JavaFX时钟小部件随机抛出异常
JavaFX时钟小部件随机抛出异常
提问于 2016-02-26 11:34:19
我编写了一个扩展Text类JavaFX的小时钟Widget。为了更新时间，我使用了一个基本上将文本设置为当前系统时间的Task。当我在Eclipse中运行这个应用程序时，它有时会在我称为NullpointerException的行中抛出一个stage.show()。
这就是我的小部件源代码的样子：
package clock;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import javafx.concurrent.Task;
import javafx.scene.text.Font;
import javafx.scene.text.Text;
public class CurrentClockText extends Text {
private final DateTimeFormatter formatter;
public static final int HOUR = 1;
public static final int HOUR_MINUTE = 2;
public static final int HOUR_MINUTE_SECOND = 3;
public static final int HOUR_MINUTE_SECOND_MILLISECOND = 4;
private final long updateInterval;
private final Task<Void> updater = new Task<Void>() {
@Override
protected Void call() throws Exception {
while (true) {
LocalDateTime now = LocalDateTime.now();
String nowTextual = formatter.format(now);
setText(nowTextual);
try {
Thread.sleep(updateInterval);
} catch (InterruptedException ignore) {
}
}
}
};
public CurrentClockText() {
this(HOUR_MINUTE);
}
public CurrentClockText(final int detailLevel) {
String timeFormat = "";
switch (detailLevel) {
case HOUR:
timeFormat = "HH";
updateInterval = 60000;
break;
case HOUR_MINUTE:
timeFormat = "HH:mm";
updateInterval = 15000;
break;
case HOUR_MINUTE_SECOND:
timeFormat = "HH:mm:ss";
updateInterval = 500;
break;
case HOUR_MINUTE_SECOND_MILLISECOND:
updateInterval = 1;
timeFormat = "HH:mm:ss.S";
break;
default:
throw new IllegalArgumentException(
"Unknown detail level for Clock: " + detailLevel);
}
setFont(new Font("Verdana", 28));
formatter = DateTimeFormatter.ofPattern(timeFormat);
Thread updaterThread = new Thread(updater, "CurrentClockText.updaterThread");
updaterThread.setDaemon(true);
updaterThread.start();
}
}这是主要的课程：
package clock;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
public class Boot extends Application {
@Override
public void start(Stage stage) throws Exception {
BorderPane pane = new BorderPane();
CurrentClockText clock = new CurrentClockText(4);
pane.setCenter(clock);
Scene scene = new Scene(pane);
stage.setScene(scene);
stage.show();
}
public static void main(String[] args) {
Boot.launch(args);
}
}这就是堆栈轨迹：
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(Unknown Source)
at com.sun.javafx.application.LauncherImpl.launchApplication(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$152(Unknown Source)
at com.sun.javafx.application.LauncherImpl$$Lambda$50/14845382.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at com.sun.javafx.text.PrismTextLayout.addTextRun(Unknown Source)
at com.sun.javafx.text.GlyphLayout.addTextRun(Unknown Source)
at com.sun.javafx.text.GlyphLayout.breakRuns(Unknown Source)
at com.sun.javafx.text.PrismTextLayout.buildRuns(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.impl_computeLayoutBounds(Unknown Source)
at javafx.scene.Node$12.computeBounds(Unknown Source)
at javafx.scene.Node$LazyBoundsProperty.get(Unknown Source)
at javafx.scene.Node$LazyBoundsProperty.get(Unknown Source)
at javafx.scene.Node.getLayoutBounds(Unknown Source)
at javafx.scene.Node.prefWidth(Unknown Source)
at javafx.scene.Node.minWidth(Unknown Source)
at javafx.scene.layout.Region.computeChildPrefAreaWidth(Unknown Source)
at javafx.scene.layout.BorderPane.getAreaWidth(Unknown Source)
at javafx.scene.layout.BorderPane.computePrefWidth(Unknown Source)
at javafx.scene.Parent.prefWidth(Unknown Source)
at javafx.scene.layout.Region.prefWidth(Unknown Source)
at javafx.scene.Scene.getPreferredWidth(Unknown Source)
at javafx.scene.Scene.resizeRootToPreferredSize(Unknown Source)
at javafx.scene.Scene.preferredSize(Unknown Source)
at javafx.scene.Scene.impl_preferredSize(Unknown Source)
at javafx.stage.Window$9.invalidated(Unknown Source)
at javafx.beans.property.BooleanPropertyBase.markInvalid(Unknown Source)
at javafx.beans.property.BooleanPropertyBase.set(Unknown Source)
at javafx.stage.Window.setShowing(Unknown Source)
at javafx.stage.Window.show(Unknown Source)
at javafx.stage.Stage.show(Unknown Source)
at clock.Boot.start(Boot.java:19)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$159(Unknown Source)
at com.sun.javafx.application.LauncherImpl$$Lambda$53/19600960.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$45/18503843.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$48/27167109.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/2180324.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$145(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda$36/3326003.run(Unknown Source)
... 1 more
Exception running application clock.Boot正如我说过的，这种异常只发生在某些运行中，而不是总是发生。这种情况主要发生在我更改detailLevel = 4的格式模式时，但在再次更改它之后，它仍然需要另一次运行。我猜想这实际上可能与Eclipse有关，但我也无法调试代码，因为异常会抛出到stage.show调用中，我完全不明白这一点。造成这种随机异常的原因是什么，我如何解决它？
回答 1
Stack Overflow用户
回答已采纳
发布于 2016-02-26 12:27:26
在JavaFX中，和大多数其他GUI工具包一样，有一个特定的线程处理所有与UI相关的操作。应用程序不得在此线程之外更新UI。如果需要从另一个线程更新UI，通常可以使用API来确保代码在UI线程的上下文中执行。如果是JavaFX，有关更多信息，请参见JavaFX教程中的并发性。
在您的情况下，最简单的解决方案是确保setText()调用在JavaFX应用程序线程上执行，而不是在与Task关联的线程上执行。
...
Platform.runLater(() -> setText(nowTextual));
...JavaFX中还有其他API可用于动画，这些API可用于在特定时间间隔调用处理程序方法--这将从循环中删除Thread.sleep()调用。有关详细信息，请参阅时间线。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/35650627
复制相关文章
相似问题
腾讯云开发者
