我正在构建一个JavaFX应用程序，我想访问在JavaFX UI中作为参数传递的值。出于某种原因，除了基本方法launchForm之外，我无法在所有方法中访问这些值。这是我的代码的样子。
public class FormBuilder extends Application {
/*
* (non-Javadoc)
* @see javafx.application.Application#start(javafx.stage.Stage)
* Scene scene
* Group root
* BorderPane borderPane
* TabPane tabPane
* Tab stocksTab
* BorderPane stockTabBorderPane
* GridPane gridPane
*
*/
private Stocks stockData = new Stocks();
private int size;
@Override
public void start(Stage stage) throws Exception {
stage.setTitle("Stock Manager");
Group root = new Group();
Scene scene = new Scene(root, 1024, 800, Color.WHITE);
TabPane tabPane = new TabPane();
BorderPane borderPane = new BorderPane();
BorderPane stockTabBorderPane = new BorderPane();
Tab stocksTab = new Tab("Stocks");
stockTabBorderPane.setTop(this.addHBox());
stockTabBorderPane.setCenter(this.createGridPane());
stocksTab.setContent(stockTabBorderPane);
tabPane.getTabs().add(stocksTab);
borderPane.setCenter(tabPane);
borderPane.prefHeightProperty().bind(scene.heightProperty());
borderPane.prefWidthProperty().bind(scene.widthProperty());
root.getChildren().add(borderPane);
stage.setScene(scene);
stage.show();
}
private HBox addHBox() {
HBox hbox = new HBox();
hbox.setPadding(new Insets(15, 12, 15, 12));
hbox.setSpacing(10);
hbox.setStyle("-fx-background-color: #336699;");
Button buttonCurrent = new Button("Current");
buttonCurrent.setPrefSize(100, 20);
Button buttonProjected = new Button("Projected");
buttonProjected.setPrefSize(100, 20);
hbox.getChildren().addAll(buttonCurrent, buttonProjected);
return hbox;
}
private GridPane createGridPane() {
GridPane gridPane = new GridPane();
gridPane.setLayoutX(39);
gridPane.setLayoutY(131.0);
gridPane.setAlignment(Pos.TOP_CENTER);
gridPane.setVgap(5.0);
gridPane.setHgap(10.0);
gridPane.add(new Label("Active"), 1,1);
gridPane.add(new Label("Stock"), 2, 1);
gridPane.add(new Label("Symbol"), 3, 1);
gridPane.add(new Label("LPP"), 4, 1);
gridPane.add(new Label("LPP"), 5, 1);
gridPane.add(new Label("HPP"), 6, 1);
gridPane.add(new Label("LTP"), 7, 1);
System.out.println(this.size);
for(int v=2;v < this.stockData.getStocks().size()+2; v++) {
gridPane.add(new CheckBox(), 1, v);
gridPane.add(new Label("Amazon"), 2, v);
gridPane.add(new TextField (), 3,v);
gridPane.add(new TextField (), 4,v);
gridPane.add(new TextField (), 5,v);
gridPane.add(new TextField (), 6,v);
gridPane.add(new TextField (), 7,v);
}
return gridPane;
}
public void launchForm(Stocks stockData) {
this.stockData = stockData;
this.size = stockData.getStocks().size();
System.out.println(stockData.getStocks().size());
System.out.println(stockData.getStocks().get(0).getSector());
launch();
}
}
现在的问题是，当我尝试访问stockData方法中createGridPane对象下的任何值时，这些值都不可用。
例子是
this.stockData.getStocks().size()在createGridPane方法中给出值0。但它在launchForm方法中给出的值为2。
还有其他值，如
this.stockData.getStocks().get(0).getSector()
在"Retail"方法中返回值launchForm。但是当我尝试在同一个类中以不同的方法访问它时，我得到一个例外。
有人可以帮我吗？
答案 0 :(得分：1)
您正在Application.launch实例方法中调用launchForm，并期望它将此方法作为应用程序类使用的实例。
然而，JavaFX的推出并不是这样的。
如果调用Application.launch，则调用该方法的类的 new 实例由launch方法本身创建，并且它是使用的新实例使用init和start。
解决此问题的最简单方法是，如果您可以在Stocks或init中创建start（可能会将某些字符串作为参数传递给launch）。
否则，您需要一些其他方式与新创建的Application子类实例进行通信，例如static成员......
