下载大量图像时出现内存泄漏问题

Posted 2023-03-22

【中文标题】下载大量图像时出现内存泄漏问题

【英文标题】：Memory leak issue while downloading large number of images

【发布时间】：2012-04-06 07:30:09

【问题描述】：

我正在尝试使用屏幕顶部的进度表循环下载 600 多张图像给用户。我用淡入淡出层挡住了我的屏幕以显示活动和进度。

我在应用程序崩溃之间收到内存警告消息。

我到达循环的步骤是：

在应用程序委托上，我检查第一个核心数据表中 isImageAvailable bool 字段中具有“0”值的所有行。 如果显示一些计数（例如 600），我会显示并使用“是”和“否”选项发出警报。 是：[self performSelector:@selector(myDownload:) withObject:nil afterDelay:0.2];

在我的下载中

NSOperationQueue *queue = [NSOperationQueue new];
// Create our NSInvocationOperation to call loadDataWithOperation, passing in nil 
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self
                                                                 selector:@selector(startUpdatingRecords:) object:nil];

// Add the operation to the queue 
[queue addOperation:operation];
[operation release];
[queue release];

在 startUpdatingRecords 中：

-(void)startUpdatingRecords:(id)sender 
    
[self performSelectorInBackground:@selector(updateProgressMeter:) withObject:    [NSString stringWithFormat:@"%d",self.loopStartIndex]];

// Variable declarations             
CGSize newSizeLarge ;
NSPredicate *predicate;
NSMutableArray *MatchingID;
Image_DB *data;

// Cache Directory path
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask,  YES);

NSData *responseData; // = [[NSData alloc]init] ;

NSURL *url = [[[NSURL alloc]init] autorelease];
NSMutableURLRequest *request = [[[NSMutableURLRequest alloc]init] autorelease];
UIImage *imgSelected_Large = [[[UIImage alloc]init] autorelease];

// Loop through all IDs
for (int i = 0; i < [self.arrayOfID count]; i++) //for (int i = loopStart; i < loopEnd; i++) 
 
if (self.abortDownload)
           
    break;
 

NSString *documentsDirectory = [[[NSString alloc] initWithFormat:@"%@",[paths objectAtIndex:0]] autorelease];
documentsDirectory = [paths objectAtIndex:0];
documentsDirectory = [documentsDirectory stringByAppendingFormat:@"/ImageFolder"]; // Image folder path

myClass *classObj = [self.arrayOfID objectAtIndex:i];   

NSString *strURl = [[[NSString alloc] initWithFormat:@"%@%@", self.MyURL,recipeObj.recipeImageStr] autorelease];
//NSLog(@"URL = %@",strURl);           

url = [NSURL URLWithString:strURl];
request = [NSMutableURLRequest requestWithURL:url];
responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:NULL error:NULL]; // Get Image Data into NSData

//imgSelected_Large = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:strURl]]];

NSLog(@"Download Count = %d",i+1);

if (responseData != nil)

    imgSelected_Large = [UIImage imageWithData:responseData];

    // Resizining image
    newSizeLarge.width = 320;    
    newSizeLarge.height = 180;     

    imgSelected_Large = [self imageWithImage:imgSelected_Large scaledToSize:newSizeLarge]; // New sized image
    NSData *dataPhoto; // no need to release it because UIImageJPEGRepresentation gives autoreleased NSData obj.
    dataPhoto  = UIImageJPEGRepresentation(imgSelected_Large, 0.6);  // Set new image representation and its Compression Quality

    documentsDirectory = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"Image_%d", classObj.nodeID]];            
    [dataPhoto writeToFile:documentsDirectory atomically:YES]; //Write file to local folder at default path

    predicate = [NSPredicate predicateWithFormat: @"(image_ID = %d )",recipeObj.nodeID];
    MatchingID = [CoreDataAPIMethods searchObjectsInContext:@"Image_DB" :predicate :@"image_ID" :YES :self.managedObjectContext];

    // Setting flag variable for available image
    for (int j = 0; j< [MatchingID count]; j++)
    
        //Assign the Authors Records in Class Object and save to Database 
        data = (Image_DB*) [MatchingID objectAtIndex:j];                
        // data.image_large = dataPhoto; // Code for storing BLOB object to DB
        data.extra_1 = @"1";
        //NSLog(@"Flag updated");
    

// Exit out code
if ( i == [self.arrayOfID count] - 1 || i == [self.arrayOfID count]) // Its the last record to be stored
    
    NSError *error;             
    if (![self.managedObjectContext save:&error])
    
        // Handle the error...
        NSLog(@"Error in updating %@",error);
     

    self.isUpdateImageCalled = NO;
    [self performSelectorOnMainThread:@selector(removeProgressMeter) withObject:nil waitUntilDone:NO];


// Update UI screen while in downloading process
[self performSelectorInBackground:@selector(updateProgressMeter:) withObject:[NSString stringWithFormat:@"%d",self.loopStartIndex+i+1]];

如果我没有释放 responseData，那么我的应用会向我显示内存警告并崩溃。如果我当时释放，[NSConcreteMutableData release]: message sent to deallocated instance 0x1e931de0 错误发生。

如何优化我的代码。任何人都可以建议我对我的代码进行修改并重新编写代码。

请帮帮我。

【问题讨论】：

希望这个链接能帮到你！！ ***.com/questions/3703734/…

【参考方案1】：

sendSynchronousRequest 返回的 responseData 是自动释放的，因此你不应该自己释放它。乍一看，我没有在您的代码中看到内存泄漏。您的应用程序可能实际上使用了太多内存，而没有泄漏它。尝试在你的 for 循环中放置一个自动释放池：

for (...) 
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    // your original code with a lot of autoreleased objects

    [pool release];

如果您将代码包装在自动释放池中，所有在包装内发送 autorelease 消息的对象将在释放池本身时实际释放：这样您就可以清除内存在每个 for 循环中。

另请参阅文档中的Using Autorelease Pools，它特别提到您应该在“如果您编写一个创建许多临时对象的循环”的情况下使用它们。