We Keep Coding

Java Swing - jComboBox not refreshing

I have an issue with my jComboBox not reflecting the changes in the model ...
In the model I have Box class that keeps an array list of Items. I have a combo box model defined this way :
myCombo.setModel(new javax.swing.DefaultComboBoxModel(box.items().toArray()));
(I use NetBeans 'design' mode). So as far as I understand, after setting the model this way, the combo box should reflect any changes in items list and at the start of the application, it indeed correctly shows the elements of the item list.
I also have a button Add to add a random instance of Item to the items list.
private void buttonAddActionPerformed(java.awt.event.ActionEvent evt) {
box.addRandomItem();
}
The method addRandomItem() simply adds some new instance of Item to the items list. So when I click the Add button, the new random item is correctly added to the items list (I can see it printed at the console) but at the GUI level, the list in combo box is not being updated so I cannot see the newly added item in it.

You should add the new item manually to the model using addElement(E element) or insertElementAt(E element, int index).
Internally, the DefaultComboBoxModel makes a copy of the items you provide as a parameter in the constructor, so there isn't any way to know that the original array has changed.

Showing a counter dynamically for JList items highlighted

I have a program that I created for work. This program takes an uploaded file, reads it, and puts the data into a JList in the GUI. The GUI actually has two lists and the user is able to move items between the left and right list by highlighting them like usual with a JList and then hitting an arrow to move the items. The lists are multiple-interval selection.
One small addition I would like to add is some type of counter that shows the user how many items they have selected before they actually move them between lists. This would need to be dynamic so if the user holds control down and begins clicking the counter will continue to update the number of highlighted items.
As the lists are often quite large and a user might need to move an odd number of transactions between the lists (Think 300 transactions in left list and the user needs to move exactly 50) it would be beneficial to have this counter.
Can anyone think of how this could be done? I'm not sure how to add an action listener to just clicking on the items. Please also let me know if I need to elaborate any more.
Generally my question is can I create an action listener just for when a user clicks a item in a JList that updates a counter for the current selected indices? Also it would need to change when they no longer have selected an indice.

Register a ListSelectionListener with your JList.
The listener could simply query how many rows are selected and update the number in the panel to that. Perhaps use getSelectedValues().size().
http://docs.oracle.com/javase/8/docs/api/javax/swing/JList.html#addListSelectionListener-javax.swing.event.ListSelectionListener-

How to manipulate JComboBox - Java. (MouseListener)

ComboBox cmbCategory, cmbType;
I have two ComboBoxes. The 2nd ComboBox depends on the first ComboBox.
For example.
If I chose "Food" on cmbCategory, the choices on cmbType would be "desert, appetizer..")
How will I do that without clicking a button. I mean when "Food" is chosen on cmbCategory, the choices for food on cmbType would showed up automatically without clicking a button. Because what I have come up to is that my cmbType is hidden and when a button is clicked, then that's the time it will be visible.
I believe this is about MouseListener or MouseClicked but I have no idea on how to do it.

You can add an ActionListener to the cmbCategory. On select call getSelectedItem() to get category.
Define a Map> the map should keep the list f items for each category. Fill the map (or you can define some logic to get list of types by selected category). Then just remove all the existing items in cmbType and add new list of types for the selected category.
See the ombobox related code snippets here

Object to ArrayList to JList and back again (A few questions)

Program Outline:
I plan to make a simple Java program that will load Vehicle objects (Vehicle being the superclass, EnginedVehicle and GoodsVehicle being the subclasses) from an XML file into an ArrayList which will then be displayed on a JList. The user will be able to show/hide the different Vehicle types using check boxes, add a new vehicle type or press the selected item in the JList and edit or delete it. The program will then put the Objects back into the ArrayList where it can be then saved back to the XML file.
Question: So, I am completely fine with the loading of the XML file into the ArrayList and putting that object onto the JList but the thing that is hurting my head is thinking about how I am going to:
What is the best way of getting the object back from the JList ready for it to be modified or deleted and put back into the ArrayList?
How would I show/hide the different types of Vehicles in the JList using the check boxes?
I understand this may seem a lot but, this is my first post and I am new to the community and I have fairly good knowledge of Java and OOP programming but I have just finished writing a fairly big website and going back to Java is a headache.

Since your ArrayList should be equal in size (item count) to your JList, your JList will have the index you're interested based on selection. Regardless if you want to modify or delete the item, store what index it was at and remove the item from the JList (You should be using a DefaultListModel). Use this index value to get the object from your ArrayList. If you're modifying, modify your object as needed, you shouldn't have to remove the object from the ArrayList for modifications, and place it back into your DefaultListModel. If it's a delete, then just remove the object from your ArrayList using the index value you stored.
As far as displaying (show/hide), clear your DefaultListModel (which will clear your JList), iterate through your ArrayList and add the items to the DefaultListModel that match your checkbox selection criteria.
EDIT:
I didn't take into consideration of possibly modifying/deleting items when items are hidden. For this, may want your objects to have a field that stores what index they are at in the ArrayList. This way when you do your filter, I would copy the items from your "Master" ArrayList into a sub list that you can populate your DefaultListModel. Then you apply the same logic to this sublist when selecting an item from you JList, then take your changes from your sublist and apply them to the "Master" ArrayList.
Keep in mind that when you remove an item, you'll have to reassign all items index location from that point on down.
I'm sure there is probably a cleaner way of doing this, but this is what first comes to mind for me.

I don't know if I'm horribly mistaken, but why change to a JList at all? Do you use your JList as a parameter to visualize the information in it? If yes, why dont you use your ArrayList instead? Then the checkboxes only change the visibility ot the Items of the List. So you dont have to care about indices, because they stay the same. And new entries, can be made as well... maybe im wrong but i guess you got kind of a GUI for the user to browse/alter/add new vehicles?

Java Swing Updating JList

I'd like to know if there is any way that I can update a Jlist after the user adds or removes an item to it and after a user sorts it. Is there any way that I can write a standardized method to update the display based on the order of items in an array or vector, and when the user remove or adds an object from the array that the JList is based on?
Thank you.

Updates should be made to the ListModel, not the Array that was used to create the model.
However, if you want to refresh the list with completely new items or change the order of the items then you create a new DefaultListModel and use the setModel(...) method of the JList to update the view.