答案 1 :(得分：0)
在JavaFX中，您基本上应该将Application子类，特别是其start()方法视为应用程序的入口点。应用程序生命周期在Application Javadocs中描述，但简而言之，JavaFX启动过程是通过调用其中一个静态Application.launch(...)方法或（使用Oracle JDK）启动，方法是启动JVM并指定Application子类作为主类（即使它没有main方法）。
然后启动过程：
Application子类init()子类上调用Application（默认实现是无操作）start()子类上调用Application，在FX应用程序线程上执行它。尽管在不同的线程上调用，但在start()完成之前，保证不会调用init()。
从您发布的代码中，您必须在其他地方实例化FormBuilder类，并在该实例上调用launchForm(...)。当您从那里调用launch()时，会创建第二个实例并在其上调用start()，如上所述。因此，在调用launchForm(...)的实例上设置的字段当然不会在调用start(...)的实例上设置。
您应该重构代码，以便FormBuilder是应用程序的入口点，或者使FormBuilder不是Application子类，并创建一个实例化和使用的新入口点它。看来你有一些加载数据的后台工作：这应该是一个单独的类，不应该是入口点。所以第一次重构看起来像：
// class that reads data and encapsulates it as a Stocks object
public class StockDataAccessor {
// ...
public Stocks getStocks() {
// ...
}
}
然后FormBuilder看起来像：
public class FormBuilder extends Application {
/*
* (non-Javadoc)
* @see javafx.application.Application#start(javafx.stage.Stage)
* Scene scene
* Group root
* BorderPane borderPane
* TabPane tabPane
* Tab stocksTab
* BorderPane stockTabBorderPane
* GridPane gridPane
*
*/
private Stocks stockData ;
private int size;
@Override
public void start(Stage stage) throws Exception {
StockDataAccessor stockDataAccessor = new StockDataAccessor();
stockData = stockDataAccessor.getStocks();
stage.setTitle("Stock Manager");
Group root = new Group();
Scene scene = new Scene(root, 1024, 800, Color.WHITE);
TabPane tabPane = new TabPane();
BorderPane borderPane = new BorderPane();
BorderPane stockTabBorderPane = new BorderPane();
Tab stocksTab = new Tab("Stocks");
stockTabBorderPane.setTop(this.addHBox());
stockTabBorderPane.setCenter(this.createGridPane());
stocksTab.setContent(stockTabBorderPane);
tabPane.getTabs().add(stocksTab);
borderPane.setCenter(tabPane);
borderPane.prefHeightProperty().bind(scene.heightProperty());
borderPane.prefWidthProperty().bind(scene.widthProperty());
root.getChildren().add(borderPane);
stage.setScene(scene);
stage.show();
}
private HBox addHBox() {
HBox hbox = new HBox();
hbox.setPadding(new Insets(15, 12, 15, 12));
hbox.setSpacing(10);
hbox.setStyle("-fx-background-color: #336699;");
Button buttonCurrent = new Button("Current");
buttonCurrent.setPrefSize(100, 20);
Button buttonProjected = new Button("Projected");
buttonProjected.setPrefSize(100, 20);
hbox.getChildren().addAll(buttonCurrent, buttonProjected);
return hbox;
}
private GridPane createGridPane() {
GridPane gridPane = new GridPane();
gridPane.setLayoutX(39);
gridPane.setLayoutY(131.0);
gridPane.setAlignment(Pos.TOP_CENTER);
gridPane.setVgap(5.0);
gridPane.setHgap(10.0);
gridPane.add(new Label("Active"), 1,1);
gridPane.add(new Label("Stock"), 2, 1);
gridPane.add(new Label("Symbol"), 3, 1);
gridPane.add(new Label("LPP"), 4, 1);
gridPane.add(new Label("LPP"), 5, 1);
gridPane.add(new Label("HPP"), 6, 1);
gridPane.add(new Label("LTP"), 7, 1);
System.out.println(this.size);
for(int v=2;v < this.stockData.getStocks().size()+2; v++) {
gridPane.add(new CheckBox(), 1, v);
gridPane.add(new Label("Amazon"), 2, v);
gridPane.add(new TextField (), 3,v);
gridPane.add(new TextField (), 4,v);
gridPane.add(new TextField (), 5,v);
gridPane.add(new TextField (), 6,v);
gridPane.add(new TextField (), 7,v);
}
return gridPane;
}
// for non-JavaFX aware environments (like your IDE...)
