I'm building an Image Store for my app, basically it's a singleton that manages images download and caching (two levels NSCache and Core Data).
I was wondering if I could use blocks instead of delegates, I mean, there can be multiple requests for the same image, I want to update all the pending requesters by "triggering" the block they provided on call.
Is it possible to store a block in an NSArray and call it when I downloaded the image? Does this make sense?
What if the block is then triggered when the calling object has been deallocated?
Thanks
If you have a list of observers for an event then you should look at NSNotifications instead.
Every time an image is downloaded your singleton should do something like
NSDictionary *info = [NSDictionary dictionaryWithObjectsAndKeys:
image, #"image",
originalURL, #"imageURL",
nil];
[[NSNotificationCenter defaultCenter] postNotificationName:#"imageDownloaded" object:self userInfo:info];
and anyone interested in that image should receive a notification about it.
You can extend this pattern to include notifications about progress and failed downloads as well :)
Related
I am attempting to create an application that will initiate a call to a priority 1 contact on a call-center-like list.
Then, if that contact does not answer (let's forget the whole problem of answering machines here), I'd like to call the priority 2 contact, and so on, until one of them answers or I exhaust my list.
Is this possible?
I've tried the following:
Hook into the CTCallCenter.CallEventHandler event, and checking the call state for CTCallStateConnected and CTCallStateDisconnected, and I get it to respond to the fact that the call disconnected, without ever connecting, and then attempt to initiate another call like I did the first, but this second attempt just sits dead in the water.
Override the DidEnterBackground method, and periodically check the CTCall.CallState property, basically again trying to respond to a disconnect that was never connected, but this does not appear to work either
I also tried adding a short delay (1 second, 2.5 seconds and 10 seconds) after detecting the disconnected state before attempting the next dial, to allow for the phone application to "settle down" after aborting the call, this did not change anything.
I'm of the opinion that this is better solved at the destination of the phone call. I would either have the phone company configure a "follow me" service, use Twilio or some other 3rd party service (as already suggested), or configure my own PBX using something like Asterisk (Asterisk includes the ability to configure "follow me" type behavior). It provides you much more flexibility and control, even if you did find a way to do this natively in iOS.
Having said that, I did get this to work in iOS assuming the following:
Your app initiates the call.
The phone app is opened, dials the number, and disconnects.
The user explicitly returns to your app. If you managed to get the events while your app was backgrounded, I want to know more :-).
On return of control to your app, the phone events are sent and a new call is initiated.
I have the following snippet of code in my UIApplicationDelegate didFinishLaunchingWithOptions method:
// In appdelegate header, ct is declared as #property (strong, nonatomic) CTCallCenter *ct;
self.ct = [[CTCallCenter alloc] init];
self.ct.callEventHandler = ^(CTCall *call) {
if (call.callState == CTCallStateConnected) {
// do some state management to track the call
} else if (call.callState == CTCallStateDisconnected) {
// check that this is the expected call and setup the
// new phone number
NSURL *telURL = [NSURL URLWithString:myNewNumberURL];
[application openURL:telURL];
}
};
This will make the new call. I'm using the iOS 5 SDK; tested on an iPhone 4s.
EDIT:
Using Return to app behavior after phone call different in native code than UIWebView as a starting point, I've managed to get this to work. Note that I have punted on memory management for clarity. Assuming you use the web view technique for getting back to your app after the call is complete, try something like this in the call completed block:
else if (call.callState == CTCallStateDisconnected) {
// check that this is the expected call and setup the
// new phone number
NSURL *telURL = [NSURL URLWithString:myNewNumberURL];
dispatch_async(dispatch_get_main_queue(), ^{
UIWebView *callWebview = [[UIWebView alloc] init] ;
[self.window.rootViewController.view addSubview:callWebview];
[callWebview loadRequest:[NSURLRequest requestWithURL:telURL]];
// and now callWebView sits around until the app is killed....so don't follow this to the letter.
});
}
However, this may not quite give you what you want either. The user will get an alert on each call request, providing an opportunity to cancel the call.
You could use http://labs.twilio.com/twimlets/findme. You could have the app call a Twilio number and it could use findme to call all the numbers in order.
