iOS多线程-自定义NSOperation(Cell下载图片缓存

作者: 学习天亦 | 来源:发表于2019-06-02 22:28 被阅读0次

复习下线程的基础知识，这里主要是参考文顶顶多线程篇复习写的。

一、cell下载图片思路 – 无沙盒(内存)缓存

主要解决下列问题
1、下载操作放在子线程不会卡UI。
2、使用operations字典解决重复下载问题，每个cell对应一个Operation
3、从字典中移除下载操作 (防止operations越来越大，保证下载失败后，能重新下载)
4、存放图片到images字典中，tableView要刷新对应行数的cell，防止正在下载时拖动tableView将当前的Cell放进缓存池，然后又将这个cell放在新的行数，导致下载完成显示对应的图片的位置不对。
5、使用占位图可以防止未下载的cell重用到其他行已经下载的的图片。
6、拖拽tableView时暂停下载操作，让tableView流程滑动。
7、接收到内存警告时移除下载操作和图片字典，待内存小时重新下载。

APPModel文件

#import <Foundation/Foundation.h>

@interface SSAPPModel : NSObject

@property(nonatomic, copy) NSString *name;
@property(nonatomic, copy) NSString *icon;
@property(nonatomic, copy) NSString *download;

+ (instancetype)appModelWithDict:(NSDictionary *)dict;
- (instancetype)initWithDict:(NSDictionary *)dict;

@end

@implementation SSAPPModel

- (instancetype)initWithDict:(NSDictionary *)dict {
    if (self = [super init]) {//KVC
        [self setValuesForKeysWithDictionary:dict];
    }
    return self;
}

+ (instancetype)appModelWithDict:(NSDictionary *)dict {
    return [[self alloc] initWithDict:dict];
}
@end

#import "SSViewController.h"
#import "SSAPPModel.h"

@interface SSViewController ()<UITableViewDataSource>

@property (nonatomic, strong) UITableView *tableView;

///数据模型
@property (nonatomic, strong) NSArray<SSAPPModel *> *apps;

///存放所有下载操作的队列
@property (nonatomic, strong) NSOperationQueue *queue;

///存放所有的下载操作（url是key，operation对象是value）
@property (nonatomic, strong) NSMutableDictionary *operations;

///存放所有下载完的图片
@property (nonatomic, strong) NSMutableDictionary *images;

@end

@implementation SSViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self configData];
    [self configSubViews];
}

//初始化数据
- (void)configData {
    // 1.加载plist
    NSString *file = [[NSBundle mainBundle] pathForResource:@"apps" ofType:@"plist"];
    NSArray *dictArray = [NSArray arrayWithContentsOfFile:file];
    
    // 2.字典 --> 模型
    NSMutableArray *appArray = [NSMutableArray array];
    for (NSDictionary *dict in dictArray) {
        SSAPPModel *app = [SSAPPModel appModelWithDict:dict];
        [appArray addObject:app];
    }
    _apps = appArray;
    
    _queue = [[NSOperationQueue alloc] init];
    _operations = [NSMutableDictionary dictionary];
    _images = [NSMutableDictionary dictionary];
}

//初始化View
- (void)configSubViews {
    _tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStylePlain];
    _tableView.dataSource = self;
    [self.view addSubview:_tableView];
}


#pragma mark - UITableViewDataSource

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *identifier = @"cellIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:identifier];
    }
    
    // 取出模型
    SSAPPModel *app = self.apps[indexPath.row];
    
    // 设置基本信息
    cell.textLabel.text = app.name;
    cell.detailTextLabel.text = app.download;
    
    // 先从images缓存中取出图片url对应的UIImage
    UIImage *image = self.images[app.icon];
    if (image) { // 说明图片已经下载成功过（成功缓存）
        cell.imageView.image = image;
    } else { // 说明图片并未下载成功过（并未缓存过）
        // 显示占位图片
        cell.imageView.image = [UIImage imageNamed:@"placeholder"];
        
        // 下载图片
        [self download:app.icon indexPath:indexPath];
    }
    return cell;
}

- (void)download:(NSString *)imageUrl indexPath:(NSIndexPath *)indexPath {
    // 取出当前图片url对应的下载操作（operation对象）
    NSBlockOperation *operation = self.operations[imageUrl];
    if (operation) {// 已经有了operation 不需要创建
        NSLog(@"已经有了operation, return");
        return;
    }
    
    // 创建操作，下载图片
    __weak typeof(self) weakSelf = self;
    operation = [NSBlockOperation blockOperationWithBlock:^{
        //   [NSThread sleepForTimeInterval:1.0];//模拟下载慢操作
        NSURL *url = [NSURL URLWithString:imageUrl];
        NSData *data = [NSData dataWithContentsOfURL:url]; // 下载
        UIImage *image = [UIImage imageWithData:data]; // NSData -> UIImage
        
        // 回到主线程
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            // 存放图片到字典中
            if (image) {
                weakSelf.images[imageUrl] = image;
            }
            
            // 从字典中移除下载操作 (防止operations越来越大，保证下载失败后，能重新下载)
            [weakSelf.operations removeObjectForKey:imageUrl];
            
            // 刷新表格
            [weakSelf.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
        }];
    }];
    NSLog(@"imageUrl == %@", imageUrl);
    // 添加操作到队列中
    [self.queue addOperation:operation];
    
    // 添加到字典中 (这句代码为了解决重复下载)
    self.operations[imageUrl] = operation;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return self.apps.count;
}


#pragma mark - 拖动暂停恢复下载

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    // 暂停下载
    [self.queue setSuspended:YES];
}

//当用户停止拖拽表格时调用
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    // 恢复下载
    [self.queue setSuspended:NO];
}


#pragma mark - 内存警告

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // 移除所有的下载操作缓存
    [self.queue cancelAllOperations];
    [self.operations removeAllObjects];
    // 移除所有的图片缓存
    [self.images removeAllObjects];
}

@end

二、cell下载图片思路 – 有沙盒缓存

应用了沙盒缓存，解决每次打开app都会下载问题。

代码示例

#import "SSViewController.h"
#import "SSAPPModel.h"

@interface SSViewController ()<UITableViewDataSource>

@property (nonatomic, strong) UITableView *tableView;

///数据模型
@property (nonatomic, strong) NSArray<SSAPPModel *> *apps;

///存放所有下载操作的队列
@property (nonatomic, strong) NSOperationQueue *queue;

///存放所有的下载操作（url是key，operation对象是value）
@property (nonatomic, strong) NSMutableDictionary *operations;

///存放所有下载完的图片
@property (nonatomic, strong) NSMutableDictionary *images;

@end

@implementation SSViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self configData];
    [self configSubViews];
}

//初始化数据
- (void)configData {
    // 1.加载plist
    NSString *file = [[NSBundle mainBundle] pathForResource:@"apps" ofType:@"plist"];
    NSArray *dictArray = [NSArray arrayWithContentsOfFile:file];
    
    // 2.字典 --> 模型
    NSMutableArray *appArray = [NSMutableArray array];
    for (NSDictionary *dict in dictArray) {
        SSAPPModel *app = [SSAPPModel appModelWithDict:dict];
        [appArray addObject:app];
    }
    _apps = appArray;
    
    _queue = [[NSOperationQueue alloc] init];
    _operations = [NSMutableDictionary dictionary];
    _images = [NSMutableDictionary dictionary];
}

//初始化View
- (void)configSubViews {
    _tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStylePlain];
    _tableView.dataSource = self;
    [self.view addSubview:_tableView];
}


#pragma mark - UITableViewDataSource

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *identifier = @"cellIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:identifier];
    }
    
    // 取出模型
    SSAPPModel *app = self.apps[indexPath.row];
    
    // 设置基本信息
    cell.textLabel.text = app.name;
    cell.detailTextLabel.text = app.download;
    
    // 先从images缓存中取出图片url对应的UIImage
    UIImage *image = self.images[app.icon];
    if (image) { // 说明图片已经下载成功过（成功缓存）
        cell.imageView.image = image;
    } else { // 说明图片并未下载成功过（并未缓存过）
        NSString *file = [self filePathWithImageUrl:app.icon];
        // 先从沙盒中取出图片
        NSData *data = [NSData dataWithContentsOfFile:file];
        if (data) { // 沙盒中存在这个文件
            cell.imageView.image = [UIImage imageWithData:data];
        } else {// 沙盒中不存在这个文件
            // 显示占位图片
            cell.imageView.image = [UIImage imageNamed:@"placeholder"];
            
