JavaFX - 如何在TableView中识别ScrollBar的位置 [英] JavaFX - how to recognize the position of ScrollBar in a TableView

问题描述

我写过这个小例子应用程序：

I have written this little example application:

package application;

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableColumn.CellEditEvent;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.scene.control.cell.TextFieldTableCell;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {

    public class Person {

        private StringProperty firstName = new SimpleStringProperty();
        private StringProperty lastName = new SimpleStringProperty();

        public Person(String firstName, String lastName) {

            this.firstName.set(firstName);
            this.lastName.set(lastName);
        }

        public String getFirstName() {
            return firstName.get();
        }

        public String getLastName() {
            return lastName.get();
        }

        public StringProperty firstNameProperty() {
            return firstName;
        }

        public StringProperty lastNameProperty() {
            return lastName;
        }

    }

    @Override
    public void start(Stage primaryStage) {

        try {
            StackPane root = new StackPane();

            TableView<Person> tv = new TableView<>();
            TableColumn<Person, String> col = new TableColumn<Person, String>("FirstName");
            col.setCellValueFactory(new PropertyValueFactory<Person, String>("firstName"));

            tv.getColumns().add(col);
            tv.setEditable(true);

            col = new TableColumn<Person, String>("LastName");
            col.setCellValueFactory(new PropertyValueFactory<Person, String>("lastName"));
            col.setCellFactory(TextFieldTableCell.forTableColumn());
            col.setOnEditCommit(new EventHandler<TableColumn.CellEditEvent<Person, String>>() {

                @Override
                public void handle(CellEditEvent<Person, String> event) {

                    System.out.println(tv.getItems().get(1).getLastName());
                }
            });

            tv.getColumns().add(col);

            for (int i = 0; i < 30; i++) {
                tv.getItems().add(new Person("Test" + i, "Test" + i));
            }

            root.getChildren().add(tv);

            Scene scene = new Scene(root, 400, 200);
            primaryStage.setScene(scene);
            primaryStage.show();

            tv.addEventFilter(MouseEvent.MOUSE_RELEASED, event -> {
                // ...
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        launch(args);
    }
}

我想在<$ c $时执行操作c> ScrollBar 已达到最低点。然后我想从数据库重新加载更多数据。但只有这样，当用户看到所有已经加载的数据时（=底部的滚动条）。你有什么好建议可以解决这个问题吗？

I want to perform action when the ScrollBar has reached the bottom. Then I want to reload more datas from the database. But only then, when the user has seen all the already loaded datas (= scrollbar on the bottom). Do you have nice suggestions to solve this issue?

我的第一个想法是抓住 MOUSE_RELEASED 事件（当时用户拖动 TableView 的栏，然后检查 ScrollBar 的位置：
- < a href =https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/ScrollBar.html#getValue-- =nofollow noreferrer> getValue（）获取栏的位置
- getMax（）最大值（=底部）。

My first idea was to catch the MOUSE_RELEASED event (when the users drags the bar) of the TableView and then to check the position of the ScrollBar: - getValue() gets the position of the bar - getMax() the maximum value (=bottom).

但我找不到方法（不使用css选择器）通过此方法）从给定的 TableView 获取 ScrollBar 。所以我无法在某个 TableView 中检查它的位置。

But I can't find a way (without using the css-selector via this method) to get the ScrollBar from a given TableView. So I can't check the position of it in a certain TableView.

你有什么想法吗？

我很兴奋。谢谢你的帮助。

I am excited. Thanks for your help.

推荐答案

获取滚动条的唯一方法是通过查找，这有点像黑客攻击，但是只要你在在场景上渲染了之后它就会工作。你需要

The only way to get the scroll bar is via a lookup, which is a bit of a hack, but it will work as long as you do it after the table has been rendered on the scene. You need

ScrollBar verticalBar = (ScrollBar) table.lookup(".scroll-bar:vertical");

请注意，不需要弄乱用户事件：您只需观察滚动条的 value 属性直接：

Note that there's no need to mess with user events: you can just observe the scroll bar's value property directly:

verticalBar.valueProperty().addListener((obs, oldValue, newValue) -> {
    if (newValue.doubleValue() >= verticalBar.getMax()) {
        // add more data...
    }
});

SSCCE：

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

import javafx.application.Application;
import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.ScrollBar;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class AddMoreTableDataOnScrollToBottom extends Application {

    @Override
    public void start(Stage primaryStage) {
        TableView<Item> table = new TableView<>();
        table.getColumns().add(column("Item", Item::nameProperty));
        table.getColumns().add(column("Value", Item::valueProperty));


        addMoreData(table, 20);

        Scene scene = new Scene(new BorderPane(table), 400, 400);
        primaryStage.setScene(scene);
        primaryStage.show();

        ScrollBar verticalBar = (ScrollBar) table.lookup(".scroll-bar:vertical");
        verticalBar.valueProperty().addListener((obs, oldValue, newValue) -> {
            if (newValue.doubleValue() >= verticalBar.getMax()) {
                addMoreData(table, 20);
            }
        });
    }

    private void addMoreData(TableView<Item> table, int numItems) {
        Task<List<Item>> dataRetrieveTask = new Task<List<Item>>() {
            @Override
            public List<Item> call() throws Exception {
                // mimic connect to db:
                Thread.sleep(500);
                List<Item> items = new ArrayList<>();
                int nextItem = table.getItems().size() + 1 ;
                for (int i = nextItem; i < nextItem + numItems; i++ ){
                    items.add(new Item("Item "+i, i));
                }
                return items ;
            }
        };
        dataRetrieveTask.setOnSucceeded(e -> table.getItems().addAll(dataRetrieveTask.getValue()));
        new Thread(dataRetrieveTask).start();
    }

    private <S,T> TableColumn<S,T> column(String title, Function<S, ObservableValue<T>> prop) {
        TableColumn<S,T> col = new TableColumn<>(title);
        col.setCellValueFactory(cellData -> prop.apply(cellData.getValue()));
        return col ;
    }

    public static class Item {

        private final StringProperty name = new SimpleStringProperty();
        private final IntegerProperty value = new SimpleIntegerProperty();

        public Item(String name, int value) {
            setName(name);
            setValue(value);
        }

        public final StringProperty nameProperty() {
            return this.name;
        }


        public final String getName() {
            return this.nameProperty().get();
        }


        public final void setName(final String name) {
            this.nameProperty().set(name);
        }


        public final IntegerProperty valueProperty() {
            return this.value;
        }


        public final int getValue() {
            return this.valueProperty().get();
        }


        public final void setValue(final int value) {
            this.valueProperty().set(value);
        }


    }

    public static void main(String[] args) {
        launch(args);
    }
}

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