IOS开发之异步加载网络图片并缓存本地实现瀑布流（一）

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</pre><pre name="code" class="objc">

在前面的一篇博客中，我写了一个瀑布流照片墙的程序，由于之前的程序加载的图片是本地的，所以在这篇文章中我来补上有关异步加载网络图片的代码，来实现之前程序的效果，希望大家批评指正呀！

这个程序中大部分的代码和之前的博客中贴出来的相同，不同的只是添加了图片缓存机制，图片异步下载线程函数，以及图片点击浏览的功能。

接下来看一下代码实现部分：

#import "MyScrollView.h"

#define COORDINATE_X_LEFT 5
#define COORDINATE_X_MIDDLE MY_WIDTH/3 + 5
#define COORDINATE_X_RIGHT MY_WIDTH/3 * 2 + 5
#define PAGESIZE 21

@interface MyScrollView ()

@end

@implementation MyScrollView

@synthesize isOnce = _isOnce;
@synthesize imagesName = _imagesName;
@synthesize loadedImageDic = _loadedImageDic;
@synthesize leftColumHeight = _leftColumHeight;
@synthesize midColumHeight = _midColumHeight;
@synthesize rightColumHeight = _rightColumHeight;
@synthesize loadedImageArray = _loadedImageArray;
@synthesize imgTag = _imgTag;
@synthesize imgTagDic = _imgTagDic;
@synthesize imageLoad = _imageLoad;
@synthesize page = _page;
@synthesize fileUtil = _fileUtil;
@synthesize imageCache = _imageCache;
@synthesize photoArray = _photoArray;
//@synthesize aDelegaet;

+ (MyScrollView *)shareInstance{
static MyScrollView *instance;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[self alloc] initWithFrame:CGRectMake(0, 0, MY_WIDTH, MY_HEIGHT)];
});

return instance;
}

/*
初始化scrollView的委托以及背景颜色，不显示它的水平，垂直显示条
*/
- (id)initWithFrame:(CGRect)frame{
self = [super initWithFrame:frame];
if(self){
self.delegate = self;
self.backgroundColor = [UIColor blackColor];
self.pagingEnabled = NO;
self.showsHorizontalScrollIndicator = NO;
self.showsVerticalScrollIndicator = NO;

self.isOnce = YES;
self.loadedImageDic = [[NSMutableDictionary alloc] init];
self.loadedImageArray = [[NSMutableArray alloc] init];
self.imgTagDic = [[NSMutableDictionary alloc] init];
self.photoArray = [[NSMutableArray alloc] init];

//初始化列的高度
self.leftColumHeight = 3.0f;
self.midColumHeight = 3.0f;
self.rightColumHeight = 3.0f;
self.imgTag = 10086;
self.page = 1;

self.fileUtil = [FileUtil shareInstance];
self.imageCache = [ImageCacher shareInstance];

_imageCache.myDelegate = self;

[self initWithPhotoBox];
}

return self;
}

/*
将scrollView界面分为大小相等的3个部分，每个部分为一个UIView, 并设置每一个UIView的tag
*/
- (void)initWithPhotoBox{
UIView *leftView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, MY_WIDTH/3, self.frame.size.height)];
UIView *middleView = [[UIView alloc] initWithFrame:CGRectMake(leftView.frame.origin.x + MY_WIDTH/3, 0, MY_WIDTH/3,
self.frame.size.height)];
UIView *rightView = [[UIView alloc] initWithFrame:CGRectMake(middleView.frame.origin.x + MY_WIDTH/3, 0, MY_WIDTH/3,
self.frame.size.height)];
//设置三个部分的tag
leftView.tag = 100;
middleView.tag = 101;
rightView.tag = 102;

//设置背景颜色
[leftView setBackgroundColor:[UIColor clearColor]];
[middleView setBackgroundColor:[UIColor clearColor]];
[rightView setBackgroundColor:[UIColor clearColor]];

[self addSubview:leftView];
[self addSubview:middleView];
[self addSubview:rightView];

self.imageLoad = [ImageLoader shareInstance];
[_imageLoad loadImage:nil];

//第一次加载图片
for(int i = 0; i < PAGESIZE; i++){
NSString *imageName = [_imageLoad.imagesArray objectAtIndex:i];
[self imageStartLoading:imageName];
}