            // 下载图片
            [self download:app.icon indexPath:indexPath];
        }
    }
    return cell;
}

- (void)download:(NSString *)imageUrl indexPath:(NSIndexPath *)indexPath {
    // 取出当前图片url对应的下载操作（operation对象）
    NSBlockOperation *operation = self.operations[imageUrl];
    if (operation) {// 已经有了operation 不需要创建
        NSLog(@"已经有了operation, return");
        return;
    }
    
    // 创建操作，下载图片
    __weak typeof(self) weakSelf = self;
    operation = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:3.0];//模拟下载慢操作
        NSURL *url = [NSURL URLWithString:imageUrl];
        NSData *data = [NSData dataWithContentsOfURL:url]; // 下载
        UIImage *image = [UIImage imageWithData:data]; // NSData -> UIImage
        
        // 回到主线程
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            // 存放图片到字典中
            if (image) {
                weakSelf.images[imageUrl] = image;
            }
            
            //将图片存入沙盒中
            // UIImage --> NSData --> File（文件）
            NSData *data = UIImagePNGRepresentation(image);
            NSString *file = [self filePathWithImageUrl:imageUrl];
            [data writeToFile:file atomically:YES];
            
            // 从字典中移除下载操作 (防止operations越来越大，保证下载失败后，能重新下载)
            [weakSelf.operations removeObjectForKey:imageUrl];
            
            // 刷新表格
            [weakSelf.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
        }];
    }];
    NSLog(@"imageUrl == %@", imageUrl);
    // 添加操作到队列中
    [self.queue addOperation:operation];
    
    // 添加到字典中 (这句代码为了解决重复下载)
    self.operations[imageUrl] = operation;
}

- (NSInteger)tableView:(nonnull UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return self.apps.count;
}


#pragma mark - 拖动暂停恢复下载

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    // 暂停下载
    [self.queue setSuspended:YES];
}

//当用户停止拖拽表格时调用
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    // 恢复下载
    [self.queue setSuspended:NO];
}


#pragma mark - 内存警告

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // 移除所有的下载操作缓存
    [self.queue cancelAllOperations];
    [self.operations removeAllObjects];
    // 移除所有的图片缓存
    [self.images removeAllObjects];
}


#pragma mark - 沙盒图片路径

- (NSString *)filePathWithImageUrl:(NSString *)imageUrl {
    NSString *cacheDir = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *path = [cacheDir stringByAppendingPathComponent:[imageUrl lastPathComponent]];
    return path;
}


@end

沙盒中图片

三、自定义NSOperation

自定义NSOperation的步骤

重写- (void)main方法，在里面实现想执行的任务
重写- (void)main方法的注意点
自己创建自动释放池（因为如果是异步操作，无法访问主线程的自动释放池）
经常通过- (BOOL)isCancelled方法检测操作是否被取消，对取消做出响应

代码示例

#import <UIKit/UIKit.h>

@class SSDownloadOperation;

@protocol SSDownloadOperationDelegate <NSObject>

@optional
- (void)downloadOperation:(SSDownloadOperation *)operation didFinishDownload:(UIImage *)image;
@end

@interface SSDownloadOperation : NSOperation
@property (nonatomic, copy) NSString *imageUrl;
@property (nonatomic, strong) NSIndexPath *indexPath;
@property (nonatomic, weak) id<SSDownloadOperationDelegate> delegate;

@end

#import "SSDownloadOperation.h"

@implementation SSDownloadOperation

- (void)main {
    @autoreleasepool {
        if (self.isCancelled) {
            return;
        }
        
        NSURL *url = [NSURL URLWithString:self.imageUrl];
        NSData *data = [NSData dataWithContentsOfURL:url]; // 下载
        UIImage *image = [UIImage imageWithData:data]; // NSData -> UIImage
        
        if (self.isCancelled) return;
        
        // 回到主线程
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            if ([self.delegate respondsToSelector:@selector(downloadOperation:didFinishDownload:)]) {
                [self.delegate downloadOperation:self didFinishDownload:image];
            }
        }];
    }
}
@end

#import "SSViewController.h"
#import "SSAPPModel.h"
#import "SSDownloadOperation.h"

@interface SSViewController ()<UITableViewDataSource, SSDownloadOperationDelegate>

