Get textbox focus event

 
Hi, everyone
My situation is I am trying to use textchanged
event of textbox, after  user change the data, then they click
somewhere else or press enter. The data should write back to DB. But if
user is typing and did not press enter or click, just click Submit button, the button
seems useless, it only captures the textchanged event, I have to click
button again to raise the button event. So I am trying to get the TextBox focus event but i have no idea how to do it. Can anyone give me some idea? 
THanks a lot
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