java - 有没有人成功地为列表单元格自动完成组合框？

Question

作为独立元素，this解决方案工作正常。

但在自定义 ListCell 中(从 ComboBoxListCell 来源镜像)，它有时会给出:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.ComboBoxPopupControl.positionAndShowPopup(ComboBoxPopupControl.java:100)
at com.sun.javafx.scene.control.skin.ComboBoxPopupControl.show(ComboBoxPopupControl.java:74)
at com.sun.javafx.scene.control.skin.ComboBoxBaseSkin.handleControlPropertyChanged(ComboBoxBaseSkin.java:115)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.handleControlPropertyChanged(ComboBoxListViewSkin.java:245)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$2.call(BehaviorSkinBase.java:189)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$2.call(BehaviorSkinBase.java:187)
at com.sun.javafx.scene.control.MultiplePropertyChangeListenerHandler$1.changed(MultiplePropertyChangeListenerHandler.java:55)
at javafx.beans.value.WeakChangeListener.changed(WeakChangeListener.java:89)
at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:176)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
at javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:178)
at javafx.beans.property.ReadOnlyBooleanWrapper$ReadOnlyPropertyImpl.access$100(ReadOnlyBooleanWrapper.java:148)
at javafx.beans.property.ReadOnlyBooleanWrapper.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:144)
at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:143)
at javafx.scene.control.ComboBoxBase.setShowing(ComboBoxBase.java:202)
at javafx.scene.control.ComboBoxBase.show(ComboBoxBase.java:407)

似乎 ComboBox 的 show() 方法可以在 JavaFX 代码中产生 NPE。

自定义 ComboBoxListCell 仅在 startEdit() 方面不同:

@Override public void startEdit() {
    if (! isEditable() || ! getListView().isEditable()) {
        return;
    }

    if (comboBox == null) {
        comboBox = createComboBox(this, items, converterProperty());

        //The only special string
        handler = new AutoCompleteComboBoxListener<>(comboBox);

        comboBox.editableProperty().bind(comboBoxEditableProperty()); 
    }

    comboBox.getSelectionModel().select(getItem());

    super.startEdit();

    if (isEditing()) {
        setText(null);
        setGraphic(comboBox);
    }
}

给出NPE的AutoCompleteComboBoxListener的代码:

@Override
public void handle(KeyEvent event) {

    if(event.getCode() == KeyCode.UP) {
        caretPos = -1;
        moveCaret(comboBox.getEditor().getText().length());
        return;
    } else if(event.getCode() == KeyCode.DOWN) {
        if(!comboBox.isShowing()) {
            comboBox.show();
        }
        caretPos = -1;
        moveCaret(comboBox.getEditor().getText().length());
        return;
    } else if(event.getCode() == KeyCode.BACK_SPACE) {
        moveCaretToPos = true;
        caretPos = comboBox.getEditor().getCaretPosition();
    } else if(event.getCode() == KeyCode.DELETE) {
        moveCaretToPos = true;
        caretPos = comboBox.getEditor().getCaretPosition();
    }

    if (event.getCode() == KeyCode.RIGHT || event.getCode() == KeyCode.LEFT
            || event.isControlDown() || event.getCode() == KeyCode.HOME
            || event.getCode() == KeyCode.END || event.getCode() == KeyCode.TAB) {
        return;
    }

    ObservableList list = FXCollections.observableArrayList();
    for (int i=0; i<data.size(); i++) {
        if(data.get(i).toString().toLowerCase().startsWith(
            AutoCompleteComboBoxListener.this.comboBox
            .getEditor().getText().toLowerCase())) {
            list.add(data.get(i));
        }
    }
    String t = comboBox.getEditor().getText();

    comboBox.setItems(list);
    comboBox.getEditor().setText(t);
    if(!moveCaretToPos) {
        caretPos = -1;
    }
    moveCaret(t.length());
    if(!list.isEmpty()) {

        //This gives NPE inside JavaFX API
        comboBox.show();
    }
}

Answer 1

好的，问题是 setItems 将当前选择跳过到 -1，然后 ListCell 将该事实视为需要提交新值(空)(如果当前选择!= -1)。在该提交之后，comboBox 没有任何可显示的内容，因为它处于非编辑状态。

所以这是一个设计问题，而不是错误。如果不特别小心，ComboBoxListCell 代码无法即时更改项目。