ios - Objective-c UIImagePNGRepresentation 导致内存泄漏

Question

我正在尝试下载一些图像(从 base64 字符串转换为 UIImage)并将其保存到设备，但不断收到内存警告。

ontracFullScreenImageViewController *etrackDiagrams = ((ontracFullScreenImageViewController*)[viewControllerDictionary objectForKey:@"E-track Diagrams"]);
    NSMutableSet *etrackSet = [[NSMutableSet alloc] init];

    for (UIImage *image in etrackDiagrams.imageArray) {


        NSAutoreleasePool *localPool = [[NSAutoreleasePool alloc] init];
        //convert the image to NSData and store it in the documents directory
        NSData *pngData = UIImagePNGRepresentation(image);
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory
        NSString * timeInMS = [NSString stringWithFormat:@"%lld", [@(floor([[NSDate date] timeIntervalSince1970] * 1000)) longLongValue]];
        NSString *filePath = [documentsPath stringByAppendingPathComponent:[ NSString stringWithFormat:@"%@_%@_etrack_diagram_%i_%i_image.png", delegate.userName, timeInMS, self.dataObject.dataPack.pack_id, [etrackDiagrams.imageViewArray indexOfObject:image]]]; //Add the file name
        [pngData writeToFile:filePath atomically:YES];
        NSLog(@"filepath %@", filePath);
        NSString *currSysVer = [[UIDevice currentDevice] systemVersion];
        if ([currSysVer isEqualToString:@"5.0.1"]) {
            [[NSURL URLWithString:filePath] setResourceValue: [NSNumber numberWithBool: YES] forKey: NSURLIsExcludedFromBackupKey error: &error];
        }
        //Add the file Path to ImageLinks
        [etrackDiagrams.imageLinks addObject:filePath];
        //save the image location in Core Data
        EtrackDiagram *etrackDiagram = [NSEntityDescription
                                        insertNewObjectForEntityForName:@"EtrackDiagram"
                                        inManagedObjectContext:context];
        etrackDiagram.locationString = filePath;
        etrackDiagram.dataObject = dataObject;
        [etrackSet addObject:etrackDiagram];
        [dataObject addEtrackDiagramsObject:etrackDiagram];
        [localPool drain];

    }
    [dataObject addEtrackDiagrams: etrackSet];

内存警告发生在 NSData *pngData = UIImagePNGRepresentation(image); 处，因为图像非常大。

不幸的是，我无法控制图像的大小，但需要一种方法将它们保存到设备上，以便稍后在图库中使用它们。

我尝试用 @autoreleasepool 包装代码，但没有什么区别。

Answer 1

真正的问题是这一行:

for (UIImage *image in etrackDiagrams.imageArray) {

这意味着您在内存中保存了一组图像。那总是很危险的。您需要将所有这些图像保存在磁盘上并一次将它们加载到内存中(并且以非缓存方式)。您的目标应该是一次最多在内存中保存一张图像。