//当前为第一页
self.page = 1;
}

/*
* @brief 图片加载通用函数
* @parma imageName 图片名
*/
- (void)imageStartLoading:(NSString *)imageName{
NSURL *url = [NSURL URLWithString:imageName];
if([_fileUtil hasCachedImage:url]){
UIImageView *imageView = [[UIImageView alloc] init];
NSString *path = [_fileUtil pathForUrl:url];
imageView = [_imageLoad compressImage:MY_WIDTH/3 imageView:nil imageName:path flag:NO];
[self addImage:imageView name:path];
[self adjustContentSize:NO];
}else{
UIImageView *imageView = [[UIImageView alloc] init];
NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:url, @"URL",
imageView, @"imageView", nil];
[NSThread detachNewThreadSelector:@selector(cacheImage:) toTarget:[ImageCacher shareInstance] withObject:dic];
}
}

/*
*调整scrollview
*/
- (void)adjustContentSize:(BOOL)isEnd{
UIView *leftView = [self viewWithTag:100];
UIView *middleView = [self viewWithTag:101];
UIView *rightView = [self viewWithTag:102];

if(_leftColumHeight >= _midColumHeight && _leftColumHeight >= _rightColumHeight){
self.contentSize = leftView.frame.size;
}else{
if(_midColumHeight >= _rightColumHeight){
self.contentSize = middleView.frame.size;
}else{
self.contentSize = rightView.frame.size;
}
}
}

/*
*得到最短列的高度
*/
- (float)getTheShortColum{
if(_leftColumHeight <= _midColumHeight && _leftColumHeight <= _rightColumHeight){
return _leftColumHeight;
}else{
if(_midColumHeight <= _rightColumHeight){
return _midColumHeight;
}else{
return _rightColumHeight;
}
}
}

/*
*添加一张图片
*规则：根据每一列的高度来决定，优先加载列高度最短的那列
*重新设置图片的x,y坐标
*imageView:图片视图
*imageName:图片名
*/
- (void)addImage:(UIImageView *)imageView name:(NSString *)imageName{
//图片是否加载
if([self.loadedImageDic objectForKey:imageName]){
return;
}

//若图片还未加载则保存
[self.loadedImageDic setObject:imageView forKey:imageName];
[self.loadedImageArray addObject:imageView];
[_photoArray addObject:imageName];

[self imageTagWithAction:imageView name:imageName];

float width = imageView.frame.size.width;
float height = imageView.frame.size.height;

//判断哪一列的高度最低
if(_leftColumHeight <= _midColumHeight && _leftColumHeight <= _rightColumHeight){
UIView *leftView = [self viewWithTag:100];
[leftView addSubview:imageView];
//重新设置坐标
[imageView setFrame:CGRectMake(2, _leftColumHeight, width, height)];
_leftColumHeight = _leftColumHeight + height + 3;
[leftView setFrame:CGRectMake(0, 0, MY_WIDTH/3, _leftColumHeight)];
}else{
if(_midColumHeight <= _rightColumHeight){
UIView *middleView = [self viewWithTag:101];
[middleView addSubview:imageView];

[imageView setFrame:CGRectMake(2, _midColumHeight, width, height)];
_midColumHeight = _midColumHeight + height + 3;
[middleView setFrame:CGRectMake(MY_WIDTH/3, 0, MY_WIDTH/3, _midColumHeight)];
}else{
UIView *rightView = [self viewWithTag:102];
[rightView addSubview:imageView];

[imageView setFrame:CGRectMake(2, _rightColumHeight, width, height)];
_rightColumHeight = _rightColumHeight + height + 3;
[rightView setFrame:CGRectMake(2 * MY_WIDTH/3, 0, MY_WIDTH/3, _rightColumHeight)];
}
}
}

/*
将图片tag保存，以及为UIImageView添加事件响应
*/
- (void)imageTagWithAction:(UIImageView *)imageView name:(NSString *)imageName{
//将要显示图片的tag保存
imageView.tag = self.imgTag;
[self.imgTagDic setObject:imageName forKey:[NSString stringWithFormat:@"%ld", (long)imageView.tag]];
self.imgTag++;

//图片添加事件响应
UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageClickWithTag:)];
tapRecognizer.delegate = self;
imageView.userInteractionEnabled = YES;
[imageView addGestureRecognizer:tapRecognizer];
[tapRecognizer release];
}

