label.setText() 时出现 NullPointerException
NullPointerException occured with label.setText()
我正在尝试使用 setText() 方法将文本设置为不同的标签。我确实尝试打印该值以检查 setText 是否收到 null。但是我能够在控制台中成功打印该值，但我的问题是为什么不能将其设置为标签。
任何建议都有助于解决此 NullPointerException。
PersonOverviewController.java
package passion.controllers;
import passion.models.Person;
import javafx.application.Platform;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
public class PersonOverviewController{
@FXML
private TableView<Person> personTable;
@FXML
private TableColumn<Person, String> firstNameColumn;
@FXML
private TableColumn<Person, String> lastNameColumn;
@FXML
private Label firstNameLabel;
@FXML
private Label lastNameLabel;
@FXML
private Label streetLabel;
@FXML
private Label postalCodeLabel;
@FXML
private Label cityLabel;
@FXML
private Label birthdayLabel;
public PersonOverviewController() {
}
@FXML
private void initialize() {
// Initialize the person table with the two columns.
firstNameColumn.setCellValueFactory(cellData -> cellData.getValue().firstNameProperty());
lastNameColumn.setCellValueFactory(cellData -> cellData.getValue().lastNameProperty());
try{
//showPersonDetails(null);
//personTable.getSelectionModel().selectedItemProperty().addListener( (observable, oldValue, newValue) -> showPersonDetails(newValue));
personTable.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<Person>(){
@Override
public void changed(ObservableValue<? extends Person> observable, Person oldValue, Person newValue) {
System.out.println(newValue);
showPersonDetails(newValue);
}
});
}catch(NullPointerException e){
e.printStackTrace();
}
}
public void showTableViewData(MainApp mainApp) {
personTable.setItems(mainApp.getPersonData());
}
public void showPersonDetails(Person person){
Platform.runLater(new Runnable(){
@Override
public void run() {
if(person != null){
System.out.println(person.getFirstName());
firstNameLabel.setText(person.getFirstName());
System.out.println("test");
lastNameLabel.setText(person.getLastName());
streetLabel.setText(person.getStreet());
postalCodeLabel.setText(Integer.toString(person.getPostalCode()));
cityLabel.setText(person.getCity());
birthdayLabel.setText(person.getBirthday().toString());
}else{
firstNameLabel.setText("");
lastNameLabel.setText("");
streetLabel.setText("");
postalCodeLabel.setText("");
cityLabel.setText("");
birthdayLabel.setText("");
}
}
});
}
}
这就是我从 MainApp.java
加载控制器的方式
public void showPersonOverview(){
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(MainApp.class.getResource("/passion/viewControllers/PersonOverView.fxml"));
AnchorPane personOverview = (AnchorPane)loader.load();
root.setCenter(personOverview);
PersonOverviewController personController = loader.getController();
personController.showTableViewData(this);
} catch (IOException e) {
e.printStackTrace();
}
}
PersonOverview.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="300.0" prefWidth="600.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8" fx:controller="passion.controllers.PersonOverviewController">
<children>
<SplitPane dividerPositions="0.29797979797979796" layoutX="200.0" layoutY="70.0" prefHeight="300.0" prefWidth="600.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<items>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
<children>
<TableView fx:id="personTable" layoutX="-12.0" layoutY="49.0" prefHeight="200.0" prefWidth="200.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="-0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<columns>
<TableColumn fx:id="firstNameColumn" prefWidth="75.0" text="First Name" />
<TableColumn fx:id="lastNameColumn" prefWidth="75.0" text="Last Name" />
</columns>
<columnResizePolicy>
<TableView fx:constant="CONSTRAINED_RESIZE_POLICY" />
</columnResizePolicy>
</TableView>
</children>
</AnchorPane>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
<children>
<Label layoutX="14.0" layoutY="14.0" text="Person Details:" AnchorPane.leftAnchor="5.0" AnchorPane.topAnchor="5.0" />
<GridPane layoutX="34.0" layoutY="38.0" AnchorPane.leftAnchor="5.0" AnchorPane.rightAnchor="5.0" AnchorPane.topAnchor="30.0">
<columnConstraints>
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
</columnConstraints>
<rowConstraints>
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
</rowConstraints>
<children>
<Label text="First Name">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="Last Name" GridPane.rowIndex="1">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="Street" GridPane.rowIndex="2">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="City" GridPane.rowIndex="3">
<padding>
<Insets left="5.0" />
</padding>
</Label>
<Label text="Postal Code" GridPane.rowIndex="4">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="Birthday" GridPane.rowIndex="5">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="firstName" text="Label" GridPane.columnIndex="1">
