多张UIImage合成单张GIF时内存泄漏致应用崩溃问题排查

尝试将多张UIImage合成一张GIF动图，当帧数（UIImage数量）超过20时，应用会因内存泄漏崩溃。调用createGIF方法生成GIF时，内存从200MB飙升至2GB并持续增长直至崩溃。以下是相关代码：

func createGIF(from images: [UIImage], loopCount: Int = 0, frameDuration: TimeInterval = 0.1, completion: @escaping (URL?) -> Void) {
    guard let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else {
        print("Error: Unable to create documentsDirectory.")
        completion(nil)
        return
    }

    let gifURL = documentsDirectory.appendingPathComponent("\(UUID().uuidString).gif")

    guard let destination = CGImageDestinationCreateWithURL(gifURL as CFURL, kUTTypeGIF, images.count, nil) else {
        print("Error: Unable to create CGImageDestination.")
        completion(nil)
        return
    }

    let gifProperties = [
        kCGImagePropertyGIFDictionary as String: [
                    kCGImagePropertyGIFLoopCount as String: loopCount
                ]
    ]
    CGImageDestinationSetProperties(destination, gifProperties as CFDictionary)

    // Process frames in batches to reduce memory usage
    let batchSize = 10
    let totalFrames = images.count

    for startIndex in stride(from: 0, to: totalFrames, by: batchSize) {
        let endIndex = min(startIndex + batchSize, totalFrames)
        let batchImages = Array(images[startIndex..<endIndex])

        for image in batchImages {
            if let cgImage = image.cgImage {
                let frameProperties = [
                    kCGImagePropertyGIFDictionary as String: [
                        kCGImagePropertyGIFDelayTime as String: frameDuration
                    ]
                ]
                CGImageDestinationAddImage(destination, cgImage, frameProperties as CFDictionary)
            } else {
                print("Error: Unable to retrieve CGImage from UIImage.")
                completion(nil)
                return
            }
        }
    }

    guard CGImageDestinationFinalize(destination) else {
        print("Error: Failed to finalize CGImageDestination.")
        completion(nil)
        return
    }

    completion(gifURL)
}

想实现贴纸动画GIF，请问代码中存在什么问题或遗漏点导致内存飙升？

你的代码里的“分批处理”逻辑完全没起到内存优化作用，反而可能额外增加开销，核心问题和解决办法如下：

核心问题 #

1. CGImageDestination的缓存机制
   CGImageDestination会把所有添加的CGImage都缓存到内存中，直到调用CGImageDestinationFinalize才会写入文件并释放内存。不管分多少批，只要把所有帧都加进去，内存就会持续累积，直到处理完成。

2. 无效的分批逻辑
   你创建的batchImages是原数组的切片拷贝，额外持有了一批UIImage实例，反而增加了内存占用，而且没有任何内存释放的逻辑。

3. 未优化图片尺寸
   贴纸动画不需要高清分辨率，如果输入的UIImage尺寸过大（比如原图是屏幕几倍大），单帧内存占用就很高，20帧叠加后直接撑爆内存。

解决办法 #

1. 用autoreleasepool及时释放单帧内存
   去掉多余的分批逻辑，直接遍历原数组，用autoreleasepool包裹每帧的处理，让系统及时回收单帧的CGImage和UIImage内存：

   for image in images {
       autoreleasepool {
           if let cgImage = image.cgImage {
               let frameProperties = [
                   kCGImagePropertyGIFDictionary as String: [
                       kCGImagePropertyGIFDelayTime as String: frameDuration
                   ]
               ]
               CGImageDestinationAddImage(destination, cgImage, frameProperties as CFDictionary)
           } else {
               print("Error: Unable to retrieve CGImage from UIImage.")
               completion(nil)
               return
           }
       }
   }
   

2. 缩小图片尺寸
   提前将所有UIImage缩到贴纸需要的合适大小（比如300x300），大幅降低单帧内存占用：

   func resizeImage(_ image: UIImage, targetSize: CGSize) -> UIImage? {
       let size = image.size
       let scaleRatio = min(targetSize.width/size.width, targetSize.height/size.height)
       let newSize = CGSize(width: size.width*scaleRatio, height: size.height*scaleRatio)
       UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
       image.draw(in: CGRect(origin: .zero, size: newSize))
       let resizedImage = UIGraphicsGetImageFromCurrentImageContext()
       UIGraphicsEndImageContext()
       return resizedImage
   }
   

   在添加到CGImageDestination前，先调用这个方法处理每一张图片。

3. 移除不必要的数组拷贝
   删除batchImages相关的切片逻辑，直接遍历原数组的元素，避免额外的内存占用。

内容的提问来源于stack exchange，提问作者Kodr.F