@property (nonatomic, strong) UITableView *tableView;

///数据模型
@property (nonatomic, strong) NSArray<SSAPPModel *> *apps;

///存放所有下载操作的队列
@property (nonatomic, strong) NSOperationQueue *queue;

///存放所有的下载操作（url是key，operation对象是value）
@property (nonatomic, strong) NSMutableDictionary *operations;

///存放所有下载完的图片
@property (nonatomic, strong) NSMutableDictionary *images;

@end

@implementation SSViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self configData];
    [self configSubViews];
}

//初始化数据
- (void)configData {
    // 1.加载plist
    NSString *file = [[NSBundle mainBundle] pathForResource:@"apps" ofType:@"plist"];
    NSArray *dictArray = [NSArray arrayWithContentsOfFile:file];
    
    // 2.字典 --> 模型
    NSMutableArray *appArray = [NSMutableArray array];
    for (NSDictionary *dict in dictArray) {
        SSAPPModel *app = [SSAPPModel appModelWithDict:dict];
        [appArray addObject:app];
    }
    _apps = appArray;
    
    _queue = [[NSOperationQueue alloc] init];
    _operations = [NSMutableDictionary dictionary];
    _images = [NSMutableDictionary dictionary];
}

//初始化View
- (void)configSubViews {
    _tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStylePlain];
    _tableView.dataSource = self;
    [self.view addSubview:_tableView];
}


#pragma mark - UITableViewDataSource

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *identifier = @"cellIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:identifier];
    }
    
    // 取出模型
    SSAPPModel *app = self.apps[indexPath.row];
    
    // 设置基本信息
    cell.textLabel.text = app.name;
    cell.detailTextLabel.text = app.download;
    
    // 先从images缓存中取出图片url对应的UIImage
    UIImage *image = self.images[app.icon];
    if (image) { // 说明图片已经下载成功过（成功缓存）
        cell.imageView.image = image;
    } else { // 说明图片并未下载成功过（并未缓存过）
        NSString *file = [self filePathWithImageUrl:app.icon];
        // 先从沙盒中取出图片
        NSData *data = [NSData dataWithContentsOfFile:file];
        if (data) { // 沙盒中存在这个文件
            cell.imageView.image = [UIImage imageWithData:data];
        } else {// 沙盒中不存在这个文件
            // 显示占位图片
            cell.imageView.image = [UIImage imageNamed:@"placeholder"];
            
            // 下载图片
            [self download:app.icon indexPath:indexPath];
        }
    }
    return cell;
}

- (void)download:(NSString *)imageUrl indexPath:(NSIndexPath *)indexPath {
    // 取出当前图片url对应的下载操作（operation对象）
    SSDownloadOperation *operation = self.operations[imageUrl];
    if (operation) {// 已经有了operation 不需要创建
        NSLog(@"已经有了operation, return");
        return;
    }
    
    // 创建操作，下载图片
    operation = [[SSDownloadOperation alloc] init];
    operation.imageUrl = imageUrl;
    operation.indexPath = indexPath;
    
    // 设置代理
    operation.delegate = self;
    
    // 添加操作到队列中
    [self.queue addOperation:operation];
    
    // 添加到字典中 (这句代码为了解决重复下载)
    self.operations[imageUrl] = operation;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return self.apps.count;
}


#pragma mark - SSDownloadOperationDelegate下载操作的代理方法

- (void)downloadOperation:(SSDownloadOperation *)operation didFinishDownload:(UIImage *)image {
    // 存放图片到字典中
    if (image) {
        self.images[operation.imageUrl] = image;
        //将图片存入沙盒中
        NSData *data = UIImagePNGRepresentation(image);
        [data writeToFile:[self filePathWithImageUrl:operation.imageUrl] atomically:YES];
    }
    
    // 从字典中移除下载操作 (防止operations越来越大，保证下载失败后，能重新下载)
    [self.operations removeObjectForKey:operation.imageUrl];
    
    // 刷新表格
    [self.tableView reloadRowsAtIndexPaths:@[operation.indexPath] withRowAnimation:UITableViewRowAnimationNone];
}


#pragma mark - 拖动暂停恢复下载

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    // 暂停下载
    [self.queue setSuspended:YES];
}

