JavaFX 中的多线程挂起 UI

问题描述

我有一个简单的 JavaFX 2 应用程序，有 2 个按钮，分别是启动和停止.单击开始按钮时，我想创建一个后台线程，该线程将进行一些处理并在执行过程中更新 UI(例如进度条).如果单击停止按钮，我希望线程终止.

I have a simple JavaFX 2 app, with 2 buttons, saying Start and Stop. When the start button is clicked, I want to create a background thread which will do some processing and update the UI (e.g a progress bar) as it goes along. If the stop button is clicked, I want the thread to terminate.

我已经尝试使用从文档中收集的 javafx.concurrent.Task 类来做到这一点，它可以很好地解决这个问题.但是每当我单击开始"时，UI 都会冻结/挂起，而不是保持正常.

I've tried to do this using the javafx.concurrent.Task class which I gathered from the documentation would work fine for this. But whenever I click Start, the UI freezes/hangs rather than staying normal.

她的代码来自主 Myprogram extends Application 类，用于显示按钮:

Her's the code from the main Myprogram extends Application class for showing the buttons:

public void start(Stage primaryStage)
{
    final Button btn = new Button();
    btn.setText("Begin");

    //This is the thread, extending javafx.concurrent.Task :
    final MyProcessor handler = new MyProcessor();
    btn.setOnAction(new EventHandler<ActionEvent>()
    {
        public void handle(ActionEvent event)
        {
           handler.run();
        }
    });

    Button stop = new Button();
    stop.setText("Stop");
    stop.setOnAction(new EventHandler<ActionEvent>()
        {
             public void handle(ActionEvent event)
             {
                handler.cancel();
             }
        }

    );
    // Code for adding the UI controls to the stage here.
}

这是MyProcessor类的代码:

import javafx.concurrent.Task;
public class MyProcessor extends Task
{
    @Override
    protected Integer call()
    {
        int i = 0;
        for (String symbol : feed.getSymbols() )
        {
            if ( isCancelled() )
            {
                Logger.log("Stopping!");
                return i;
            }
            i++;
            Logger.log("Doing # " + i);
            //Processing code here which takes 2-3 seconds per iteration to execute
            Logger.log("# " + i + ", DONE! ");
        }
        return i;
    }
}

非常简单，但是每当我单击开始"按钮时 UI 都会挂起，尽管控制台消息继续显示(Logger.log 只是执行 System.out.println)

Pretty simple, but the UI hangs whenever I click the Start button, though the console messages continue to get displayed (Logger.log simply does System.out.println )

我做错了什么?

推荐答案

Task 实现了Runnable，所以当你调用handler.run();code> 实际上是在 UI 线程中运行 call 方法.这将挂起 UI.

Task implements Runnable, so when you call handler.run(); you actually run the call method in the UI Thread. That will hang the UI.

您应该在后台线程中启动任务，通过执行程序或简单地调用new Thread(handler).start();.

You should start the task in a background thread, either via an executor or simply by calling new Thread(handler).start();.

这在 javadoc 中有解释(可能不是很清楚)或在 JavaFX 并发教程中.

This is explained (maybe not very clearly) in the javadoc or in the JavaFX concurrency tutorial.

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