Question

我用javafx ui编写了一个java程序来显示事务的实时计数器，许多线程需要将更新的值写入单个标签，我这样做：

1 - ＆＃34; SOME_NUMBER＆＃34;是主类中的整数变量（不是fx控制器类本身，让我们考虑它的名称＆＃34; MainClass＆＃34;）定义这种方式：

public static Integer SOME_NUMBER;

2-Many Threads更新＆＃34; SOME_NUMBER＆＃34;的值这样：

synchronized(SOME_NUMBER){
    MainClass.SOME_NUMBER--;
}
synchronized(SOME_NUMBER){
    MainClass.SOME_NUMBER++;
}

3 - 最后结果以这种方式显示来自其他类：

label.setText(String.valueOf(SOME_NUMBER));

数字应该每秒更新一次，所以我不想在特定的时间间隔内使用Task更新我的视图，而且也不想使用Platform.runLater因为当你每秒大约有5-20笔交易时，它会显着延迟... 所以我想要一种安全的方式来实现这样的事情以满足我的需求，因为我当前的实现导致了这样的错误，我删除了ui更新所有这些都消失了：

> java.lang.NullPointerException
    at com.sun.javafx.text.PrismTextLayout.createLine(Unknown Source)
    at com.sun.javafx.text.PrismTextLayout.layout(Unknown Source)
    at com.sun.javafx.text.PrismTextLayout.ensureLayout(Unknown Source)
    at com.sun.javafx.text.PrismTextLayout.getBounds(Unknown Source)
    at javafx.scene.text.Text.getLogicalBounds(Unknown Source)
    at javafx.scene.text.Text.getYRendering(Unknown Source)

有没有机会使用可观察的值或类似的东西？

Answer 1

如果您不想使用Task，只需稍加修改即可进行复制和粘贴，以使用与任务使用相同的技术（以下代码只是来自任务源的复制和粘贴）。

如果您知道自己的值是整数，那么您可能希望使用AtomicInteger而不是AtomicReference。

代码将为您提供一个message属性，您可以尝试从任何线程（通过updateMessage API）更新其值，但只有在JavaFX应用程序线程准备好处理它时才会发生更新。您还可以观察属性以进行更改，并将JavaFX UI组件安全地绑定到属性，因为知道该属性本身甚至已在JavaFX应用程序线程上更新。

/**
 * Used to send message updates in a thread-safe manner from the subclass
 * to the FX application thread. AtomicReference is used so as to coalesce
 * updates such that we don't flood the event queue.
 */
private AtomicReference<String> messageUpdate = new AtomicReference<>();

private final StringProperty message = new SimpleStringProperty(this, "message", "");
@Override public final String getMessage() { checkThread(); return message.get(); }
@Override public final ReadOnlyStringProperty messageProperty() { checkThread(); return message; }

/**
 * Updates the <code>message</code> property. Calls to updateMessage
 * are coalesced and run later on the FX application thread, so calls
 * to updateMessage, even from the FX Application thread, may not
 * necessarily result in immediate updates to this property, and
 * intermediate message values may be coalesced to save on event
 * notifications.
 * <p>
 *     <em>This method is safe to be called from any thread.</em>
 * </p>
 *
 * @param message the new message
 */
protected void updateMessage(String message) {
    if (isFxApplicationThread()) {
        this.message.set(message);
    } else {
        // As with the workDone, it might be that the background thread
        // will update this message quite frequently, and we need
        // to throttle the updates so as not to completely clobber
        // the event dispatching system.
        if (messageUpdate.getAndSet(message) == null) {
            runLater(new Runnable() {
                @Override public void run() {
                    final String message = messageUpdate.getAndSet(null);
                    Task.this.message.set(message);
                }
            });
        }
    }
}

private void checkThread() {
    if (started && !isFxApplicationThread()) {
        throw new IllegalStateException("Task must only be used from the FX Application Thread");
    }
}

javafx：标签值更新在大量设置值时会导致错误

1 个答案: