IOS 自定义Operation(下载功能)

 一个下载操作就交给一个HMDownloadOperation对象

HMDownloadOperation.h / .m

@class HMDownloadOperation;

@protocol HMDownloadOperationDelegate <NSObject>
@optional
- (void)downloadOperation:(HMDownloadOperation *)operation didFinishDownload:(UIImage *)image;
@end

@interface HMDownloadOperation : NSOperation
@property (nonatomic, copy) NSString *url;
@property (nonatomic, strong) NSIndexPath *indexPath;
@property (nonatomic, weak) id<HMDownloadOperationDelegate> delegate;
@end

#import "HMDownloadOperation.h"

@implementation HMDownloadOperation

/**
 *  在main方法中实现具体操作
 */
- (void)main
{
    @autoreleasepool {
        
        NSURL *downloadUrl = [NSURL URLWithString:self.url];
        NSData *data = [NSData dataWithContentsOfURL:downloadUrl]; // 这行会比较耗时
        UIImage *image = [UIImage imageWithData:data];

        if ([self.delegate respondsToSelector:@selector(downloadOperation:didFinishDownload:)]) {
            dispatch_async(dispatch_get_main_queue(), ^{ // 回到主线程, 传递图片数据给代理对象
                [self.delegate downloadOperation:self didFinishDownload:image];
            });
        }
    }
}

控制器View 调用

@interface HMViewController () <HMDownloadOperationDelegate>
@property (nonatomic, strong) NSArray *apps;
@property (nonatomic, strong) NSOperationQueue *queue;
/** key:url value:operation对象 */
@property (nonatomic, strong) NSMutableDictionary *operations;

/** key:url value:image对象*/
@property (nonatomic, strong) NSMutableDictionary *images;
@end

@implementation HMViewController

- (NSArray *)apps
{
    if (!_apps) {
        NSArray *dictArray = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"apps.plist" ofType:nil]];
        
        NSMutableArray *appArray = [NSMutableArray array];
        for (NSDictionary *dict in dictArray) {
            HMApp *app = [HMApp appWithDict:dict];
            [appArray addObject:app];
        }
        _apps = appArray;
    }
    return _apps;
}

- (NSOperationQueue *)queue
{
    if (!_queue) {
        _queue = [[NSOperationQueue alloc] init];
        _queue.maxConcurrentOperationCount = 3; // 最大并发数 == 3
    }
    return _queue;
}

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

- (NSMutableDictionary *)images
{
    if (!_images) {
        _images = [NSMutableDictionary dictionary];
    }
    return _images;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
}

#pragma mark - 数据源方法
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return self.apps.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *ID = @"app";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:ID];
    }
    
    HMApp *app = self.apps[indexPath.row];
    cell.textLabel.text = app.name;
    cell.detailTextLabel.text = app.download;
    
    // 显示图片
    // 保证一个url对应一个HMDownloadOperation
    // 保证一个url对应UIImage对象
    
    UIImage *image = self.images[app.icon];
    if (image) { // 缓存中有图片
        cell.imageView.image = image;
    } else { // 缓存中没有图片, 得下载
        cell.imageView.image = [UIImage imageNamed:@"57437179_42489b0"];
        
        HMDownloadOperation *operation = self.operations[app.icon];
        if (operation) { // 正在下载
            // ... 暂时不需要做其他事
            
        } else { // 没有正在下载
            // 创建操作
            operation = [[HMDownloadOperation alloc] init];
            operation.url = app.icon;
            operation.delegate = self;
            operation.indexPath = indexPath;
            [self.queue addOperation:operation]; // 异步下载
            
            self.operations[app.icon] = operation;
        }
    }
    
    // SDWebImage : 专门用来下载图片
    return cell;
}

#pragma mark - HMDownloadOperationDelegate
- (void)downloadOperation:(HMDownloadOperation *)operation didFinishDownload:(UIImage *)image
{
    // 1.移除执行完毕的操作
    [self.operations removeObjectForKey:operation.url];
    
    if (image) {
        // 2.将图片放到缓存中(images)
        self.images[operation.url] = image;
        
        // 3.刷新表格
        [self.tableView reloadRowsAtIndexPaths:@[operation.indexPath] withRowAnimation:UITableViewRowAnimationNone];
        
        // 3.将图片写入沙盒
//        NSData *data = UIImagePNGRepresentation(image);
//        [data writeToFile:@"" atomically:<#(BOOL)#>];
    }
    
}

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    // 开始拖拽
    // 暂停队列
    [self.queue setSuspended:YES];
}

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
    [self.queue setSuspended:NO];
}

@end