Question

I’m new to Objective-C, and I’ve read some memory management articles but am having trouble.

I hava a class something like this:

-(UIWebView*)getWebView{
    //UIWebView* webview = [UIWebView initWithFrame:self.frame];  edited,the original wrong line
    UIWebView* webview = [[UIWebView alloc] initWithFrame:self.frame]; 
    return webview; 
}
-(void)addToSelf{
    UIWebView* view = [self getWebView];
    [self addSubview:view];
    [view release];  //release here
}

In my thought, objc objects are all like C pointers (it is ?)
And thinking like this:

UIWebView* webview = [[UIWebView alloc] initWithFrame:self.frame];  //retain +1
UIWebView* view = [self getWebView];  //just a pointer to the same object ?
[self addSubview:view]; //retain +1
[view release];   //retain -1

Now view’s retainCount = 1.
Then this viewController will handle the webview’s life cycle.

There must be something wrong with my thought (sure also the code),
but I don’t know why .

UIWebView* webview = [[[UIWebView alloc] initWithFrame:self.frame] autorelease];

When I remove the last release line, code works fine, why?
What’s the difference?

————–edit line—————

Few minutes ago , there’s an answer about it but it’s disappeared , now I rewrite my thought:

The answer says:

When returning object from method , i must use autorelease to tell compiler I have end with it, and then using addSubview , finish (no need releasing).

I know this is right , but why it’s right ?

In most of codes:

-(void)someMethod{
    UIWebView* webview = [[UIWebView alloc] initWithFrame:self.frame]; 
    [self addSubview:webview];
    [webview release];
}

this works fine, but when separate the code to two methods like the top ,it’s not.

Why i must use autorelease when returning object?

Answer 1

It looks as if you don’t alloc the UIWebView:

UIWebView* webview = [[UIWebView alloc] initWithFrame:self.frame];

That means you probably don’t have a valid UIWebView, and a retain count that is undefined, since the code for UIWebView is actually using some unknown piece of memory. If this works, you are lucky.