iOS多线程实现多图下载功能

// XMGAPP.h 
 
#import <Foundation/Foundation.h> 
 
@interface XMGAPP : NSObject 
 
/** APP的名称 */ 
@property (nonatomic, strong) NSString *name; 
/** APP的图片的url地址 */ 
@property (nonatomic, strong) NSString *icon; 
/** APP的下载量 */ 
@property (nonatomic, strong) NSString *download; 
 
 (instancetype)appWithDict:(NSDictionary *)dict; 
@end 

// XMGAPP.m 
 
#import "XMGAPP.h" 
 
@implementation XMGAPP 
 
 (instancetype)appWithDict:(NSDictionary *)dict 
{ 
  XMGAPP *appM = [[XMGAPP alloc]init]; 
  //KVC 
  [appM setValuesForKeysWithDictionary:dict]; 
   
  return appM; 
} 
@end 

// ViewController.m 
 
#import "ViewController.h" 
#import "XMGAPP.h" 
 
@interface ViewController () 
/** tableView的数据源 */ 
@property (nonatomic, strong) NSArray *apps; 
/** 内存缓存 */ 
@property (nonatomic, strong) NSMutableDictionary *images; 
/** 队列 */ 
@property (nonatomic, strong) NSOperationQueue *queue; 
/** 操作缓存 */ 
@property (nonatomic, strong) NSMutableDictionary *operations; 
@end 
 
@implementation ViewController 
 
#pragma mark ---------------------- 
#pragma mark lazy loading 
-(NSOperationQueue *)queue 
{ 
  if (_queue == nil) { 
    _queue = [[NSOperationQueue alloc]init]; 
    //设置最大并发数 
    _queue.maxConcurrentOperationCount = 5; 
  } 
  return _queue; 
} 
-(NSMutableDictionary *)images 
{ 
  if (_images == nil) { 
    _images = [NSMutableDictionary dictionary]; 
  } 
  return _images; 
} 
-(NSArray *)apps 
{ 
  if (_apps == nil) { 
     
    //字典数组 
    NSArray *arrayM = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle]pathForResource:@"apps.plist" ofType:nil]]; 
     
    //字典数组---->模型数组 
    NSMutableArray *arrM = [NSMutableArray array]; 
    for (NSDictionary *dict in arrayM) { 
      [arrM addObject:[XMGAPP appWithDict:dict]]; 
    } 
    _apps = arrM; 
  } 
  return _apps; 
} 
 
-(NSMutableDictionary *)operations 
{ 
  if (_operations == nil) { 
    _operations = [NSMutableDictionary dictionary]; 
  } 
  return _operations; 
} 
 
#pragma mark ---------------------- 
#pragma mark UITableViewDatasource 
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView 
{ 
  return 1; 
} 
 
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{ 
  return self.apps.count; 
} 
 
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
  static NSString *ID = @"app"; 
   
  //1.创建cell 
  UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID]; 
   
  //2.设置cell的数据 
  //2.1 拿到该行cell对应的数据 
  XMGAPP *appM = self.apps[indexPath.row]; 
   
  //2.2 设置标题 
  cell.textLabel.text = appM.name; 
   
  //2.3 设置子标题 
  cell.detailTextLabel.text = appM.download; 
   
  //2.4 设置图标 
   
  //先去查看内存缓存中该图片时候已经存在,如果存在那么久直接拿来用,否则去检查磁盘缓存 
  //如果有磁盘缓存,那么保存一份到内存,设置图片,否则就直接下载 
  //1)没有下载过 
  //2)重新打开程序 
   
  UIImage *image = [self.images objectForKey:appM.icon]; 
  if (image) { 
    cell.imageView.image = image; 
    NSLog(@"%zd处的图片使用了内存缓存中的图片",indexPath.row) ; 
  }else 
  { 
    //保存图片到沙盒缓存 
    NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject]; 
    //获得图片的名称,不能包含/ 
    NSString *fileName = [appM.icon lastPathComponent]; 
    //拼接图片的全路径 
    NSString *fullPath = [caches stringByAppendingPathComponent:fileName]; 
     
     
    //检查磁盘缓存 
    NSData *imageData = [NSData dataWithContentsOfFile:fullPath]; 
    //废除 
    imageData = nil; 
     
    if (imageData) { 
      UIImage *image = [UIImage imageWithData:imageData]; 
      cell.imageView.image = image; 
       
      NSLog(@"%zd处的图片使用了磁盘缓存中的图片",indexPath.row) ; 
      //把图片保存到内存缓存 
      [self.images setObject:image forKey:appM.icon]; 
       
//      NSLog(@"%@",fullPath); 
    }else 
    { 
      //检查该图片时候正在下载,如果是那么久什么都捕捉,否则再添加下载任务 
      NSBlockOperation *download = [self.operations objectForKey:appM.icon]; 
      if (download) { 
         
      }else 
      { 
         
        //先清空cell原来的图片 
        cell.imageView.image = [UIImage imageNamed:@"Snip20160221_306"]; 
         
        download = [NSBlockOperation blockOperationWithBlock:^{ 
          NSURL *url = [NSURL URLWithString:appM.icon]; 
          NSData *imageData = [NSData dataWithContentsOfURL:url]; 
          UIImage *image = [UIImage imageWithData:imageData]; 
           
           NSLog(@"%zd--下载---",indexPath.row); 
           
          //容错处理 
          if (image == nil) { 
            [self.operations removeObjectForKey:appM.icon]; 
            return ; 
          } 
          //演示网速慢的情况 
          //[NSThread sleepForTimeInterval:3.0]; 
         
          //把图片保存到内存缓存 
          [self.images setObject:image forKey:appM.icon]; 
           
          //NSLog(@"Download---%@",[NSThread currentThread]); 
          //线程间通信 
          [[NSOperationQueue mainQueue] addOperationWithBlock:^{ 
             
            //cell.imageView.image = image; 
            //刷新一行 
            [self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationLeft]; 
            //NSLog(@"UI---%@",[NSThread currentThread]); 
          }]; 
           
           
          //写数据到沙盒 
          [imageData writeToFile:fullPath atomically:YES]; 
           
          //移除图片的下载操作 
          [self.operations removeObjectForKey:appM.icon]; 
           
        }]; 
         
        //添加操作到操作缓存中 
        [self.operations setObject:download forKey:appM.icon]; 
         
        //添加操作到队列中 
        [self.queue addOperation:download]; 
      } 
       
    } 
  } 
   
  //3.返回cell 
  return cell; 
} 
 
-(void)didReceiveMemoryWarning 
{ 
  [self.images removeAllObjects]; 
   
  //取消队列中所有的操作 
  [self.queue cancelAllOperations]; 
} 
 
//1.UI很不流畅 --- > 开子线程下载图片 
//2.图片重复下载 ---> 先把之前已经下载的图片保存起来(字典) 
//内存缓存--->磁盘缓存 
 
//3.图片不会刷新--->刷新某行 
//4.图片重复下载(图片下载需要时间,当图片还未完全下载之前,又要重新显示该图片) 
//5.数据错乱 ---设置占位图片 
 
/* 
 Documents:会备份,不允许 
 Libray 
  Preferences:偏好设置 保存账号 
  caches:缓存文件 
 tmp:临时路径(随时会被删除) 
 */ 
 
@end