經(jīng)常會(huì)遇到這樣的應(yīng)用場景,例如在調(diào)用iOS系統(tǒng)分享功能前(UIActivityViewController),需要將所有的圖片事先準(zhǔn)備好,但是圖片都在網(wǎng)絡(luò)上.
這時(shí),就需要先將圖片都下載好后再進(jìn)行調(diào)用.
可能是這個(gè)功能的實(shí)現(xiàn)太簡單了,所以像SDWebImage,AFNetwork等都沒有提供可以直接調(diào)用的API方法.
所以只好花了2秒鐘自己寫了一個(gè)方法;

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

@implementation ImagesDownloadManager

/**
 批量下載圖片
 保持順序;
 全部下載完成后才進(jìn)行回調(diào);
 回調(diào)結(jié)果中,下載正確和失敗的狀態(tài)保持與原先一致的順序;
 
 @return resultArray 中包含兩類對象: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){
                                        //在對應(yīng)的位置放一個(gè)error對象
                                         [resultDict setObject:error forKey:@(i)];
                                     }else{
                                         [resultDict setObject:image forKey:@(i)];
                                     }
                                     if(resultDict.count == imgsArray.count) {
                                         //全部下載完成
                                         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

調(diào)用方法:

                //下載圖片
                [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對象，其他類型忽略之
                            [items addObject:obj];
                        }
                    }
                    //調(diào)用系統(tǒng)自帶的分享功能，把選中的圖片們分享出去
                    UIActivityViewController *activityVC = [[UIActivityViewController alloc] initWithActivityItems:items applicationActivities:nil];
                    [self presentViewController:activityVC animated:YES completion:nil];
                }];