Removing all Items from a combo box in Java

问题

I need to remove all items from the combo box

    int itemCount = combo.getItemCount();

    for(int i=0;i<itemCount;i++){
        combo.removeItemAt(0);
     }

This code will remove all items except the last one. It gives a NullPointerException. How to fix that?

回答1:

The code in the question would normally work. However, it looks like a threading issue. Another thread may be messing with the items.

However, I sugeest you should better use the removeAllItems(); method:

combo.removeAllItems();

回答2:

How about JComboBox.removeAllItems()?

回答3:

In second line:

combo.removeItemAt(0);

I think instead of 0 it should be i.

do it in reverse order as:

for(int i=combo.getItemCount()-1;i>=0;i--){
    combo.removeItemAt(i);
}

But in my case combo.removeAllItems() works fine

回答4:

You can use

this.combo.removeAllItems();

to remove all the items in JComboBox.

回答5:

use .removeAllItems() methods to remove all items from combo box.

回答6:

The assumption that it is related to another thread is not always true. It can be the thread itself causing the issue.

This exception may happen because an event is triggered when a combo item is removed and in this event handling method you still refer to combobox items.

For example when you delete somewhere (other than in actionPeformed()) in your code the last item from a combo box with combo.removeItemAt(0) or removeAllItems() then still the event actionPerformed will be fired/executed. But very often the actionPerformed() method contains code to react on user actions (user clicked somewhere on the combobox). So, when the last item has been deleted there is no more item in the combobox and any reference to an item or index in actionPerformed() will cause an exception.

The solution to this is to move the code from actionPerformed() to e.g. mouseClicked() or another event handler depending on what you want to do.

回答7:

removeAllItems() it does remove all things but after the add data to the combo box it will not show there ,the nullPointException will shows

回答8:

Use this to remove all the elements from the combo box :

DefaultComboBoxModel model = (DefaultComboBoxModel) ComboBox.getModel();
model.removeAllElements();

回答9:

Usually it happens because you have an event associated JComboBox. It is solved if you have control item in the JComboBox to act, for example:

jComboBoxExample.addActionListener (new ActionListener () {
   public void actionPerformed (ActionEvent e) {
     do_run ();
   }
});



public void do_run() {
  int n=jComboBoxPerfilDocumentos.getItemCount(); <--THIS IS THE SOLUTION
  if (n> 0) { 
    String x = jComboBoxPerfilDocumentos.getSelectedItem (). ToString ();
  }
}

来源：https://stackoverflow.com/questions/12249336/removing-all-items-from-a-combo-box-in-java

标签

java

swing

jcombobox