对UITextField的键盘处理方法<摘抄>

- (void)registerForKeyboardNotifications
{
    //添加自己做为观察者，以获取键盘显示时的通知
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWasShown:)
                                                 name:UIKeyboardDidShowNotification object:nil];
    //添加自己做为观察者，以获取键盘隐藏时的通知
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWasHidden:)
                                                 name:UIKeyboardDidHideNotification object:nil];
}

// 键盘出现时调用此方法
- (void)keyboardWasShown:(NSNotification*)aNotification
{
    //如果键盘是显示状态，不用做重复的操作
    if (keyboardShown)
        return;

    //获得键盘通知的用户信息字典
    NSDictionary* info = [aNotification userInfo];

    // 取得键盘尺寸.
    NSValue* aValue = [info objectForKey:UIKeyboardBoundsUserInfoKey];
    CGSize keyboardSize = [aValue CGRectValue].size;

    // 重新设置scrollView的size
    CGRect viewFrame = [myScrollView frame];
    viewFrame.size.height -= keyboardSize.height;
    myScrollView.frame = viewFrame;


    // 把当前被挡住的text field滚动到view中适当的可见位置.
    CGRect textFieldRect = [activeField frame];
    [myScrollView scrollRectToVisible:textFieldRect animated:YES];


    //记录当前textField的偏移量，方便隐藏键盘时，恢复textField到原来位置
    oldContentOffsetValue = [myScrollView contentOffset].y;

    //计算textField滚动到的适当位置
    CGFloat value = (activeField.frame.origin.y+myScrollView.frame.origin.y+activeField.frame.size.height - self.view.frame.size.height + keyboardSize.height)+2.0f;

    //value>0则表示需要滚动，小于0表示当前textField没有被挡住，不需要滚动
    if (value > 0) {
        //使textField滚动到适当位置
        [myScrollView setContentOffset:CGPointMake(0, value) animated:YES];
        isNeedSetOffset = YES;//更改状态标志为需要滚动
    }

    //更改键盘状态标志为已显示
    keyboardShown = YES;
}


// 键盘隐藏时调用此方法
- (void)keyboardWasHidden:(NSNotification*)aNotification
{


    NSDictionary* info = [aNotification userInfo];

    // Get the size of the keyboard.
    NSValue* aValue = [info objectForKey:UIKeyboardBoundsUserInfoKey];
    CGSize keyboardSize = [aValue CGRectValue].size;

    // Reset the height of the scroll view to its original value
    CGRect viewFrame = [myScrollView frame];
    viewFrame.size.height += keyboardSize.height;
    myScrollView.frame = viewFrame;

    //如果状态标志为需要滚动，则要执行textFiled复位操作
    if (isNeedSetOffset) {
        //oldContentOffsetValue记录了textField原来的位置，复位即可
        [myScrollView setContentOffset:CGPointMake(0, oldContentOffsetValue) animated:YES];
    }

    //复位状态标志
    isNeedSetOffset = NO;
    keyboardShown = NO;
}