Trying to parse two different URLs which has XML data.
static NSString *string1 = #"http://abc.com/abc1.xml";
NSURLRequest *URL1 =[NSURLRequest requestWithURL:[NSURL URLWithString:string1]];
self.URL1Connection =[[[NSURLConnection alloc] initWithRequest:URL1 delegate:self] autorelease];
static NSString *string2 = #"http://abc.com/abc2.xml";
NSURLRequest *URL2 =[NSURLRequest requestWithURL:[NSURL URLWithString:string2]];
self.URL2Connection =[[[NSURLConnection alloc] initWithRequest:URL2 delegate:self] autorelease];
I have two different NSOperation class both working independently as both have their own work to finish.
I have a parseQueue which is NSOperationqueue in which I have added two different operations.
TestOperation *testOperation = [[TestOperation alloc]
initWithData:self.data1 delegate:self ];
[self.parseQueue addOperation:testOperation];
[testOperation release]; // once added to the NSOperationQueue it's retained, we don't need it anymore
testOperation = nil;
Test1Operation *test1Operation = [[Test1Operation alloc]
initWithData:self.data2];
[self.parseQueue addOperation:test1Operation];
[test1Operation release]; // once added to the NSOperationQueue it's retained, we don't need it anymore
test1Operation = nil;
Basically I am trying to parse the two xml data separately and want to have concurrent operations. But when the second operation gets over adding in the queue, it still looks at the first class operation. I am lost in this since I have no idea why it is still looking for the first class even after release. Can anybody throw some ideas and help me.
I figured out the answer.
Need to call each XML URL in their own respective class and call NSOperation for each call seperately. Instead of calling on application delegate method, call on viewdidload or viewdidappear method as required.
Once finished parsing, notify the main thread that the parsing is over and return the result.
Sagos
Related
I have a view where I show an UIImageView which complimentary internet, I use to bring data NSXMLparser which are loaded correctly, the problem was that I use to make the parser NSOperationQueue background so then I refresh the image in my main view. image which form no refresh them in any way
I leave here the code below
- (void)viewDidLoad
{
[Base64 initialize];
[super viewDidLoad];
NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self
selector:#selector(loadDataWithOperation)
object:nil];
[queue addOperation:operation];
[operation release];
}
- (void) loadDataWithOperation {
getData=NO;
NSURL *url1 = [ NSURL URLWithString:[url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
NSData *xmlData = [NSData dataWithContentsOfURL:url1];
NSXMLParser *parser = [[NSXMLParser alloc]initWithData:xmlData];
[parser setDelegate:self];
[parser parse];
[self performSelectorOnMainThread:#selector(showImage)withObject:nil waitUntilDone:NO];
}
-(void)showImage
{
NSArray *imagen =[[NSArray alloc] initWithArray:xml];
NSString *hola1 =[[imagen objectAtIndex:5]objectForKey:#"imagen"];
NSData * dataa = [Base64 decode:hola1];
img = [UIImage imageWithData:dataa];
self.images.image = img;
[images setImage:img];
[img release];
}
What am I doing wrong? appreciate your help please
I don't see anything obvious (though obviously we don't see the building of the xml array nor do we know precisely what the XML itself looks like). You should NSLog (or set a breakpoint and manually inspect) the xml as well as hola1 and dataa results in showImage, to identify at precisely what's going on at each step.
There are two possible problems with background operations and downloading XML. Neither of these seem applicable here, but I'll mention it just in case:
But there's nothing that would prevent the downloading and parsing of your XML like you have demonstrated here. If you were using NSURLConnection to download the XML (perhaps you simplified it here for the purposes of demonstration), there are issues in using NSURLConnection in a background queue. But if you use dataWithContentsOfURL (or better, NSXMLParser method initWithContentsOfURL) that wouldn't be an issue.
It looks like you're downloading a single XML, but if you were downloading multiple XML sources simultaneously, you should appreciate that many servers impose a limit as to how many concurrent connections they'll allow from a single client. You can use NSOperationQueue property maxConcurrentOperationCount to mitigate that problem. Four is a typical value.
Unrelated, but there are a couple of minor memory management things you might want to look at:
if you already have xml you don't need to create a new imagen;
you should probably release the queue object after adding the operation, or if you need to keep it around to reuse it, you should make it a class property or instance variable;
you could get rid of operation completely if you did:
[queue addOperationWithBlock:^{
[self loadDataWithOperation];
}];
you should release the parser object when you're done with it;
if you keep imagen in your code you should also release it when done; and
you should not release the img object since imageWithData returns an autorelease object
The routine memory management stuff probably would be pointed out to you if you did a static analysis (choose "Analyze" from the "Product" menu).
One final observation:
I notice that you have:
NSData *xmlData = [NSData dataWithContentsOfURL:url1];
NSXMLParser *parser = [[NSXMLParser alloc]initWithData:xmlData];
Clearly that xmlData is not necessary because you could have also just have done:
NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:url1];
What is the best way to check which request is which inside the delegate method:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
}
Right now I have a NSURLConnection that I set to the NSURLConnection before making a request and inside didReceiveResponse I do:
if (self.tempConnection == connection)
however there is a possiblity this won't work for race conditions. Is there a better way to do this?
There is a better way in OS5. Forget about all those bothersome delegate messages. Let the connection build the data for you, and put your finished code right in line with your start code:
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.site.com"]];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response;
NSLog(#"got response %d, data = %#, error = %#", [httpResponse statusCode], data, error);
}];
I've looked at a bunch of different ways to do this, and I've found that by far the cleanest and easiest in order to manage is to use a block pattern. That way you are guaranteed to be responding to the right request upon completion, avoid race conditions, and you don't have any issues with variables or objects going out of scope during the asynchronous call. It's also a lot easier to read/maintain your code.
Both ASIHTTPRequest and AFNetworking APIs provide a block pattern (however ASI is no longer supported so best to go with AFNetworking for new stuff). If you don't want to use one of these libraries, but want to do it yourself, you can download the source for AFNetworking and review their implementation. However, that seems like a lot of extra work for little value.
Consider creating a separate class to serve as the delegate. Then, for each NSURLConnection spawned, instantiate a new instance of the delegate class to for that NSURLConnection
Here's some brief code to illustrate this:
#interface ConnectionDelegate : NSObject <NSURLConnectionDelegate>
...then implement the methods in the .m file
Now, I'm guessing you probably have the code you posted in a UIViewController subclass (or some other class serving different purposes)?
Wherever you are kicking off the requests, use this code:
ConnectionDelegate *newDelegate = [[ConnectionDelegate alloc] init];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"<url here">]];
[NSURLConnection connectionWithRequest:request delegate:newDelegate];
//then you can repeat this for every new request you need to make
//and a different delegate will handle this
newDelegate = [[ConnectionDelegate alloc] init];
request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"<url here">]];
[NSURLConnection connectionWithRequest:request delegate:newDelegate];
// ...continue as many times as you'd like
newDelegate = [[ConnectionDelegate alloc] init];
request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"<url here">]];
[NSURLConnection connectionWithRequest:request delegate:newDelegate];
You might consider storing all the delegate objects in a NSDictionary or some other data structure to keep track of them. I'd consider using an NSNotification in connectionDidFinishLoading to post a notification that the connection is done, and to serve whatever object created from the response. Lemme know if you want code to help you visualize that. Hope this helps!
A brief over view of what I am trying to do.
I am using the tableView:didSelectRowAtIndexPath: method inside my UITableViewController subclass which is catching a row selection from that view like so...
//..... inside tableView:didSelectRowAtIndexPath:
if (indexPath.section == 0) {
//--- Get the subview ready for use
VehicleSearchResponseTableViewController *vehicleSearchResponseTableViewController = [[VehicleSearchResponseTableViewController alloc] initWithNibName:#"VehicleSearchResponseTableViewController" bundle:nil];
// ...
//--- Sets the back button for the new view that loads
self.navigationItem.backBarButtonItem = [[[UIBarButtonItem alloc] initWithTitle:#"Back" style: UIBarButtonItemStyleBordered target:nil action:nil] autorelease];
// Pass the selected object to the new view controller.
