Xcode - iOS - AWS S3 - Downloaded Image Doesn't Appear On First Download - ios

Question

Here is the code I use to download an image from an AWS S3 server and assign it to be the image displayed in an image view:
let s3BucketName = "bucketName"
let fileName = Globals.currAuthorName.filter { $0 != Character(" ") } + ".jpg"
let downloadFilePath = NSTemporaryDirectory().stringByAppendingPathComponent(fileName)
let downloadingFileURL = NSURL.fileURLWithPath(downloadFilePath)
// Create a credential provider for AWS requests
let credentialsProvider = AWSCognitoCredentialsProvider(
regionType: AWSRegionType.USEast1,
identityPoolId: "us-east-1:********-****-****-****-************")
// Create a service configuration for AWS requests
let defaultServiceConfiguration = AWSServiceConfiguration(
region: AWSRegionType.USEast1,
credentialsProvider: credentialsProvider)
// Create a new download request to S3, and set its properties
AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = defaultServiceConfiguration
let downloadRequest = AWSS3TransferManagerDownloadRequest()
downloadRequest.bucket = s3BucketName
downloadRequest.key = "folderName/" + fileName
downloadRequest.downloadingFileURL = downloadingFileURL
let transferManager = AWSS3TransferManager.defaultS3TransferManager()
transferManager.download(downloadRequest)
// Set the UIImageView to show the file that was downloaded
let image = UIImage(contentsOfFile: downloadFilePath)
authorImage.contentMode = UIViewContentMode.ScaleAspectFit
authorImage.image = image
The problem is that when I run the iOS Simulator and navigate to the appropriate page, the image is never loaded the first time I visit the page. However, it is always loaded when I navigate away from the page and then return the page, and every subsequent time I visit the page. The image is still loaded when I stop running the app and then start it again and visit the page again. The image is only not loaded the very first time I visit the page for a certain iOS Simulator (i.e. it happens once in the iPhone 6 simulator, the iPhone 5 simulator, etc)
I tried to fix the problem by adding this bit of code:
while (image == nil) {
transferManager.download(downloadRequest)
let image = UIImage(contentsOfFile: downloadFilePath)
}
But that simply resulted in an infinite while loop the first time I visited the page. Also the console eventually output this error:
2015-07-06 23:26:28.529 CCBF[19839:92323] 19839: CFNetwork internal error (0xc01a:/SourceCache/CFNetwork_Sim/CFNetwork-711.3.18/Foundation/NSURLRequest.mm:798)
2015-07-06 23:26:28.564 AuthorProject[19839:92323] AWSiOSSDKv2 [Error] AWSURLSessionManager.m line:240 | __41-[AWSURLSessionManager taskWithDelegate:]_block_invoke222 | Invalid AWSURLSessionTaskType.
EDIT:
I tried to implement the following continuewithblock:
var image : UIImage!
let task = transferManager.download(downloadRequest)
task.continueWithBlock({
if task.error != nil {
println(task.error)
} else {
dispatch_async(dispatch_get_main_queue(), {
image = UIImage(contentsOfFile: downloadFilePath)
self.authorImage.contentMode = UIViewContentMode.ScaleAspectFit
self.authorImage.image = image
})
}
return nil
}())
However, when I ran it and tried to load the image, I got a runtime error that pointed me to the code for a "continueWithExecutor" method. Specifically, the line of code:
result = block(self);
With the message being:
EXC_BAD_ACCESS(code: 1, address=0x10)
EDIT2:
I seem to have found a solution that works:
var image : UIImage!
let taskTODO = transferManager.download(downloadRequest)
taskTODO.continueWithBlock{ (task: AWSTask!) -> AnyObject! in
if task.error != nil {
println(task.error)
} else {
dispatch_async(dispatch_get_main_queue(), {
image = UIImage(contentsOfFile: downloadFilePath)
self.authorImage.contentMode = UIViewContentMode.ScaleAspectFit
self.authorImage.image = image
})
}
return nil
}
Does this seem like the correct way to do it?

Answer 1

transferManager.download(downloadRequest) is asynchronous, meaning it takes about 20 miliseconds to download the image. However, the first time into the screen you are trying to assign the image immediately (which has not yet been downloaded). In subsequent screen loads - the image has already been downloaded and cached - so it's immediately ready to be displayed, . What you need is a completion block that indicates when the image is has finished downloading and is ready for display and in that block you shall assign the image. See example below:
let readRequest1 : AWSS3TransferManagerDownloadRequest = AWSS3TransferManagerDownloadRequest()
readRequest1.bucket = "shrikar-picbucket"
readRequest1.key = "bingo"
readRequest1.downloadingFileURL = downloadingFileURL1
let task = transferManager.download(readRequest1)
task.continueWithBlock { (task) ->; AnyObject! in
println(task.error)
if task.error != nil {
} else {
dispatch_async(dispatch_get_main_queue()
, { () ->; Void in
self.selectedImage.image = UIImage(contentsOfFile: downloadingFilePath1)
self.selectedImage.setNeedsDisplay()
self.selectedImage.reloadInputViews()
})
println("Fetched image")
}
return nil
}