的UIImageView设定的图像属性将导致重大的滞后 [英] Setting image property of UIImageView causes major lag

问题描述

让我告诉你我遇到的问题，以及如何我试图解决这个问题。我有它加载子视图为一个滚动由左到右一个UIScrollView。每个子视图有大约每10-20 400x200的图像。当我从视图中滚动查看，我体验到相当多的滞后。

Let me tell you about the problem I am having and how I tried to solve it. I have a UIScrollView which loads subviews as one scrolls from left to right. Each subview has 10-20 images around 400x200 each. When I scroll from view to view, I experience quite a bit of lag.

经过调查，我发现所有卸载的意见，并再次尝试后，滞后不见了。我想通了图像的同步高速缓存是滞后的原因。因此，我创建的UIImageView的子类加载的图像异步。装载code如下所示（ self.dispatchQueue 返回一个串行调度队列）。

After investigating, I discovered that after unloading all the views and trying it again, the lag was gone. I figured that the synchronous caching of the images was the cause of the lag. So I created a subclass of UIImageView which loaded the images asynchronously. The loading code looks like the following (self.dispatchQueue returns a serial dispatch queue).

- (void)loadImageNamed:(NSString *)name {
    dispatch_async(self.dispatchQueue, ^{
        UIImage *image = [UIImage imageNamed:name];

        dispatch_sync(dispatch_get_main_queue(), ^{
            self.image = image;
        });
    });
}

不过，我所有的UIImageViews的更改为此子后，我还是经历了滞后（我不知道，如果它是减少或没有）。我归结问题，以 self.image =影像事业; 。这是为什么造成这么大的滞后（但仅限于第一负载）？

However, after changing all of my UIImageViews to this subclass, I still experienced lag (I'm not sure if it was lessened or not). I boiled down the cause of the problem to self.image = image;. Why is this causing so much lag (but only on the first load)?

请帮助我。 =（

推荐答案

编辑2：这是一个包含了一些改进，迅捷的版本。 （未经测试）。
https://gist.github.com/fumoboy007/d869e66ad0466a9c246d

EDIT 2: Here is a Swift version that contains a few improvements. (Untested.) https://gist.github.com/fumoboy007/d869e66ad0466a9c246d

编辑：其实，我相信一切必要如下。 （未经测试）。

Actually, I believe all that is necessary is the following. (Untested.)

- (void)loadImageNamed:(NSString *)name {
    dispatch_async(self.dispatchQueue, ^{
        // Determine path to image depending on scale of device's screen,
        // fallback to 1x if 2x is not available
        NSString *pathTo1xImage = [[NSBundle mainBundle] pathForResource:name ofType:@"png"];
        NSString *pathTo2xImage = [[NSBundle mainBundle] pathForResource:[name stringByAppendingString:@"@2x"] ofType:@"png"];

        NSString *pathToImage = ([UIScreen mainScreen].scale == 1 || !pathTo2xImage) ? pathTo1xImage : pathTo2xImage;


        UIImage *image = [[UIImage alloc] initWithContentsOfFile:pathToImage];

        // Decompress image
        if (image) {
            UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale);

            [image drawAtPoint:CGPointZero];

            image = UIGraphicsGetImageFromCurrentImageContext();

            UIGraphicsEndImageContext();
        }


        // Configure the UI with pre-decompressed UIImage
        dispatch_async(dispatch_get_main_queue(), ^{
            self.image = image;
        });
    });
}

---

原来的答案：事实证明，这不是 self.image =图像; 直接。该UIImage的图像加载方法不DECOM preSS和处理图像数据的时候了;他们这样做的时候认为刷新其显示。因此，解决办法是去一个水平低到核芯显卡和DECOM preSS和处理图像数据的自己。新的code看起来像下面这样。

---

ORIGINAL ANSWER: It turns out that it wasn't self.image = image; directly. The UIImage image loading methods don't decompress and process the image data right away; they do it when the view refreshes its display. So the solution was to go a level lower to Core Graphics and decompress and process the image data myself. The new code looks like the following.

- (void)loadImageNamed:(NSString *)name {
    dispatch_async(self.dispatchQueue, ^{
        // Determine path to image depending on scale of device's screen,
        // fallback to 1x if 2x is not available
        NSString *pathTo1xImage = [[NSBundle mainBundle] pathForResource:name ofType:@"png"];
        NSString *pathTo2xImage = [[NSBundle mainBundle] pathForResource:[name stringByAppendingString:@"@2x"] ofType:@"png"];

        NSString *pathToImage = ([UIScreen mainScreen].scale == 1 || !pathTo2xImage) ? pathTo1xImage : pathTo2xImage;


        UIImage *uiImage = nil;

        if (pathToImage) {
            // Load the image
            CGDataProviderRef imageDataProvider = CGDataProviderCreateWithFilename([pathToImage fileSystemRepresentation]);
            CGImageRef image = CGImageCreateWithPNGDataProvider(imageDataProvider, NULL, NO, kCGRenderingIntentDefault);


            // Create a bitmap context from the image's specifications
            // (Note: We need to specify kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little
            // because PNGs are optimized by Xcode this way.)
            CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
            CGContextRef bitmapContext = CGBitmapContextCreate(NULL, CGImageGetWidth(image), CGImageGetHeight(image), CGImageGetBitsPerComponent(image), CGImageGetWidth(image) * 4, colorSpace, kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);


            // Draw the image into the bitmap context
            CGContextDrawImage(bitmapContext, CGRectMake(0, 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);

            //  Extract the decompressed image
            CGImageRef decompressedImage = CGBitmapContextCreateImage(bitmapContext);


            // Create a UIImage
            uiImage = [[UIImage alloc] initWithCGImage:decompressedImage];


            // Release everything
            CGImageRelease(decompressedImage);
            CGContextRelease(bitmapContext);
            CGColorSpaceRelease(colorSpace);
            CGImageRelease(image);
            CGDataProviderRelease(imageDataProvider);
        }


        // Configure the UI with pre-decompressed UIImage
        dispatch_async(dispatch_get_main_queue(), ^{
            self.image = uiImage;
        });
    });
}

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