field.returnKeyType = UIReturnKeyDone;
[field addTarget:self action:@selector(onKeyBoardDown:) forControlEvents:UIControlEventEditingDidEndOnExit];// 取消第一响应
-(void)onKeyBoardDown:(id)sender{
[sender resignFirstResponder];
}
原文：http://www.cnblogs.com/pjl111/p/4196415.html