I didn't take a deeper look at it, but the Deutsche Telekom SDK might contain what you're looking after:
http://www.developergarden.com/fileadmin/microsites/ApiProject/Dokumente/Dokumentation/ObjectiveC-SDK-2.0/en/interface_voice_call_service.html
I really am not sure though (don't have time to really look at it at the moment) - I just remembered I'd read somewhere that they have an iOS SDK that is supposed to also handle call management, so I'm posting the link here for you to find out (and hopefully tell us if it works).
#pragma mark -
#pragma mark Call Handler Notification
-(void)notificationCallHandler {
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(callReceived:) name:CTCallStateIncoming object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(callEnded:) name:CTCallStateDisconnected object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(callConnected:) name:CTCallStateConnected object:nil];
}
-(void)callEnded:(NSNotification*)notification {
NSLog(#"callEnded");
}
-(void)callReceived:(NSNotification*)notification {
NSLog(#"callReceived");
}
-(void)callConnected:(NSNotification*)notification {
NSLog(#"callConnected");
}
May this will help you
if you wanna setup a new call, while app is in background, i dont see any proper way for this, a lil hack could be, getting location update (because u can get location updates while app is in background), and location service automatically wakes up your application when new location data arrives, and small amount of time is given to application in which u can execute some code, in that time you may start a new call.
u can read further here:
search this ''Starting the Significant-Change Location Service'' in this link Location Aware programming guide
, and read the paragraph that is written after the code block.
I have a UITableView with a list of items, each having it's own image. I thought Apple's LazyTableImages sample project would be perfect to learn from, and use to implement the same kind of process of downloading images asynchronously, after the original list data is retrieved.
For the most part, it works quite well, except I did notice a subtle difference in behavior, between this sample app, and how the actual app store downloads images.
If you launch the LazyTableImages sample, then do a quick flick-scroll down, you'll see that the images do not get displayed until after the scrolling comes to a complete stop.
Now, if you do the same test with a list of items in the actual app store, you'll see that the images start displaying as soon as the new items come into view, even if scrolling hasn't stopped yet.
I'm trying to achieve these same results, but so far I'm not making any progress. Does anyone have any ideas on how to do this?
Thanks!
I'm baffled that nobody could answer this...
So, I eventually figured out how to acheive the exact same effect that is used in the actual app store, in regards to how the icons are downloaded/displayed.
Take the LazyTableImages sample project and make a few simpled modifications.
Go into the root view controller and remove all checks regarding is table scrolling and/or decelerating in cellForRowAtIndexPath
Remove all calls to loadImagesForOnScreenRows, and thus remove that method as well.
Go into IconDownload.m and change the startDownload method to not do an async image downlaod, but instead do a sync download on a background thread. Remove all the code in startDownload, and add the following, so it looks like this:
- (void)startDownload
{
NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:#selector(loadImage) object:nil];
[queue addOperation:operation];
[operation release];
[queue release];
}
Then, add a loadImage, like this:
- (void)loadImage
{
NSData *imageData = [[NSData alloc] initWithContents OfURL:[NSURL URLWithString:appRecord.imageURLString]];
self.apprecord.appIcon = [UIImage imageWithData:imageData];
[imageData release];
[self performSelectorOnMainThread:#selector(notifyMainThread) withObject:nil waitUntilDone:NO];
}
Then, add notifyMainThread like this:
- (void)notifyMainThread
{
[delegate appImageDidLoad:self.indexPathInTableView];
}
Done! Run it, and you will see the exact app store behavior, no more waiting to request image downloads until scrolling stops, and no more waiting for images to display until scrolling stops, or until user has removed their finger from the screen.
Images are downloaded as soon as the cell is ready to be displayed, and the image is displayed as soon as it is downloaded, period.
Sorry for any typos, I didn't paste this from my app, I typed it in, since I'm away from my mac right now...
Anyway, I hope this helps you all...
