Re: singleton design pattern
Re: singleton design pattern
- Subject: Re: singleton design pattern
- From: Alejandro Marcos Aragón <email@hidden>
- Date: Wed, 19 May 2010 11:30:00 -0500
Hi Abhinay,
Why declaring the static variable outside the function? If I have it inside, I make sure that it's initialized before it's being used.
aa
On May 18, 2010, at 5:58 PM, Abhinay Kartik Reddyreddy wrote:
>
> On May 18, 2010, at 6:42 PM, Mike Abdullah wrote:
>
>>
>> On 18 May 2010, at 23:28, Alejandro Marcos Aragón wrote:
>>
>>> Hi all,
>>>
>>> I've been staring at this piece of code now to try to find out what's wrong with it and I can't think of anything at this point. I'm trying to have a single instance of an NSMutableDictionary inside a class:
>>>
>>>
>>>
>>> // in .h file
>>> @interface ClassA : NSObject {
>>>
>>> }
>>>
>>> + (NSMutableDictionary*) uniqueInstance;
>>>
>>> @end
>>>
>>> // in .m file
>>> @implementation ClassA
> static NSMutableDictionary* uniqueInstance = nil;
> // the static variable has to be initialized before you enter the uniqueInstance method.
>>>
>>>
>>> + (NSMutableDictionary*) uniqueInstance {
>>>
>>> //static NSMutableDictionary* uniqueInstance = nil;
>> you don't actually need '= nil' unless you prefer it.
>>
>>>
>>> if (uniqueInstance == nil) {
>>>
>>> // directory to save files
>>> NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
>>> NSString *dir = [paths objectAtIndex:0];
>>>
>>> NSFileManager *fileManager = [NSFileManager defaultManager];
>> uh, this never gets used.
>>
>>>
>>> NSString *customFilePath = [[NSString alloc] initWithString:
>>> [dir stringByAppendingPathComponent:@"dict.plist"]];
>> nonsense, [dir stringByAppendingPathComponent:@"dict.plist"] by itself is what you want.
>>>
>>>
>>> uniqueInstance = [[NSMutableDictionary alloc] initWithContentsOfFile:customFilePath];
>>> }
>>>
>>> return uniqueInstance;
>>> }
>>>
>>>
>>> I can't use this code because there is a EXC_BAD_ACCESS according to the debugger.
>> What's the backtrace? Very hard for us to debug without. Your singleton method looks fine provided it's only ever accessed from a single thread at a time. From my comments above, sure you've posted all the relevant code?
>>>
>>> I tried moving the definition of the uniqueInstance outside the function and that didn't help. This code seems alright to me, but I can't find why it doesn't work. Can someone point out the problem?
>>>
>>> aa
>>>
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