制器類用於在TableView中顯示數據庫查詢，但是我在NullPointerException時出現了“ setCellValueFactory（new PropertyValueFactory”）錯誤。

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

有什么辦法嗎？

Answer 1

控制器中的實例字段之一缺少@FXML注釋。 由於該字段是私有字段，因此FXML加載程序無法在加載期間將控件引用注入到該字段中。 這是您的實例字段聲明：

@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;

請注意，最后一個字段tbcNome沒有注釋。 結果，在調用您的initialize方法時， tbcNome字段包含null引用，從而導致異常。

要解決你的問題，你可能需要做的是添加@FXML注釋的實例字段聲明tbcNome 。

您可能通過養成在類型聲明中列出多個變量的習慣而鼓勵了該錯誤，例如。 private Button btAdicionar, btConsultar; 。 在我看來，這是一種不良習慣，會助長此類錯誤的發生。 我建議您嘗試采用每個實例字段都有其自己的類型聲明語句的編碼樣式。