Custom Gridview Filters

I am developing custom gridview with built in filter functionality in the header row.

I was able to populate the textboxes in the headers of the gridview columns during Row Created event and add events/delegates to change the gridview information when the user changes the information in the textboxes. I've create special Event Filter_changed which is raised by the filter Text Box changes . Theis event is handled by the aspx page which hosts the custom gridview control. It works fine at this point.

I am still faced with 2 problems which I am not sure how to deal with.

1) I've added all the event handlers for the TextBox_Changed event of the textbox. This event does not fire when somebody just cleans the content of the TextBox instead of changing the contents. Why ? It is suppose to work this way ?

2) I'd like to save the information typed in all filter textboxes during the postbacks. I've tried using ViewState but It only saves the information to the next postback. After that it is completely lost. I am setting ViewState variable name dynamically based on the names of the the textboxes, so it should be unique. Why do you think it is happening and what is the workaround ?

Thanks

Mikhail