Thread still running of old view

Question

I have an app where there are five screens.

On each screen, in viewDidLoad I am accessing data from server.

On each screen I have next button.

When I go from screen one to screen five (by clicking Next 4 times), in NSLog, I still see the process done by all previous four view controller.

Is there any way, how can I kill those threads?

In short, I don't want to do any process when I go away from that view i.e. if I go from view 3 to 4, I want to stop the task that I was for view 3.

Getting data of earlier views & waiting for that data (which is unwanted) is not good for app, hence I want like what I explained above.

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Edit 1

Below is the code I use for reading the data.

.h

@property(nonatomic, retain) NSMutableData *webData;
@property(nonatomic, retain) NSMutableData *data;

Using below I request the data

.m

NSString *myTMainURL = [NSString stringWithFormat:@"http://www.google.com"];
NSURL *url = [NSURL URLWithString:myTMainURL];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[[NSURLConnection alloc] initWithRequest:request delegate:self];

For reading, below is how I read.

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    NSLog(@"didReceiveResponse");
    data = [[NSMutableData alloc] init ];
    [webData setLength: 0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)theData {
    NSLog(@"didReceiveData");
    [data appendData:theData];
    [webData appendData:data];
    NSLog(@"didreceveidata leng===%d===%d", [webData length], [data length]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"connectionDidFinishLoading");

    NSString *myDataFromLink = [[NSString alloc] initWithBytes: [data mutableBytes] length:[data length] encoding:NSUTF8StringEncoding];

    NSLog(@"myDataFromLink====%@--", myDataFromLink);

}

Answer 1

In viewWillDisappear:, send cancel to whatever operation is running.

This, of course, assumes you have a cancelable task/method/operation.

For example, for network requests, if you use NSURLConnection this is the case when you employ the delegate approach. With NSURLConnection's convenient class method sendAsynchronousRequest:queue:completionHandler: this is not possible. Thus, any serious application would use the delegate approach, since a long running asynchronous operation must be cancelable.

Answer 2

Since you are using NSURLConnection, You can cancel that connection and stop the NSURLRequest which you are using with your NSURLConnection with following code:

-(void)viewDidDisappear
{
[super viewDidDisappear];
[connection cancel];   // Here connection is your NSURLConnection object.
}

Answer 3

You can use NSOperation and cancel the operation when you go to the next view may be in the action of the next button or just in viewWillDisappear: method

Edit

Since You are using NSURLConnection then you can call cancel on the connection in viewWillDisappear:

.h

@property(nonatomic, retain) NSMutableData *webData;
@property(nonatomic, retain) NSMutableData *data;
@property(nonatomic, retain) NSURLConnection *connection;

.m

NSString *myTMainURL = [NSString stringWithFormat:@"http://www.google.com"];
NSURL *url = [NSURL URLWithString:myTMainURL];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

in viewWillDisappear:

[self.connection cancel]