[self.navigationController pushViewController:vehicleSearchResponseTableViewController animated:YES];
if(indexPath.row == 0) {
vehicleSearchResponseTableViewController.title = #"Mans";
EngineRequests *engineRequest = [[EngineRequests alloc] init];
[engineRequest getMans];
[engineRequest release];
}
if(indexPath.row == 1) {
//.... etc etc
As you can see in this method I set up a few things, pushing the new view onto the viewstack and changing the back buttons text, then I go into catching the different rows and then initiating a method in a subclass of nsobject where I want to have all my connection/request stuff going on.
Inside my NSObject I have several different methods for the different cells that you can select on the UITableViewController, basicly they specify different strings that will then initialize my ASIHTTPRequest wrapper to make a connection to the php script and catch all the data that will come back from the database.. NSObject looks like this.
//.... NSObject.m
- (IBAction) getMans
{
NSString *mansString = [[NSString alloc] initWithString:#"mans.php"];
[self grabURLInBackground:mansString];
[manusString release];
}
//....cont....
//--- Connect to server and send request ---------------->>
- (IBAction)grabURLInBackground:(NSString *)setUrlString
{
NSString *startURL = [NSString stringWithFormat:#"http://127.0.0.1:8888/CodeTest/%#", setUrlString];
NSURL *url = [NSURL URLWithString:startURL];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[request startAsynchronous];
}
- (void)requestFinished:(ASIHTTPRequest *)request
{
NSString *responseString = [request responseString]; //Pass request text from server over to NSString
NSData *responseData = [responseString dataUsingEncoding:NSUTF8StringEncoding]; //Create NSData object for Parser Delegate and load with responseString
NSLog(#"stuff %#",responseData);
}
- (void)requestFailed:(ASIHTTPRequest *)request
{
NSError *error = [request error];
NSLog(#"%#", error);
}
From here I would like to pass the data I am getting from the requestFinished method back over to the newly pushed UITableView.. However I have an error before I am able to get this far that I need to solve... if I run the simulator and click back and forth between the views (the main UITableViewController with the cells and then the newly popped view where I want to put the data) the application falls over and pops up an error in main.m Thread 1: program receive signal EXC_BAD_ACCESS.. I just don;t know whats causing because from what I can tell my code is not so bad.
Also when I debug my application I notice that once grabURLInBackground method has finished it bounces out back to the getMans method then goes back over to the UITableViewController and continues through the if statements, completely neglecting the requestFinished and requestFailed methods, and I just cannot figure out why.
I guess I am not sure if I am calling the methods and functions I need to use in the right places so if you have any suggestions or answers on how I can improve or if you know where my error is coming form that would be greatly appreciated.
There's a few issues with the code above but I'd guess that your bad access exception is due to the handling of your EngineRequests and use of AsiHttpRequest.
The code here
EngineRequests *engineRequest = [[EngineRequests alloc] init];
[engineRequest getMans];
[engineRequest release];
effectively creates an object then deallocates as soon as getMans has finished running.
Then inside the engineRequest object this code
[request setDelegate:self];
[request startAsynchronous];
requests that AsiHttpRequest notify the almost certainly released object once the request has completed.
There may be other issues at work here but I'd start by restructuring to try to keep this object around until at least after it's received the response from AsiHttpRequest.
Hard to tell from the brief overview, but generally when you bad_access and end up in the main application method, it's usually because you autoreleased something, then released it, and it craps out when the autorelease pool is drained. Might want to turn on NSZombiesEnabled and look for memory problems.
Who does receive your request?
The sender (and receiver) object is engineRequest.
But you release Engine Request in that very moment after you issued the async request (by mens of the getMans Method.
I would suggest that you
1. move the code
vehicleSearchResponseTableViewController.title = #"Mans";
EngineRequests *engineRequest = [[EngineRequests alloc] init];
[engineRequest getMans];
[engineRequest release];
from your UITableViewController's didSelectRowAtIndexPath method to your vehicleSearchResponseTableViewController's viewDidLoad method.
