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 zeroPagination pagination1 = new Pagination();//Creates a Pagination control with 5 pages//and the current page index equal to zeroPagination pagination2 = new Pagination(5);//Creates a Pagination control with 5 pages//and the current selected index equal to 2Pagination 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：