JavaFX 中的 NullPointerException 在 TableView 中初始化

Question

我有这个控制器 class 用于在 TableView 中显示数据库查询，但是我遇到了 "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);
    }
}

空指针异常：

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$FXHelper.main(Unknown Source)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication2(Unknown Source)
    at com.sun.javafx.application.LauncherImpl$$Lambda/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$launchApplication19(Unknown Source)
    at com.sun.javafx.application.LauncherImpl$$Lambda/1031257736.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait2(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda/186276003.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$null0(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda/1529876784.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater1(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda/237061348.run(Unknown Source)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null5(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$$Lambda/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

有什么解决办法吗？

Answer 1

您的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 加载器无法在加载期间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。因此，当您的初始化方法被调用时，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 tbcNome 的实例字段声明中。

您可能养成了在类型声明中列出多个变量的习惯，从而助长了这一错误，例如。 private Button btAdicionar, btConsultar;。在我看来，这是一个坏习惯，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自己的类型声明语句的编码风格。

JavaFX 中的 NullPointerException 在 TableView 中初始化

NullPointerException in JavaFX initialize in TableView

java

javafx

tableview

javafx-8