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。

    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