2. to retain your EngineRequests object and keep it in some instance variable within vehicleSearchResponseTableViewControllerand do not release it before the request is completely processed, either successfully or in error.
I can't say I really understand the memory handling in Objective-C so I have a couple of questions concerning that.
Do I have to remove the objects "url" and "urlRequest" in the box below or does "urlConnection" take on the responsibility for doing that?
NSURL* url = [NSURL URLWithString:url];
NSURLRequest* urlRequest = [[NSURLRequest alloc] initWithURL:url];
NSURLConnection* urlConnection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self];
What is the difference between the following object creations. Is the ref. counter retained in all cases?
[[NSString alloc] init];
[[NSString alloc] initWithFormat:...];
[NSString stringWithString:...];
When assigning a property, is the ref. count always retained regardless of whether "assign" or "retain" was set as attribute?
Generally speaking if you obtain an object through a method begining alloc, new or copy, you become responsible for releasing that object. Hence in your first query you'll need to release urlRequest and urlConnection. The url object is an example of an object which you don't need to release, as it is instantiated using a static factory method (URLWithString).
[[NSString alloc] init];
Will initialise a NSString with a reatin count of 1.
[[NSString alloc] initWithFormat:...];
Again, results in a NSString with retain count of 1. The only difference is you've called a different initializer.
[NSString stringWithString:...];
Creates an autoreleased NSString that is guranteed to remain valid during the current event loop.
As for property attributes, assign will not retain the object passed to the setter.
I know it's a bit dry but the Memory Management Guidelines are a really good reference for this type of question.
I have a class that updates two .plist files in the app documents directory via an NSURLConnection. The class acts as its own delegate for NSURLConnection. It works properly when I ask for a single file, but fails when I try to update two files. Does it look like I should start a new thread for each of the getNewDatabase messages?
- (void)getAllNewDatabases {
[self performSelectorOnMainThread:#selector(getNewDatabase:) withObject:#"file1" waitUntilDone:YES];
[self performSelectorOnMainThread:#selector(getNewDatabase:) withObject:#"file2" waitUntilDone:YES];
}
- (BOOL)getNewDatabase:(NSString *)dbName
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSMutableString *apiString = [[NSMutableString alloc] initWithString:kAPIHost];
[apiString appendFormat:#"/%#.plist",dbName];
NSURLRequest *myRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:apiString] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSURLConnection *myConnection = [[NSURLConnection alloc] initWithRequest:myRequest delegate:self];
[apiString release];
if( myConnection )
{
//omitted for clarity here
}
[pool release];
}
//NSURLConnection delegate methods here ...
I found something interesting with NSURLConnection and NSThread - the thread will only live as long as it takes to perform the method that you call from it.
In the case above the thread will live only as long as getNewDatabase:(NSString *)dbName takes to complete, therefore killing off any of its delegate methods before they actually have time to do anything.
I found this website that gives a better explanation and a solution to the problem
I tweaked it a little bit so I could have a custom time out if it didn't complete in a given time frame (handy when someone is walking around between access points)
start = [NSDate dateWithTimeIntervalSinceNow:3];
while(!isFinished && [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate:[NSDate distantFuture]]){
if([start compare:[NSDate date]] == NSOrderedAscending){
isFinished = YES;
}
}
As it stands currently in the code you provided, getNewDatabase: is running on the main thread of your application. The problem in this particular case then is something other than the life cycle of the thread, as James observed in his case.
If you did intend to perform this operation in the background, I'd recommend looking into using NSOperationQueue and NSOperation rather than solving the problem with the current code. I think your case is a great fit for NSOperationQueue, especially given that you have more than one download task to perform.
Dave Dribin has an excellent article about using asynchronous API, such as NSURLConnection, inside an NSOperation. Alternatively, as long as you're running in a background thread, you can also simplify the process and just use a synchronous API method instead in your NSOperation, such as initWithContentsOfURL:.
Marcus Zarra has also written a tutorial that demonstrates how easy it is to incorporate and use NSOperationQueue for simple background operations.