当键盘弹出时有可能遮挡住输入框，直接给出一个简单的解决方案
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
//注册键盘弹起与收起通知
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardWillShow:)
name:UIKeyboardWillShowNotification
object:nil];
}
-(void)keyboardWillShow:(NSNotification *)note
{
NSDictionary *info = [note userInfo];
CGSize keyboardSize = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;
_keyBoardHeight = keyboardSize.height;
CGRect frame = _userNameTextfield.frame;
int offset = frame.origin.y + 32 - (self.view.frame.size.height -_keyBoardHeight);
NSTimeInterval animationDuration = 0.30f;
[UIView beginAnimations:@"ResizeForKeyboard" context:nil];
[UIView setAnimationDuration:animationDuration];
//将视图的Y坐标向上移动offset个单位，以使下面腾出地方用于软键盘的显示
if(offset > 0)
self.view.frame = CGRectMake(0.0f, -offset, self.view.frame.size.width, self.view.frame.size.height);
[UIView commitAnimations];
}
//当用户按下return键或者按回车键，keyboard消失
-(BOOL)textFieldShouldReturn:(UITextField *)textField
{
[textField resignFirstResponder];
return YES;
}
//输入框编辑完成以后，将视图恢复到原始状态
-(void)textFieldDidEndEditing:(UITextField *)textField
{
NSTimeInterval animationDuration = 0.30f;
[UIView beginAnimations:@"ResizeForKeyboard" context:nil];
[UIView setAnimationDuration:animationDuration];
self.view.frame =CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
[UIView commitAnimations];
}