iOS 多线程编程<十三、NSOperation图片下载，SDWebImage底层实现原理>

NSOperation图片下载，SDWebImage底层实现原理

//
//  ViewController.m
//  DownLoadImage
//
//  Created by fe on 2016/10/21.
//  Copyright © 2016年 fe. All rights reserved.
//

#import "ViewController.h"
#import "DownloadModel.h"
@interface ViewController ()
@property (nonatomic,strong) NSArray *sourceArray;//数据源数组
@property (nonatomic,strong) NSMutableDictionary *bufferMemonry;//图片内存缓存
@property (nonatomic,strong) NSOperationQueue *operationQueue;//下载图片的队列
@property (nonatomic,strong) NSMutableDictionary *operationMemonry;//操作缓存，避免重复添加操作
@end

@implementation ViewController
- (NSArray *)sourceArray
{
if (!_sourceArray) {
NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"SourceList.plist" ofType:nil];
NSArray *dicArray = [NSArray arrayWithContentsOfFile:plistPath];
NSMutableArray *objectArray = [NSMutableArray array];
for (NSDictionary *dic in dicArray) {
DownloadModel *sourceModel = [DownloadModel downloadModelWithDic:dic];
[objectArray addObject:sourceModel];
}
_sourceArray = objectArray;
}
return _sourceArray;
}
- (NSOperationQueue *)operationQueue
{
if (!_operationQueue) {
_operationQueue = [[NSOperationQueue alloc] init];
_operationQueue.maxConcurrentOperationCount = 5;
}
return _operationQueue;
}
//懒加载方式创建内存缓存字典
- (NSMutableDictionary *)bufferMemonry
{
if (!_bufferMemonry) {
_bufferMemonry = [[NSMutableDictionary alloc] init];
}
return _bufferMemonry;
}
- (NSMutableDictionary *)operationMemonry
{
if (!_operationMemonry) {
_operationMemonry = [[NSMutableDictionary alloc] init];
}
return _operationMemonry;
}
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return self.sourceArray.count;
}
/*
要显示图片的时候，首先去内存中查看是否存在，如果存在，直接拿来用，
如果不存在，去沙河里面找，如果沙河里面存在，直接拿来用，并且保存一份到内存。
如果沙河里面不存在，下载图片，并且保存一份到内存，再保存一份到沙河。
*/
/*
Documents:存在该文件夹下的数据会备份，不能把下载的文件存放在该文件夹下，
如果把下载的文件存放在该文件夹下，苹果会拒绝你的产品上架
Library:
cache:用于保存下载的文件
perference:存储偏好设置，和一些设备信息
tmp:临时文件夹
*/
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *reuseIdentifier = @"downloadImage";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseIdentifier];
DownloadModel *sourceModel = self.sourceArray[indexPath.row];
//先判断缓存中是否已经有这张图片
UIImage *image = [self.bufferMemonry objectForKey:sourceModel.icon];
if (image)
{
cell.imageView.image = [self.bufferMemonry objectForKey:sourceModel.icon];
}else//如果缓存中没有，去沙河中看看是否存在
{
//获取cache路径
NSString *cache = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject];
//获取图片后缀名
NSString *imagePath = [sourceModel.icon lastPathComponent];
//拼接全路径
NSString *fullPath = [cache stringByAppendingPathComponent:imagePath];
NSData *data = [NSData dataWithContentsOfFile:fullPath];
UIImage *image =[UIImage imageWithData:data];
if (image)
{
cell.imageView.image = image;
[self.bufferMemonry setObject:image forKey:sourceModel.icon];
}else//如果缓存和沙河中都没有，则从服务端下载图片
{
//下载之前先判断操作队列里是否已经存在操作任务，如果不存在再添加任务
NSOperation *operation = self.operationMemonry[sourceModel.icon];
if (operation == nil) {
NSBlockOperation *download = [NSBlockOperation blockOperationWithBlock:^{
NSURL *url = [NSURL URLWithString:sourceModel.icon];
NSData *imageData = [NSData dataWithContentsOfURL:url];
if (imageData == nil) {
[self.operationMemonry removeObjectForKey:sourceModel.icon];
return ;
}
UIImage *image = [UIImage imageWithData:imageData];
//如果图片存在把图片写入缓存,保存到沙河
if (image)
{

[self.bufferMemonry setObject:image forKey:sourceModel.icon];
[imageData writeToFile:fullPath atomically:YES];
}
//回到主线程刷新UI
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
//cell.imageView.image = image;
//只刷新对应的行，提高tableview的性能
[tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
}];

[self.operationMemonry removeObjectForKey:sourceModel.icon];
}];
[self.operationQueue addOperation:download];
[self.operationMemonry setObject:download forKey:sourceModel.icon];
}

}

}

cell.textLabel.text = sourceModel.title;
cell.detailTextLabel.text = sourceModel.subTitle;
return cell;
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end