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