如何解决需要为指定了保留标志的属性调用保留
| 我是Objective-C的新手,并且像大多数新手一样,我对引用管理有疑问。 我编写了一个使用NSURLConnection下载数据的类。该代码类似于http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLConnection.html中的Apple示例。唯一的区别是,receivedData变量声明为\“ @属性(非原子,保留)NSMutableData * receivedData; \”在.m文件中,我具有\“ @ synthesize receiveData = _receivedData; \”。 我有connectionStart函数,它开始下载数据。在此功能中,我有以下代码:if (theConnection) {
// Create the NSMutableData to hold the received data.
// receivedData is an instance variable declared elsewhere.
self.receivedData = [NSMutableData data];
} else {
// Inform the user that the connection Failed.
}
程序崩溃并显示以下消息:
2011-06-12 12:47:22.298 Webgallery[1212:207] *** -[NSConcreteMutableData release]: message sent to deallocated instance 0x118a6fe0
如果我将receiveData分配更改为以下代码:
self.receivedData = [[NSMutableData data] retain];
然后,程序可以正常运行,并且没有检测到内存泄漏。
如您所见,我需要在NSMutableData上调用keep,并且我正在使用属性,该属性声明为\“ retain \”。
为什么会这样?
编辑:.m文件的完整内容:
#import \"galleryData.h\"
#import \"XmlParser.h\"
@implementation galleryData
@synthesize receivedData = _receivedData;
@synthesize imagesData = _imagesData;
@synthesize delegate = _delegate;
@synthesize currentObjectType = _currentObjectType;
@synthesize currentObjectIndex = _currentObjectIndex;
- (id) init
{
[super init];
_imagesData = [[NSMutableArray alloc] init];
return self;
}
- (void) dealloc
{
[_imagesData release];
_imagesData = nil;
[super dealloc];
}
- (void) connectionStart:(NSURL *)theURL
{
NSURLRequest *theRequest = [NSURLRequest requestWithURL:theURL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData to hold the received data.
// receivedData is an instance variable declared elsewhere.
//ASK: Kodėl čia reikia daryti retain jei @property jau nustatyta retain?
self.receivedData = [[NSMutableData data] retain];
} else {
// Inform the user that the connection Failed.
}
}
- (void) startLoading
{
NSLog(@\"Loading started\");
self.currentObjectIndex = 0;
self.currentObjectType = ObjectTypeXML;
[self connectionStart:[NSURL URLWithString:@\"http://www.aleksandr.lt/gallery/data.xml\"]];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
[self.receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[self.receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
[connection release];
[self.receivedData release];
NSLog(@\"Connection Failed! Error - %@ %@\",[error localizedDescription],[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
[connection release];
if (self.currentObjectType == ObjectTypeXML) {
NSXMLParser *nsXmlParser = [[NSXMLParser alloc] initWithData:self.receivedData];
XmlParser *parser = [[XmlParser alloc] initXmlParser:self.imagesData];
[nsXmlParser setDelegate:parser];
[nsXmlParser parse];
[nsXmlParser release];
[parser release];
[self.receivedData release];
self.receivedData = nil;
if ([self.imagesData count]) {
self.currentObjectIndex = 0;
self.currentObjectType = ObjectTypeThumbImage;
ImageData *firstimage = [self.imagesData objectAtIndex:0];
NSURL *theURL = [NSURL URLWithString:firstimage.thumbImageURL];
[self connectionStart:theURL];
} else {
[self.delegate loadingFinished];
return;
}
} else if (self.currentObjectType == ObjectTypeThumbImage) {
ImageData *currentimage;
currentimage = [self.imagesData objectAtIndex:self.currentObjectIndex];
UIImage *thumbImage = [[UIImage alloc] initWithData:self.receivedData];
if (thumbImage == nil) {
NSLog(@\"image was not created\");
}
[currentimage setThumbImageScaled:thumbImage];
[thumbImage release];
[self.receivedData release];
self.receivedData = nil;
if (self.currentObjectIndex == ([self.imagesData count] - 1)) {
[self.delegate loadingFinished];
return;
}
self.currentObjectIndex++;
currentimage = [self.imagesData objectAtIndex:self.currentObjectIndex];
NSLog(@\"\'%@\'\",currentimage.thumbImageURL);
NSURL *theURL = [NSURL URLWithString:currentimage.thumbImageURL];
[self connectionStart:theURL];
}
}
@end
解决方法
不要调用
[self.receivedData release]
-这会使内部指针悬空。保留属性的全部意义在于它会释放自身。只要做self.receivedData = nil
。
, 这是您的问题:
[self.receivedData release];
self.receivedData = nil;
您将释放该属性两次(通过分配nil显式第一次,隐式第二次)。
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