Question

我想过滤数据库中的字符串数据，并从comboBox中选择行的ID，但是出现以下错误。

Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: java.lang.String cannot be cast to com.kwesiaryee.combo.Country
at com.kwesiaryee.combo.ComboBoxSample$1.changed(ComboBoxSample.java:45)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:361)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
at javafx.beans.property.ReadOnlyObjectPropertyBase.fireValueChangedEvent(ReadOnlyObjectPropertyBase.java:74)
at javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:102)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:146)
at javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:102)
at javafx.scene.control.ComboBox.lambda$new$152(ComboBox.java:249)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:361)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(ObjectPropertyBase.java:105)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:146)
at javafx.scene.control.ComboBoxBase.setValue(ComboBoxBase.java:150)
at com.sun.javafx.scene.control.skin.ComboBoxPopupControl.setTextFromTextFieldIntoComboBoxValue(ComboBoxPopupControl.java:405)
at com.sun.javafx.scene.control.skin.ComboBoxPopupControl.lambda$new$291(ComboBoxPopupControl.java:82)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:361)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
at javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(ReadOnlyBooleanPropertyBase.java:72)
at javafx.scene.Node$FocusedProperty.notifyListeners(Node.java:7718)
at javafx.scene.Scene$13.invalidated(Scene.java:2077)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:111)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:146)
at javafx.scene.Scene$KeyHandler.setFocusOwner(Scene.java:3924)
at javafx.scene.Scene$KeyHandler.requestFocus(Scene.java:3971)
at javafx.scene.Scene$KeyHandler.access$1900(Scene.java:3910)
at javafx.scene.Scene.requestFocus(Scene.java:2044)
at javafx.scene.Node.requestFocus(Node.java:7879)
at com.sun.javafx.scene.control.behavior.TextFieldBehavior.mousePressed(TextFieldBehavior.java:248)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:95)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:394)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:432)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)

我尝试了几种补救措施，但似乎没有任何效果。提供的数据来自mysql数据库。我得到的建议是获得一个字符串生成器，但我再次陷入困境。当我这样访问自动完成时，会发生错误； new AutoCompleteComboBoxListener<>(combo);

然后尝试像这样获取id值；

    combo.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<Country>() {
        @Override
        public void changed(ObservableValue<? extends Country> observable, Country oldValue, Country newValue) {

            System.out.println(newValue.getName());
////                System.out.println(newValue.getContinent());
//                System.out.println("=================");

        }
    });

迫切需要帮助。请帮忙。

谢谢。

Answer 1

此异常清楚地表明您想要将String强制转换为Object。默认值Property为String，因此默认情况下无法强制转换。有两个选项可以处理它。首先，您可以为这个特殊的Box设置一个Converter，如下例：

combo.setConverter(new StringConverter <Country>() {

        @Override
        public String toString(Country object) {
            if(object == null) {
                return "";
            }
            return object.toString();
        }

        @Override
        public Country fromString(String string) {
            return combo
                    .getItems()
                    .stream()
                    .filter(country -> country.toString().equals(string))
                    .findFirst()
                    .orElseGet(()-> combo.getSelectionModel().getSelectedItem());
        }

    });

第二个选项是选择该对象的位置：

public static<T> T getComboBoxValue(ComboBox<T> comboBox){
    if (comboBox.getSelectionModel().getSelectedIndex() < 0) {
        return null;
    } else {
        return comboBox.getItems().get(comboBox.getSelectionModel().getSelectedIndex());
    }
}

我在这里也有一个很好的自动完成组合框实现：

public class AutoCompleteComboBox {

public interface AutoCompleteComparator<T> {
    boolean matches(String typedText, T objectToCompare);
}

public static<T> void autoCompleteComboBoxPlus(ComboBox<T> comboBox, AutoCompleteComparator<T> comparatorMethod) {
    ObservableList<T> data = comboBox.getItems();

    comboBox.setEditable(true);
    comboBox.getEditor().focusedProperty().addListener(observable -> {
        if (comboBox.getSelectionModel().getSelectedIndex() < 0) {
            comboBox.getEditor().setText(null);
        }
    });
    comboBox.addEventHandler(KeyEvent.KEY_PRESSED, t -> comboBox.hide());
    comboBox.addEventHandler(KeyEvent.KEY_RELEASED, new EventHandler<KeyEvent>() {

        private boolean moveCaretToPos = false;
        private int caretPos;

        @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();
            } else if (event.getCode() == KeyCode.ENTER) {
                return;
            }

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

            ObservableList<T> list = FXCollections.observableArrayList();
            for (T aData : data) {
                if (aData != null && comboBox.getEditor().getText() != null && comparatorMethod.matches(comboBox.getEditor().getText(), aData)) {
                    list.add(aData);
                }
            }
            String t = comboBox.getEditor().getText();

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

        private void moveCaret(int textLength) {
            if (caretPos == -1) {
                comboBox.getEditor().positionCaret(textLength);
            } else {
                comboBox.getEditor().positionCaret(caretPos);
            }
            moveCaretToPos = false;
        }
    });
}

public static<T> T getComboBoxValue(ComboBox<T> comboBox){
    if (comboBox.getSelectionModel().getSelectedIndex() < 0) {
        return null;
    } else {
        return comboBox.getItems().get(comboBox.getSelectionModel().getSelectedIndex());
    }
}

}

您可以像这样使组合框自动完成：

AutoCompleteComboBox.autoCompleteComboBoxPlus(combo, (typedText, itemToCompare) -> itemToCompare.toString().toLowerCase().contains(typedText.toLowerCase()) || itemToCompare.toString().equals(typedText));

像这样获得您的价值：

Country searchedCountry = AutoCompleteComboBox.getComboBoxValue(combo);

我希望这对您有很大帮助，但这只是来自我自己的项目。干杯：）

Javafx ComboBox自动完成返回错误

1 个答案: