Adding a modal loading view to Master-Detail application (in applicationDidBecomeActive method) - ios

Question

In Xcode 5.0.2 I have created a blank Master Detail application for iPhone and it works okay in the simulator:
When the iPhone app is being started or awaken from a background, I would like to display a modal view with a Label "Loading..." in its middle, fetch a web page (in this test case; in the real app this will be game updates and player scores) and then dismiss the modal view on the web page fetch completion or error or timeouts.
So I have created 2 new files, LoadingViewController.h and LoadingViewController.m (with no custom code by me for now).
And since it is Xcode version 5, there are no xib files, but a Main.storyboard - so I have dragged a View Controller from the Object Library onto the storyboard. Then on the right side I have selected the LoadingViewController class as the Custom Class in the Identity Inspector:
And finally I have added 3 methods to the AppDelegate.m:
- (void)applicationDidBecomeActive:(UIApplication *)application
{
[self showLoadingView];
}
- (void)applicationWillResignActive:(UIApplication *)application
{
[self dismissLoadingView];
}
- (void)showLoadingView
{
NSLog(#"%s", __PRETTY_FUNCTION__);
[self fetchHttp];
LoadingViewController *other = [[LoadingViewController alloc] init];
[self.window.rootViewController presentViewController:other animated:YES completion:nil];
}
- (void)dismissLoadingView
{
NSLog(#"%s", __PRETTY_FUNCTION__);
[self.window.rootViewController dismissViewControllerAnimated:YES completion:nil];
}
- (void)fetchHttp
{
NSLog(#"%s", __PRETTY_FUNCTION__);
NSString *urlAsString = #"http://stackoverflow.com";
NSURL *url = [NSURL URLWithString:urlAsString];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[NSURLConnection
sendAsynchronousRequest:urlRequest
queue:queue
completionHandler:^(NSURLResponse *response,
NSData *data,
NSError *error) {
if ([data length] > 0 &&
error == nil) {
NSString *html = [[NSString alloc] initWithData:data
encoding:NSUTF8StringEncoding];
NSLog(#"HTML = %u", [html length]);
}
else if ([data length] == 0 &&
error == nil) {
NSLog(#"Nothing was downloaded.");
}
else if (error != nil) {
NSLog(#"Error happened = %#", error);
}
// XXX how to dismiss the modal view here, it's a different thread?
}];
}
Unfortunately now I get a black screen in the simulator and the following output:
2013-12-01 22:37:01.332 LoadingTest[3840:a0b] -[AppDelegate showLoadingView]
2013-12-01 22:37:01.334 LoadingTest[3840:a0b] -[AppDelegate fetchHttp]
2013-12-01 22:37:01.857 LoadingTest[3840:a0b] Unbalanced calls to begin/end appearance transitions for <UINavigationController: 0x8c74f10>.
2013-12-01 22:37:01.870 LoadingTest[3840:4607] HTML = 196885
It is difficult for me to understand, how to use storyboard here (and I'd like to use it, if possible) - because the books I'm reading (in O'Reilly Safari) all talk about xib files (probably for the older Xcode versions?).
And also I don't understand how to dismiss the modal view from my completionHandler since it is in a different thread and I probably shouldn't call dismissViewControllerAnimated from there?
UPDATE:
I've added a "Storyboard ID" to my View: loadingView and the following code to AppDelegate.m:
- (void)showLoadingView
{
NSLog(#"%s", __PRETTY_FUNCTION__);
[self fetchHttp];
UIStoryboard *board = [self.window.rootViewController storyboard]; //[UIStoryboard storyboardWithName:#"Main.storyboard" bundle:nil];
LoadingViewController *other = [board instantiateViewControllerWithIdentifier:#"loadingView"];
[self.window.rootViewController presentViewController:other animated:YES completion:nil];
}
- (void)fetchHttp
{
NSLog(#"%s", __PRETTY_FUNCTION__);
NSString *urlAsString = #"http://stackoverflow.com";
NSURL *url = [NSURL URLWithString:urlAsString];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
[NSURLConnection
sendAsynchronousRequest:urlRequest
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response,
NSData *data,
NSError *error) {
if ([data length] > 0 &&
error == nil) {
NSString *html = [[NSString alloc] initWithData:data
encoding:NSUTF8StringEncoding];
NSLog(#"HTML = %u", [html length]);
}
else if ([data length] == 0 &&
error == nil) {
NSLog(#"Nothing was downloaded.");
}
else if (error != nil) {
NSLog(#"Error happened = %#", error);
}
[self dismissLoadingView];
}];
}
but now I get the warning below and the loadingView isn't dismissed (probably because the web page loads faster than the modal view is shown?):
2013-12-03 01:49:12.208 LoadingTest[631:70b] -[AppDelegate showLoadingView]
2013-12-03 01:49:12.210 LoadingTest[631:70b] -[AppDelegate fetchHttp]
2013-12-03 01:49:12.756 LoadingTest[631:70b] HTML = 200949
2013-12-03 01:49:12.757 LoadingTest[631:70b] -[AppDelegate dismissLoadingView]
2013-12-03 01:49:12.757 LoadingTest[631:70b] Warning: Attempt to dismiss from view controller <UINavigationController: 0x8a70ce0> while a presentation or dismiss is in progress!
2013-12-03 01:49:12.844 LoadingTest[631:70b] Unbalanced calls to begin/end appearance transitions for <UINavigationController: 0x8a70ce0>.

Answer 1

First thing, when you instantiate a controller in a storyboard, you don't use alloc init, you use the UIStoryboard method instantiateViewControllerWithIdentifier:. You need to give your controller a "Storyboard ID", which I can see from your image that you haven't done yet (and if you don't understand storyboards, read Apple's documents about it).
You can dismiss your modal view from the completion handler -- the handler is the code that's called after the async operation finishes, so you you should use [NSOperationQueue mainQueue] as the queue argument.