不可能说出空指针异常的原因,因为您没有显示堆栈跟踪,没有识别引发异常的行,也没有发布足够的代码(回调中的任何代码都不能引发空指针异常,所以其他地方出了问题)。
对于您的实际单元实现,您没有显示您是否有cellValueFactory
设置在柱上。如果你不这样做,那么item
will always be null
,因此您将永远不会在该列的单元格中看到任何文本。您可以检查empty
属性(或方法参数)作为检查单元格是否位于空行或包含实际数据的行中的一种方法。 (请注意,这意味着该列实际上根本不需要提供任何数据:它可以是TableColumn<Task, Void>
.)
此外,依赖使用可能更安全updateIndex(...)
代替updateItem(...)
. updateIndex
当索引改变时保证被调用;如果你实施updateItem
您假设索引是在项目之前设置的,这意味着您依赖于实现细节。
如果您使用 Java 8 lambda 表达式,您的代码会更短且更容易阅读:
taskIndexCol.setCellFactory(col -> new TableCell<Task, String>() {
@Override
protected void updateIndex(int index) {
super.updateIndex(index);
if (isEmpty() || index < 0) {
setText(null);
} else {
setText(Integer.toString(index));
}
}
});
或者替代地
taskIndexCol.setCellFactory(col -> {
TableCell<Task, String> cell = new TableCell<>();
cell.textProperty().bind(Bindings.when(cell.emptyProperty())
.then("")
.otherwise(cell.indexProperty().asString()));
return cell ;
});
这是一个 SSCCE:
import java.util.function.Function;
import static javafx.beans.binding.Bindings.when ;
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ObservableValue;
import javafx.scene.Scene;
import javafx.scene.control.TableCell;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
public class TableViewWithIndexColumn extends Application {
@Override
public void start(Stage primaryStage) {
TableView<Person> table = new TableView<>();
table.setEditable(true);
table.getItems().addAll(
new Person("Jacob", "Smith", "[email protected] /cdn-cgi/l/email-protection"),
new Person("Isabella", "Johnson",
"[email protected] /cdn-cgi/l/email-protection"),
new Person("Ethan", "Williams", "[email protected] /cdn-cgi/l/email-protection"),
new Person("Emma", "Jones", "[email protected] /cdn-cgi/l/email-protection"),
new Person("Michael", "Brown", "[email protected] /cdn-cgi/l/email-protection"));
TableColumn<Person, String> firstNameCol = createColumn("First Name",
Person::firstNameProperty, 150);
TableColumn<Person, String> lastNameCol = createColumn("Last Name",
Person::lastNameProperty, 150);
TableColumn<Person, String> emailCol = createColumn("Email",
Person::emailProperty, 150);
// index column doesn't even need data...
TableColumn<Person, Void> indexCol = createColumn("Index", person -> null, 50);
// cell factory to display the index:
// indexCol.setCellFactory(col -> {
//
// // just a default table cell:
// TableCell<Person, Void> cell = new TableCell<>();
//
// cell.textProperty().bind(
// when(cell.emptyProperty())
// .then("")
// .otherwise(cell.indexProperty().asString()));
//
// return cell ;
// });
indexCol.setCellFactory(col -> new TableCell<Person, Void>() {
@Override
public void updateIndex(int index) {
super.updateIndex(index);
if (isEmpty() || index < 0) {
setText(null);
} else {
setText(Integer.toString(index));
}
}
});
table.getColumns().add(indexCol);
table.getColumns().add(firstNameCol);
table.getColumns().add(lastNameCol);
table.getColumns().add(emailCol);
primaryStage.setScene(new Scene(new BorderPane(table), 600, 400));
primaryStage.show();
}
private <S, T> TableColumn<S, T> createColumn(String title,
Function<S, ObservableValue<T>> property, double width) {
TableColumn<S, T> col = new TableColumn<>(title);
col.setCellValueFactory(cellData -> property.apply(cellData.getValue()));
col.setPrefWidth(width);
return col;
}
public static class Person {
private final StringProperty firstName = new SimpleStringProperty();
private final StringProperty lastName = new SimpleStringProperty();
private final StringProperty email = new SimpleStringProperty();
public Person() {
this("", "", "");
}
public Person(String firstName, String lastName, String email) {
setFirstName(firstName);
setLastName(lastName);
setEmail(email);
}
public final StringProperty firstNameProperty() {
return this.firstName;
}
public final java.lang.String getFirstName() {
return this.firstNameProperty().get();
}
public final void setFirstName(final java.lang.String firstName) {
this.firstNameProperty().set(firstName);
}
public final StringProperty lastNameProperty() {
return this.lastName;
}
public final java.lang.String getLastName() {
return this.lastNameProperty().get();
}
public final void setLastName(final java.lang.String lastName) {
this.lastNameProperty().set(lastName);
}
public final StringProperty emailProperty() {
return this.email;
}
public final java.lang.String getEmail() {
return this.emailProperty().get();
}
public final void setEmail(final java.lang.String email) {
this.emailProperty().set(email);
}
}
public static void main(String[] args) {
launch(args);
}
}