Problem with Combobox in ExtJS

I am developing a website, which is going to be accessed by an embedded system with a touchscreen interface. In order to provide the data to an ExtJS combobox, the user uses an on-screen keyboard (such as the add-ons provided by chrome and firefox, which are developed in javascript). When I select the combobox, I can type the first character (the combobox looses the focus when the keyboard button is pressed and then f开发者_JAVA百科ocuses once again when the key in the keyboard is released). When I try to insert the second character, the first one is erased instead of being concatenated to the end.

Is there any way to make sure that the new characters are appended to ones that are already in the combobox?(instead of erasing them).

Any help on this matter would be nice.

Would need to see code like the previous answerer, but make sure selectOnFocus is false on the combobox, or else you would be typing over everything for each letter the way you described it.