<padding>
<Insets left="5.0" />
</padding>
</Label>
<Label fx:id="lastName" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="1">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="street" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="2">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="city" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="3">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="postal" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="4">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="birthday" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="5">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
</children>
</GridPane>
<HBox layoutX="229.0" layoutY="244.0" spacing="5.0" AnchorPane.bottomAnchor="10.0" AnchorPane.rightAnchor="10.0">
<children>
<Button layoutX="229.0" layoutY="244.0" mnemonicParsing="false" text="New..." />
<Button layoutX="289.0" layoutY="244.0" mnemonicParsing="false" text="Edit..." />
<Button layoutX="351.0" layoutY="244.0" mnemonicParsing="false" text="Delete" />
</children>
</HBox>
</children>
</AnchorPane>
</items>
</SplitPane>
</children>
</AnchorPane>
控制台：
Person [firstName=StringProperty [value: Satya], lastName=StringProperty [value: Vema], street=StringProperty [value: some street], postalCode=IntegerProperty [value: 1234], city=StringProperty [value: some city], birthday=ObjectProperty [value: 1999-02-21]]
Person [firstName=StringProperty [value: Satya], lastName=StringProperty [value: Vema], street=StringProperty [value: some street], postalCode=IntegerProperty [value: 1234], city=StringProperty [value: some city], birthday=ObjectProperty [value: 1999-02-21]]
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at passion.controllers.PersonOverviewController.run(PersonOverviewController.java:69)
at com.sun.javafx.application.PlatformImpl.lambda$null0(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda/32693051.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater1(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda/2180324.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/3326003.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
缺少连接（fx:id 到变量名称 @FXML 或 @FXML("...")）。
<Label text="First Name" fx:id="firstNameLabel">
因此无法将组件设置为 FXML 生成的对话框的实际组件。
我认为您遗漏了一部分代码。
TextView firstNameLabel = (TextView)findIdById(R.id.yourTextViewIdInLayout);
并且您必须对所有小部件执行此操作，以免获得 NullPointerException。
我正在尝试使用 setText() 方法将文本设置为不同的标签。我确实尝试打印该值以检查 setText 是否收到 null。但是我能够在控制台中成功打印该值，但我的问题是为什么不能将其设置为标签。
任何建议都有助于解决此 NullPointerException。
PersonOverviewController.java
package passion.controllers;
import passion.models.Person;
import javafx.application.Platform;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
public class PersonOverviewController{
@FXML
private TableView<Person> personTable;
@FXML
private TableColumn<Person, String> firstNameColumn;
@FXML
private TableColumn<Person, String> lastNameColumn;
@FXML
private Label firstNameLabel;
@FXML
private Label lastNameLabel;
@FXML
private Label streetLabel;
@FXML
private Label postalCodeLabel;
@FXML
private Label cityLabel;
@FXML
private Label birthdayLabel;
public PersonOverviewController() {
}
@FXML
private void initialize() {
// Initialize the person table with the two columns.
firstNameColumn.setCellValueFactory(cellData -> cellData.getValue().firstNameProperty());
lastNameColumn.setCellValueFactory(cellData -> cellData.getValue().lastNameProperty());
try{
//showPersonDetails(null);
//personTable.getSelectionModel().selectedItemProperty().addListener( (observable, oldValue, newValue) -> showPersonDetails(newValue));
personTable.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<Person>(){
@Override
public void changed(ObservableValue<? extends Person> observable, Person oldValue, Person newValue) {
System.out.println(newValue);
showPersonDetails(newValue);
}
});
}catch(NullPointerException e){
e.printStackTrace();
}
}
public void showTableViewData(MainApp mainApp) {
personTable.setItems(mainApp.getPersonData());
}
public void showPersonDetails(Person person){
Platform.runLater(new Runnable(){
@Override
public void run() {
if(person != null){
System.out.println(person.getFirstName());
firstNameLabel.setText(person.getFirstName());
System.out.println("test");
lastNameLabel.setText(person.getLastName());
streetLabel.setText(person.getStreet());
postalCodeLabel.setText(Integer.toString(person.getPostalCode()));
cityLabel.setText(person.getCity());
birthdayLabel.setText(person.getBirthday().toString());
}else{
firstNameLabel.setText("");
lastNameLabel.setText("");
streetLabel.setText("");
postalCodeLabel.setText("");
cityLabel.setText("");
birthdayLabel.setText("");
}
}
});
}
}
这就是我从 MainApp.java
加载控制器的方式public void showPersonOverview(){
try {
FXMLLoader loader = new FXMLLoader();
