Re: singleton design pattern
Re: singleton design pattern
- Subject: Re: singleton design pattern
- From: Abhinay Kartik Reddyreddy <email@hidden>
- Date: Tue, 18 May 2010 18:58:29 -0400
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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