Android webview中的“提交”按钮不是默认设置

I have a form that I want to submit it in Android web view, but my submit button is not working as its default.

I mean it is not redirected to the submit.php page! (It just submits data) What should I do for it to use its default ?

Here is an example form:

<form  id="form" method="post" action="submit.php" enctype="multipart/form-data" >
// other elements ...
<input type="file" name="file" />
</form>

How can I force it to use its default again?