避免弹出键盘遮盖住视图上的控件

当需要输入文字时，弹出的键盘通常会将需要输入文字的UITextField遮盖住。这段代码利用scrollview来解决这个问题。

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad 
{
    [super viewDidLoad];
 
    // register for keyboard notifications
    [[NSNotificationCenter defaultCenter] addObserver:self
        selector:@selector(keyboardWillShow:）
        name:UIKeyboardWillShowNotification
        object:self.view.window];
    // register for keyboard notifications
    [[NSNotificationCenter defaultCenter] addObserver:self
        selector:@selector(keyboardWillHide:) 
        name:UIKeyboardWillHideNotification
        object:self.view.window];
    keyboardIsShown = NO;
    //make contentSize bigger than your scrollSize 
    //(you will need to figure out for your own use case)
    CGSize scrollContentSize = CGSizeMake(320, 345);
    self.scrollView.contentSize = scrollContentSize;
}
 
- (void)viewDidUnload {
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
 
    // unregister for keyboard notifications while not visible.
    [[NSNotificationCenter defaultCenter] removeObserver:self
        name:UIKeyboardWillShowNotification
        object:nil]; 
    // unregister for keyboard notifications while not visible.
    [[NSNotificationCenter defaultCenter] removeObserver:self
        name:UIKeyboardWillHideNotification
        object:nil];  
}
 
- (void)dealloc {
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
 
    // unregister for keyboard notifications while not visible.
    [[NSNotificationCenter defaultCenter] removeObserver:self
        name:UIKeyboardWillShowNotification
        object:nil]; 
    // unregister for keyboard notifications while not visible.
    [[NSNotificationCenter defaultCenter] removeObserver:self
        name:UIKeyboardWillHideNotification
        object:nil];  
}
 
- (void)keyboardWillHide:(NSNotification *)n
{
    NSDictionary* userInfo = [n userInfo];
    // get the size of the keyboard
    CGSize keyboardSize = 
        [[userInfo objectForKey:UIKeyboardFrameBeginUserInfoKey]
            CGRectValue].size;
    // resize the scrollview
    CGRect viewFrame = self.scrollView.frame;
    // I'm also subtracting a constant kTabBarHeight because my UIScrollView 
    // was offset by the UITabBar so really only the portion of the keyboard that 
    // is leftover pass the UITabBar is obscuring my UIScrollView.
    viewFrame.size.height += (keyboardSize.height - kTabBarHeight);
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationBeginsFromCurrentState:YES];
    // The kKeyboardAnimationDuration I am using is 0.3
    [UIView setAnimationDuration:kKeyboardAnimationDuration];
    [self.scrollView setFrame:viewFrame];
    [UIView commitAnimations];
    keyboardIsShown = NO;
}
 
- (void)keyboardWillShow:(NSNotification *)n
{
    // This is an ivar I'm using to ensure that we do not do the frame size 
    // adjustment on the UIScrollView if the keyboard is already shown.  
    // This can happen if the user, after fixing editing a UITextField, 
    // scrolls the resized UIScrollView to another UITextField and attempts 
    // to edit the next UITextField.  If we were to resize the UIScrollView again, 
    // it would be disastrous. NOTE: The keyboard notification will fire 
    // even when the keyboard is already shown.
    if (keyboardIsShown) {
        return;
    }
 
    NSDictionary* userInfo = [n userInfo];
 
    // get the size of the keyboard
    CGSize keyboardSize = 
        [[userInfo objectForKey:UIKeyboardFrameBeginUserInfoKey]
            CGRectValue].size;
 
    // resize the noteView
    CGRect viewFrame = self.scrollView.frame;
    // I'm also subtracting a constant kTabBarHeight because my UIScrollView 
    // was offset by the UITabBar so really only the portion of the keyboard 
    // that is leftover pass the UITabBar is obscuring my UIScrollView.
    viewFrame.size.height -= (keyboardSize.height - kTabBarHeight);
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationBeginsFromCurrentState:YES];
    // The kKeyboardAnimationDuration I am using is 0.3
    [UIView setAnimationDuration:kKeyboardAnimationDuration];
    [self.scrollView setFrame:viewFrame];
    [UIView commitAnimations];
    keyboardIsShown = YES;
}