I have a connection class that uses NSURLConnection to connect to the server. While in main class I call a class method of this class, the class method then allocates instance of itself and when the delegate ConnectionDidFinish is received, I release same class from within. Is this approach correct or this will lead to some problem.
Main Class :
[ConnectionClass connectToServer];
Connection Class :
#implementation ConnectionClass
+(void)connectToServer{
connectionClass = [[ConnectionClass alloc] init];
[connectionClass createConnection];
}
-(void)createConnection{
NSURLConnection *connection = [[NSURLConnection alloc] initWithDelegate:self];
// create asynchronous connection
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
[self release];
}
#end
Is it good to release self within its own method ?
What if I do it something this way;
Main Class :
[connectionClass setDelegate:self];
[connectionClass connectToServer];
Connection Class :
#implementation ConnectionClass
-(void)connectToServer{
[connectionClass createConnection];
}
-(void)createConnection{
NSURLConnection *connection = [[NSURLConnection alloc] initWithDelegate:self];
// create asynchronous connection
}
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
[self.delegate finishedConnection:self]; // added delegate and then called to the main class and pass the self object for main to release it
}
#end
And in the main class delegate we, release the object,
-(void)finishedConnection:(ConnectionClass*)connection
{
[connection release];
}
IS there any problem in releasing the object this way ?
[self release] & [self retain] sound totally crazy to me. It makes no sense at all IMHO.
And I don't see the point of making (void)connectToServer a class method !
Your second way is the way to go. You could also make one step of the two, creating a method like :
[connectionClass connectToServerWithDelegate:self];
I would do this:
#implementation ConnectionClass
+ (void)connectToServer {
connectionClass = [[ConnectionClass alloc] init];
[connectionClass createConnection];
[connectionClass release];
}
- (void)createConnection {
[self retain];
NSURLConnection *connection = [[NSURLConnection alloc] initWithDelegate:self];
// create asynchronous connection
[connection release];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
[self release];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
[self release];
}
#end
That way the ConnectionClass object is self retaining, and you're not putting the retain/release responsibility in different places of code, that are not tightly related.
Edit: As Rabskatran points out, if you're just learning about retain/release, then this is not the optimal solution.
Your second example with the delegate is better. I'd let the connectionClass object be an instance variable, so you can message the connection object to cancel the operation when the main class (which would be the connection's delegate) gets deallocated.
Related
Here is my actual issue, as some suggested I want to write a class for handling the multiple download progress in a UITableView. I have no idea how to write a class for this, can somebody help with some tips or ideas?
The group to look at is NSURLRequest and NSURLConnection. The former let's you specify the request (URL, http method, params, etc) and the latter runs it.
Since you want to update status as it goes (I answered a sketch of this in your other question, I think), you'll need to implement the NSURLConnectionDelegate protocol that hands over chunks of data as it arrives from the connection. If you know how much data to expect, you can use the amount received to calculate a downloadProgress float as I suggested earlier:
float downloadProgress = [responseData length] / bytesExpected;
Here's some nice looking example code in SO. You can extend for multiple connections like this...
MyLoader.m
#interface MyLoader ()
#property (strong, nonatomic) NSMutableDictionary *connections;
#end
#implementation MyLoader
#synthesize connections=_connections; // add a lazy initializer for this, not shown
// make it a singleton
+ (MyLoader *)sharedInstance {
#synchronized(self) {
if (!_sharedInstance) {
_sharedInstance = [[MyLoader alloc] init];
}
}
return _sharedInstance;
}
// you can add a friendlier one that builds the request given a URL, etc.
- (void)startConnectionWithRequest:(NSURLRequest *)request {
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
NSMutableData *responseData = [[NSMutableData alloc] init];
[self.connections setObject:responseData forKey:connection];
}
// now all the delegate methods can be of this form. just like the typical, except they begin with a lookup of the connection and it's associated state
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
NSMutableData *responseData = [self.connections objectForKey:connection];
[responseData appendData:data];
// to help you with the UI question you asked earlier, this is where
// you can announce that download progress is being made
NSNumber *bytesSoFar = [NSNumber numberWithInt:[responseData length]];
NSDictionary *userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
[connection URL], #"url", bytesSoFar, #"bytesSoFar", nil];
[[NSNotificationCenter defaultCenter] postNotificationName:#"MyDownloaderDidRecieveData"
object:self userInfo:userInfo];
// the url should let you match this connection to the database object in
// your view controller. if not, you could pass that db object in when you
// start the connection, hang onto it (in the connections dictionary) and
// provide it in userInfo when you post progress
}
I wrote this library to do exactly that. You can checkout the implementation in the github repo.
