Cast String in JavaFX ComboBox

Question

I am trying to use this to select a value from a custom combo box:

import java.util.List;
import javafx.application.Application;
import static javafx.application.Application.launch;
import static javafx.application.Application.launch;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.Callback;
import javafx.util.StringConverter;

public class MainApp extends Application
{

    public static void main(String[] args)
    {
        launch(args);
    }

    @Override
    public void start(Stage stage)
    {

        final ComboBox<ListGroupsObj> listGroups = new ComboBox();

        listGroups.setButtonCell(new GroupListCell());
        listGroups.setCellFactory(new Callback<ListView<ListGroupsObj>, ListCell<ListGroupsObj>>()
        {
            @Override
            public ListCell<ListGroupsObj> call(ListView<ListGroupsObj> p)
            {
                return new GroupListCell();
            }
        });

        listGroups.setEditable(true);
        listGroups.setConverter..............

        // Insert Some data
        ListGroupsObj ob = ListGroupsObj.newInstance().groupId(12).groupName("Test");
        listGroups.getItems().addAll(ob);
        ListGroupsObj osb = ListGroupsObj.newInstance().groupId(13).groupName("Test2");
        listGroups.getItems().addAll(osb);
        listGroups.setValue(ob);

        // Display the selected Group
        listGroups.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<ListGroupsObj>()
        {

            @Override
            public void changed(ObservableValue<? extends ListGroupsObj> arg0, ListGroupsObj arg1, ListGroupsObj arg2)
            {
                if (arg2 != null)
                {
                    System.out.println("Selected Group: " + arg1.getGroupId() + " - " + arg2.getGroupName());
                }
            }
        });

        final StackPane layout = new StackPane();
        layout.getChildren().add(listGroups);
        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 15;");
        stage.setScene(new Scene(layout));
        stage.show();
    }

    class GroupListCell extends ListCell<ListGroupsObj>
    {
        @Override
        protected void updateItem(ListGroupsObj item, boolean empty)
        {
            super.updateItem(item, empty);
            if (item != null)
            {
                setText(item.getGroupId() + " - " + item.getGroupName());
            }
        }
    }

    private List<ListGroupsObj> listGroups;

    public static class ListGroupsObj
    {

        private int groupId;
        private String groupName;

        public static ListGroupsObj newInstance()
        {
            return new ListGroupsObj();
        }

        public ListGroupsObj()
        {
        }

        public ListGroupsObj groupId(int groupId)
        {
            this.groupId = groupId;
            return this;
        }

        public ListGroupsObj groupName(String groupName)
        {
            this.groupName = groupName;
            return this;
        }

        public int getGroupId()
        {
            return groupId;
        }

        public String getGroupName()
        {
            return groupName;
        }

        @Override
        public String toString()
        {
            return groupId + " - " + groupName;
        }
    }

    public class GroupConverter extends StringConverter<ListGroupsObj>
    {

        @Override
        public String toString(ListGroupsObj obj)
        {
            return obj.getGroupId() + " - " + obj.getGroupName();
        }

        @Override
        public ListGroupsObj fromString(String obj)
        {

            //TODO when you type for example "45 - NextGroup" you want to take only tyhe number"
            return ListGroupsObj.newInstance().groupName(obj);
        }

    }
}

I get this error when I go beyond the comboBox:

Exception in thread "JavaFX Application Thread" java.lang.ClassCastException: java.lang.String cannot be cast to com.selectmenuexample.MainApp$ListGroupsObj

I found that this can be done using a converter, but now I know how to use it. Can you help with this implementation?

Answer 1

Here's what's wrong:

• You invoked the combobox group listGroups and the list of listGroups elements . So, in your startup code, you were hiding this variable. Therefore, I deleted this useless variable, since you can manipulate elements directly in ComboBox.
• /, . " -" . GroupConverter cellFactory. , toString() ListGroupsObj, .

, ComboBox. , ComboBox - TextField. , StringConverter. ListGroupsObj .

ListGroupsObj String, toString() .

ListGroupsObj, , ComboBox . , comboBox, fromString(). ListGroupsObj, ListGroupsObj .

, getValue() ComboBox ListGroupsObj, StringConverter.

:

import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.StringConverter;

public class MainApp extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) {

        final ComboBox<ListGroupsObj> comboBox = new ComboBox();

        comboBox.setEditable(true);
        comboBox.setConverter(new StringConverter<ListGroupsObj>() {

            @Override
            public String toString(ListGroupsObj obj) {
                return obj.toString();
            }

            @Override
            public ListGroupsObj fromString(String obj) {
                //Here we try to identify if the given String actually represents one item of our list
                for(ListGroupsObj tempObj:comboBox.getItems()){
                    if(tempObj.toString().equals(obj)){
                        return tempObj;
                    }
                }
                //If not we just create a new one
                return ListGroupsObj.newInstance().groupName(obj);
            }
        });

        // Insert Some data
        ListGroupsObj ob = ListGroupsObj.newInstance().groupId(12).groupName("Test");
        comboBox.getItems().addAll(ob);
        ListGroupsObj osb = ListGroupsObj.newInstance().groupId(13).groupName("Test2");
        comboBox.getItems().addAll(osb);
        comboBox.setValue(ob);

        final StackPane layout = new StackPane();
        layout.getChildren().add(comboBox);
        layout.setStyle("-fx-background-color: cornsilk; -fx-padding: 15;");
        stage.setScene(new Scene(layout));
        stage.show();
    }

    public static class ListGroupsObj {

        private int groupId;
        private String groupName;

        public static ListGroupsObj newInstance() {
            return new ListGroupsObj();
        }

        public ListGroupsObj() {
        }

        public ListGroupsObj groupId(int groupId) {
            this.groupId = groupId;
            return this;
        }

        public ListGroupsObj groupName(String groupName) {
            this.groupName = groupName;
            return this;
        }

        public int getGroupId() {
            return groupId;
        }

        public String getGroupName() {
            return groupName;
        }

        @Override
        public String toString() {
            return groupId + " - " + groupName;
        }
    }
}

PS: JavaFX Tracker, , ( ): https://javafx-jira.kenai.com/browse/RT-29118