javafx listview NullPointer填充Items时

Question

我正在按照这个答案，在制作自己的Listview时，除了在我尝试更新我的nullpointer时给我一个listview时，一切都很顺利，当它尝试时会发生这种情况在TextFields中将数据设置到我的ListCell这里是我的Controller类代码

 private ArrayList <RoadItem> roadListItem = new ArrayList<>();
 private ObservableList observableList = FXCollections.observableArrayList();

  public void setRoadListView()
  {
  RoadItem item = new RoadItem();
  item.setDirection("left");
  item.setRegNo(""+2325);
  item.setWidth(345);
  item.setSpeed(233);
  roadListItem.add(item);

  observableList.setAll(roadListItem);
  roadItemListView.setItems(observableList);
  roadItemListView.setCellFactory(new Callback<ListView<RoadItem>, javafx.scene.control.ListCell<RoadItem>>()
  {

    @Override
    public ListCell<RoadItem> call(ListView<RoadItem> arg0) {
        // TODO Auto-generated method stub
        return new RoadListCell();
    }
  });

} 我的RoadItem类

@FXML ImageView imageView;
@FXML TextField txt_plateNumber;
@FXML TextField txt_speed;
@FXML TextField txt_width;
@FXML TextField txt_direction;
@FXML AnchorPane anchorPane;

public RoadListItem()
{
    FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("/application/carsListCell.fxml"));
    fxmlLoader.setController(this);
    try
    {
        fxmlLoader.load();
    }
    catch (IOException e)
    {
        throw new RuntimeException(e);
    }
}


public void setCellItem(RoadItem item )
{

    //Where NullPointer is occuring
    if(item.getImage() != null)
    imageView.setImage(item.getImage());
    txt_plateNumber.setText(""+item.getRegNo());
    txt_speed.setText(""+item.getSpeed()+"Km/h");
    txt_width.setText(""+item.getWidth()+"mtrs");
    txt_direction.setText(item.getDirection());
}

public AnchorPane getAnchorPane()
{
    return this.anchorPane;
}

我的RoadListCell类

public class RoadListCell extends ListCell<RoadItem>
{
public void updateItem(RoadItem item, boolean empty)
{
    super.updateItem(item, empty);
    if(item != null)
    {
        RoadListItem listItem = new RoadListItem();
        listItem.setCellItem(item);
        setGraphic(listItem.anchorPane);
    }
}

RoadItem类

public class RoadItem {



private Image image;
private String regNo;
private float speed;
private float width;
private String direction;


public RoadItem() {
    super();
    this.image = new Image("assets/eyeMediumsec.png");;
    this.regNo = "";
    this.speed = 0;
    this.width = 0;
    this.direction = "";
}


public RoadItem(Image image, String regNo, float speed, float width, String direction) {
    super();
    this.image = image;
    this.regNo = regNo;
    this.speed = speed;
    this.width = width;
    this.direction = direction;
}


public Image getImage() {
    return image;
}
public void setImage(Image image) {
    this.image = image;
}
public String getRegNo() {
    return regNo;
}
public void setRegNo(String regNo) {
    this.regNo = regNo;
}
public float getSpeed() {
    return speed;
}
public void setSpeed(float speed) {
    this.speed = speed;
}
public float getWidth() {
    return width;
}
public void setWidth(float width) {
    this.width = width;
}
public String getDirection() {
    return direction;
}
public void setDirection(String direction) {
    this.direction = direction;
}

