IOS使用scrollview显示大量图片，实现缓存，节省内存

一般大家在用scrollview加载图片的时候少量还好，若是大量图片则很容易引起内存不足，这里介绍一种省内存的办法，只加载前后加当前一共三张即可，然后来回切换加载图片，相当的省内存，用到两个自己写的类，一个是Myscrollview，一个是easyImageLoader，不罗嗦，上代码

#import <UIKit/UIKit.h>@protocol MyScrollViewDelegate <NSObject>;-(void)singleTapGesture;@end@interface MyScrollView : UIScrollView <UIScrollViewDelegate>{UIImage *image;UIImageView *imageView;}@property (assign, nonatomic) id<MyScrollViewDelegate>  scollViewDelegate;@property (nonatomic, retain) UIImage *image;@property (nonatomic, retain) UIImageView    *imageView;@end#import "MyScrollView.h"@implementation MyScrollView@synthesize image;@synthesize imageView;@synthesize scollViewDelegate;#pragma mark -#pragma mark === Intilization ===#pragma mark -- (id)initWithFrame:(CGRect)frame{    if ((self = [super initWithFrame:frame])){self.delegate = self;self.minimumZoomScale = 0.5;self.maximumZoomScale = 2.5;self.showsVerticalScrollIndicator = NO;self.showsHorizontalScrollIndicator = NO;imageView  = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];imageView.contentMode = UIViewContentModeScaleAspectFit;[self addSubview:imageView];    }    return self;}- (void)setImage:(UIImage *)img{imageView.image = img;}#pragma mark -#pragma mark === UIScrollView Delegate ===#pragma mark -- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{return imageView;}- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale                                                                        //双指放大缩小{//NSLog(@"%s", _cmd);CGFloat zs = scrollView.zoomScale;zs = MAX(zs, 1.0);zs = MIN(zs, 2.0);[UIView beginAnimations:nil context:NULL];[UIView setAnimationDuration:0.3];scrollView.zoomScale = zs;[UIView commitAnimations];}#pragma mark -#pragma mark === UITouch Delegate ===#pragma mark -- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{UITouch *touch = [touches anyObject];if ([touch tapCount] == 2)                                                      //双击放大图片{CGFloat zs = self.zoomScale;zs = (zs == 1.0) ? 2.0 : 1.0;[UIView beginAnimations:nil context:NULL];[UIView setAnimationDuration:0.3];self.zoomScale = zs;[UIView commitAnimations];}    if ([scollViewDelegate respondsToSelector:@selector(singleTapGesture)]) {        [scollViewDelegate performSelector:@selector(singleTapGesture)];    }}-(void)scrollViewDidScroll:(UIScrollView *)scrollView {}-(BOOL)touchesShouldBegin:(NSSet *)touches withEvent:(UIEvent *)event inContentView:(UIView *)view{    return NO;}@end#import <UIKit/UIKit.h>#import "MyScrollView.h"@interface easyImageLoader : UIScrollView<MyScrollViewDelegate,UIScrollViewDelegate>@property (strong, nonatomic) NSMutableArray  *viewControllers;@property (strong, nonatomic) NSMutableArray *_imageArray;@property (strong, nonatomic) NSMutableArray *_imagePathArray;@property (strong, nonatomic) NSMutableArray *scrollViewArray;///供固定的大量图片使用-(void)loadImageWithImageArray:(NSMutableArray*)imageArray;////供网络获取而来的图片使用，可刷新-(void)loadImageWithImageArrayFromPathArray:(NSMutableArray *)imagePathArray;-(void)reloadImageAt:(NSInteger)index;@end#import "easyImageLoader.h"@implementation easyImageLoader@synthesize viewControllers;@synthesize _imageArray;@synthesize _imagePathArray;@synthesize scrollViewArray;- (id)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        self.delegate = self;        // Initialization code    }    return self;}-(void)loadImageWithImageArray:(NSMutableArray*)imageArray{    _imageArray = [[NSMutableArray alloc]initWithArray:imageArray];    [self loadImageShow];}////////////-(void)loadImageWithImageArrayFromPathArray:(NSMutableArray *)imagePathArray{    _imagePathArray = [[NSMutableArray alloc]initWithArray:imagePathArray];    for (NSString *path in imagePathArray) {            [_imageArray addObject:NULL];    }}-(void)reloadImageAt:(NSInteger)index{    UIViewController  *controller2 = [self.viewControllers objectAtIndex:index];    if ((NSNull *)controller2 != [NSNull null])    {        for (UIImageView *imageView in controller2.view.subviews) {            imageView.image = nil;        }    }    [self.viewControllers replaceObjectAtIndex:index withObject:[NSNull null]];    UIImage *image = nil;    if (_imagePathArray.count) {        image = [[UIImage alloc] initWithContentsOfFile: [_imagePathArray objectAtIndex:index]];    }    else{        image = [[UIImage alloc]init];        image = [_imageArray objectAtIndex:index];    }    [_imageArray replaceObjectAtIndex:index withObject:image];    [self loadScrollViewWithPage:index];    [image release];}////////-(void)singleTapGesture{}-(void)loadImageShow{        NSLog(@"page89023147987491028");    if ([self.viewControllers count]) {    }    else{        NSMutableArray *controllers = [[NSMutableArray alloc] init];        for (unsigned i = 0; i < [_imageArray count]; i++)        {            [controllers addObject:[NSNull null]];        }        self.viewControllers = controllers;        [controllers release];    }    self.contentSize = CGSizeMake(self.frame.size.width * [_imageArray count], self.frame.size.height);    CGFloat pageWidth = self.frame.size.width;    int page = floor((self.contentOffset.x - pageWidth / 2) / pageWidth) + 1;    if (page<[_imageArray count]-1) {        if (page>0) {            UIViewController  *controller1 = [self.viewControllers objectAtIndex:page-1];            if ((NSNull *)controller1 != [NSNull