I have searched and tried a lot but in my application (which is using iOS 5 sdk) the NSURLConnection delegate methods gets called only when I initialise and start the connection in viewDidLoad method or on click event of any button.
But I want to call it after parsing my JSON file. And create a new connection for every record in JSON.
Can anyone tell me what is happening? Is something changed in ios sdk 5.
Here is my code:
-(void)getData:(NSString*)URL{
NSURLRequest *urlRequest = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:URL]];
shortURL = [NSString stringWithString:URL];
connection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self];
//NSAssert(connection!=nil, #"no connection", nil);
[connection start];
}
- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)response
{
// application specific stuff
}
The getData function is written in a class inherited from NSObject. And it is called from
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
method of UITableView.
Please help me with this.
Assuming that the JSON parsing code is happening in a background thread, you have to create an NSRunLoop for that thread.
The NSURLConnection class is simply adding itself to the runloop, if none exists, no processing or delegate methods will get invoked.
connection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self];
[[NSRunLoop currentRunLoop] run];
Note: The run method will block
Related
A weird problem.
I wanna load an image from web, so i use NSURLConnection to do it.
Everything is ok when i do testing my code on ios4.3.
But when i'm launch my app on ios5.0, i found the connection:didreceiveData haven't been called whatever what i did.
otherelse functions is called normally, just like connectionDidFinishLoading in ios4.3 and connectionDidFinishDownloading in ios5.0.
so u guys, who can help me, thanks advanced!
-(void)load
{
if(isDownloading){
return;
}
if(conn != nil){
[conn release];
}
if(data != nil){
[data release];
data = nil;
}
[self isDownloading:YES];
ImageDownloadData* imageDownloadData = [imageList objectAtIndex:count];
NSURL* url = [imageDownloadData url];
NSURLRequest* request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];
if(conn){
[conn start];
}
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)rd
{
NSLog(#"data");
if(!data){
data = [[NSMutableData alloc] initWithData:rd];
return;
}
[data appendData:rd];
}
I can't be sure if this is the same problem you're having, but I had a similar issue, and resolved it by taking out the in methods and references to NSURLConnectionDownloadDelegate. Apparently delegates of NSURLConnection can only implement one of the two protocols that are derived from NSURLConnectionDelegate at a time.
There's been some odd API changes between 4.3 and 5.0. Apple changed the NSURLConnectionDelegate from an informal protocol to a formal one, and branched out some of the methods into two additional subprotocols: NSURLConnectionDataDelegate and NSURLConnectionDownloadDelegate. (Oddly though, they depreciated the identical methods in NSURLConnectionDelegate but didn't document where they moved to.)
I've been noticing when compiling my code against the 6.0 API that I've been having trouble getting Cocoa Touch to call connection: didReceiveData: if I Implement methods from both NSURLConnectionDataDelegate and NSURLConnectionDownloadDelegate. All the other methods I implemented were called as expected.
I have a webservice that returning 20 results each time (it is a limitation of the service provider). I want to call this service 10-20 times repeatingly and update my UI each time.
Is there best practice for this situation? I do not want to block the ui while calling the server. This causes problems if the user want to perform actions while the action in progress
(like navigating away from the current page)
Thanks!!!
what you can do is call the webservice in a background thread, collect the required data and jump back to main thread and update the UI.
We are doing the above(i.e jumping from background thread to main thread) because it is not recommended to update any UI in the background process.
you can call you webService in background by using
[self performSelectorInBackground:#selector(MyWebService) withObject:nil];//you can pass any object if you have
and to come back on main thread when the background task is over you can do..
[self performSelectorOnMainThread:#selector(myMainFunction) withObject:nil waitUntilDone:YES];
you can change the last parameter i.e. waitUntilDone:No also. By doing this, user will not have to wait till the UI is updated. they can carry there task.
you can use NSTimer for periodic calling your webService.
hope that helped :)
It depends on how you want to display the information.
