Object deallocates immediately after it has been initialized

Question

I am trying to make a class that plays YouTube videos, but I am having several problems with it.

Here is my class that handles YouTube videos:

// this is the only property declared in the .h file:
@property (strong, nonatomic) UIView * view

// the rest of this is the .m file:
#import "MyYouTube.h"
@interface MyYouTube()
@property (strong, nonatomic) NSDictionary * contentData;
@property (strong, nonatomic) UIWebView * webView;
@property (nonatomic) int videoOffset;
@end

@implementation MyYouTube
@synthesize view,contentData,webView,videoOffset;

- (MyYouTube*) initIntoView: (UIView*) passedView withContent: (NSDictionary*) contentDict {
    NSLog(@"YOUTUBE: begin init");
    self=[super init];
    videoOffset=0;
    view=[[UIView alloc] initWithFrame:passedView.bounds];
    [view setBackgroundColor:[UIColor blackColor]];
    [view setAutoresizesSubviews:YES];
    [view setAutoresizingMask:UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth];
    contentData=contentDict;

    NSString * compiledUrl=[[NSString alloc] initWithFormat:@"http://_xxx_.com/app/youtube.php?yt=%@",[contentData objectForKey:@"cnloc"]];
    NSURL * url=[[NSURL alloc] initWithString:compiledUrl];
    NSURLRequest * request=[[NSURLRequest alloc] initWithURL:url];

    webView=[[UIWebView alloc] initWithFrame:passedView.bounds];
    [webView loadRequest:request];
    [webView setAutoresizingMask:UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight];
    [[webView scrollView] setScrollEnabled:NO];
    [[webView scrollView] setBounces:NO];
    [webView setMediaPlaybackRequiresUserAction:NO];
    [webView setDelegate:self];

    NSLog(@"YOUTUBE: self: %@",self);
    NSLog(@"YOUTUBE: delegate: %@",webView.delegate);

    [view addSubview:webView];
    NSLog(@"YOUTUBE: end init");
    return self;
}

-(void)webViewDidFinishLoad:(UIWebView*)myWebView {
    NSLog(@"YOUTUBE: send play command");
    [webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"playVideo(%d)", videoOffset]];
}

- (void) dealloc {
    NSLog(@"YOUTUBE: dealloc");
}
@end

Here is the code that calls this class (this code is located in the appDelegate):

NSLog(@"about to load youtube");
ytObj=[[MyYouTube alloc] initIntoView:mainView withContent:cn];
NSLog(@"loaded youtube");
[mainView addSubview:[ytObj view]];

FYI mainView and ytObj are declared as this:

@property (nonatomic,strong) UIView * mainView;
@property (nonatomic,strong) MyYouTube * ytObj;

When this code is run, the app crashes and I get this in the console:

about to load youtube
YOUTUBE: begin init
YOUTUBE: self: <MyYouTube: 0x16503d40>
YOUTUBE: delegate: <MyYouTube: 0x16503d40>
YOUTUBE: end init
YOUTUBE: dealloc
loaded youtube
*** -[MyYouTube respondsToSelector:]: message sent to deallocated instance 0x166f19f0

If I set the UIWebView delegate to nil then the app doesn't crash, but, as expected, the YouTube video doesn't autoplay.

Can anyone explain to me:

• Why does the object deallocates immediately after it has been initialized?

• Why the respondsToSelector: message is sent to an instance other than the MyYouTube one?

• How can I get the YouTube video to autoplay without the app crashing?

Many thanks.

---

EDIT

Totally my bad - ytObj is a strong property - I forgot to mention this. Ive added the code to reflect this.

---

EDIT 2

Ive added a breakpoint on the dealloc method, and this is the call stack:

0 -[MyYouTube dealloc]
1 objc-object::sidetable_release(bool)
2 -[MyAppDelegate playYouTube:]

The last entry here (playYouTube:) is the method that contains the code in my app delegate that is in the original post above. So, one more question:

• What is objc-object::sidetable_release(bool), what does it do, and why is it releasing my YouTube object?

Answer 1

Why does the object deallocates immediately after it has been initialised?

Because nothing owns it.

You set it as the delegate to a view, but the delegate property of UIWebView is an assign property. The view doesn't take ownership of its delegate. This means that when ytObj goes out of scope (possibly before, depending on optimisation) nothing owns it, so it goes away.

EDIT

You also need to make sure that when a ytObj is deallocated, you set the delegate property of any views it is still a delegate of to nil. Otherwise the views will continue to try to send messages to the deallocated object.

How can I get the YouTube video to autoplay without the app crashing?

You need to make sure that ytObj lasts as long as the view of which it is the delegate and when it is deallocated, it's view's delegate is set to nil.

---

Another minor issue. Your -init function should test that self is not nil after invoking self = [super init]. It shouldn't run any of the rest of the initialisation code if self is nil.

Answer 2

1) (my first answer to your first question, before your edit)

This is happening because you're using ARC (automated reference counting) and you are not keeping your local "ytObj" variable ((which is NOT the "self.ytObj" property) around in the object that you created it in. As soon as the function that created the local "ytObj" variable finishes up and returns, the object is automagically dealloc'd.

Change this:

ytObj=[[MyYouTube alloc] initIntoView:mainView withContent:cn];

to this:

self.ytObj=[[MyYouTube alloc] initIntoView:mainView withContent:cn];

And for "best practices", I'd also suggest not doing so much work and/or code in your application delegate. App delegates are meant to receive application specific messages (like "application is suspending", "application is becoming active again", etc.), and you should do stuff like this in a subclassed view controller.

2)

The "respondsToSelector:" error you're seeing is because your YouTube object has been automagically dealloc'd. If it were still living, you wouldn't see that message.

3)

If you search here on Stackoverflow, you'll find other questions and answers that explain how to do autoplaying... like how about this one?

Answer 3

The object ytObj since is not strong referenced anywhere, it exists only inside the scope where is defined. Delegates most of time are declared as weak properties. None is keeping a strong reference to this object, thus ARC releases it.
Create a strong properties to ytObj and you will see everything working fine.