将 NSError 作为返回参数传回的问题

Question

我在传回 NSError 对象时遇到问题。访问对象的第一行代码（在本例中，我插入了一个 NSLog）导致“EXC_BAD_ACCESS”。

这是因为我没有显式创建一个 NSError 对象，而是从 NSURLRequest 中获取一个并将其传回吗？在这个特定的函数 (downloadFile:) 中，我想从其他函数中检索一些错误，但我在函数中的另外两个场合创建了 NSError。

感谢任何帮助。

这是有问题的代码：

-(void)someCode {
NSError *err = nil;

localPool = [[NSAutoreleasePool alloc] init];

if (!iap) {
    iap = [[InAppPurchaseController alloc] init];
}

if (![self.iap downloadFile:@"XXXXX.plist" withRemoteDirectory:nil withLocalDelete:YES withContentType:@"text/xml" Error:&err] ) {
    //"EXC_BAD_ACCESS" on calling NSLog on the next line? 
    NSLog(@"Error downloading Plist: %@", [err localizedDescription]);

    [self performSelectorOnMainThread:@selector(fetchPlistFailed:) withObject:err waitUntilDone:NO];
    [localPool drain], localPool = nil;
    return NO;
}
//Removed the remainder of the code for clarity.

[localPool drain], localPool = nil;
return YES;
}


-(BOOL)downloadFile:(NSString *)fileName
withRemoteDirectory:(NSString *)remoteDirectory
 withLocalDelete:(BOOL)withLocalDelete
 withContentType:(NSString *)contentTypeCheckString
     Error:(NSError **)error {

UIApplication *app = [UIApplication sharedApplication];
app.networkActivityIndicatorVisible = YES; 

NSError *localError = nil;

NSAutoreleasePool *localPool = [[NSAutoreleasePool alloc] init];

NSString *urlString = [NSString stringWithFormat:@"http://XXXXX/%@", fileName];

NSLog(@"Downloading file: %@", urlString);

NSURL *url = [NSURL URLWithString:urlString];

NSURLRequest *req = [[NSURLRequest alloc] initWithURL:url];

NSHTTPURLResponse *response = nil;

NSData *responseData = [NSURLConnection sendSynchronousRequest:req returningResponse:&response error:&localError];

[req release];

if (response == nil || localError) {
    NSLog(@"Error retrieving file:%@", [localError localizedDescription]);
    if (error != NULL) {
        *error = localError;
        //THIS NSLog call works just fine.
        NSLog(@"Error copied is:%@", [*error localizedDescription]);
    }
 [localPool drain], localPool = nil;
 app.networkActivityIndicatorVisible = NO; 
 return NO;
}

//Rest of function omitted for simplicity.
}

Answer 1

我猜你的NSError 对象是autoreleased 并穿上你的localPool。你耗尽了localPool，从而破坏了NSError。

你真的需要localPool 吗？如果没有，只需删除localPools。

另外，您似乎忘记在someCode 中排空localPool。希望你只是没有复制它......

-(void)someCode {
    NSError *err = nil;

    localPool = [[NSAutoreleasePool alloc] init];

    if (!iap) {
        iap = [[InAppPurchaseController alloc] init];
    }

    if (![self.iap downloadFile:@"XXXXX.plist" withRemoteDirectory:nil withLocalDelete:YES withContentType:@"text/xml" Error:&err] ) {
             ....
            [localPool drain], localPool = nil;
            return NO;
    }
    [localPool drain], localPool = nil; // missing
}