loader.setLocation(MainApp.class.getResource("/passion/viewControllers/PersonOverView.fxml"));
AnchorPane personOverview = (AnchorPane)loader.load();
root.setCenter(personOverview);
PersonOverviewController personController = loader.getController();
personController.showTableViewData(this);
} catch (IOException e) {
e.printStackTrace();
}
}
PersonOverview.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="300.0" prefWidth="600.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8" fx:controller="passion.controllers.PersonOverviewController">
<children>
<SplitPane dividerPositions="0.29797979797979796" layoutX="200.0" layoutY="70.0" prefHeight="300.0" prefWidth="600.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<items>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
<children>
<TableView fx:id="personTable" layoutX="-12.0" layoutY="49.0" prefHeight="200.0" prefWidth="200.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="-0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<columns>
<TableColumn fx:id="firstNameColumn" prefWidth="75.0" text="First Name" />
<TableColumn fx:id="lastNameColumn" prefWidth="75.0" text="Last Name" />
</columns>
<columnResizePolicy>
<TableView fx:constant="CONSTRAINED_RESIZE_POLICY" />
</columnResizePolicy>
</TableView>
</children>
</AnchorPane>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
<children>
<Label layoutX="14.0" layoutY="14.0" text="Person Details:" AnchorPane.leftAnchor="5.0" AnchorPane.topAnchor="5.0" />
<GridPane layoutX="34.0" layoutY="38.0" AnchorPane.leftAnchor="5.0" AnchorPane.rightAnchor="5.0" AnchorPane.topAnchor="30.0">
<columnConstraints>
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
</columnConstraints>
<rowConstraints>
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
</rowConstraints>
<children>
<Label text="First Name">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="Last Name" GridPane.rowIndex="1">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="Street" GridPane.rowIndex="2">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="City" GridPane.rowIndex="3">
<padding>
<Insets left="5.0" />
</padding>
</Label>
<Label text="Postal Code" GridPane.rowIndex="4">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label text="Birthday" GridPane.rowIndex="5">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="firstName" text="Label" GridPane.columnIndex="1">
<padding>
<Insets left="5.0" />
</padding>
</Label>
<Label fx:id="lastName" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="1">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="street" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="2">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="city" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="3">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="postal" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="4">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
<Label fx:id="birthday" text="Label" GridPane.columnIndex="1" GridPane.rowIndex="5">
<GridPane.margin>
<Insets left="5.0" />
</GridPane.margin>
</Label>
</children>
</GridPane>
<HBox layoutX="229.0" layoutY="244.0" spacing="5.0" AnchorPane.bottomAnchor="10.0" AnchorPane.rightAnchor="10.0">
<children>
<Button layoutX="229.0" layoutY="244.0" mnemonicParsing="false" text="New..." />
<Button layoutX="289.0" layoutY="244.0" mnemonicParsing="false" text="Edit..." />
<Button layoutX="351.0" layoutY="244.0" mnemonicParsing="false" text="Delete" />
</children>
</HBox>
</children>
</AnchorPane>
</items>
</SplitPane>
</children>
</AnchorPane>
控制台：
Person [firstName=StringProperty [value: Satya], lastName=StringProperty [value: Vema], street=StringProperty [value: some street], postalCode=IntegerProperty [value: 1234], city=StringProperty [value: some city], birthday=ObjectProperty [value: 1999-02-21]]
Person [firstName=StringProperty [value: Satya], lastName=StringProperty [value: Vema], street=StringProperty [value: some street], postalCode=IntegerProperty [value: 1234], city=StringProperty [value: some city], birthday=ObjectProperty [value: 1999-02-21]]
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at passion.controllers.PersonOverviewController.run(PersonOverviewController.java:69)
at com.sun.javafx.application.PlatformImpl.lambda$null0(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda/32693051.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$$Lambda/2180324.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null5(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda/3326003.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
缺少连接（fx:id 到变量名称 @FXML 或 @FXML("...")）。
<Label text="First Name" fx:id="firstNameLabel">
因此无法将组件设置为 FXML 生成的对话框的实际组件。
我认为您遗漏了一部分代码。
TextView firstNameLabel = (TextView)findIdById(R.id.yourTextViewIdInLayout);
并且您必须对所有小部件执行此操作，以免获得 NullPointerException。