EDIT: I actually traced it to the line where I call [in open]; and try to open the input stream. For some reason, my custom class may be an invalid delegate? I saw somebody else had the same error and did not have the problem after moving everything to a ViewController subclass rather than a custom class extending NSObject. However, I would still like to use my own custom class and not one of the ViewControllers.
I have a Connection class which I coded myself and I use NSInputStream and NSOutputStream. I initialize the streams in the init method:
- (id)init {
self = [super init];
if(self) {
messages = [NSMutableArray new];
CFReadStreamRef readStream;
CFWriteStreamRef writeStream;
CFStreamCreatePairWithSocketToHost(NULL, (CFStringRef)HOST, PORT, &readStream, &writeStream);
[self setIn: (__bridge_transfer NSInputStream *)readStream];
[self setOut: (__bridge_transfer NSOutputStream *)writeStream];
NSLog(#"Streams opened.");
NSLog(#"ConnectionController initialized...");
}
return self;
}
Also, here's the definition for my connection class in the .h
#interface ConnectionController : NSObject <NSStreamDelegate> {
NSMutableArray *messages;
}
#property (strong, nonatomic) NSInputStream *in;
#property (strong, nonatomic) NSOutputStream *out;
-(void)sendMessage:(NSString*)msg;
-(void)stream:(NSStream *)eStream handleEvent:(NSStreamEvent)eventCode;
-(void)messageReceived:(NSString*)msg;
#end
When I call this method openStreams, I get EXC_BAD_ACCESS
- (void)openStreams {
[in setDelegate:self];
[out setDelegate:self];
[in scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[out scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[in open];
[out open];
}
When I comment out setDelegate:self, the error does not occur. However, I need this in order to use the event-driven method for handling NSStreamEvents
How do I fix this? Thanks!
What is happening is whatever instance of the Connection class (which is set to be the delegate) is being deallocated (causing EXC_BAD_ACCESS in the run loop) either because you didn't retain it, or you are using ARC (pretty likely) and you do not have a reference to it.
The solution is to either call retain on the connection class, like so:
Connection *connection = [[Connection alloc] init];
[connection retain];
Or if you do have ARC enabled, make an instance variable in the class where you alloc Connection, and store your instance of connection there. That way ARC will not dealloc it, because the instance var counts as a reference.
I can't seem to find any info on this question, so I thought I'd ask the community.
Basically, I have a UITableView and I want to show an activity indicator while its data is loading from my server.
Here is some example code of what I'm trying to do (I'm using ASIHttpRequest).
//self.listData = [[NSArray alloc] initWithObjects:#"Red", #"Green", #"Blue", #"Indigo", #"Violet", nil]; //this works
NSString *urlStr=[[NSString alloc] initWithFormat:#"http://www.google.com"]; //some slow request
NSURL *url=[NSURL URLWithString:urlStr];
__block ASIHTTPRequest *request=[ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[request setCompletionBlock:^{
self.listData = [[NSArray alloc] initWithObjects:#"Red", #"Green", #"Blue", #"Indigo", #"Violet", nil]; //this doesn't work...
[table reloadData];
}];
[request setFailedBlock:^{
}];
[request startAsynchronous];
The dummy request to google.com does nothing - it just creates a delay and in the response I hope to repopulate the table with some JSON response from my own website.
But when I try to populate the table with the colours, nothing happens! I just get a blank table... If I uncomment the line above, it works fine, it's just on http responses things don't work for me.
Any suggestions greatly appreciated.
Edit:
I did a [self.tableView reloadData]; and now it works...
Stop using ASIHTTPRequest. NSURLConnection is not hard to use and will result in better, more performant code.
Your JSON response should be fed into a data structure not the UI. I recommend Core Data.
The data structure should feed your UITableView. Again, I recommend Core Data.
I would suggest reviewing how MVC works, you are short circuiting the design and that is the core problem.
SPOILER
Here is a more detailed how to. First you want the data retrieval to be async. Easiest and most reusable way to do that is build a simple NSOperation subclass.
#class CIMGFSimpleDownloadOperation;
#protocol CIMGFSimpleDownloadDelegate <NSObject>
- (void)operation:(CIMGFSimpleDownloadOperation*)operation didCompleteWithData:(NSData*)data;
- (void)operation:(CIMGFSimpleDownloadOperation*)operation didFailWithError:(NSError*)error;
#end
#interface CIMGFSimpleDownloadOperation : NSOperation
#property (nonatomic, assign) NSInteger statusCode;
- (id)initWithURLRequest:(NSURLRequest*)request andDelegate:(id<CIMGFSimpleDownloadDelegate>)delegate;
#end
This subclass is the most basic way to download something from a URL. Construct it with a NSURLRequest and a delegate. It will call back on a success or failure. The implementation is only slightly longer.
