[英]toFront() throwing UnsupportedOperationException
I want to create a StackPane
where, whatever is added, a node of my choice is always at the front (rather than having to be careful about the order I add things in, or remembering to call toFront()
on that particular node whenever anything is added.) 我想创建一个
StackPane
,无论添加什么,我选择的节点总是在前面(而不是要小心我添加内容的顺序,或者记住在任何时候调用该特定节点上的toFront()
被添加。)
In order to do this, I simply place a listener on the child list of the relevant StackPane
object, so that whenever anything changes, it calls toFront()
on the relevant node, for example: 为了做到这一点,我只是将一个监听器放在相关
StackPane
对象的子列表上,这样无论何时发生任何变化,它都会调用相关节点上的toFront()
,例如:
public class Test extends Application {
@Override
public void start(Stage stage) {
StackPane root = new StackPane();
final Rectangle r1 = new Rectangle(50, 50);
root.getChildren().add(r1);
root.getChildren().addListener(new ListChangeListener<Node>() {
@Override
public void onChanged(ListChangeListener.Change<? extends Node> change) {
try {
while(change.next()) {
if(change.wasAdded()) {
r1.toFront();
}
}
}
catch(Exception ex) {
ex.printStackTrace();
}
}
});
root.getChildren().add(new Rectangle(50, 50));
stage.setScene(new Scene(root));
stage.show();
}
}
In Java 7, this works just fine. 在Java 7中,这很好用。 However, in JFX8 (latest build downloaded just now), it fails with the following:
但是,在JFX8(刚刚下载的最新版本)中,它失败并出现以下情况:
java.lang.UnsupportedOperationException
at java.util.Collections$UnmodifiableList.add(Collections.java:1374)
at javafx.collections.ListChangeBuilder.nextRemove(ListChangeBuilder.java:208)
at javafx.collections.ObservableListBase.nextRemove(ObservableListBase.java:150)
at javafx.collections.ModifiableObservableListBase.remove(ModifiableObservableListBase.java:181)
at com.sun.javafx.collections.VetoableListDecorator.remove(VetoableListDecorator.java:284)
at com.sun.javafx.collections.VetoableListDecorator.remove(VetoableListDecorator.java:209)
at javafx.scene.Parent.impl_toFront(Parent.java:624)
at javafx.scene.Node.toFront(Node.java:1713)
at test.Test$1.onChanged(Test.java:34)
at com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(ListListenerHelper.java:315)
at com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(ListListenerHelper.java:72)
at com.sun.javafx.collections.VetoableListDecorator$1.onChanged(VetoableListDecorator.java:77)
at com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(ListListenerHelper.java:315)
at com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(ListListenerHelper.java:72)
at javafx.collections.ObservableListBase.fireChange(ObservableListBase.java:233)
at javafx.collections.ListChangeBuilder.commit(ListChangeBuilder.java:482)
at javafx.collections.ListChangeBuilder.endChange(ListChangeBuilder.java:541)
at javafx.collections.ObservableListBase.endChange(ObservableListBase.java:205)
at javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:155)
at java.util.AbstractList.add(AbstractList.java:108)
at com.sun.javafx.collections.VetoableListDecorator.add(VetoableListDecorator.java:200)
at test.Test.start(Test.java:41)
at com.sun.javafx.application.LauncherImpl$8.run(LauncherImpl.java:837)
at com.sun.javafx.application.PlatformImpl$7.run(PlatformImpl.java:331)
at com.sun.javafx.application.PlatformImpl$6$1.run(PlatformImpl.java:297)
at com.sun.javafx.application.PlatformImpl$6$1.run(PlatformImpl.java:294)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl$6.run(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
at java.lang.Thread.run(Thread.java:744)
And yes, test.Test$1.onChanged(Test.java:34)
does indeed refer to r1.toFront();
是的,
test.Test$1.onChanged(Test.java:34)
确实引用了r1.toFront();
. 。
Is this to be considered a bug, or am I breaking some rule I'm unaware of by trying to achieve things this way? 这是否被视为一个错误,或者我是否打破了一些我不知道通过这种方式实现事情的规则? I did wonder whether the list was still being changed while the
onChanged()
method was executing, and toFront()
would also change the list contents, hence the exception - but the Javadoc to onChanged()
clearly says: 我确实想知道在执行
onChanged()
方法时列表是否仍然被更改,并且toFront()
也会更改列表内容,因此异常 - 但是onChanged()
的Javadoc清楚地说:
Called after a change has been made to an ObservableList.
在对ObservableList 进行了更改后调用。
(Bolding is mine.) (博尔丁是我的。)
EDIT: At this point I'm more certain that it's a bug, so the related bug report is here . 编辑:此时我更确定这是一个错误,所以相关的错误报告就在这里 。
It seems that you are not allowed to modify a (JavaFX) list inside an event handler that is currently handling another (previous) modification event of the same list. 您似乎不允许修改当前正在处理同一列表的另一个(上一个)修改事件的事件处理程序内的(JavaFX)列表。 Although this seems reasonable it is not self-evident, so there should be a more obvious exception in that case.
虽然这似乎是合理的,但这并不是不证自明的,因此在这种情况下应该有一个更明显的例外。
Unfortunately non-speeking exceptions are very common in JavaFX. 不幸的是,非Speeking异常在JavaFX中非常常见。
Fortunately the solution/workaround is pretty easy: Call your modifying code (here: r1.toFront
) by Platform.runLater()
, it will delay your modification to happen after the originating event: 幸运的是,解决方案/解决方法非常简单:通过
Platform.runLater()
调用修改代码(此处: r1.toFront
Platform.runLater()
,它将延迟您的修改发生在原始事件之后:
root.getChildren().addListener(new ListChangeListener<Node>() {
@Override
public void onChanged(ListChangeListener.Change<? extends Node> change) {
Platform.runLater(new Runnable() {
public void run() { r1.toFront(); }
});
}
});
Sidenote: toFront
does nothing, if the component is already at front. 旁注:如果组件已经在前面,
toFront
什么toFront
做。 This prevents infinite loops. 这可以防止无限循环。 Nevertheless, as this is not explicitely mentioned in the documentation, you might not rely on that.
尽管如此,由于文档中没有明确提及,您可能不会依赖它。
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