如何将多个按钮添加到tilepane？

Question

我在边框的中心有一个标题栏。对于链接哈希图中的每个条目，我想在标题栏中添加一个按钮。这个标题栏已经存在于fxml文件中，并且具有fx： id field dContainer。

如果一次添加一个键值对，按钮将一个接一个出现。但是，当我试图通过从文本文件导入链接的hashmap一次添加它们时，按钮不会出现。它将加载一个条目，然后抛出nullpointerexception。

导入文本文件和将条目添加到地图的方法似乎都运行良好。我认为问题出在field dContainer上。我不明白为什么它只会一个接一个地添加按钮，而不是一次全部添加。有人能解释一下我的代码出了什么问题吗？

更新：我通过将field dContainer分配给Controller类顶部的一个新TilePane来修复nullpointerxcept：

@FXML
private TilePane fieldContainer = new TilePane();

错误消失了，它会打印整个地图，但仍然不会显示按钮。任何人

FXML：

<BorderPane fx:id="container" stylesheets="/css/main.css" xmlns="http://javafx.com/javafx/8.0.121" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
<top>
// Some code
</top>

<center>
    <TilePane fx:id="fieldContainer" prefColumns="2" prefTileHeight="100.0" prefTileWidth="135.0">
    </TilePane>
</center>

<bottom>
// Some code
</bottom>

类寄存器（使用导入方法）：

public class Register {
    private Controller ctrl;

    public Register(Controller ctrl) {
        this.ctrl = ctrl;
    }

    public void exportTo(File file) {
        LinkedHashMap<String, BigDecimal> pMap = ctrl.getProductMap();
        try (
                FileOutputStream fos = new FileOutputStream(file);
                PrintWriter writer = new PrintWriter(fos);
        ) {
            for(Map.Entry<String, BigDecimal> entry : pMap.entrySet()) {
                writer.printf("%s|%s%n",
                        entry.getKey(),
                        entry.getValue());
            }
        } catch(IOException ioe) {
            System.out.printf("Problem saving %s %n", file);
            ioe.printStackTrace();
        }
    }

    public void importFrom(File file) {
        try (
                FileInputStream fis = new FileInputStream(file);
                BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
        ) {
            String line;
            while((line = reader.readLine()) != null) {
                String[] args = line.split("\\|");
                ctrl.addProduct(args[0], new BigDecimal(args[1]));
            }
        } catch(IOException ioe) {
            System.out.printf("Problems loading %s %n", file);
            ioe.printStackTrace();
        }
    }
}

类控制器（按钮创建）：

public class Controller {
    private static LinkedHashMap<String, BigDecimal> mProductMap = new LinkedHashMap<>();

    @FXML
    private TilePane fieldContainer;

    public LinkedHashMap<String, BigDecimal> getProductMap() {
        return mProductMap;
    }

    // Puts key and value to the Map and creates a button for each entry
    public void addProduct(String product, BigDecimal price) {
        mProductMap.put(product, price);
        System.out.println(mProductMap);

        fieldContainer.getChildren().clear();

        for (Map.Entry<String, BigDecimal> entry : mProductMap.entrySet()) {
            StackPane newField = new StackPane();
            Button main = new Button();
            Button multiply = new Button("X");
            Button subtract = new Button("-");
            main.setText(entry.getKey() + "\n" + entry.getValue());
            multiply.getStyleClass().add("inner-button");
            subtract.getStyleClass().add("inner-button");
            StackPane.setAlignment(multiply, Pos.BOTTOM_LEFT);
            StackPane.setAlignment(subtract, Pos.BOTTOM_CENTER);
            StackPane.setMargin(multiply, new Insets(0, 0, 8, 8));
            StackPane.setMargin(subtract, new Insets(0, 0, 8, 16));
            // Three buttons on top of each other
            newField.getChildren().add(main);
            newField.getChildren().add(multiply);
            newField.getChildren().add(subtract);

            fieldContainer.setAlignment(Pos.TOP_LEFT);
            // this should add a button for each entry, 
            // but it only works when you add them one by one
            fieldContainer.getChildren().add(newField);
        }
    }
}

主要内容：

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setScene(new Scene(root, 300, 500));
        primaryStage.show();

        Controller controller = new Controller();
        Register register = new Register(controller);
        register.importFrom(new File("prices.txt"));
    }

    @Override
    public void stop(){
        Controller controller = new Controller();
        Register register = new Register(controller);
        register.exportTo(new File("prices.txt"));
    }

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

错误：

Exception in Application start method
{Coffee=1.50}  // the first entry from the Map prints
java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:473)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:372)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:945)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:973)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:198)
    at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.lang.NullPointerException
    at sample.Controller.addProduct(Controller.java:54) // fieldContainer.getChildren().clear();
    at sample.Register.importFrom(Register.java:40) // ctrl.addProduct(args[0], new BigDecimal(args[1]));
    at sample.Main.start(Main.java:23) // register.importFrom(new File("prices.txt"));
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:919)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$11(PlatformImpl.java:449)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(PlatformImpl.java:418)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:417)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
    ... 1 more
Exception running application sample.Main

Answer 1

我自己修的。现在，所有按钮都会在运行Main时立即加载。下面是我所做的：

我没有在main中调用寄存器的importFrom方法，而是从控制器类中调用它，就像在initialize方法中那样：

private Register mRegister;

public Controller() {
    this.mRegister = new Register(this);
}

@FXML
private void initialize() {
    mRegister.importFrom(new File("prices.txt"));
}