JComboBox AddItem

[ideru]

For the purpose of discussion and learning for a newbi like me

I have a JComboBox in my window , and will fill it after retrieving some values from the Database. I use "addItem" to insert each data (String ) to my ComboBox and it works fine.

The problem was when there is no data retrieved. In this case I just use the same "addItem" function to insert an item to the combobox.

String noStr  = new String("DB Empty");
this.comboDataList.addItem(noStr);

The code above, will return an Null Exception;

I tried using "insertItemAt()", and it will insert the item to the comboBox but when I tried to select the Item, it will give the same NULL exception.

I found this solution using the "setModel"

 
String [] testStr = new String[1];
 
for(int i=0; i < 1; i++ )
{
	testStr[i] = new String("DB Empty");
}
 
this.comboDataList.setModel(new DefaultComboBoxModel(testStr));

This was the solution that works among all the tutorials I found. I probably don't need to loop it since I only have one data to add anyway.

Is there some kind of problem with addItem? Any Idea.

Im using NetBeans IDE 5.5.1 and JDK 1.6

[Norm]

"The code above, will return an Null Exception"
Is comboDataList null?
You need to create an object before you can use it.
Can you show the full text of the error message?

[ideru]

@Norm, the combobox object was created during the initialization and is used during insertion of items to it.


Right , Ive noticed that the behavior of addItems is inconsistent.

this is how the original code looks like

 
	ArrayList<ParameterBean> beanList= new ArrayList<ParamaterBean>();
	beanList= getListNames();  //  this will return all names retrieve from the DB
 
   if( beanList.size() > 0 )
   {
		   //get each item from the list and insert to the comboBox using addItems
	}
   else
   {
	   // set a temporary value to combobox
	  String strTemp = new String("DB Is Empty " );
	  this.comboDataList.addItem(strTemp)
 
   }

the else part will cause an exception. In "ParameterBean" , I have a getName() function that returns a String. So for each Parameter, I insert the String value using addItem to the ComboBox and no Problems. But I explicitly insert a String like the one in ELSE part, it will cause and exception.

[Norm]

Can you show the full text of the error message?

[keang]

@Norm, the combobox object was created during the initialization and is used during insertion of items to it.

When you create the JComboBox are you suppling a ComboBoxModel and if so is it mutable?

As well as the full error message requested twice now by Norm, please also show the insertion code that works.