Check out UIScrollViewDelegate. I've implemented something like this by listening for scrollViewDidScroll:, calculating the scroll speed (by checking the contentOffset against the last recorded contentOffset, divided by the difference in time), and starting to load images once the speed drops below a certain threshold. (You could achieve something similar with UIScrollViewDelegate's scrollViewDidEndDragging:willDecelerate: as well).
Of course, you don't have to check the speed; you could just load images on UITableViewDelegate's tableView:willDisplayCell:forRowAtIndexPath: whenever you see a new cell, but I've found that if the user is flipping through tons of cells, you don't need to bother until you see that they're going to slow down to browse.
I'm developing an iPhone application that uses the iPod library to play some songs. I load the songs with the code below. The problem is, when running this code right after the device has been synced with iTunes, there is a problem. Apparently the iPod Library needs to be updated, and it takes some time. If I go to the iPod Application right after a sync I seen a message saying "Updating Library..". If i call "[query items]" from my application while that is happening, I get an empty array indicating there is no songs in the library. Everything works perfect when the update is over. Is there any way to solve this problem? Maybe a way to detect when the update is over. I have tried to listen to alle NSNotifications, but none were called when the update finished.
MPMediaQuery *query = [MPMediaQuery songsQuery];
// convert all items to abstracted media item
NSArray *items = [query items];
NSMutableArray *convertedItems = [[NSMutableArray alloc] initWithCapacity:[items count]];
for (MPMediaItem *item in items) {
REMediaItem *mediaItem = [[REMediaItem alloc] initWithMediaItem:item];
[convertedItems addObject:mediaItem];
[mediaItem release];
}
I hope someone can help.
Peter
I discovered that there actually is a way to see when the update is complete. The device will post a notification when the update is over.
[[MPMediaLibrary defaultMediaLibrary] beginGeneratingLibraryChangeNotifications]
NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
[notificationCenter addObserver:self
selector:#selector(iPodLibraryDidChange)
name: MPMediaLibraryDidChangeNotification
object:nil];
The only problem is that I can't find a way to determinate if the device is updating the iPod Library and I should wait for it to finish or the device simply doesnt have any songs in the library. [query items] will return an empty array in both cases.
#Peter is right - and actually I found a walkaround for his problem.
At first I found that MPMediaPickerController returns nil when allocated and initiated while syncing - at first I thought it will work to check if there's an access to the library but sometimes it doesn't work.
The only way for now I found is to check lastModificationDate of MPMediaLibrary - as long as it's changing you won't get results using MPMediaQuery - delay your changes to a moment when that property stops changing (by any way you like) and you should be fine.
Already sent a bug report on that - the documentation says you should reload your cached objects from library when the notification fires but you clearly can't do it if MPMediaQuery returns nil for every object you try to find.
First, I'm using an NSURLConnection to download JSON data from twitter. Then, I'm using a second NSURLConnection to download corresponding user avatar images (the urls to the images are parsed from the first data download).
For the first data connection, I have my TwitterViewController set as the NSURLConnection delegate. I've created a separate class (ImageDownloadDelegate) to function as the delegate for a second NSURLConnection that handles the images. After the tweets are finished downloading, I'm using this code to get the avatars:
for(int j=0; j<[self.tweets count]; j++){
ImageDownloadDelegate *imgDelegate = [[ImageDownloadDelegate alloc] init];
Tweet *myTweet = [self.tweets objectAtIndex:j];
imgDelegate.tweet = myTweet;
imgDelegate.table = timeline; //to reload the data
NSURLRequest* request = [NSURLRequest requestWithURL:[NSURL URLWithString:myTweet.imageURL]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60];
imgConnection = [[NSURLConnection alloc] initWithRequest:request delegate:imgDelegate];
[imgDelegate release];
}
So basically a new instance of the delegate class is created for each image that needs to be downloaded. Is this the best way to go about this? If I were to create only one instance of the delegate class there's no way to figure out which image is associated with which tweet, correct? Nor would I be able to figure out the exact order in which the images are being downloaded.
The algorithm works fine... I'm just wondering if I'm going about it the most efficient way .
Put image downloads into something like an NSOperationQueue.
When the image download is done, save it to the caches directory, then send out a notification containing the original image URL, and the filename the image is now located at.
