我正在尝试将下载的文件预览到系统，并且在执行名为 previewController:previewItemAtIndex: 的方法时程序崩溃。我假设是在显示之前释放预览控制器，但是当文件已经在文档文件夹中时，不会发生此错误。只有在下载文件后立即尝试打开文件时才会发生这种情况。
这是代码：
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
NSUInteger row = [indexPath row];
NSUInteger count = [listSessionsST count];
[tableView deselectRowAtIndexPath:indexPath animated:YES];
Signature *object = [listSessionsST objectAtIndex:row];
UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
UILabel *lblInComplete = (UILabel*)[cell viewWithTag:4];
UIImageView *imgCheck = (UIImageView*)[cell viewWithTag:3];
//Sets the File Name
self.File = [[[NSString stringWithFormat:@"%@_%@.%@",object.FileName,object.ModDate,object.Extension]
componentsSeparatedByCharactersInSet: [NSCharacterSet whitespaceCharacterSet]] componentsJoinedByString: @""];
//Shows the loading screen while the file is being downloaded
[DejalBezelActivityView activityViewForView:self.view withLabel:@"Downloading" width:0 LoadingType:@"Full"];
[DejalActivityView currentActivityView].showNetworkActivityIndicator = YES;
//Calls the method that will begin downloading the file
[self performSelector:@selector(startDownload:) withObject:object.Location afterDelay:0.2];
}
- (void)startDownload:(NSString *)strLocation{
NSString *filePath = [NSString stringWithFormat:@"%@/tmp/%@", NSHomeDirectory(),self.File];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:filePath];
if (fileExists)
{
[DejalBezelActivityView removeViewAnimated:YES];
//QuickLook APIs directly to preview the document
QLPreviewController *previewController = [[QLPreviewController alloc] init];
previewController.dataSource = self;
previewController.delegate = self;
[[self navigationController] pushViewController:previewController animated:YES];
[previewController release];
}
else
{
NSDictionary *dictionary = [Signature downloadFile:self.File Path:strLocation];
if ([dictionary valueForKey:@"Error"] == nil)
{
//If no error has occurred while downloading then preview the file.
//QuickLook APIs directly to preview the document
QLPreviewController *previewController = [[QLPreviewController alloc] init];
previewController.dataSource = self;
previewController.delegate = self;
[[self navigationController] pushViewController:previewController animated:YES];
[previewController release];
[DejalBezelActivityView removeViewAnimated:YES];
}
else
{
//If an error occurred while downloading then display message to user.
[DejalBezelActivityView removeViewAnimated:YES];
UIAlertView *alert = [[UIAlertView alloc]
initWithTitle:@""
message:[dictionary valueForKey:@"Response"]
delegate:self
cancelButtonTitle:@"Ok"
otherButtonTitles:nil];
[alert show];
[alert release];
}
}
}
// Returns the number of items that the preview controller should preview
- (NSInteger)numberOfPreviewItemsInPreviewController:(QLPreviewController *)previewController{
return 1;
}
// returns the item that the preview controller should preview
- (id)previewController:(QLPreviewController *)controller previewItemAtIndex:(NSInteger)index{
NSString *path = [NSString stringWithFormat:@"%@/tmp/%@", NSHomeDirectory(),self.File];
return [NSURL fileURLWithPath:path];
}
The method that downloads the file and saves it to the tmp folder
---------------------------------------------------------------
+ (NSDictionary *)downloadFile:(NSString *)strFile Path:(NSString *)strPath{
float freeSpace = 0.0f;
NSError *error = nil;
NSDictionary *dictionary = [[NSFileManager defaultManager] attributesOfFileSystemForPath:[NSString stringWithFormat:@"%@/tmp", NSHomeDirectory()]
error: &error];
if (dictionary)
{
NSNumber *fileSystemFreeSizeInBytes = [dictionary objectForKey: NSFileSystemFreeSize];
freeSpace = [fileSystemFreeSizeInBytes floatValue];
}
else
{
//Handle error
NSLog(@"Error;%@",error);
return [NSDictionary dictionaryWithObjectsAndKeys:@"An error has occurred while downloading the file.",@"Response",@"Y",@"Error", nil];
}
if (freeSpace > 0.0f)
{
NSDictionary *dict = nil;
BOOL blnHasErroroccurred = NO;
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
NSString *encoded = (NSString *)CFURLCreateStringByAddingPercentEscapes(NULL,
(CFStringRef)strPath,
NULL,
(CFStringRef)@"!*'\"();:@&=+$,/?%#[]%",
kCFStringEncodingUTF8 );
NSString *strURL = [NSString stringWithFormat:@"%@/DataTransfer/DownloadFile?EMP_ID=%@&FilePath=%@",
appDelegate.ServerAddress,
appDelegate.UserId,
encoded];
[encoded release];
NSURL *url = [NSURL URLWithString:strURL];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url
cachePolicy: NSURLRequestUseProtocolCachePolicy
timeoutInterval:20.0];
[request setHTTPMethod:@"POST"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
NSURLResponse* response = nil;
NSError* resultError = nil;
NSData* dataResult = [NSURLConnection sendSynchronousRequest:request
returningResponse:&response
error:&resultError];
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response;
if ([httpResponse statusCode] == 200)
{
@try
{
if (dataResult.length < freeSpace)
{
//Get the tmp directory
NSFileManager *fileManager =[NSFileManager defaultManager];
NSString *fileName = [NSString stringWithFormat:@"%@/tmp/%@", NSHomeDirectory(),strFile];
//Write the data to using the tmp directory
BOOL filecreationSuccess = [fileManager createFileAtPath:fileName contents:dataResult attributes:nil];
if(filecreationSuccess == YES)
{
dict = [NSDictionary dictionaryWithObjectsAndKeys:@"",@"Response",nil,@"Error", nil];
}
else
{
blnHasErroroccurred = YES;
}
}
}
@catch (NSException *exception)
{
blnHasErroroccurred = YES;
}
}
else
{
blnHasErroroccurred = YES;
}
if(blnHasErroroccurred == YES)
{
dict = [NSDictionary dictionaryWithObjectsAndKeys:@"An error has occurred while downloading the file.", @"Response", @"Yes",@"Error",nil];
}
[dataResult release];
return dict;
}
else
{
return [NSDictionary dictionaryWithObjectsAndKeys:@"Not enough disk space to download file.",@"Response",@"Y",@"Error", nil];
}
}