#import "CIMGFSimpleDownloadOperation.h"
#interface CIMGFSimpleDownloadOperation()
#property (nonatomic, retain) NSURLRequest *request;
#property (nonatomic, retain) NSMutableData *data;
#property (nonatomic, assign) id<CIMGFSimpleDownloadDelegate> delegate;
#end
#implementation CIMGFSimpleDownloadOperation
- (id)initWithURLRequest:(NSURLRequest*)request andDelegate:(id<CIMGFSimpleDownloadDelegate>)delegate
{
if (!(self = [super init])) return nil;
[self setDelegate:delegate];
[self setRequest:request];
return self;
}
- (void)dealloc
{
[self setDelegate:nil];
[self setRequest:nil];
[self setData:nil];
[super dealloc];
}
- (void)main
{
[NSURLConnection connectionWithRequest:[self request] delegate:self];
CFRunLoopRun();
}
- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSHTTPURLResponse*)resp
{
[self setStatusCode:[resp statusCode]];
[self setData:[NSMutableData data]];
}
- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)newData
{
[[self data] appendData:newData];
}
- (void)connectionDidFinishLoading:(NSURLConnection*)connection
{
[[self delegate] operation:self didCompleteWithData:[self data]];
CFRunLoopStop(CFRunLoopGetCurrent());
}
- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
{
[[self delegate] operation:self didFailWithError:error];
CFRunLoopStop(CFRunLoopGetCurrent());
}
#synthesize delegate;
#synthesize request;
#synthesize data;
#synthesize statusCode;
#end
Now this class is VERY reusable. There are other delegate methods for NSURLConnection that you can add depending on your needs. NSURLConnection can handle redirects, authentication, etc. I strongly suggest you look into its documentation.
From here you can either spin off the CIMGFSimpleDownloadOperation from your UITableViewController or from another part of your application. For this demonstration we will do it in the UITableViewController. Depending on your application needs you can kick off the data download wherever makes sense. For this example we will kick it off when the view appears.
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
NSURLRequest *request = ...;
CIMGFSimpleDownloadOperation *op = [[CIMGFSimpleDownloadOperation alloc] initWithURLRequest:request andDelegate:self];
[[NSOperationQueue mainQueue] addOperation:op];
[self setDownloadOperation:op]; //Hold onto a reference in case we want to cancel it
[op release], op = nil;
}
Now when the view appears an async call will go and download the content of the URL. In this code that will either pass or fail. The failure first:
- (void)operation:(CIMGFSimpleDownloadOperation*)operation didFailWithError:(NSError*)error;
{
[self setDownloadOperation:nil];
NSLog(#"Failure to download: %#\n%#", [error localizedDescription], [error userInfo]);
}
On success we need to parse the data that came back.
- (void)operation:(CIMGFSimpleDownloadOperation*)operation didCompleteWithData:(NSData*)data;
{
[self setDownloadOperation:nil];
NSLog(#"Download complete");
//1. Massage the data into whatever we want, Core Data, an array, whatever
//2. Update the UITableViewDataSource with the new data
//Note: We MIGHT be on a background thread here.
if ([NSThread isMainThread]) {
[[self tableView] reloadData];
} else {
dispatch_sync(dispatch_get_main_queue(), ^{
[[self tableView] reloadData];
});
}
}
And done. A few more lines of code for you to write but it replaces 13K+ lines of code that gets imported with ASI resulting in a smaller, leaner, faster application. And more importantly it is an app that you understand every single line of code.
This is the problem
request setCompletionBlock:^{
self.listData = [[NSArray alloc] initWithObjects:#"Red", #"Green", #"Blue", #"Indigo", #"Violet", nil]; //this doesn't work...
[table performSelectorOnMainThread:#selector(reloadTable) withObject:nil waitUntilDone:NO];
}];
The reload table needs to be done on the main thread.
I tried NWCoder's solution, and it didn't work because its calling the wrong method. This is what i used.
[self.tableView performSelectorOnMainThread:#selector(reloadData) withObject:nil waitUntilDone:NO];
I have a ViewController declared as:
#interface DownloadViewController : UIViewController
<UITableViewDataSource, UITableViewDelegate>
and I want to use NSURLConnection to download files. NSURLConnection simply "doesn't start", the delegate methods don't work (for example connection:didReceiveResponse is never called) . I noticed in some sample code that the class was subclassing NSObject instead of UIViewController.
