JavaFX8初探（分页控件）

JavaFX8初探（分页控件）

本章我们主要介绍如何在javaFX应用中加入分页控件，以及如何用CSS样式来装饰它。
分页控件用来把内容分割到不同的页面中，最典型的应用就是在右面框中显示邮件信息，我们可以在分页控件中只显示邮件的主题的方法来导航邮件。下面是一个分页控件的实例：

创建分页控件

分页控件包含页面内容和页面导航区，页面内容根据业务逻辑需要来展示，页面导航区域包含一个预制控制预览特定内容的一部分。下图说明了导航区的基本元素：

你可以通过点击页面指示按钮来导航，也可以通过点击上一页和下一页来导航，当第一页选中的时候，上一页按钮不可用，同样，当最后一页被选中的时候下一页按钮不可用。
JavaFX提供了Pagination 类，让我们添加分页控件到应用中，可用的构造方法如下：

//Creates a Pagination control with an INDETERMINATE page count 
//and the current page index equal to zero
Pagination pagination1 = new Pagination();
//Creates a Pagination control with 5 pages
//and the current page index equal to zero
Pagination pagination2 = new Pagination(5);
//Creates a Pagination control with 5 pages
//and the current selected index equal to 2
Pagination pagination3 = new Pagination(5, 2);

显示如下图：

需要指出的是，页面的下标从0开始。因此，如果你想让第3也选中，那么你需要设置currentPageIndexProperty 的值为2.
第3也的内容是空的，因为我们没有添加过任何内容。
你不能直接向分页控件添加任何内容，一个页面工厂是必须得，我们可以使用setPageFactory 方法来设置一个页面工厂。

实现页面工厂

setPageFactory 方法为分页控件设置一个页面工厂，应用开发者通过创建一个回调方法，并且把页面工厂传递给这个回调方法。当页面被选中的时候，这个回调方法就会被调用，就会加载选中页面的内容。如果选中的页面下标不存在必须返回null。

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Pagination;
import javafx.scene.control.Hyperlink;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;


public class PaginationSample extends Application {
    private Pagination pagination;

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

    public int itemsPerPage() {
        return 8;
    }

    public VBox createPage(int pageIndex) {
        VBox box = new VBox(5);
        int page = pageIndex * itemsPerPage();
        for (int i = page; i < page + itemsPerPage(); i++) {
            VBox element = new VBox();
            Hyperlink link = new Hyperlink("Item " + (i+1));
            link.setVisited(true);
            Label text = new Label("Search results\nfor "+ link.getText());
            element.getChildren().addAll(link, text);
            box.getChildren().add(element);
        }
        return box;
    }

    @Override
    public void start(final Stage stage) throws Exception {
        pagination = new Pagination(28, 0);
        pagination.setStyle("-fx-border-color:red;");
        pagination.setPageFactory((Integer pageIndex) -> createPage(pageIndex));

        AnchorPane anchor = new AnchorPane();
        AnchorPane.setTopAnchor(pagination, 10.0);
        AnchorPane.setRightAnchor(pagination, 10.0);
        AnchorPane.setBottomAnchor(pagination, 10.0);
        AnchorPane.setLeftAnchor(pagination, 10.0);
        anchor.getChildren().addAll(pagination);
        Scene scene = new Scene(anchor);
        stage.setScene(scene);
        stage.setTitle("PaginationSample");
        stage.show();
    }
}

我们可以通过调用Pagination 类的构造方法来指定页的数量，我们也可以通过setPageCount 方法来指定页数。通过setCurrentPageIndex 方法来指定当前页。
createPage 方法来指定页面的内容，当调用setPageFactory 方法的时候这个方法会被调用。createPage方法创建了超链接和相应的标签。安排他们是竖直排列。
运行编译这段代码显示如下图所示：

当前实例中包含有10个页面指示标识，当然这是可以设置的，我们可以通过如下代码来改变页面只是表示的数量：

pagination.setMaxPageIndicatorCount(7);. 

给上面的实例加上此代码后，运行如下图所示：

下面的例子是分页控件的另一种使用方式，每个页面显示一段文本，文本的数量是5，但是有28个页面。为了避免产生ArrayIndexOutOfBoundsException 我们需要检查下标，当超过5的时候直接返回null。

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Pagination;
import javafx.scene.control.TextArea;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class PaginationSample extends Application {

    private Pagination pagination;
    final String[] textPages = new String[]{
        "The apple is the pomaceous fruit of the apple tree, species Malus "
        + "domestica in the rose family (Rosaceae). It is one of the most "
        + "widely cultivated tree fruits, and the most widely known of "
        + "the many members of genus Malus that are used by humans. "
        + "The tree originated in Western Asia, where its wild ancestor, "
        + "the Alma, is still found today.",
        "The hawthorn is a large genus of shrubs and trees in the rose family,"
        + "Rosaceae, native to temperate regions of the Northern Hemisphere "
        + "in Europe, Asia and North America. The name hawthorn was "
        + "originally applied to the species native to northern Europe, "
        + "especially the Common Hawthorn C. monogyna, and the unmodified "
        + "name is often so used in Britain and Ireland.",
        "The ivy is a flowering plant in the grape family (Vitaceae) native to "
        + " eastern Asia in Japan, Korea, and northern and eastern China. "
        + "It is a deciduous woody vine growing to 30 m tall or more given "
        + "suitable support, attaching itself by means of numerous small "
        + "branched tendrils tipped with sticky disks.",
        "The quince is the sole member of the genus Cydonia and is native to "
        + "warm-temperate southwest Asia in the Caucasus region. The "
        + "immature fruit is green with dense grey-white pubescence, most "
        + "of which rubs off before maturity in late autumn when the fruit "
        + "changes color to yellow with hard, strongly perfumed flesh.",
        "Aster (syn. Diplopappus Cass.) is a genus of flowering plants "
        + "in the family Asteraceae. The genus once contained nearly 600 "
        + "species in Eurasia and North America, but after morphologic "
        + "and molecular research on the genus during the 1990s, it was "
        + "decided that the North American species are better treated in a "
        + "series of other related genera. After this split there are "
        + "roughly 180 species within the genus, all but one being confined "
        + "to Eurasia."
    };

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

    public int itemsPerPage() {
        return 1;
    }

    public VBox createPage(int pageIndex) {
        VBox box = new VBox(5);
        int page = pageIndex * itemsPerPage();
        for (int i = page; i < page + itemsPerPage(); i++) {
            TextArea text = new TextArea(textPages[i]);
            text.setWrapText(true);
            box.getChildren().add(text);
        }
        return box;
    }

    @Override
    public void start(final Stage stage) throws Exception {
        pagination = new Pagination(28, 0);
        pagination.setStyle("-fx-border-color:red;");
        pagination.setPageFactory((Integer pageIndex) -> {
            if (pageIndex >= textPages.length) {
                return null;
            } else {
                return createPage(pageIndex);
            }
        });

        AnchorPane anchor = new AnchorPane();
        AnchorPane.setTopAnchor(pagination, 10.0);
        AnchorPane.setRightAnchor(pagination, 10.0);
        AnchorPane.setBottomAnchor(pagination, 10.0);
        AnchorPane.setLeftAnchor(pagination, 10.0);
        anchor.getChildren().addAll(pagination);
        Scene scene = new Scene(anchor, 400, 250);
        stage.setScene(scene);
        stage.setTitle("PaginationSample");
        stage.show();
    }
}

编译运行，如下图所示：