public static void main(String[] args) {
launch(args);
}
}
然后启动FormBuilder作为您的主要课程将满足您的需求。
如果要将应用程序入口点完全排除在FormBuilder类之外，则替代重构（非常相似）如下所示：
public class FormBuilder {
/*
* (non-Javadoc)
* @see javafx.application.Application#start(javafx.stage.Stage)
* Scene scene
* Group root
* BorderPane borderPane
* TabPane tabPane
* Tab stocksTab
* BorderPane stockTabBorderPane
* GridPane gridPane
*
*/
private Stocks stockData ;
private int size;
private Group root ;
public FormBuilder() {
StockDataAccessor stockDataAccessor = new StockDataAccessor();
stockData = stockDataAccessor.getStocks();
root = new Group();
TabPane tabPane = new TabPane();
BorderPane borderPane = new BorderPane();
BorderPane stockTabBorderPane = new BorderPane();
Tab stocksTab = new Tab("Stocks");
stockTabBorderPane.setTop(this.addHBox());
stockTabBorderPane.setCenter(this.createGridPane());
stocksTab.setContent(stockTabBorderPane);
tabPane.getTabs().add(stocksTab);
borderPane.setCenter(tabPane);
borderPane.prefHeightProperty().bind(scene.heightProperty());
borderPane.prefWidthProperty().bind(scene.widthProperty());
root.getChildren().add(borderPane);
}
public Parent getView() {
return root ;
}
private HBox addHBox() {
HBox hbox = new HBox();
hbox.setPadding(new Insets(15, 12, 15, 12));
hbox.setSpacing(10);
hbox.setStyle("-fx-background-color: #336699;");
Button buttonCurrent = new Button("Current");
buttonCurrent.setPrefSize(100, 20);
Button buttonProjected = new Button("Projected");
buttonProjected.setPrefSize(100, 20);
hbox.getChildren().addAll(buttonCurrent, buttonProjected);
return hbox;
}
private GridPane createGridPane() {
GridPane gridPane = new GridPane();
gridPane.setLayoutX(39);
gridPane.setLayoutY(131.0);
gridPane.setAlignment(Pos.TOP_CENTER);
gridPane.setVgap(5.0);
gridPane.setHgap(10.0);
gridPane.add(new Label("Active"), 1,1);
gridPane.add(new Label("Stock"), 2, 1);
gridPane.add(new Label("Symbol"), 3, 1);
gridPane.add(new Label("LPP"), 4, 1);
gridPane.add(new Label("LPP"), 5, 1);
gridPane.add(new Label("HPP"), 6, 1);
gridPane.add(new Label("LTP"), 7, 1);
System.out.println(this.size);
for(int v=2;v < this.stockData.getStocks().size()+2; v++) {
gridPane.add(new CheckBox(), 1, v);
gridPane.add(new Label("Amazon"), 2, v);
gridPane.add(new TextField (), 3,v);
gridPane.add(new TextField (), 4,v);
gridPane.add(new TextField (), 5,v);
gridPane.add(new TextField (), 6,v);
gridPane.add(new TextField (), 7,v);
}
return gridPane;
}
}
然后创建一个入口点：
public class StockApp extends Application {
@Override
public void start(Stage stage) {
FormBuilder formBuilder = new FormBuilder();
Scene scene = new Scene(formBuilder.getView(), 1024, 800, Color.WHITE);
stage.setTitle("Stock Manager");
stage.setScene(scene);
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}