从JavaFX中从Task API调用的嵌套函数更新标签 [英] Update label from nested function called from Task API in JavaFX

问题描述

我正在使用此类执行一些后台任务

 类下载扩展任务{
 protected Object call（）抛出异常{
 try {
 updateMessage（建立连接）; 
 DownloadHelper downloadHelper = new DownloadHelper（）; 
 downloadHelper.performTask（）; 
返回null; 
} catch（IOException | ParseException ex）{
 logger.error（ExceptionUtils.getStackTrace（ex））; 
抛出前; 
} 
} 
} 
  

此任务依次调用DownloadHelper执行某项任务。

  class DownloadHelper {
 public DownloadHelper（）{
} 
 
 public void performTask（）{
 ---- 
 ---- 
} 
} 
  

有没有办法从DownloadHelper类更新Task API（updateMessage（））的状态消息。？

解决方案

权宜之计是将下载任务的引用作为参数传递给 DownloadHelper 构造函数。为了最小化耦合，您可以将 updateMessage（）的实现引用传递为类型

  import java.util.function.Consumer; 
 import javafx.application.Application; 
 import javafx.beans.InvalidationListener; 
 import javafx.beans.Observable; 
 import javafx.concurrent.Task; 
 import javafx.scene.Scene; 
 import javafx.scene.control.Label; 
 import javafx.scene.layout.StackPane; 
 import javafx.stage.Stage; 
 
 / ** 
 * @see https://stackoverflow.com/q/45708923/230513 
 * / 
公共类MessageTest扩展应用程序{
 
 @Override 
 public void start（Stage primaryStage）{
 primaryStage.setTitle（MessageTest）; 
 StackPane root = new StackPane（）; 
 Label label = new Label（）; 
 root.getChildren（）。add（label）; 
场景场景=新场景（root，320,120）; 
 primaryStage.setScene（scene）; 
 primaryStage.show（）; 
下载任务=新下载（）; 
 task.messageProperty（）。addListener（（Observable o） - > {
 label.setText（task.getMessage（））; 
}）; 
 Thread thread = new Thread（task）; 
 thread.setDaemon（true）; 
 thread.start（）; 
} 
 
私有静态类下载扩展任务< String> {
 
 @Override 
 protected String call（）抛出异常{
 updateMessage（建立连接）; 
 DownloadHelper helper = new DownloadHelper（this :: updateMessage）; 
 helper.performTask（）; 
返回MessageTest; 
} 
 
 @Override 
 protected void updateMessage（String message）{
 super.updateMessage（message）; 
} 
} 
 
私有静态类DownloadHelper {
 
 Consumer< String>更新; 
 
 public DownloadHelper（Consumer< String> updater）{
 this.updater = updater; 
} 
 
 public void performTask（）{
 updater.accept（Helper message）; 
} 
} 
 
 public static void main（String [] args）{
 launch（args）; 
} 
 
} 
  

I am performing some background task using this class

class Download extends Task{
     protected Object call() throws Exception {
        try {
            updateMessage("Establishing Connection");
            DownloadHelper downloadHelper = new DownloadHelper();
            downloadHelper.performTask();
            return null;
        } catch (IOException | ParseException ex) {
            logger.error(ExceptionUtils.getStackTrace(ex));
            throw ex;
        }
    }
}

This Task in turn calls DownloadHelper to perform some task.

class DownloadHelper{
    public DownloadHelper(){
    }

    public void performTask(){
    ----
    ----
    }
}

Is there a way to update the status message of the Task API (updateMessage()) from the DownloadHelper class.?

解决方案

The expedient approach is to pass a reference to the Download task as a parameter to the DownloadHelper constructor. To minimize coupling, you can instead pass a reference to your implementation of updateMessage() as a parameter of type Consumer, "an operation that accepts a single input argument and returns no result."

DownloadHelper helper = new DownloadHelper(this::updateMessage);

Your helper's implementation of performTask() can then ask the updater to accept() messages as needed.

Consumer<String> updater;

public DownloadHelper(Consumer<String> updater) {
    this.updater = updater;
}

public void performTask() {
    updater.accept("Helper message");
}

A related example is seen here.

import java.util.function.Consumer;
import javafx.application.Application;
import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

/**
 * @see https://stackoverflow.com/q/45708923/230513
 */
public class MessageTest extends Application {

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("MessageTest");
        StackPane root = new StackPane();
        Label label = new Label();
        root.getChildren().add(label);
        Scene scene = new Scene(root, 320, 120);
        primaryStage.setScene(scene);
        primaryStage.show();
        Download task = new Download();
        task.messageProperty().addListener((Observable o) -> {
            label.setText(task.getMessage());
        });
        Thread thread = new Thread(task);
        thread.setDaemon(true);
        thread.start();
    }

    private static class Download extends Task<String> {

        @Override
        protected String call() throws Exception {
            updateMessage("Establishing connection");
            DownloadHelper helper = new DownloadHelper(this::updateMessage);
            helper.performTask();
            return "MessageTest";
        }

        @Override
        protected void updateMessage(String message) {
            super.updateMessage(message);
        }
    }

    private static class DownloadHelper {

        Consumer<String> updater;

        public DownloadHelper(Consumer<String> updater) {
            this.updater = updater;
        }

        public void performTask() {
            updater.accept("Helper message");
        }
    }

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

}

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