//当用户停止拖拽表格时调用
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    // 恢复下载
    [self.queue setSuspended:NO];
}


#pragma mark - 内存警告

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // 移除所有的下载操作缓存
    [self.queue cancelAllOperations];
    [self.operations removeAllObjects];
    // 移除所有的图片缓存
    [self.images removeAllObjects];
}


#pragma mark - 沙盒图片路径

- (NSString *)filePathWithImageUrl:(NSString *)imageUrl {
    NSString *cacheDir = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *path = [cacheDir stringByAppendingPathComponent:[imageUrl lastPathComponent]];
    return path;
}

@end

附件

效果图

placeholder.png

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
    <dict>
        <key>name</key>
        <string>植物大战僵尸</string>
        <key>icon</key>
        <string>http://p16.qhimg.com/dr/48_48_/t0125e8d438ae9d2fbb.png</string>
        <key>download</key>
        <string>10311万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>捕鱼达人2</string>
        <key>icon</key>
        <string>http://p19.qhimg.com/dr/48_48_/t0101e2931181bb540d.png</string>
        <key>download</key>
        <string>9982万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>保卫萝卜</string>
        <key>icon</key>
        <string>http://p17.qhimg.com/dr/48_48_/t012d281e8ec8e27c06.png</string>
        <key>download</key>
        <string>8582万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>找你妹</string>
        <key>icon</key>
        <string>http://p18.qhimg.com/dr/48_48_/t0184f949337481f071.png</string>
        <key>download</key>
        <string>5910万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>水果忍者</string>
        <key>icon</key>
        <string>http://p17.qhimg.com/dr/48_48_/t015f10076f95e27e74.png</string>
        <key>download</key>
        <string>5082万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>鳄鱼小顽皮</string>
        <key>icon</key>
        <string>http://p16.qhimg.com/dr/48_48_/t01885f5596e1d30172.png</string>
        <key>download</key>
        <string>3918万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>神偷奶爸</string>
        <key>icon</key>
        <string>http://p19.qhimg.com/dr/48_48_/t0164ad383c622aabef.png</string>
        <key>download</key>
        <string>3681万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>时空猎人</string>
        <key>icon</key>
        <string>http://p17.qhimg.com/dr/48_48_/t017bc3cfcf3981b197.png</string>
        <key>download</key>
        <string>3645万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>愤怒的小鸟</string>
        <key>icon</key>
        <string>http://p18.qhimg.com/dr/48_48_/t012fea7312194537c2.png</string>
        <key>download</key>
        <string>3552万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>滑雪大冒险</string>
        <key>icon</key>
        <string>http://p18.qhimg.com/dr/48_48_/t01e61cbba53fb9eb82.png</string>
        <key>download</key>
        <string>3487万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>爸爸去哪儿</string>
        <key>icon</key>
        <string>http://p18.qhimg.com/dr/48_48_/t0108c33d3321352682.png</string>
        <key>download</key>
        <string>3117万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>我叫MT </string>
        <key>icon</key>
        <string>http://p17.qhimg.com/dr/48_48_/t01077fd80ffb5c8740.png</string>
        <key>download</key>
        <string>2386万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>3D终极狂飙</string>
        <key>icon</key>
        <string>http://p17.qhimg.com/dr/48_48_/t01f55acd4a3ed024eb.png</string>
        <key>download</key>
        <string>2166万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>杀手2</string>
        <key>icon</key>
        <string>http://p16.qhimg.com/dr/48_48_/t018f89d6e0922f75a1.png</string>
        <key>download</key>
        <string>1951万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>俄罗斯方块</string>
        <key>icon</key>
        <string>http://p0.qhimg.com/dr/48_48_/t0183a670f1dbff380f.png</string>
        <key>download</key>
        <string>1290万</string>
    </dict>
    <dict>
        <key>name</key>
        <string>刀塔传奇</string>
        <key>icon</key>
        <string>http://p16.qhimg.com/dr/48_48_/t01c3f62a27c3de7af5.png</string>
        <key>download</key>
        <string>1249万</string>
    </dict>
</array>
</plist>

iOS多线程-自定义NSOperation(Cell下载图片缓存

一、cell下载图片思路 – 无沙盒(内存)缓存

二、cell下载图片思路 – 有沙盒缓存

三、自定义NSOperation

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