适用于iOS的AWS S3 SDK v2 - 将映像文件下载到UIImage

Question

似乎这应该相对简单.我正在使用适用于iOS的AWS SDK(v2),我正在尝试下载.png文件并将其显示在UIImage中的屏幕上.一切都有效!非常奇怪......

这是我的代码:

    AWSStaticCredentialsProvider *credentialsProvider = [AWSStaticCredentialsProvider credentialsWithAccessKey:@"MY_ACCESS_KEY" secretKey:@"MY_SECRET_KEY"];
    AWSServiceConfiguration *configuration = [AWSServiceConfiguration configurationWithRegion:AWSRegionUSWest1 credentialsProvider:credentialsProvider];
    [AWSServiceManager defaultServiceManager].defaultServiceConfiguration = configuration;

    AWSS3 *transferManager = [[AWSS3 alloc] initWithConfiguration:configuration];
    AWSS3GetObjectRequest *getImageRequest = [AWSS3GetObjectRequest new];
    getImageRequest.bucket = @"MY_BUCKET";
    getImageRequest.key = @"MY_KEY";

    [[transferManager getObject:getImageRequest] continueWithBlock:^id(BFTask *task) {
        if(task.error)
        {
            NSLog(@"Error: %@",task.error);
        }
        else
        {
            NSLog(@"Got image");
            NSData *data = [task.result body];
            UIImage *image = [UIImage imageWithData:data];
            myImageView.image = image;
        }
        return nil;
    }];

当执行此代码时,执行continueWithBlock,没有任务错误,因此记录了Got图像.这种情况发生得相当快.但是,直到大约10秒钟后,UIImageView才会在屏幕上更新.我甚至通过调试器来查看该行后面的任何NSLog(@"Got image");行是否需要很长时间,而不是.它们都执行得非常快,但UIImageView不会在UI上更新.

Answer 1

问题是您正在从后台线程更新UI组件.该continueWithBlock:块在后台线程中执行,并导致上述行为.您有两种选择:

1. 在块中使用Grand Central Dispatch并在主线程上运行它:

   ...
   NSURL *fileURL = [task.result body];
   NSData *data = // convert fileURL to data
   dispatch_async(dispatch_get_main_queue(), ^{
       UIImage *image = [UIImage imageWithData:data];
       myImageView.image = image;
   });
   ...
   

2. 用于mainThreadExecutor在主线程上运行块:

   [[transferManager getObject:getImageRequest] continueWithExecutor:[BFExecutor mainThreadExecutor]
                                                           withBlock:^id(BFTask *task) {
   ...
   

希望这可以帮助,