How to make the screen freeze during extensive computing?

Question

Ok, so I'm trying to change the pixel data of a specific image. I want to use a UIView that moves to the right each time it loops like a progressbar. However, what happens, the screen freezes during the calculation, and nothing happens until it ends. The clock in the status bar will also not be updated. Is there any way to move these calculations to the background somehow and still use the screen real estate?

func lock() {

    let lockView =  UIImageView(image: self.photoBackgroundView.image!)
    var progressBar = UIView(frame: CGRectMake(-self.view.width,0,self.view.width,20)
    let increment = progressBar.width/self.photoBackgroundView.width
    var password = self.textField.text!
    if password == "" {
        password = " "
    }
    var currentIndex = 0



    let imageRect = CGRectMake(0, 0, self.photoBackgroundView.image!.size.width,self.photoBackgroundView.image!.size.height)

    UIGraphicsBeginImageContext(self.photoBackgroundView.image!.size)
    let context = UIGraphicsGetCurrentContext()

    CGContextSaveGState(context)
    CGContextDrawImage(context, imageRect, self.photoBackgroundView.image!.CGImage)
    for x in 0...Int(self.photoBackgroundView.image!.size.width) {
        print(x)

        progressBar.frame.origin.x += (CGFloat(x) * increment)
        self.view.addSubView(progressBar)


        for y in 0...Int(self.photoBackgroundView.image!.size.height) {
            let pointColor = lockView.layer.colorOfPoint(CGPoint(x: x, y: y))

            if currentIndex == Array(password.characters).count {
                currentIndex = 0
            }
            let red = encrypt(pointColor.components.red, passwordChar: Array(password.characters)[currentIndex], currentIndex: currentIndex, x: x, y: y)
            currentIndex++
            if currentIndex == Array(password.characters).count {
                currentIndex = 0
            }
            let green = encrypt(pointColor.components.green, passwordChar: Array(password.characters)[currentIndex], currentIndex: currentIndex, x: x, y: y)
            currentIndex++
            if currentIndex == Array(password.characters).count {
                currentIndex = 0
            }
            let blue = encrypt(pointColor.components.blue, passwordChar: Array(password.characters)[currentIndex], currentIndex: currentIndex, x: x, y: y)
            currentIndex++

            CGContextSetRGBFillColor(context, red, green, blue, pointColor.components.alpha)
            CGContextFillRect(context, CGRectMake(CGFloat(x), CGFloat(y), 1, 1))

        }



    }

    CGContextRestoreGState(context)
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    self.photoBackgroundView.image = newImage
    self.slideView.addSubview(photoBackgroundView)
    self.view.addSubview(self.slideView)
}

Answer 1

You can perform these calculations in the background thread .

Swift 2:

let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
dispatch_async(dispatch_get_global_queue(priority, 0)) {
    // Put the calculations here
    dispatch_async(dispatch_get_main_queue()) {
        // any updates of the UI need to be here to do them in the main thread after your background task. For example adding subviews
    }
}

Swift 3:

See this answer

Answer 2

, . , mainThread, mainThread , .

. , mainThread, BGthread.

NSOperationQueue GCD (Grand Central Dispatch), .

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