1. iphone/ipad大小

2. UIScreen bounds and applicationFrame

[UISCreen mainScreen].bounds, 永远返回portait模式的width/height, 也就是说width:320 height:480 for iPhone

[UISCreen mainScreen].applicationFrame更加复杂一些，它考虑了status bar的高度。

portait模式， x:0, y:20, width:320, height:460

landscape,   x:20, y:0, width:300, height:480

关于frame和bounds的区别，请参考UIView中的frame和bounds属性的区别

3. status bar height: 20, tool bar height: 44, tab bar height:44

4. UIScrollView

• contentSize和contentInSet

• contentOffSet:

// Called when the UIKeyboardDidShowNotification is sent.
- (void)keyboardWasShown:(NSNotification*)aNotification
{
    NSDictionary* info = [aNotification userInfo];
    CGSize kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
 
    UIEdgeInsets contentInsets = UIEdgeInsetsMake(0.0, 0.0, kbSize.height, 0.0);
    scrollView.contentInset = contentInsets;
    scrollView.scrollIndicatorInsets = contentInsets;
 
    // If active text field is hidden by keyboard, scroll it so it's visible
    // Your application might not need or want this behavior.
    CGRect aRect = self.view.frame;
    aRect.size.height -= kbSize.height;
    if (!CGRectContainsPoint(aRect, activeField.frame.origin) ) { //判断该text field是否在可见区域
        CGPoint scrollPoint = CGPointMake(0.0, instance); //这里需要计算需要scroll的长度，假设instance是计算出来的结果。
        [scrollView setContentOffset:scrollPoint animated:YES];
    }
}

• UIScroll view使用翻页模式

原文来自这里， 这里介绍几个关键的内容：

1.  pagingMode需要设置为YES

2. contentSize是所有页数的width总和， 例如你需要显示100页，那contentSize的宽度就是100*scroll.frame.size.width

3. showsHorizontalScrollIndicator和showsVerticalScrollIndicator设置为NO

然后需要在scroll view的delegate中实现scrollViewDidScroll:方法，这个方法在scroll view的contentOffSet发生变化的时候被调用。翻页模式的核心思想就是scroll view需要显示下一页的时候，创建一个view, 在这个view上准备好数据，然后把这个view加到scroll view当前显示的位置。

代码如下所示，另外还可以改进的一个地方是需要翻页之前，需要把后面一页的内容也显示出来，否则会有一半黑的屏幕显示。 

-(void) loadPageView:(NSUInteger)page
{
    UIView* view = [[UIView alloc] init];
    view.backgroundColor = [UIColor whiteColor];
    
    CGRect rc = self.view.frame;
    rc.origin.y = 0;
    rc.origin.x = page * self.view.frame.size.width;  //创建一个view，调整x直，因为其他直和scroll view都是一样的
    view.frame = rc;
    
    UILabel* label = [[UILabel alloc] initWithFrame:CGRectMake(0, 20, rc.size.width, 40)];
    label.text = [NSString stringWithFormat:@"current page is :%d", page];
    [view addSubview:label];
    
    [(UIScrollView*)self.view addSubview:view];
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    if (scrollView.contentOffset.x >= (myCurrentPage+0.5) * self.view.frame.size.width) //需要显示下一页了
    {
        myCurrentPage++;
        [self loadPageView:myCurrentPage];
    }
}