iOS 8 Load Images Fast From PHAsset

Question

I have an app that lets people combine up to 4 pictures. However when I let them choose from their photos (up to 4) it can be very slow even when I set image quality to FastFormat. It will take 4 seconds (about 1 second per photo). On highest quality, 4 images takes 6 seconds.

Can you suggest anyway I get get the images out faster?

Here is the block where I process images.

func processImages()
    {
        _selectediImages = Array()
        _cacheImageComplete = 0
        for asset in _selectedAssets
        {
            var options:PHImageRequestOptions = PHImageRequestOptions()
            options.synchronous = true
            options.deliveryMode = PHImageRequestOptionsDeliveryMode.FastFormat
            PHImageManager.defaultManager().requestImageForAsset(asset, targetSize:CGSizeMake(CGFloat(asset.pixelWidth), CGFloat(asset.pixelHeight)), contentMode: .AspectFit, options: options)
                {
                    result, info in
                    var minRatio:CGFloat = 1
                    //Reduce file size so take 1/3 the screen w&h
                    if(CGFloat(asset.pixelWidth) > UIScreen.mainScreen().bounds.width/2 || CGFloat(asset.pixelHeight) > UIScreen.mainScreen().bounds.height/2)
                    {
                        minRatio = min((UIScreen.mainScreen().bounds.width/2)/(CGFloat(asset.pixelWidth)), ((UIScreen.mainScreen().bounds.height/2)/CGFloat(asset.pixelHeight)))
                    }
                    var size:CGSize = CGSizeMake((CGFloat(asset.pixelWidth)*minRatio),(CGFloat(asset.pixelHeight)*minRatio))
                    UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
                    result.drawInRect(CGRectMake(0, 0, size.width, size.height))
                    var final = UIGraphicsGetImageFromCurrentImageContext()
                    var image = iImage(uiimage: final)
                    self._selectediImages.append(image)
                    self._cacheImageComplete!++
                    println(self._cacheImageComplete)
                    if(self._cacheImageComplete == self._selectionCount)
                    {
                        self._processingImages = false
                        self.selectionCallback(self._selectediImages)
                    }
            }

        }
    }

Answer 1

Why did you say synchronous? Obviously that's going to slow things way down. Moreover, saying synchronous on the main thread is absolutely forbidden!!!! Read the docs and obey them. That is the primary issue here.

There are then many other considerations. Basically you're using this call all wrong. Once you've removed the synchronous, do not process the image like that! Remember, this callback is going to be called many times as the image is provided in better and better versions. You must not do anything time-consuming here.

(Also, why are you resizing the image? If you wanted the image at a certain size, you should have asked for that size when you requested it. Let the image-fetcher do the work for you.)