响应键盘事件

通过对键盘事件的响应，让控件不被遮挡。
通过下面第一个方法添加监听，当键盘显示和隐藏的时候会分别调用下面第二和第三个方法，对于界面的定制就写在第二跟第三个方法中。

-(void)registerForKeyboardNotifications
{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWasShown:)
                                                 name:UIKeyboardDidShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWasHidden:)
                                                 name:UIKeyboardDidHideNotification object:nil];
}

-(void)keyboardWasShown:(NSNotification*)noti
{
    NSDictionary * info = [noti userInfo];
    //UIKeyboardBoundsUserInfoKey Deprecated(已过时)
//    NSValue *value = [info objectForKey:UIKeyboardBoundsUserInfoKey];
//    CGSize keyboardSize = [value CGRectValue].size;
//    CGFloat keyboardHeight = keyboardSize.height;
   
    NSValue *value = [info objectForKey:UIKeyboardFrameEndUserInfoKey];   
    CGRect rect = [value CGRectValue];   
   
    //获得的这个rect表示的是在屏幕坐标系统里的键盘的frame,没有考虑任何方向旋转造成的影响,也就是说实际使用中要经过转换,否则可能造成宽度和高度对调
    CGRect keyboardFrame = [self.view convertRect:rect fromView:[[UIApplication sharedApplication] keyWindow]];
    CGFloat keyboardHeight = keyboardFrame.size.height;
    NSLog(@"%f",keyboardHeight);
   
    //让View的高度减少一个键盘的高度
    CGRect frame = self.view.frame;
    frame.size.height -= keyboardHeight;
    self.view.frame = frame;
   
    //如果是ScrollView,还可以让其滚动到指定位置
    //......  

}

-(void)keyboardWasHidden:(NSNotification*)noti
{
    NSDictionary * info = [noti userInfo];
    //UIKeyboardBoundsUserInfoKey Deprecated(已过时)
//    NSValue *value = [info objectForKey:UIKeyboardBoundsUserInfoKey];
//    CGSize keyboardSize = [value CGRectValue].size;
//    CGFloat keyboardHeight = keyboardSize.height;
       
    NSValue *value = [info objectForKey:UIKeyboardFrameEndUserInfoKey];
    CGRect rect = [value CGRectValue];
   
    //获得的这个rect表示的是在屏幕坐标系统里的键盘的frame,没有考虑任何方向旋转造成的影响,也就是说实际使用中要经过转换,否则可能造成宽度和高度对调
    CGRect keyboardFrame = [self.view convertRect:rect fromView:[[UIApplication sharedApplication] keyWindow]];
    CGFloat keyboardHeight = keyboardFrame.size.height;
    NSLog(@"%f",keyboardHeight);

    //让View的高度增大一个键盘的高度,回到原高度
    CGRect frame = self.view.frame;
    frame.size.height += keyboardHeight;
    self.view.frame = frame;
}