我是 Java 和 OOP 新手,并且陷入了向 tableview 列添加图像的困境。代码似乎有效,我可以看到学生的姓名正确,但图像未显示在列中。我收到此错误并且无法理解如何使其工作:
javafx.scene.control.cell.PropertyValueFactory getCellDataReflectively
WARNING: Can not retrieve property 'picture' in PropertyValueFactory: javafx.scene.control.cell.PropertyValueFactory@5b0da50f with provided class type: class model.StudentModel
java.lang.IllegalStateException: Cannot read from unreadable property picture
学生模型:
package model;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.image.ImageView;
import java.util.ArrayList;
import java.util.List;
public class StudentModel {
private ImageView picture;
private String name;
private SubjectModel major;
private SubjectModel minor;
private String accountPassword;
public String getAccountPassword()
{
return accountPassword;
}
public List<LectureModel> lectureModelList = new ArrayList<>();
public StudentModel(String name, SubjectModel major, SubjectModel minor, ImageView picture, String accountPassword)
{
this.name = name;
this.major = major;
this.minor = minor;
this.picture = picture;
this.accountPassword = accountPassword;
}
public String getName()
{
return name;
}
public ObservableList<LectureModel> myObservableLectures(){
ObservableList<LectureModel> observableList = FXCollections.observableArrayList(lectureModelList);
return observableList;
}
public ImageView getPhoto(){
return picture;
}
public void setPhoto(ImageView photo)
{
this.picture = photo;
}
}
我有桌面视图的参与者场景:
public class ParticipantsScene extends Scene {
private final StudentController studentController;
private final ClientApplication clientApplication;
private final TableView<StudentModel> allParticipantsTable;
private final ObservableList<StudentModel> enrolledStudents;
private LectureModel lecture;
public ParticipantsScene(StudentController studentController, ClientApplication application, LectureModel lecture) {
super(new VBox(), 800 ,500);
this.clientApplication = application;
this.studentController = studentController;
this.lecture = lecture;
enrolledStudents=lecture.observeAllParticipants();
TableColumn<StudentModel, String > nameCol = new TableColumn<>("Name");
nameCol.setMinWidth(200);
nameCol.setCellValueFactory(new PropertyValueFactory<>("name"));
TableColumn<StudentModel, ImageView> picCol = new TableColumn<>("Images");
picCol.setPrefWidth(200);
picCol.setCellValueFactory(new PropertyValueFactory<>("picture"));
allParticipantsTable = new TableView<>();
allParticipantsTable.getColumns().addAll(nameCol,picCol);
allParticipantsTable.setItems(enrolledStudents);
VBox vBox = new VBox(10, allParticipantsTable, createButtonBox());
vBox.setAlignment(Pos.CENTER);
setRoot(vBox);
}
private HBox createButtonBox() {
var backButton = new Button("Back");
backButton.setOnAction(event -> clientApplication.showAllLecturesScene());
var buttonBox = new HBox(10, backButton);
buttonBox.setAlignment(Pos.CENTER);
return buttonBox;
}
}
还添加讲座模型,以防有帮助:
public class LectureModel {
private String lectureName;
private String lectureHall;
private String subjectName;
private SubjectModel subject;
private TimeSlot timeSlot;
//private Button actionButton1;
//private Button actionButton2;
private List<StudentModel> enrolledStudents = new ArrayList<>();
private String name;
public LectureModel(String lectureName, String lectureHall, SubjectModel subject, TimeSlot timeSlot){
this.lectureName = lectureName;
this.lectureHall = lectureHall;
this.subject = subject;
this.timeSlot = timeSlot;
this.subjectName = this.subject.getSubjectName();
}
public String getLectureName()
{
return lectureName;
}
public String getLectureHall()
{
return lectureHall;
}
public SubjectModel getSubject()
{
return subject;
}
public String getSubjectName()
{
return subjectName;
}
public List<StudentModel> getEnrolledStudents()
{
return enrolledStudents;
}
public ObservableList<StudentModel> observeAllParticipants() {
ObservableList<StudentModel> observableList = FXCollections.observableArrayList(getEnrolledStudents());
return observableList;
}
public TimeSlot getTimeSlot() {
return timeSlot;
}
public void addStudent(StudentModel studentModel){ enrolledStudents.add(studentModel);}
public void removeStudent(StudentModel studentModel)
{
enrolledStudents.remove(studentModel);
};
感谢任何形式的帮助, 谢谢!
