Hello Myat Su,
Thank you for your reply.
To make the buttons small immediately after you add them to the RadBubbleBar you should modify the ItemsChanged event handler of the BubbleBarElement items collection to look like the following code snippet. You already have it in the code you just have to add the bottom two lines in the If statement:
operation = ItemsChangeOperation.Inserted
operation = ItemsChangeOperation.
SizeF(0.65F, 0.65F), 5, 30)
I hope this will help. Feel free to write back for any further help you may need.
the Telerik team
Q2’11 SP1 of RadControls for WinForms is available for download (see what's new); also available is the Q3'11 Roadmap for Telerik Windows Forms controls.