If you're using the asynchronous connection (in my opinion, more effective than calling a synchronous connection in the background) and its delegate, it should not block the user interface:
- (void)loadData {
NSString *urlString = #"http://www.stackoverflow.com";
NSURL *url = [NSURL URLWithString:urlString];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[NSURLConnection connectionWithRequest:request delegate:self];
}
// delegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
// clear out or intialize instance data variable
[myData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[myData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
// convert data to whatever it's supposed to be (for example, array)
NSString *dataString = [[NSString alloc] initWithData:myData encoding:NSUTF8StringEncoding];
NSArray *dataArray = [parser parseStringToArray:dataString];
[myArray addObjectsFromArray:dataArray];
//update tableview either using reload data (instant) or using updates (for smooth animation)
}
You can then recall the loadData method at the end of didFinishLoading: method to loop it.
Guys, I was retrieving an XML response from a .php script on my server using the following code:
NSString *xmlString = [NSString stringWithContentsOfURL:[NSURL URLWithString:urlString]
encoding:NSUTF8StringEncoding error:&error];
and
//tried also: if(error)
if(!xmlString)
{
NSString * errorString = [NSString stringWithFormat:#"Unable to download xml data (Error code %i )", [error code]];
UIAlertView * errorAlert = [[UIAlertView alloc] initWithTitle:#"Error loading content" message:errorString delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[errorAlert show];
[errorAlert release];
}
//*** now I have a touchXML xPath query code that extracts what I need from XML
My .php script wasn't working today and my iApp was freezing without any alerts, errors or notifications? I thought that the code above will handle errors but it doesn't???
A) Then what type of error does it catch?
Then I remembered that i I should try working with NSURLConnection and its delegate methods to catch any error that occurs.
//Inside viewDidLoad method
NSMutableData *responseData = [[NSMutableData alloc] init];
NSURL *baseURL = [[NSURL URLWithString:self.chosenDrawRss] retain];
NSURLRequest *request = [NSURLRequest requestWithURL:baseURL];
[[[NSURLConnection alloc] initWithRequest:request delegate:self] autorelease];
NSString *xmlString = [[NSString alloc] initWithData:self.responseData encoding:NSUTF8StringEncoding];
The problem I had using this approach was that app ran the Connection in the background and continued executing the rest of the code found in viewDidLoad, so I had to reorganize my code a bit by moving it to another method that I call from delegate method connectionDidFinishLoading. The problem I have is that my delegate methods are not called. Well, all except didFailWithError: if I try to load URL that doesn't exist.
UPDATE:
delegate methods are called but it takes one minute or so for delegate method to be called and until alert message pops out...
B) Could I use stringWithContentsOfURL and still have an alert to the user if anything happens?
C) If not, then I need help with setting up NSURLConnection approach? I mean, what I'm missing here is why aren't my delegate methods called?
I truly hope my questions make sense :D
L
If your delegate method is called in didFailWithError then i suppose it will even be called in
connectionDidFinishLoading. Check by enabling a breakpoint in the delegate methods and track the flow. It may have happened the function returns before you call the delegate.
NSString *xmlString = [[NSString alloc] initWithData:self.responseData encoding:NSUTF8StringEncoding]
should be called in your delegate connectionDidFinishLoading method and in
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[responseData appendData:data];
}
I dont see why the alert should pop up after a minute unless you are doing some processing before displaying it.
I am developing an app in which I have a table. In the table cell I have an imageview ( the images are displayed via url ) and a textview/webview. I start threads for each row to get the images in the
- (UITableViewCell *)tableView:(UITableView *)theTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
method ( if image is not already got ) and set the text of textview/webview from an array.
The problem arises when the images are being received and I pop the view, the application crashes giving the following message:
bool _WebTryThreadLock(bool), 0x1a0670: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now...
Now the situation becomes more weird if I don't release the textview/webview that I added to the cell, then every thing works fine.
Edit: the crash does not happens when I replace textview/webview with a label
Hoping I am clear in my question. If any thing is confusing please comment. I need to resolve this.
Thanks,
Nikhil
That's a huge mistake to use threads. Try to avoid using threads if you have other solutions !