}

My Cell FXML

<AnchorPane fx:id="anchorPane" prefHeight="60.0" prefWidth="350.0"    
xmlns="http://javafx.com/javafx/8.0.40" xmlns:fx="http://javafx.com/fxml/1" >
   <children>
      <Card prefHeight="60.0" prefWidth="350.0">
       <children>
        <Region prefHeight="60.0" prefWidth="300.0" />
         <HBox prefHeight="60.0" prefWidth="350.0">
            <children>
               <ImageView fx:id ="imageView" fitHeight="60.0" 
                  fitWidth="60.0" pickOnBounds="true">
                  <image>
                    <Image   url="@../../../../Downloads/african_sad_girl_by_psymfonius-d4bglwk.jpg" />
                 </image>
              </ImageView>
              <Separator maxWidth="1.0" orientation="VERTICAL" prefHeight="60.0" prefWidth="1.0" scaleX="0.5" />
              <VBox prefHeight="200.0" prefWidth="110.0">
                 <children>
                    <Label text="Plate No:" translateX="6.0">
                       <font>
                          <Font size="10.0" />
                       </font></Label>
                    <Separator prefWidth="200.0" scaleY="0.5" />
                    <TextInput id="txt_plateNumber" translateY="3.0" />
                 </children>
              </VBox>
              <Separator maxWidth="6.0" orientation="VERTICAL" prefHeight="60.0" prefWidth="2.0" scaleX="0.5" />
              <VBox prefHeight="200.0" prefWidth="110.0">
                 <children>
                    <Label text="Speed" translateX="12.0">
                       <font>
                          <Font size="10.0" />
                       </font>
                    </Label>
                    <Separator prefWidth="200.0" scaleY="0.5" />
                    <TextInput id="txt_speed" translateY="3.0" />
                 </children>
              </VBox>
              <Separator maxWidth="1.0" orientation="VERTICAL" prefHeight="60.0" prefWidth="1.0" scaleX="0.5" />
              <VBox prefHeight="200.0" prefWidth="110.0">
                 <children>
                    <Label text="Width" translateX="12.0">
                       <font>
                          <Font size="10.0" />
                       </font>
                    </Label>
                    <Separator prefWidth="200.0" scaleY="0.5" />
                    <TextInput id="txt_width" translateY="3.0" />
                 </children>
              </VBox>
              <Separator maxWidth="1.0" orientation="VERTICAL" prefHeight="60.0" prefWidth="1.0" scaleX="0.5" />
              <VBox prefHeight="200.0" prefWidth="110.0">
                 <children>
                    <Label text="Direction" translateX="6.0">
                       <font>
                          <Font size="10.0" />
                       </font>
                    </Label>
                    <Separator prefWidth="200.0" scaleY="0.5" />
                    <TextInput id="txt_direction" translateY="3.0" />
                 </children>
              </VBox>
              <Separator maxWidth="1.0" orientation="VERTICAL" prefHeight="60.0" prefWidth="1.0" scaleX="0.5" />
              <VBox prefHeight="200.0" prefWidth="110.0">
                 <children>
                    <Label text="Type" translateX="12.0">
                       <font>
                          <Font size="10.0" />
                       </font>
                    </Label>
                    <Separator prefWidth="200.0" scaleY="0.5" />
                    <TextInput id="txt_vehicleType" translateY="3.0" />
                 </children>
              </VBox>
              <Separator maxWidth="6.0" opacity="0.0" orientation="VERTICAL" prefHeight="60.0" prefWidth="4.0" />
           </children>
        </HBox>
     </children>
   </Card>
   </children>
  </AnchorPane>

我的StackTrace

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at adapters.RoadListItem.setCellItem(RoadListItem.java:44)
at adapters.RoadListCell.updateItem(RoadListCell.java:14)
at adapters.RoadListCell.updateItem(RoadListCell.java:1)
at javafx.scene.control.ListCell.updateItem(Unknown Source)
at javafx.scene.control.ListCell.indexChanged(Unknown Source)
at javafx.scene.control.IndexedCell.updateIndex(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.setCellIndex(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.getCell(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.getCellLength(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.computeViewportOffset(Unknown Source)
at com.sun.javafx.scene.control.skin.VirtualFlow.layoutChildren(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Parent.layout(Unknown Source)
at javafx.scene.Scene.doLayoutPass(Unknown Source)
at javafx.scene.Scene.preferredSize(Unknown Source)
at javafx.scene.Scene.impl_preferredSize(Unknown Source)
at javafx.stage.Window$9.invalidated(Unknown Source)
at javafx.beans.property.BooleanPropertyBase.markInvalid(Unknown Source)
at javafx.beans.property.BooleanPropertyBase.set(Unknown Source)
at javafx.stage.Window.setShowing(Unknown Source)
at javafx.stage.Window.show(Unknown Source)
at javafx.stage.Stage.show(Unknown Source)
at loginManager.LoginManager.showMainView(LoginManager.java:151)
at loginManager.LoginManager.authenticated(LoginManager.java:51)
at application.LoginController$1.handle(LoginController.java:67)
at application.LoginController$1.handle(LoginController.java:1)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at javafx.event.Event.fireEvent(Unknown Source)
at javafx.scene.Node.fireEvent(Unknown Source)
at javafx.scene.control.Button.fire(Unknown Source)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at javafx.event.Event.fireEvent(Unknown Source)
at javafx.scene.Scene$MouseHandler.process(Unknown Source)
at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(Unknown Source)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
at com.sun.glass.ui.View.notifyMouse(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Answer 1

类中的

RoadItem是默认值设置的图像，还是仍然为空？如果为null - 那就是proplem observableList.setAll（roadListItem）; - 按项目设置，并且在roadListItem中有项目，这不是null，但是imageView - null这就是为什么我们有NullPointerException