How do I combine it? I want to use ViewController methods but then I can't use NSURLConnection.
It's not so easy to find a fully explained example how to download file with NSURLConnection. Everyone only concentrates on the easy methods like didReceiveResponse.
Using a UIViewController instead of an NSObject should not be your problem here !
I'm using a NSURLConnection in an UIViewController with no issue !
Here is a part of my code (not sure it will compile as it is) :
//
// MyViewController.h
//
#import <Foundation/Foundation.h>
#interface MyViewController : UIViewController {
#protected
NSMutableURLRequest* req;
NSMutableData* _responseData;
NSURLConnection* nzbConnection;
}
- (void)loadFileAtURL:(NSURL *)url;
#end
-
//
// MyViewController.m
//
#import "MyViewController.h"
#implementation MyViewController
- (void)loadView {
// create your view here
}
- (void) dealloc {
[_responseData release];
[super dealloc];
}
#pragma mark -
- (void)loadFileAtURL:(NSURL *)url {
// allocate data buffer
_responseData = [[NSMutableData alloc] init];
// create URLRequest
req = [[NSMutableURLRequest alloc] init];
[req setURL:_urlToHandle];
nzbConnection = [[NSURLConnection alloc] initWithRequest:req delegate:self startImmediately:YES];
[req release];
req = nil;
}
#pragma mark -
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
// Append data in the reception buffer
if (connection == nzbConnection)
[_responseData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
if (connection == nzbConnection) {
[nzbConnection release];
nzbConnection = nil;
// Print received data
NSLog(#"%#",_responseData);
[_responseData release];
}
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
// Something went wrong ...
if (connection == nzbConnection) {
[nzbConnection release];
[_responseData release];
}
}
#end
If you plan to download large files, consider storing the received packets in a file instead of storing it in memory !
If you're having problems, you could consider using the well regarded ASIHTTPRequest library to manage your download. It takes care of everything for you.
For example, just 2 lines will do it.
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDownloadDestinationPath:fullPathOfWhereToStoreFile];
Use "NSURLConnection asynchronously" search for the term and you'll find source. Or just NSURLConnection.
For example:
NSURLConnection NSURLRequest proxy for asynchronous web service calls
Using NSURLConnection from apple with example code
Objective-C Programming Tutorial – Creating A Twitter Client Part 1
I'm in the process of trying to move code from a UITableViewController class to a "helper" class.
The code utilizes NSURLConnection to grab and parse JSON and then populate an NSMutableArray.
What I'd like to do is call a method in my helper class that returns a NSMutableArray. What I don't understand is how to return the array from the connectionDidFinishLoading delegate class of NSURLConnection (where the array is actually built) as though it was from the originally called method that started the connection. In other words, how does the method that calls NSURLConnection get control back so it can return a value from the whole operation?
Here are the relevant methods from the helper class. How do I get the getMovies method to return the listOfMovies that is built in the connectionDidFinishLoading delegate class?
-(NSMutableArray)getMovies:(NSURL*)url {
responseData = [[NSMutableData data] retain];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
//NSURLRequest* request = [NSURLRequest requestWithURL: url cachePolicy: NSURLRequestUseProtocolCachePolicy timeoutInterval: 30.0];
connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
[responseData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[responseData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
//TODO error handling for connection
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//---initialize the array---
listOfMovies = [[NSMutableArray alloc] init];
tmdbMovies = [[NSArray alloc] init];
posters = [[NSArray alloc] init];
thumbs = [[NSDictionary alloc] init];
NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
SBJsonParser *json = [[SBJsonParser new] autorelease];
tmdbMovies = [json objectWithString:responseString];
// loop through all the top level elements in JSON
for (id movie in tmdbMovies) {
// 0 - Name
// 1 - Meta
// 2 - Url
if ((NSNull *)[movie objectForKey:#"name"] != [NSNull null]) {
if (![[movie objectForKey:#"name"] isEqualToString:#""]) {
name = [movie objectForKey:#"name"];
}
}
if ((NSNull *)[movie objectForKey:#"info"] != [NSNull null]) {
if (![[movie objectForKey:#"info"] isEqualToString:#""]) {
meta = [movie objectForKey:#"info"];
}
}
if ((NSNull *)[movie objectForKey:#"thumb"] != [NSNull null]) {
if (![[movie objectForKey:#"thumb"] isEqualToString:#""]) {
thumbUrl = [movie objectForKey:#"thumb"];
}
}
NSLog(#"Name: %#", name);
NSLog(#"Info: %#", meta);
NSLog(#"Thumb: %#", thumbUrl);
NSMutableArray *movieData = [[NSMutableArray alloc] initWithObjects:name,meta,thumbUrl,nil];
// add movieData array to listOfJMovies array
[listOfMovies addObject:movieData];
[movieData release];
}
//FIXME: Connection warning
if (connection!=nil) {
[connection release];
}
[responseData release];
[responseString release];
}
What you really need to do here is create a #protocol that creates a delegate for your helper class. Then change -(NSMutableArray)getMovies:(NSURL*)url to -(void)getMovies:(NSURL*)url
The class that is calling your helper method needs to implement your helper method's delegate.
