contentsize、contentoffset和contentInset详解

下面我用怎么做一个书架的例子和大家说说contentsize、contentoffset 和contentInset的区别。

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NSString *path = nil; 
UIImage *back = nil; 
NSString *str = nil; 
UIImage *aImage = nil; 
 
path = [[NSBundle mainBundle] pathForResource:@"shujia" ofType:@"jpg"]; 
back = [UIImage imageWithContentsOfFile:path];//加载图片 
 
_scrollView = [[UIScrollView  alloc] initWithFrame:CGRectMake(96, 84,back.size.width,back.size.height)]; 
_scrollView.showsVerticalScrollIndicator = NO;      //将竖直方向的滚动条隐藏  
 
//将shujia.jpg作为_scrollerView的背景 
UIColor *color=[[UIColor alloc]initWithPatternImage:back]; 
[_scrollView setBackgroundColor:color]; 
 
_buttonList=[NSMutableArray arrayWithCapacity:9]; 
for(int i=0;i<9;i++) 
{ 
    str=[NSString stringWithFormat:@"menubook%d",i+1]; 
    path = [[NSBundle mainBundle] pathForResource:str ofType:@"png"]; 
    aImage = [UIImage imageWithContentsOfFile:path]; 
    int x = (i%3)* (aImage.size.width+15); 
    int y = (i/3)* (aImage.size.height+30); 
    _whichPeople = [UIButton buttonWithType:UIButtonTypeCustom]; 
    _whichPeople.frame = CGRectMake(x+10,y+30,aImage.size.width,aImage.size.height); 
    _whichPeople.tag = i; 
    [_whichPeople setImage:aImage forState:UIControlStateNormal];//这个图片是在布点击时响应 
    path = nil; 
    aImage = nil; 
    str = nil; 
     
    str=[NSString stringWithFormat:@"menubook%d_1",i+1]; 
    path = [[NSBundle mainBundle] pathForResource:str ofType:@"png"]; 
    aImage = [UIImage imageWithContentsOfFile:path]; 
    [_whichPeople setImage:aImage forState:UIControlStateHighlighted];//图片在点击的时候响应 
    [_whichPeople addTarget:self action:@selector(ButtonClick:) forControlEvents:UIControlEventTouchUpInside]; 
    [_scrollView addSubview:_whichPeople]; 
    [_buttonList addObject:_whichPeople]; 
    path = nil; 
    aImage = nil; 
    str =  nil; 
     
} 
 
//控制可以滚动的区域 
_scrollView.contentSize = CGSizeMake(480, 580);  
//当前显示区域顶点相对于frame顶点的偏移量 
_scrollView.contentOffset = CGPointMake(0, 0); 
//scrollview的contentview的顶点相对于scrollview的位置 
_scrollView.contentInset = UIEdgeInsetsMake(0 , 0, 0, 0); 
[self.view addSubview:_scrollView];  
contentSize是scrollview可以滚动的区域，比如frame = (0 ,0 ,320 ,480) contentSize = (320 ,960)，代表你的scrollview可以上下滚动，滚动区域为frame大小的两倍。
contentOffset是scrollview当前显示区域顶点相对于frame顶点的偏移量，比如上个例子你拉到最下面，contentoffset就是(0 ,480)，也就是y偏移了480
contentInset是scrollview的contentview的顶点相对于scrollview的位置，例如你的contentInset = (0 ,100)，那么你的contentview就是从scrollview的(0 ,100)开始显示