JavaFX TextArea appendText 在初始化中有效，但在其他地方无效

Question

问题很简单，但它让我抓狂。

在我的程序中我有一个TextArea，定义为：

<TextArea fx:id="output" editable="false" prefHeight="300.0" prefWidth="200.0" text="Output" GridPane.columnSpan="2" GridPane.rowIndex="4" />

@FXML private TextArea output;

...

public void initialize(URL url, ResourceBundle rb) {
    output.setText("Test"); //Test appears correctly in output
    ...
}

@FXML
public void download() {
    String outputTemplate = templateField.getText();
    String url = urlField.getText();
    System.out.println("Downloading from " + url);
    try {
        Process down = Runtime.getRuntime().exec("youtube-dl -o \"" + outputTemplate + "\" " + url);
        BufferedReader reader = new BufferedReader(new InputStreamReader(down.getInputStream()));
        String line;
        while ((line = reader.readLine()) != null) {
            System.out.println(line); //Prints as expected
            output.appendText(line + "\n"); //Has no effect
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

任何关于如何让文本出现的想法都很好，我以前在不同的程序上这样做过，只是出于某种原因，这次它很坏

编辑：经过进一步修改，它实际上会打印出结果，但只有在 Process 结束并退出循环之后。

Answer 1

问题是您是在主线程中执行此操作。所以阶段不能更新，直到循环结束。在新线程中尝试：

@FXML
public void download() {
    Task<Void> task = new Task<Void>() {
        @Override
        protected Void call() {
            String outputTemplate = templateField.getText();
            String url = urlField.getText();
            System.out.println("Downloading from " + url);
            try {
                Process down = Runtime.getRuntime().exec("youtube-dl -o \"" + outputTemplate + "\" " + url);
                BufferedReader reader = new BufferedReader(new InputStreamReader(down.getInputStream()));
                String line;
                while ((line = reader.readLine()) != null) {
                    System.out.println(line); // Prints as expected
                    output.appendText(line + "\n"); // Has no effect
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }
    };
    new Thread(task).start();
}

Answer 2

UI 中显示的文本随布局脉冲而变化。布局脉冲在 JavaFX 应用程序线程上完成。事件处理程序，例如同一线程上的 download 方法运行有效地阻止它在完成之前进行任何布局或处理以及其他事件。这就是为什么你不应该用 long运行ning 任务阻塞这个线程，而是在不同的线程上执行它们。

由于对 UI 的更新应该从应用程序线程完成，因此请使用 Platform.runLater 附加文本：

@FXML
public void download() {
    String outputTemplate = templateField.getText();
    String url = urlField.getText();
    Runnable r  = () -> {
        System.out.println("Downloading from " + url);
        try {
            Process down = Runtime.getRuntime().exec("youtube-dl -o \"" + outputTemplate + "\" " + url);
            BufferedReader reader = new BufferedReader(new InputStreamReader(down.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line); //Prints as expected
                final String printText = line + "\n";

                // append the line on the application thread
                Platform.runLater(() -> output.appendText(printText));
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    };
    // run task on different thread
    Thread t = new Thread(r);
    t.start();
}

JavaFX TextArea appendText 在初始化中有效，但在其他地方无效

JavaFX TextArea appendText works in initialize but not elsewhere

javafx

fxml