Locks the BaseAppearanceCollection, preventing change notifications (and visual updates) from being raised by the object until the EndUpdate or CancelUpdate method is called.
Once the BeginUpdate method has been called, modifying the BaseAppearanceCollection and its elements does not result in immediate visual updates. So, multiple modifications can be made to the BaseAppearanceCollection and its elements without a major impact on performance or screen flickering. After all the desired operations have been finished, call the EndUpdate or CancelUpdate method. Use the EndUpdate method to immediately perform a visual update, reflecting all the changes made. If no immediate visual update is required (for example, if no visual setting has been affected by the operations performed), call the CancelUpdate method.
The BeginUpdate, EndUpdate and CancelUpdate methods use an internal counter to implement the update functionality. The counter's initial value is 0. The BeginUpdate method increments the counter. The EndUpdate and CancelUpdate decrement the counter.
The object's visual updates (change notifications) are forbidden if the counter's value is greater than 0, and the updates are enabled if the counter's value is 0.
Each call to BeginUpdate must be paired with a call to EndUpdate or CancelUpdate. To ensure that EndUpdate/CancelUpdate is always called even if an exception occurs, use the try...finally statement.