ComboBoxItemCollection.BeginUpdate() Method

Locks the ComboBoxItemCollection by preventing change notifications from being fired, preventing visual updates until the EndUpdate method is called.

Namespace: DevExpress.XtraEditors.Controls

Assembly: DevExpress.XtraEditors.v20.1.dll

Declaration

public virtual void BeginUpdate()
Public Overridable Sub BeginUpdate

Remarks

Use BeginUpdate along with the EndUpdate method to prevent superfluous change notifications from being sent while performing multiple changes on the ComboBoxItemCollection. Enclose the code that performs multiple changes on the collection with the BeginUpdate and EndUpdate methods. The result will be that the change notification will fire only once, triggered by the EndUpdate method.

The BeginUpdate and EndUpdate methods use an internal counter to implement the update functionality. The counter's initial value is 0. The BeginUpdate method increments the counter. EndUpdate decrements the counter, and if its new value is zero, change notification is enabled. Note that each call to BeginUpdate must be paired with a call to EndUpdate. If you call BeginUpdate but forget to call EndUpdate afterwards or EndUpdate is not called because an exception occurred, change notifications will no longer be fired. To ensure that EndUpdate is always called even if an exception occurs, use the try...finally statement.

Examples

The following code creates a combo box editor and adds three items to the item collection. Each item in the example is a PersonInfo class object, which stores a person's first and last names.

The ComboBoxItemCollection.BeginUpdate and ComboBoxItemCollection.EndUpdate methods are called to prevent excessive updates when the item collection is changed (three items are added).

The BaseListBoxControl.SelectedIndex property is set to -1 for demonstration purposes (the property is set to -1 by default). This ensures that no item is currently selected in the combo box.

  ComboBoxEdit combo = new ComboBoxEdit();
  ComboBoxItemCollection coll = combo.Properties.Items;
  coll.BeginUpdate();
  try {
    coll.Add(new PersonInfo("Sven", "Petersen"));
    coll.Add(new PersonInfo("Cheryl", "Saylor"));
    coll.Add(new PersonInfo("Dirk", "Luchte"));
  }
  finally {
    coll.EndUpdate();
  }
  combo.SelectedIndex = -1;

  Controls.Add(combo);


//...

  public class PersonInfo {
    private string _firstName;
    private string _lastName;

    public PersonInfo(string firstName, string lastName) {
      _firstName = firstName;
      _lastName = lastName;
    }

    public override string ToString() {
      return _firstName + " " + _lastName;
    }
  }
See Also