JavaFX ComboBox OnChangeListener回滚更改 [英] JavaFX ComboBox OnChangeListener rollback change

问题描述

我要重设 ComboBox 的选择，如下所示：

I'm trying to reset the selection of a ComboBox like follows:

// private ListView<MyEntityType> f_lItems

f_lItems.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<Object>() {
    @Override
    public void changed(ObservableValue<?> ov, Object t, Object t1) {
        if (t1 != null && t1 instanceof MyEntityType) {

            MyEntityType pv = (MyEntityType) t1;
            // do some condition testing
            if (condition) {
                // accept 
            } else 
                // roll back to previous item
                f_lItems.getSelectionModel().select((MyEntityType) t);
            }
        }
    }
});

所以，在尝试将列表重置为旧值后，我得到这个异常：

So, after trying to reset the list to the old value I get this Exception:

Exception in thread "JavaFX Application Thread" java.lang.IndexOutOfBoundsException
    at com.sun.javafx.scene.control.ReadOnlyUnbackedObservableList.subList(Unknown Source)
    at javafx.collections.ListChangeListener$Change.getAddedSubList(Unknown Source)
    at com.sun.javafx.scene.control.behavior.ListViewBehavior.lambda$new$177(Unknown Source)
    at javafx.collections.WeakListChangeListener.onChanged(Unknown Source)
    at com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(Unknown Source)

看起来我没有得到 List s / ObservableList s。

As it seems I don't get the underlying behaviour of Lists / ObservableLists for this case.

有没有人建议我如何使这项工作？

Does anyone have suggestions how I could make this work?

感谢提前
Adam

Thanks in advance Adam

推荐答案

根据你的意见，你想要的是：当code> ComboBox 更改，检查一个条件，然后如果这个条件不满足，将 ComboBox 的值设置回上一个。

Based on your comment what you want is: When the (selected) value of the ComboBox is changed, check for a condition and then if this condition is not met, set back the value of the ComboBox value to the previous one.

为此，您可以使用 valueProperty 与监听器的ComboBox。监听器主体只是检查条件，并且值更新嵌套在 Platform.runLater {...} 块中。

For this you can use for example the valueProperty of the ComboBox with a listener. The listener body is just to check for the condition and the value update is nested in a Platform.runLater{...} block.

在示例中，它是一个

In the example it is a ComboBox which can be set only to "Two".

ComboBox<String> cb = new ComboBox<String>(FXCollections.observableArrayList("One", "Two", "Three", "Four"));

cb.valueProperty().addListener(new ChangeListener<String>() {

    @Override
    public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
        // If the condition is not met and the new value is not null: "rollback"
        if(newValue != null && !newValue.equals("Two")){

            Platform.runLater(new Runnable(){
                @Override
                public void run() {
                    cb.setValue(oldValue);
                }});
        }
    }
});

...或者您可以使用 selectedItemProperty 也具有相同的结构...

... or you can use the selectedItemProperty also with the same structure ...

cb.getSelectionModel().selectedItemProperty().addListener((obs, oldVal, newVal)->{
    if(newVal != null && !newVal.equals("Two")){
        Platform.runLater(() -> cb.setValue(oldVal));
    }
});

注意：此解决方案不是阻止如标题：回滚已执行的选择。

Note: This solution is not to "prevent" the selection, just as in the title: "roll-back" an already performed selection.

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