How to keep the changed to the button text after pressing the back button

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Mobile

Android

in my project i one edit text and one button.

when the project load and i press the button.

the text of the button changed loaded the text from the edit text
but when i press the back button .

the changed did not save.
for example the text loaded from the edit text did not save to the button after pressing the back button.
i included the snapshot which can describe my problem better.![this image show that the edit text contain the text android should be load to the button after pressing the Button.but when i press back button and reopen the app the change did not save and button showed the first text as Button][1]


[1]: http://i.stack.imgur.com/XVbvF.jpg
[1]: http://i.stack.imgur.com/dGoyw.jpg
[1]: http://i.stack.imgur.com/QOqUX.jpg
[1]: http://i.stack.imgur.com/qHoki.jpg