iOS 批量下载多张图片,保持原始顺序

经常会遇到这样的应用场景,例如在调用iOS系统分享功能前(UIActivityViewController),需要将所有的图片事先准备好,但是图片都在网络上.
这时,就需要先将图片都下载好后再进行调用.
可能是这个功能的实现太简单了,所以像SDWebImage,AFNetwork等都没有提供可以直接调用的API方法.
所以只好花了2秒钟自己写了一个方法;

#import "ImagesDownloadManager.h"
#import "SDWebImageDownloader.h"

@implementation ImagesDownloadManager

/**
 批量下载图片
 保持顺序;
 全部下载完成后才进行回调;
 回调结果中,下载正确和失败的状态保持与原先一致的顺序;
 
 @return resultArray 中包含两类对象:UIImage , NSError
 */
+ (void)downloadImages:(NSArray<NSString *> *)imgsArray completion:(void(^)(NSArray *resultArray))completionBlock {
    SDWebImageDownloader *manager = [SDWebImageDownloader sharedDownloader];
    manager.downloadTimeout = 20;
    __block NSMutableDictionary *resultDict = [NSMutableDictionary new];
    for(int i=0;i<imgsArray.count;i++) {
        NSString *imgUrl = [imgsArray objectAtIndex:i];
        [manager downloadImageWithURL:[NSURL URLWithString:imgUrl]
                              options:SDWebImageDownloaderUseNSURLCache|SDWebImageDownloaderScaleDownLargeImages
                             progress:^(NSInteger receivedSize, NSInteger expectedSize, NSURL * _Nullable targetURL) {
                                 
                             } completed:^(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, BOOL finished) {
                                 if(finished){
                                     if(error){
                                        //在对应的位置放一个error对象
                                         [resultDict setObject:error forKey:@(i)];
                                     }else{
                                         [resultDict setObject:image forKey:@(i)];
                                     }
                                     if(resultDict.count == imgsArray.count) {
                                         //全部下载完成
                                         NSArray *resultArray = [ImagesDownloadManager createDownloadResultArray:resultDict count:imgsArray.count];
                                         if(completionBlock){
                                             completionBlock(resultArray);
                                         }
                                     }
                                 }
                                 
                             }];
    }
}

+ (NSArray *)createDownloadResultArray:(NSDictionary *)dict count:(NSInteger)count {
    NSMutableArray *resultArray = [NSMutableArray new];
    for(int i=0;i<count;i++) {
        NSObject *obj = [dict objectForKey:@(i)];
        [resultArray addObject:obj];
    }
    return resultArray;
}

@end

调用方法:

                //下载图片
                [ImagesDownloadManager downloadImages:imgs completion:^(NSArray *resultArray) {
                    NSMutableArray *items = [NSMutableArray new];
                    for(int i=0;i<resultArray.count;i++) {
                        NSObject *obj = [resultArray objectAtIndex:i];
                        if([obj isKindOfClass:[UIImage class]]) {
                            //只取UIImage对象，其他类型忽略之
                            [items addObject:obj];
                        }
                    }
                    //调用系统自带的分享功能，把选中的图片们分享出去
                    UIActivityViewController *activityVC = [[UIActivityViewController alloc] initWithActivityItems:items applicationActivities:nil];
                    [self presentViewController:activityVC animated:YES completion:nil];
                }];