I'm developing an iPhone application where the data comes from a webservice that returns a json file. I'm using the following command in the viewDidLoad of the UITableViewController where I want to bind the data:
responseData = [[NSMutableData data] retain];
NSURLRequest *request = [NSURLRequest requestWithURL:
[NSURL URLWithString:#"webservice url"]];
[[NSURLConnection alloc] initWithRequest:request delegate:self];
and then I get the data from the json result into a NSDictionary in the connectionDidFinishedLodading Delegate.
The problem is that the numberOfRowsInSection delegate from UITableView executes before the connection finishes downloading data, which makes my table view with zero rows and doesn't show anything.
What am I doing wrong? Did I misunderstand the concept of the viewDidLoad and should be loading this data elsewhere?
Call reloadData on the tableView when you are done processing the data.
[self.tableView reloadData];
This triggers all UITableViewDatasource methods anew.
Related
I have a UITableView that gets JSON data from a Twitter search. I'm using polling to auto-refresh the view.
In my viewDidLoad, I have:
[NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:#selector(autoTweets:) userInfo:nil repeats:YES];
and then I have:
-(void) autoTweets : (NSTimer *)theTweets
{
NSURL *url = [NSURL URLWithString:#"http://search.twitter.com/search.json?q=%23hatlive%20-%22RT%20%40%22"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
connection = [NSURLConnection connectionWithRequest:request delegate:self];
if (connection)
{
webData = [[NSMutableData alloc] init];
}
[[self myTableView]setDelegate:self];
[[self myTableView]setDataSource:self];
array = [[NSMutableArray alloc] init];
}
Doing this refreshes the data every 10 seconds. The problem is, if I scroll on the 10th second when the code is executed, the app just crashes. If I don't scroll, it updates just fine. Does anyone know why?
Assuming array is the data used by the table view's data source, then the problem is that you change the contents of the array at the start of the connection. Then the contents get updated as the connection completes in the background. Meanwhile, as the table is scrolling, it is still trying to access the old contents of the array.
One solution is to setup a temporary array used to deal with the new connection. Don't update the old array with the new array until just before you call reloadData on the table.
Try [self.tableView beginUpdates]; and [self.tableView endUpdates]; while updating your data. Also you dont have to reset the datasource and delegate all the time. You may even call [self.tableView reloadData];.
You can disable touch on the table view right before the refresh, then enable after the data is set.
self.myTableView.userInteractionEnabled = YES; // before refresh
self.myTableView.userInteractionEnabled = NO; // after
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.
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
I'm using Apple Document to create an app.I succeed in connection to the server, but I receive 0 bytes from the server (no response data). I take the following steps:
I create a view-based App and add a property 'receivedData':
In ViewController.h:
#property (nonatomic, retain) NSMutableData *receivedData;
In ViewController.m:
#synthesize receivedData;
ViewController.m's action 'ViewDidLoad', I add:
receivedData = [NSMutableData alloc];
Add a button in the View and add action for it:
// create the request
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:#"http://..."]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// create the connection with the request
// and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData that will hold
// the received data
// receivedData is declared as a method instance elsewhere
receivedData=[[NSMutableData data] retain];
} else {
// inform the user that the download could not be made
}
When I debugging these codes, I find that receivedData returns 0 bytes. Any ideas about what goes wrong? A simple modify of my code will be appreciated.
Your code only creates the HTTP connection - the data will only be written to and available in receivedData after the delegate callbacks have been called by the framework (once the HTTP response is received). You can get more information and sample code from Apple's documentation
The answer is the same as it was the last time I answered it for you, over at How can I receive data from URL on iPhone?. I gave a detailed explanation-- did you read it?