/*
//若三列中最短列距离底部高度超过30像素，则请求加载新的图片
*/
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
//可视检查
//[self checkImageIsVisible];
if((self.contentOffset.y + self.frame.size.height) - [self getTheShortColum] > 30){
[self pullRefreshImages];
}
}

/*
上拉时加载新的图片
*/
- (void)pullRefreshImages{
int index = self.page *PAGESIZE;
NSUInteger imgNum = [self.imageLoad.imagesArray count];

if(index >= imgNum){
//图片加载完毕
[self adjustContentSize:YES];
}else{
if((imgNum - self.page*PAGESIZE) > PAGESIZE){
for (int i = index; i < PAGESIZE; i++) {
NSString *imageName = [_imageLoad.imagesArray objectAtIndex:i];
[self imageStartLoading:imageName];
}
}else{
for (int i = index; i < imgNum; i++) {
NSString *imageName = [_imageLoad.imagesArray objectAtIndex:i];
[self imageStartLoading:imageName];
}
}
self.page++;
}
}

/*
检查图片是否可见，如果不在可见视线内，则把图片替换为nil
*/
- (void)checkImageIsVisible{
for (int i = 0; i < [_loadedImageArray count]; i++) {
UIImageView *imgView = [_loadedImageArray objectAtIndex:i];

if((self.contentOffset.y - imgView.frame.origin.y) > imgView.frame.size.height ||
imgView.frame.origin.y > (self.frame.size.height + self.contentOffset.y)){
//不显示图片
imgView.image = nil;
}else{
//重新根据tag值显示图片
NSString *imageName = [self.imgTagDic objectForKey:[NSString stringWithFormat:@"%ld", (long)imgView.tag]];
if((NSNull *)imageName == [NSNull null]){
return;
}

UIImageView *view = [_imageLoad compressImage:MY_WIDTH/3 imageView:nil imageName:imageName flag:NO];
imgView.image = view.image;
}
}
}

//点击图片事件响应
- (void)imageClickWithTag:(UITapGestureRecognizer *)sender{
UIImageView *view = (UIImageView *)sender.view;
NSString *imageName = [self.imgTagDic objectForKey:[NSString stringWithFormat:@"%ld", (long)view.tag]];

PhotoViewController *photoView = [[PhotoViewController alloc] init];
photoView.imageArray = _photoArray;
photoView.imageName = imageName;
UIWindow *window = [[UIApplication sharedApplication].delegate window];
[window addSubview:photoView.view];
}

- (void)dealloc{
[_imagesName release];
[_imgTagDic release];
[_loadedImageArray release];
[_imageCache release];
[_fileUtil release];
[_imageLoad release];
[_photoArray release];
[super dealloc];
}

@end

当程序第一次加载或者下拉刷新时，就开始下载图片，函数：imageStartLoading用于下载图片，该函数为每一次下载图片都开启一个线程，在ImageCacher类中有cacheImage函数，用于判断该图片是否已经存在本地，并且将图片放入到视图中去。

以下是ImageCacher类的代码

#import "ImageCacher.h"

@implementation ImageCacher
@synthesize fileUtil = _fileUtil;
@synthesize imageLoader = _imageLoader;
@synthesize myDelegate = _myDelegate;

+ (ImageCacher *)shareInstance{
static ImageCacher *instance;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[self alloc] init];
});

return instance;
}

- (id)init{
self = [super init];
if(self){
self.fileUtil = [FileUtil shareInstance];
self.imageLoader = [ImageLoader shareInstance];
}
return self;
}

- (void)cacheImage:(NSDictionary*)dic{
NSURL *url = [dic objectForKey:@"URL"];
NSFileManager *fileManage = [NSFileManager defaultManager];
NSData *data = [NSData dataWithContentsOfURL:url];

NSString *fileName = [_fileUtil pathForUrl:url];
if(data){
[fileManage createFileAtPath:fileName contents:data attributes:nil];
}

UIImageView *imageView = [dic objectForKey:@"imageView"];
imageView.image = [UIImage imageWithData:data];
imageView = [_imageLoader compressImage:MY_WIDTH/3 imageView:imageView imageName:nil flag:YES];
[self.myDelegate addImage:imageView name:fileName];
[self.myDelegate adjustContentSize:NO];
}

- (void)dealloc{
[super dealloc];
}

@end

由于时间的关系，详细的讲解就留到下期来说吧！