Month: June 2011

Asynchronous Request within UITableViewCell

The Problem:
I have an image that needs to be loaded for each table cell. Unfortunately this causes the UI to become unresponsive for a couple seconds when you click to go to that table view.

The Solution:
Make the call to get the image data asynchronous.

First in our tableview delegate method, cellForRowAtIndexPath, we’ll use NSURLConnection to create the connection.


NSURLRequest *req = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://www.test.com/image_url"]];
NSURLConnection *imgCon = [NSURLConnection alloc];
..... /** Code added later  **/
[imgCon initWithRequest:req delegate:self startImmediately:YES];

There are 2 delegate methods that you need to have to make this work. (There are others that you’ll probably want to implement as well. Apple Docs)


-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
-(void)connectionDidFinishLoading:(NSURLConnection *)connection;

The didReceiveData method will probably be called multiple times. So we need to create a variable to keep on appending the data to it. Since we are creating multiple connections we need to map each connection to the data. But we also need to know which table cell we need to update once we have all the data.
So we create 2 NSMutableDictionary objects. One to map the table cells indexPath to the data and one to map the connection to the indexPath.


NSMutableDictionary *indexPathImgData;
NSMutableDictionary *connectionIndexPath;

The problem that arrises from trying to map the connection to the indexPath is that NSURLConnection doesn’t conform to the NSCopying Protocol. To get around this we need to use CFMutableDictionary. When adding values to a CFMutableDictionary “the keys and values are not copied—they are retained” (Apple Docs on CFMutableDictionary)

So to add the values to our NSMutableDictionary we will use the CFDictionaryAddValue function.

Now our cellForRowAtIndexPath method will look like this:


NSURLRequest *req = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://www.test.com/image_url"]];
NSURLConnection *imageCon = [NSURLConnection alloc];

CFDictionaryAddValue((CFMutableDictionaryRef)self.connectionIndexPath, imageCon, indexPath);
NSMutableData *imageData = [NSMutableData dataWithCapacity:0];
CFDictionaryAddValue((CFMutableDictionaryRef)self.indexPathImgData, indexPath, imageData);

[imageCon initWithRequest:req delegate:self startImmediately:YES];

And our NSURLConnection Delegate methods will look something like this:


- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

    [[self.indexPathImgData objectForKey:[self.connectionIndexPath objectForKey:connection]] appendData:data];
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSIndexPath *temp = [self.connectionIndexPath objectForKey:connection];
    [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:temp] withRowAnimation:UITableViewRowAnimationNone];

}

Now in your cellForRowAtIndexPath method you’ll want to do a check if the dictionary object has data for that indexPath and if so display it otherwise you’ll want to create a new connection.

iPhone Push Notifications

iPhone Push Notification Testing:

Testing out the interaction after receiving a remote push notifications on the iphone can be very annoying. Apple does not make it easy to setup remote push notifications. Plus development time is much slower if you try to build and test this interaction while waiting for remote notifications. And unfortunately Apple doesn’t provide a way to test out remote notifications on the simulator.

So instead of using a remote notification I used a local notification for testing this interaction.
In your UIApplication delegate instead of using this delegate method:


- (void)application:(UIApplication *)application 
     didReceiveRemoteNotification:(NSDictionary *)userInfo

I used this:


- (void)application:(UIApplication *)application 
        didReceiveLocalNotification: (UILocalNotification *)notification

You can then schedule a local notification (Apple Docs). This will then simulate receiving a notification when you are in the app.

To simulate the notification when the app isn’t in the foreground I created a local notification inside the delegate method:


-(void)applicationDidEnterBackground:(UIApplication *)application.

I set it up so as soon as you closed the app the notification would fire showing the default alert box.

Here is the code I used to create the local notification inside the DidEnterBackground method.


NSDate *nowDate = [NSDate date];
NSTimeInterval seconds = 0;
NSDate *newDate = [nowDate dateByAddingTimeInterval:seconds];

UILocalNotification *localNotif = [[UILocalNotification alloc] init];
if (localNotif != nil)
{
  localNotif.fireDate = newDate;
  localNotif.timeZone = [NSTimeZone defaultTimeZone];

  localNotif.alertBody = @"You have new notifications";
  localNotif.alertAction = NSLocalizedString(@"View", nil);

  localNotif.soundName = UILocalNotificationDefaultSoundName;
  localNotif.applicationIconBadgeNumber = 2;

  NSDictionary *infoDict = [NSDictionary dictionaryWithObject:@"2" 
       forKey:@"NewNotifications"];
  localNotif.userInfo = infoDict;

  [[UIApplication sharedApplication] scheduleLocalNotification:localNotif];
  [localNotif release];
}

When you click the “View” button on the alert box, the application will come to the foreground and the didReceiveLocalNotification will be called. You can then do what you need to do based on what data you passed to it via the NSDictionary object in the local notification.

So the main difference in your code between the local and remote notification is that in the local notification you’ll have to access the data you sent to it with [notification userInfo] and in the remote notification, the dictionary object is what is passed to it.