单击按钮时，JavaFX 在新线程上运行任务

Question

当在 JavaFX 中单击按钮时，我正在尝试检索 XLS 文件并将其加载到 TableView 中。我正在使用 Task 类和 ExecutorService 来启动新线程。我需要阅读器类可重用，但 FileChooser 没有出现。

这是我编写一些并发代码的尝试。我想知道我做错了什么以及如何改进我的代码，因为一切都是事件驱动的？

控制器类代码

public void retrieveCustomersFromXLS() {
        try {
            loader.setOnSucceeded(workerStateEvent -> {
                File file = null;
                try {
                    file = loader.get();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                if (file != null && file.exists()) {
                    reader.setWorkingFile(file);
                    executor.submit(reader);
                }
            });
            reader.setOnSucceeded(workerStateEvent1 -> {
                Object[][] XLSFile = new Object[0][];
                try {
                    XLSFile = reader.get();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                if (XLSFile != null) {
                    tableInterface.setEntries(XLSFile);
                    tableInterface.setEntryType("customers");
                    executor.submit(tableInterface);
                }
            });
            tableInterface.setOnSucceeded(workerStateEvent2 -> {
                customerList = FXCollections.observableArrayList(tableInterface.getCustomerEntries());
                column_customerReference.setCellValueFactory(new PropertyValueFactory<customers, Integer>("customerReference"));
                column_customerName.setCellValueFactory(new PropertyValueFactory<customers, String>("customerName"));
                column_customerAddress.setCellValueFactory(new PropertyValueFactory<customers, String>("customerAddress"));
                column_customerPost.setCellValueFactory(new PropertyValueFactory<customers, Integer>("customerPost"));
                column_customerRegion.setCellValueFactory(new PropertyValueFactory<customers, String>("customerRegion"));
                column_customerID_DDV.setCellValueFactory(new PropertyValueFactory<customers, String>("customerDDV"));
                table_customerImports.setItems(customerList);
            });
            executor.submit(loader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

阅读器类文件

@Override
    protected File call() throws Exception {
        FileChooser fileChooser = new FileChooser();
        fileChooser.setTitle("Choose Excel file");
        fileChooser.getExtensionFilters().addAll(new FileChooser.ExtensionFilter("Excel", "*.xlsx", "*.xls", "*.csv"));
        File selectedFile = fileChooser.showOpenDialog(new Stage());
        if (selectedFile != null) {
            path = selectedFile.getAbsolutePath();
            file = new File(path);
        }
        return file;
    }

Answer 1

您必须在 JavaFX 应用程序线程上调用 FileChooser#showXXXDialog 方法。如果您观察到您的任务失败，您会看到IllegalStateException 带有一条消息，说明您尝试在错误的线程上执行操作。此外，您不需要后台任务来提示用户首先输入文件。

这是一个提示用户输入文本文件的示例，读取Task 中的文本文件，并将结果放入ListView。

App.java

package com.example;

import java.io.IOException;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class App extends Application {

  @Override
  public void start(Stage primaryStage) throws IOException {
    Scene scene = new Scene(FXMLLoader.load(getClass().getResource("/App.fxml")));
    primaryStage.setScene(scene);
    primaryStage.setTitle("FileChooser Example");
    primaryStage.show();
  }

}

App.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ListView?>
<?import javafx.scene.control.Separator?>
<?import javafx.scene.layout.VBox?>

<VBox xmlns="http://javafx.com/javafx/13" xmlns:fx="http://javafx.com/fxml/1" spacing="5" prefWidth="600"
      prefHeight="400" alignment="CENTER" fx:controller="com.example.Controller">
    <padding>
        <Insets topRightBottomLeft="5"/>
    </padding>
    <Button text="Open File..." onAction="#handleOpenFile"/>
    <Separator/>
    <ListView fx:id="listView" VBox.vgrow="ALWAYS"/>
</VBox>

Controller.java

package com.example;

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import javafx.collections.FXCollections;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.ListView;
import javafx.stage.FileChooser;
import javafx.stage.FileChooser.ExtensionFilter;

public class Controller {

  private final Executor executor = Executors.newSingleThreadExecutor(r -> {
    Thread t = new Thread(r, "controller-thread");
    t.setDaemon(true);
    return t;
  });

  @FXML private ListView<String> listView;

  @FXML
  private void handleOpenFile(ActionEvent event) {
    event.consume();

    FileChooser chooser = new FileChooser();
    chooser.getExtensionFilters()
        .add(new ExtensionFilter("Text Files", "*.txt", "*.json", "*.xml", "*.html", "*.java"));

    File file = chooser.showOpenDialog(listView.getScene().getWindow());
    if (file != null) {
      ReadFileTask task = new ReadFileTask(file.toPath());
      task.setOnSucceeded(wse -> listView.setItems(FXCollections.observableList(task.getValue())));
      task.setOnFailed(wse -> task.getException().printStackTrace());
      executor.execute(task);
    }
  }

  private static class ReadFileTask extends Task<List<String>> {

    private final Path file;

    private ReadFileTask(Path file) {
      this.file = Objects.requireNonNull(file);
    }

    @Override
    protected List<String> call() throws Exception {
      return Files.readAllLines(file);
    }

  }

}