iOS多线程-NSOperation简单语法

//1)封装操作2)把操作添加到队列中

    [queue addOperationWithBlock:^{
       NSLog(@"7----%@",[NSThreadcurrentThread]);
    }];

#import "ViewController.h"
#import "appItem.h"
@interface ViewController ()
//保存app模型数组
@property (nonatomic, strong) NSMutableArray *appArr;
//内存缓存
@property (nonatomic, strong) NSMutableDictionary *imageDict;
//队列数组
@property (nonatomic, strong) NSMutableDictionary *operationDict;
@end

@implementation ViewController
- (NSMutableDictionary *)imageDict{
    if (_imageDict == nil) {
        _imageDict = [NSMutableDictionary dictionary];
    }
    return _imageDict;
}
- (NSMutableDictionary *)operationDict{
    if (_operationDict == nil) {
        _operationDict = [NSMutableDictionary dictionary];
    }
    return _operationDict;
}
- (NSMutableArray *)appArr{
    if (_appArr == nil) {
        NSMutableArray *models = [NSMutableArray array];
        NSString *str = [[NSBundle mainBundle] pathForResource:@"apps.plist" ofType:nil];
        NSArray *arrDict = [NSArray arrayWithContentsOfFile:str];
        for (NSDictionary *dict in arrDict) {
            appItem *app = [appItem appItemWithDict:dict];
            [models addObject:app];
        }
        _appArr = [models copy];
    }
    return _appArr;
}
#pragma mark - 数据源方法
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return self.appArr.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *ID = @"app";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
    
    appItem *app = self.appArr[indexPath.row];
    cell.textLabel.text = app.name;
    cell.detailTextLabel.text = app.download;
    
    //从内存中去
    UIImage *image = [self.imageDict objectForKey:app.icon];
    if (image) { //如果图片存在内存中
        cell.imageView.image = image;
        NSLog(@"内存中取%i",indexPath.row);
    }else{
        NSData *data = [NSData dataWithContentsOfFile:[self getFullPath:app.icon]];
        data = nil;
        if (data) { //如果图片存在沙盒中
            //沙盒的图片数据转换成图片
            UIImage *image = [UIImage imageWithData:data];
            cell.imageView.image = image;
            //保存一份到内存
            [self.imageDict setObject:image forKey:app.icon];
        }else{
            //下载的时候还没下载完用占位图片显示
            cell.imageView.image = [UIImage imageNamed:@"屏幕快照"];
            //取出操作
            NSOperation *operation = [self.operationDict objectForKey:app.icon];
            if (operation) { //已有下载操作
                //什么都不干
                NSLog(@"%i已在下载", indexPath.row);
            }else{
                NSOperationQueue *queue = [[NSOperationQueue alloc] init];
                NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
                    [NSThread sleepForTimeInterval:2];
                    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]];
                    UIImage *image = [UIImage imageWithData:data];
                    cell.imageView.image = image;
                    
                    //如果图片的链接是错的情况
                    if (image == nil) {
                        //取消队列中的操作
                        [self.operationDict removeObjectForKey:app.icon];
                        return;
                    }
                    
                    //保存到内存中
                    [self.imageDict setObject:image forKey:app.icon];
                    //保存到沙盒
                    NSString *fullPath = [self getFullPath:app.icon];
                    //写入
                    [data writeToFile:fullPath atomically:YES];
                    NSLog(@"下载%i",indexPath.row);
                    
                    //回到主线程刷新ui
                    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                        [tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationTop];
                    }];
                    
                    //下载完毕后要移除下载操作
                    [self.operationDict removeObjectForKey:app.icon];
                }];
                
                [queue addOperation:operation];
                //保存操作进队列数组
                [self.operationDict setObject:operation forKey:app.icon];
            }            
        }
    }
    return cell;
}
//获得全路径
- (NSString *)getFullPath:(NSString *)urlName{
    NSString *cache = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).lastObject;
    //获得文件名称
    NSString *name = [urlName lastPathComponent];
    //拼接文件全路径
    NSString *fullPath = [cache stringByAppendingPathComponent:name];
    return  fullPath;
}