Then - (void)connectionDidFinishLoading:(NSURLConnection *)connection calls the delegate method(s). It's best to have a one for success and one for failure.
=Update Begin=
You will need to also define an id delegate in your helper file which the calling class sets to self after init but before calling -(void)getMovies:(NSURL*)url. That way the helper file knows where to call back to.
getMovies *movieListCall = [[getMovies alloc] init];
movieListCall.delegate = self;
[movieListCall getMovies:<your NSURL goes here>];
You will see some additional lines for the inclusion of a delegate in both the getMovies.h and getMovies.m files.
=Update End=
in your getMovies.h file add:
#protocol getMoviesDelegate
#required
- (void)getMoviesSucceeded:(NSMutableArray *)movieArray;
- (void)getMoviesFailed:(NSString *)failedMessage;
#end
#interface getMovies : NSOBject {
id delegate;
}
#property (nonatomic, assign) id delegate;
in your getMovies.m file add:
#synthesize delegate;
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
//TODO error handling for connection
if ([delegate respondsToSelector:#selector(getMoviesFailed:)]) {
[delegate getMoviesFailed:[error localizedDescription]];
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//finishes with
if ([delegate respondsToSelector:#selector(getMoviesSucceeded:)]) {
[delegate getMoviesSucceeded:listOfMovies];
}
}
update your calling class .h file to use getMoviesDelegate:
#interface MoviesView : UIViewController <getMoviesDelegate>{
.
.
.
}
add the getMoviesDelegate methods to your calling class .m file
- (void)getMoviesSucceeded:(NSMutableArray *)movieArray {
//deal with movieArray here
}
- (void)getMoviesFailed:(NSString *)failedMessage {
//deal with failure here
}
This is not tested but hopefully gives you a road map to work with.
Protocols are nice because you can make both required and optional delegate methods and it helps in refining your helper methods to become very reusable across projects. The compiler will also warn you if you have implemented a protocol but not implemented the protocol's required delegate methods. If you follow this path be sure to use conformsToProtocol: and respondsToSelector:
Fundamentally, what's happening is that you're starting an asynchronous network load (asynchronous is the right way to do this, almost assuredly), and then you need some way to resume whatever operation you were doing before the load began. You have a few options:
Create your own delegate protocol. Your UITableViewController would then set itself as the helper's delegate, and the helper would call helperDidLoad or whatever you named that method. There's more information on writing delegates in the Cocoa Programming Guide.
Use blocks and continuation passing style. This is a bit more advanced but I like it. In your UITableViewController you'd write something like this:
[helper doSomething:^ (id loaded) {
[modelObject refresh:loaded]; // or whatever you need to do
}];
And then in your helper you'd write:
- (void)doSomething:(void ^ (id))continuation {
_continuation = continuation;
//kick off network load
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
_continuation(_data);
}
Use notifications. Read the NSNotificationCenter docs.
Use KVO. The KVO programming guide has a lot of good info on Key-Value Observing.
How to i get the getMovies method to return the listOfMovies that is built in the connectionDidFinishLoading delegate class?
I'm going to argue that you should not do that.
Network requests should be made asynchronously. If your getMovies were to make a synchronous request and return only when it had data you would block that entire thread while you waiting for a network connection to finish. This is a bad idea in general and a terrible idea if your main thread is calling getMovies. Blocking the main thread will prevent you from responding to touches or updating the UI, your app will appear frozen, and the OS will terminate it if your users don't quit in frustration first.
Instead have the helper class notify the caller when data is available (or when it failed to retrieve data) through a delegate call back, notification, KVO, or whatever mechanism you prefer.
Here are the steps, pseudocode like style:
[helperInstance setDelegate:self]; // where self is your UITableViewController class
in your helper class, in the connectionDidFinishLoading do something like this:
[delegate finishedLoadingData:JSONData];
Also you can define a protocol for your delegate, and the declare the delegate like this in your helper class:
#property (nonatomic, assign) id<YourProtocol> delegate;
Hope this helps,
Moszi