Update an NSTextField with X of Y when downloading files - macos

Question

I am attempting to update a "status label", NSTextField, with the current (X) of total (Y) when downloading files from an NSURLConnection. Below is some code that is working, but not 100%, or the way I would like.
X = runningCurrent
Y = runningTotal
The following code updates the (Y) or ofTotal correctly, however, the (X) or current jumps all over the place and does not increment 1, 2, 3 .. etc.
ApplicationController
- (void) updateLabelWithCurrent:(int)current ofTotal:(int)total
{
[txtStatus setStringValue:[NSString stringWithFormat:#"Downloading %i of %i",current,total]];
[txtStatus setNeedsDisplay:YES];
}
XML Data Source
for (int x = 0; x < [catArray count]; x++)
{
/* download each file to the corresponding category sub-directory */
[[WCSWallpaperDownloader alloc]
initWithWallpaperURL: [NSURL URLWithString:[[catArray objectAtIndex:x] objectForKey:#"imageUrl"]]
andFileOutput: [NSString stringWithFormat:#"%#/%#_0%i.jpg",cat,catName,x] withCurrent:x ofTotal:[catArray count]];
}
WCSWallpaperDownloader
- (id)initWithWallpaperURL:(NSURL *)imageUrl andFileOutput:(NSString*)fileOutput withCurrent:(int)current ofTotal:(int)total
{
self = [super init];
if (self)
{
appController = [[ApplicationController alloc] init];
self.fileOut = fileOutput;
NSURLRequest *imageRequest =
[NSURLRequest requestWithURL:imageUrl cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:1800.0];
[[NSURLConnection alloc] initWithRequest:imageRequest delegate:self];
runningCurrent = current;
runningTotal = total;
}
return self;
}
#pragma mark NSURLConenction
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
receivedData = [[NSMutableData data] retain];
[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
/* release the connection, and the data object */
[connection release];
[receivedData release];
NSLog(#"Connection failed! Error - %# %#",
[error localizedDescription],
[[error userInfo] objectForKey:NSErrorFailingURLStringKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
/* updates the status label with the current download of total objects being downloaded */
[appController updateLabelWithCurrent: runningCurrent ofTotal: runningTotal];
/* skip existing files */
if ( ! [MANAGER fileExistsAtPath:fileOut] )
{
[receivedData writeToFile:fileOut atomically:YES];
[receivedData release];
}
[[appController txtStatus] setStringValue:#""];
}
Solution
The following code correctly increments the download status as each object finishes.
- (void) incrementStatusLabelWithTotal:(int)total
{
runningCurrent++;
[txtStatus setStringValue:[NSString stringWithFormat:#"Downloading %i of %i",runningCurrent,total]];
}

Answer 1

It looks like you are setting off your downloads one by one, but they are not finishing in the same order - so you create each object telling it that it is loading item X of Y, but if the object downloading item 6 finishes before the object downloading item 4, your X is going to go, as you say, all over the place.
Each wallpaper downloader should just tell the appController that it has finished, and let the appController hold the number of items that have been downloaded so far, and the total number.
In fact, the wallpaper downloaders don't really need to know how many downloads are happening, or which particular number they are. Your XML data source should be telling your "app controller" the total number of downloads, and then each downloader, as it finishes, should tell the controller that it is done.
So, your current init method would just be:
- (id)initWithWallpaperURL:(NSURL *)imageUrl andFileOutput:(NSString*)fileOutput
I'm not sure you should be allocating a new instance of appController each time in this method - the rest of the code looks like there should be a single one of these which is displaying one label, effectively a delegate for the downloader? Perhaps this should be assigned by the XML data source when it creates each object?
After the download is complete, your connectionDidFinishLoading method would be something like this:
[appController downloaderDidFinishDownloading:self];
Which would call a method in your appController that looks something like this:
-(void)downloaderDidFinishDownloading:(WCSWallpaperDownloader*)downloader
{
completedDownloads++;
[txtStatus setStringValue:[NSString stringWithFormat:#"Downloaded %i of %i",completedDownloads,totalDownloads]];
}
Where completedDownloads and totalDownloads are ivars in your app controller class.