2016 - 1- 19 利用多线程优化从网上加载图片的Demo

//
//  ZZTableViewController.m
//  多图片下载
//
//  Created by Mac on 16/1/19.
//  Copyright © 2016年 Mac. All rights reserved.
//

#import "ZZTableViewController.h"
#import "ZZApp.h"
@interface ZZTableViewController ()
// 用来存放模型
@property (nonatomic, strong) NSArray *apps;

@property (nonatomic, strong) NSMutableDictionary *iconDic;

// 用于存放下载操作
@property (nonatomic, strong) NSMutableDictionary *operations;

@property (nonatomic, strong) NSOperationQueue *queue;

@end

@implementation ZZTableViewController

- (NSOperationQueue *)queue
{
    if (!_queue) {
        _queue = [[NSOperationQueue alloc] init];

    }
    return _queue;
}

- (NSMutableDictionary *)operations
{
    if (!_operations) {
        _operations = [NSMutableDictionary dictionary];

    }
    return _operations;
}

- (NSMutableDictionary *)iconDic{
    if (!_iconDic) {
         _iconDic = [NSMutableDictionary dictionary];
    }
    return _iconDic;
}

- (NSArray *)apps
{
    if (!_apps) {
         NSMutableArray *tmpArray = [NSMutableArray array];

         NSString *path = [[NSBundle mainBundle] pathForResource:@"apps.plist" ofType:nil];

         NSArray *dicArray = [NSArray arrayWithContentsOfFile:path];

         for (NSDictionary *dic in dicArray) {
                ZZApp *app = [ZZApp appWithdic:dic];
                [tmpArray addObject:app];
         }
        _apps = tmpArray;
    }
    return _apps;
}

- (void)viewDidLoad {
    [super viewDidLoad];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
//#warning Incomplete implementation, return the number of sections
    return ;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
#warning Incomplete implementation, return the number of rows
    return self.apps.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
        static NSString *ID = @"app";
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
        ZZApp *app = self.apps[indexPath.row];
        cell.textLabel.text = app.name;
        cell.detailTextLabel.text = app.download;
        UIImage *image =  self.iconDic[app.icon];

        if (image) {// 先判断内存中有没有图片
            cell.imageView.image = image;
        }else{
            NSString *cachePath =  [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
            // 获得文件名
            NSString *fileName = [app.icon lastPathComponent];
            // 计算出文件全路径
            NSString *file = [cachePath stringByAppendingString:fileName];
            // 加载沙盒数据
            NSData *data = [NSData dataWithContentsOfFile:file];
            // 判断沙盒里有没有数据

            if (data) {// 沙盒中有数据

                    cell.imageView.image = [UIImage imageWithData:data];
//                    cell.imageView.image =
                    // 把数据加载到内存里
                    [self.iconDic setObject:cell.imageView.image forKey:app.icon];

            }else{// 下载图片
//                    cell.imageView.image = [UIImage imageNamed:@"屏幕快照 2016-01-19 下午9.54.43"];
                // 添加下载操作到字典里
                    NSOperation *operation =  [self.operations objectForKey:app.icon];
                    if (!operation) {
                       operation = [NSBlockOperation blockOperationWithBlock:^{
                           NSURL *url = [NSURL URLWithString:app.icon];
                           NSData *data = [NSData  dataWithContentsOfURL:url];
                           if (!data) {// 如果下载失败，移除字典里的操作
                               [self.operations removeObjectForKey:app.icon];
                               return ;
                           }

                            // 回到主线程显示图片
                           [[NSOperationQueue mainQueue] addOperationWithBlock:^{
//                               cell.imageView.image = [UIImage imageWithData:data];
                               [tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
                           }];

                            // 放到沙盒里
                           [data writeToFile:file atomically:YES];

                           // 将图片存到缓存中
                           [self.iconDic setObject:[UIImage imageWithData:data] forKey:app.icon];

                           // 下载完成，移除操作
                           [self.operations removeObjectForKey:app.icon];

                        }];
                        // 添加到队列里面去
                        [self.queue addOperation:operation];
                        // 添加到操作字典里去
                        [self.operations setObject:operation forKey:app.icon];
                }
            }
        }
    return cell;
}

@end

效果：

1.第一次打开从网络上加载时：

2.第二次打开时，从沙盒中加载：