null])            {                for (UIImageView *imageView in controller1.view.subviews) {                    imageView.image = nil;                }            }        }        UIViewController  *controller2 = [self.viewControllers objectAtIndex:page];        if ((NSNull *)controller2 != [NSNull null])        {            for (UIImageView *imageView in controller2.view.subviews) {                imageView.image = nil;            }        }        UIViewController  *controller3 = [self.viewControllers objectAtIndex:page+1];        if ((NSNull *)controller3 != [NSNull null])        {            for (UIImageView *imageView in controller3.view.subviews) {                imageView.image = nil;            }        }        NSLog(@"lologPageHeieI   1");        if (page>0) {            [self.viewControllers replaceObjectAtIndex:page-1 withObject:[NSNull null]];        }        NSLog(@"lologPageHeieI     2");        [self.viewControllers replaceObjectAtIndex:page withObject:[NSNull null]];        [self.viewControllers replaceObjectAtIndex:page+1 withObject:[NSNull null]];        if (page >0) {            [self loadScrollViewWithPage:page-1];        }        [self loadScrollViewWithPage:page];        [self loadScrollViewWithPage:page+1];    }    NSLog(@"lologPageHeieI     3");}-(UIViewController*)getTheController:(NSInteger)page viewController:(UIViewController*)viewController{    NSLog(@"wwwwwww");    UIImage *getImage = [_imageArray objectAtIndex:page];    MyScrollView  *scrollViewForScale = [[MyScrollView alloc]initWithFrame:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];    scrollViewForScale.scollViewDelegate = self;    scrollViewForScale.image = getImage;    [scrollViewArray addObject:scrollViewForScale];    [viewController.view addSubview:scrollViewForScale];    [scrollViewForScale release];    scrollViewForScale = nil;    NSLog(@"ttttttttttt");    return viewController;}- (void)loadScrollViewWithPage:(int)page{    NSLog(@"pagezzy");    if (page < 0)        return;    if (page >= [_imageArray count])        return;    // replace the placeholder if necessary    UIViewController  *controller = [self.viewControllers objectAtIndex:page];    if ((NSNull *)controller == [NSNull null])    {        controller = [[UIViewController alloc] init];        [self getTheController:page viewController:controller];        [self.viewControllers replaceObjectAtIndex:page withObject:controller];        [controller release];    }    // add the controller's view to the scroll view    if (controller.view.superview == nil)    {        CGRect frame = self.frame;        frame.origin.x = frame.size.width * page;        frame.origin.y = 0;        controller.view.frame = frame;        [self addSubview:controller.view];    }    NSLog(@"pagezzyyyyyy");}- (void)scrollViewDidScroll:(UIScrollView *)sender{    NSLog(@"page1233");    // We don't want a "feedback loop" between the UIPageControl and the scroll delegate in    // which a scroll event generated from the user hitting the page control triggers updates from    // the delegate method. We use a boolean to disable the delegate logic when the page control is used.    // Switch the indicator when more than 50% of the previous/next page is visible    CGFloat pageWidth = self.frame.size.width;    int page = floor((self.contentOffset.x - pageWidth / 2) / pageWidth) + 1;    // load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)    [self loadScrollViewWithPage:page - 1];    [self loadScrollViewWithPage:page];    [self loadScrollViewWithPage:page + 1];    if (page>2 &&page<[_imageArray count]-3) {        UIViewController  *controller1 = [self.viewControllers objectAtIndex:page-2];        if ((NSNull *)controller1 != [NSNull null])        {            for (UIImageView *imageView in controller1.view.subviews) {                imageView.image = nil;            }        }        UIViewController  *controller2 = [self.viewControllers objectAtIndex:page-3];        if ((NSNull *)controller2 != [NSNull null])        {            for (UIImageView *imageView in controller2.view.subviews) {                imageView.image = nil;            }        }        UIViewController  *controller3 = [self.viewControllers objectAtIndex:page+2];        if ((NSNull *)controller3 != [NSNull null])        {            for (UIImageView *imageView in controller3.view.subviews) {                imageView.image = nil;            }        }        UIViewController  *controller4 = [self.viewControllers objectAtIndex:page+3];        if ((NSNull *)controller4 != [NSNull null])        {            for (UIImageView *imageView in controller4.view.subviews) {                imageView.image = nil;            }        }        [self.viewControllers replaceObjectAtIndex:page-2 withObject:[NSNull null]];        [self.viewControllers replaceObjectAtIndex:page-3 withObject:[NSNull null]];        [self.viewControllers replaceObjectAtIndex:page+2 withObject:[NSNull null]];        [self.viewControllers replaceObjectAtIndex:page+3 withObject:[NSNull null]];    }    NSLog(@"%d",page);    // A possible optimization would be to unload the views+controllers which are no longer visible}/*// Only override drawRect: if you perform custom drawing.// An empty implementation adversely affects performance during animation.- (void)drawRect:(CGRect)rect{    // Drawing code}*/@end