In your case, just use an asynchronous NSURLConnection which will take care of downloading your image while not slowing your app ;)
Here is part of the code :
- (void) startDownload {
self.activeDownload = [NSMutableData data];
NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:
[NSURLRequest requestWithURL:
[NSURL URLWithString:#"blablabla"]] delegate:self];
self.imageConnection = conn;
[conn release];
}
#pragma mark -
#pragma mark Download support (NSURLConnectionDelegate)
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[self.activeDownload appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(#"ERROR DOWNLOADING");
// Clear the activeDownload property to allow later attempts
self.activeDownload = nil;
// Release the connection now that it's finished
self.imageConnection = nil;
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSLog(#"FINISH DOWNLOAD");
UIImage *image = [[UIImage alloc] initWithData:self.activeDownload];
self.activeDownload = nil;
self.imageConnection = nil;
//do whatever you want with your image
[image release];
}
Why doesn't this code work? It shows the Google screen but it doesn't change the text box value. I confirmed that the JS does work by running it in Safari, and this code seems to work otherwise since running alert('hi') does work.
NSURL *web_url = [NSURL URLWithString:#"http://www.google.com"];
NSURLRequest *web_request = [NSURLRequest requestWithURL:web_url];
[web_screen loadRequest:web_request];
NSString *js_result = [web_screen stringByEvaluatingJavaScriptFromString:#"document.getElementsByTagName('input')[1].value='test';"];
Just expanding on the previous answer. You need to conform to the UIWebViewDelegate protocol by setting the delegate property of the UIWebView like this:
web_screen.delegate = self;
Then you can implement one of the delegate methods to know when a request has finished loading and is therefore ready to have scripts run like so:
- (void)webViewDidFinishLoad:(UIWebView *)webView {
NSString *js_result = [webView stringByEvaluatingJavaScriptFromString:#"document.getElementsByTagName('input')[1].value='test';"];
}
For more information on the UIWebViewDelegate protocol visit the Apple site http://developer.apple.com/library/ios/#documentation/uikit/reference/UIWebViewDelegate_Protocol/Reference/Reference.html
The Load URL action takes place asynchronously. It does not even start until your method has ended. So your javascript is being pushed into an empty UIWebView, then your method ends, then the load happens.
You need to let your method end before the js is pushed in. The standard approach for this is to use a Delegate object, which will have a method called on it when the load completes. Only then does it make sense to push in the javascript.
Does it work if you wait for the page to finish loading first?
Consider looking at NSURLConnection and its delegate methods. You can use these to check on the status of a download.
#interface
...
NSURLConnection *connectionInProgress;
NSData *googleRequestResponseData;
NSURL *googleURL;
...
#implementation
...
- (void) setUpRequest {
googleURL = [[NSURL URLWithString:#"http://www.google.com/"] retain];
googleRequestResponseData = [[NSMutableData data] retain];
NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:30.0];
connectionInProgress = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
}
#pragma mark NSURLConnection delegate methods
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[googleRequestResponseData appendData:data];
}
- (void) connectionDidFinishLoading:(NSURLConnection *)connection {
[web_screen loadData:googleRequestResponseData MIMEType:#"application/octet-stream" textEncodingName:#"utf-8" baseURL:googleURL];
NSString *js_result = [web_screen stringByEvaluatingJavaScriptFromString:#"document.getElementsByTagName('input')[1].value='test';"];
NSLog (js_result);
[googleURL release];
[googleRequestResponseData release];
[connectionInProgress release];
connectionInProgress = nil;
}
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog (#"Connection failed to load data from Google!");
[googleURL release];
[googleRequestResponseData release];
[connectionInProgress release];
connectionInProgress = nil;
}
Alternatively, check out Ben Copsey's ASIHTTPRequest wrapper, which includes a simplified approach to asynchronous downloads (see ASINetworkQueue, specifically).
You can use ASINetworkQueue to run a method of your choice (to run the Javascript code, for example), once the request download is complete.
add '.innerHTML' after what you are searching for
In your case do the following
- (void)webViewDidFinishLoad:(UIWebView *)webView {
NSString *js_result = [webView stringByEvaluatingJavaScriptFromString:#"document.getElementsByTagName('input')[1].value='test'.innerHTML"];
}
This worked for me .
check this for more info here