Anything that wants the image can listen for the notification. If nothing cares anymore (say cells that have scrolled off the screen) then they will have unsubscribed from notifications, so the image will just sit there until the system cleans out your cache directory...
It's also trivial with this system to check and see if an image already exists on disk before you download it, just keep somewhere a mapping of URL's to filenames.
You might perhaps use the queuing feature of ASIHTTPRequest instead. You can create an ASINetworkQueue to handle a ordered queue of requests, and each request can perform behaviors on completion, so that you can track requests with responses.
Requests are based on the NSOperation class, and the queue on NSOperationQueue, so this framework does a lot of the coding work for you.
For a game I'm developing, I have several model classes that trigger notifications when their state changes. Then, the view subscribes to those notifications and can react on them.
I'm doing my unit tests for the model with OCUnit, and want to assert that the expected notifications were posted. For that, I'm doing something like this:
- (void)testSomething {
[[NSNotificationCenter defaultCenter] addObserver:notifications selector:#selector(addObject:) name:kNotificationMoved object:board];
Board *board = [[Board alloc] init];
Tile *tile = [Tile newTile];
[board addTile:tile];
[board move:tile];
STAssertEquals((NSUInteger)1, [notifications count], nil);
// Assert the contents of the userInfo as well here
[board release];
}
The idea is that the NSNotificationCenter will add the notifications to the NSMutableArray by calling its addObject: method.
When I run it, however, I see that addObject: is being sent to some other object (not my NSMutableArray) causing OCUnit to stop working. However, if I comment out some code (such as the release calls, or add a new unit test) everything starts working as expected.
I'm assuming this has to o with a timing issue, or NSNotificationCenter relying on the run loop in some way.
Is there any recommendation to test this? I know I could add a setter in Board and inject my own NSNotificationCenter, but I'm looking for a quicker way to do it (maybe some trick on how to replace the NSNotificationCenter dynamically).
Found the problem. When testing notifications you need to remove the observer after you have tested it. Working code:
- (void)testSomething {
[[NSNotificationCenter defaultCenter] addObserver:notifications selector:#selector(addObject:) name:kNotificationMoved object:board];
Board *board = [[Board alloc] init];
Tile *tile = [Tile newTile];
[board addTile:tile];
[board move:tile];
STAssertEquals((NSUInteger)1, [notifications count], nil);
// Assert the contents of the userInfo as well here
[board release];
[[NSNotificationCenter defaultCenter] removeObserver:notifications name:kNotificationMoved object:board];
}
If you fail to remove the observer, after a test runs and some local variables are released, the notification center will try to notify those old objects when running any subsequent test that triggers the same notification.
There are no timing issues or runloop related problems since everything in your code is non-concurrent and should be executed immediately. NSNotificationCenter only postpones notification delivery if you use an NSNotificationQueue.
I think everything is correct in the snippet you posted. Maybe there's an issue with the mutable array 'notifications'. Did you init and retain it correctly? Try to add some object manually instead of using the notification trick.
If you suspect your tests have timing issues - you may want to consider injecting your own notification mechanism into your board object (which is probably just a wrapper of the existing apple version).
That is:
Board *board = [[Board alloc] initWithNotifier: someOtherNotifierConformingToAProtocol];
Presumably your board object posts some notification - you would use your injected notifier in that code:
-(void) someBoardMethod {
// ....
// Send your notification indirectly through your object
[myNotifier pushUpdateNotification: myAttribute];
}
In your test - you now have a level of indirection that you can use for testing, so you can implement a test class the conforms to your AProtocol - and maybe counts up the pushUpdateNotification: calls. In your real code you encapsulate the code you probably already have in Board that does the notification.
This of course is a classic example of where MockObjects are useful - and there is OCMock which well let you do this without having to have a test class to do the counting (see: http://www.mulle-kybernetik.com/software/OCMock/)
your test would problably have a line something like:
[[myMockNotifer expect] pushUpdateNotification: someAttribute];
Alternatively you could consider using a delegate instead of notifications. There is a good pro/con set of slides here: http://www.slideshare.net/360conferences/nsnotificationcenter-vs-appdelegate.