您错误命名了 PropertyValueFactory 中使用的属性名称。
一般情况下,不要使用 PropertyValueFactories,而是使用 lambda:
此外,作为一般原则,将数据放置在模型中,而不是节点中。例如,在模型中存储图像或图像的 URL,而不是 ImageView。然后仅在模型视图中使用节点。例如,要在表格单元格中显示图像,请使用单元格工厂。
如果需要,可以将 LRU 缓存 用于图像(可能不需要)。
表格中显示的图像通常可能小于全尺寸图像,即缩略图。为了提高效率,您可能需要使用调整图像大小的构造函数在后台加载图像。
如果您需要帮助放置和定位图像资源,请参阅:
示例代码
本答案中的示例使用了答案文本中的一些原则:
虽然我没有测试它,但这个解决方案应该可以很好地扩展到具有数千行的表,每行都有不同的图像。
此处提供了此答案中使用的图像:
ImageCell.java
import javafx.scene.control.TableCell;
import javafx.scene.image.ImageView;
public class ImageCell<S> extends TableCell<S, String> {
private final ImageView imageView = new ImageView();
private final ImageCache imageCache = ImageCache.getInstance();
@Override
protected void updateItem(String url, boolean empty) {
super.updateItem(url, empty);
if (url == null || empty || imageCache.getThumbnail(url) == null) {
imageView.setImage(null);
setGraphic(null);
} else {
imageView.setImage(imageCache.getThumbnail(url));
setGraphic(imageView);
}
}
}
ImageCache.java
import javafx.scene.image.Image;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Objects;
public class ImageCache {
private static final int IMAGE_CACHE_SIZE = 10;
private static final int THUMBNAIL_SIZE = 64;
private static final ImageCache instance = new ImageCache();
public static ImageCache getInstance() {
return instance;
}
private final Map<String, Image> imageCache = new LruCache<>(
IMAGE_CACHE_SIZE
);
private final Map<String, Image> thumbnailCache = new LruCache<>(
IMAGE_CACHE_SIZE
);
public Image get(String url) {
if (!imageCache.containsKey(url)) {
imageCache.put(
url,
new Image(
Objects.requireNonNull(
ImageCache.class.getResource(
url
)
).toExternalForm(),
true
)
);
}
return imageCache.get(url);
}
public Image getThumbnail(String url) {
if (!thumbnailCache.containsKey(url)) {
thumbnailCache.put(
url,
new Image(
Objects.requireNonNull(
ImageCache.class.getResource(
url
)
).toExternalForm(),
THUMBNAIL_SIZE,
THUMBNAIL_SIZE,
true,
true,
true
)
);
}
return thumbnailCache.get(url);
}
private static final class LruCache<A, B> extends LinkedHashMap<A, B> {
private final int maxEntries;
public LruCache(final int maxEntries) {
super(maxEntries + 1, 1.0f, true);
this.maxEntries = maxEntries;
}
@Override
protected boolean removeEldestEntry(final Map.Entry<A, B> eldest) {
return super.size() > maxEntries;
}
}
}
学生.java
public record Student(
String last,
String first,
String avatar
) {}
StudentTableApp.java
import javafx.application.Application;
import javafx.beans.property.ReadOnlyStringWrapper;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class StudentTableApp extends Application {
@Override
public void start(Stage stage) {
TableView<Student> table = createTable();
populateTable(table);
VBox layout = new VBox(
10,
table
);
layout.setPadding(new Insets(10));
layout.setPrefSize(340, 360);
layout.setStyle("-fx-font-size:20px; -fx-base: antiquewhite");
stage.setScene(new Scene(layout));
stage.show();
}
private TableView<Student> createTable() {
TableView<Student> table = new TableView<>();
TableColumn<Student, String> lastColumn = new TableColumn<>("Last");
lastColumn.setCellValueFactory(
p -> new ReadOnlyStringWrapper(
p.getValue().last()
).getReadOnlyProperty()
);
TableColumn<Student, String> firstColumn = new TableColumn<>("First");
firstColumn.setCellValueFactory(
p -> new ReadOnlyStringWrapper(
p.getValue().first()
).getReadOnlyProperty()
);
TableColumn<Student, String> avatarColumn = new TableColumn<>("Avatar");
avatarColumn.setCellValueFactory(
p -> new ReadOnlyStringWrapper(
p.getValue().avatar()
).getReadOnlyProperty()
);
avatarColumn.setCellFactory(
p -> new ImageCell<>()
);
avatarColumn.setPrefWidth(70);
//noinspection unchecked
table.getColumns().addAll(lastColumn, firstColumn, avatarColumn);
return table;
}
private void populateTable(TableView<Student> table) {
table.getItems().addAll(
new Student("Dragon", "Smaug", "Dragon-icon.png"),
new Student("Snake-eyes", "Shifty", "Medusa-icon.png"),
new Student("Wood", "Solid", "Treant-icon.png"),
new Student("Rainbow", "Magical", "Unicorn-icon.png")
);
}
}