内存泄漏NSMutableArray，NSArray，iPhone SDK中的NSString

Question

In my app, I got Memory leaks in NSMutableArray, NSArray and NSString.

Here is the code.

    NSString *subQuery = [NSString stringWithFormat:@"SELECT %@ FROM tbl_lang WHERE glossary = '%@'",append1,glossaryName];
    NSArray *subArray1 = [[[self returnExecuteQuery:subQuery] mutableCopy] autorelease];        
    [subArray addObjectsFromArray:subArray1];

    NSString *columnQuery = [NSString stringWithFormat:@"select AutoID,%@ from tbl_lang where glossary='%@'",lblshortName.text,glossaryName];
    NSArray *newArray =[[[self returnExecuteQuery:columnQuery] mutableCopy] autorelease];
    [langArray addObjectsFromArray:newArray];

    NSMutableArray *tempArray = [[NSMutableArray alloc] init];

    for (int i=0; i<[newArray count]; i++) {
        NSString *cellText = [[newArray objectAtIndex:i] valueForKey:[NSString stringWithFormat:@"%@",lblshortName.text]];

        if (cellText != (NSString *)[NSNull null] && ![cellText isEqualToString:@""] ) {
            NSString *decodedString3 = [NSString stringWithUTF8String:[cellText cStringUsingEncoding:[NSString defaultCStringEncoding]]];

            [tempArray addObject:[NSString stringWithFormat:@"%@ : %@",lblshortName.text, decodedString3]];
        }
        else {
            [tempArray addObject:@"<empty>"];
        }

        NSString *detail = @"_________________";

        for (int j=0; j<[lableNameArray count]; j++) {

            NSString *checkNull=[[subArray1 objectAtIndex:i] valueForKey:[NSString stringWithFormat:@"%@",[lableNameArray objectAtIndex:j]]];

            if(checkNull != (NSString *)[NSNull null] && checkNull.length > 0)
            {
                NSString *decodedString4 = [NSString stringWithUTF8String:[checkNull cStringUsingEncoding:[NSString defaultCStringEncoding]]];
                detail = [NSString stringWithFormat:@"%@\n%@ : %@ ",detail,[lableNameArray objectAtIndex:j],decodedString4];
            }               
        }   
        [detailTextArray addObject:detail]; 

    }

When I run in Instruments I got leaks in

-subArray1 in second line.

-detail (NSString) in second for loop.

And subArray and langArray are my global arrays.

If I remove mutableCopy from NSArray *newArray =[[[self returnExecuteQuery:columnQuery] mutableCopy] autorelease]; and NSArray *subArray1 = [[[self returnExecuteQuery:subQuery] mutableCopy] autorelease]; then subArray and langArray doesnot retain values.

How to avoid memory leak in this code?

Answer 1

Not sure what is causing the memory leak, but this may help. This is a more direct way of copying the arrays, and may result in avoiding the leak:

NSArray *langArray =[[NSArray alloc] initWithArray: [self returnExecuteQuery:columnQuery] copyItems: YES];

This basically makes a one-level deep copy of the array returned by returnExecuteQuery. You can read about it in more detail in Collections Programming Topics .

I'm not sure how mutableCopy works and that may have something to do with the leak. If it copies the objects in the old array & then adds them to the new array, they may enter the array with a retain count of 2 (1 from the copy, and 1 from being added to an array.) It doesn't make much sense that it should work this way. But, if it does, that could account for the leak.

Answer 2

Olease try this one, in above code you are creating two many objects that belong to autorelease pool here is one version where I tried to handle release of those string variables.

Second this is that the leak of detail is because you are de-referencing it many times in your code. And for subArray1 please see the comment

    NSMutableString *subQuery =[ [NSMutableString alloc] initWithFormat:@"SELECT %@ FROM tbl_lang WHERE glossary = '%@'",append1,glossaryName];
   // please make returnExecuteQuery's returned array autorelease if it is not.  
   NSArray *subArray1 = [[self returnExecuteQuery:subQuery] mutableCopy] ;
    [subArray addObjectsFromArray:subArray1];

    [subQuery release]; 
    NSMutableString *columnQuery ==[ [NSMutableString alloc] initWithFormat:@"select AutoID,%@ from tbl_lang where glossary='%@'",lblshortName.text,glossaryName];
    NSArray *newArray =[[self returnExecuteQuery:columnQuery] mutableCopy] ;
    [langArray addObjectsFromArray:newArray];
    [columnQuery relese];
    NSMutableArray *tempArray = [[NSMutableArray alloc] init];

    for (int i=0; i<[newArray count]; i++) {
        NSMutableString *tempKey = [[NSMutableString  alloc]initWithFormat:@"%@",lblshortName.text]];


        NSString *cellText = [[newArray objectAtIndex:i] valueForKey:tempKey];
        [tempKey release];

        if (cellText != (NSString *)[NSNull null] && ![cellText isEqualToString:@""] ) {
            NSString *decodedString3 = [NSString stringWithUTF8String:[cellText cStringUsingEncoding:[NSString defaultCStringEncoding]]];
            NSMutableString *tempString  = [[NSMutableString alloc] initWithFormat:@"%@ : %@",lblshortName.text, decodedString3]];

            [tempArray addObject:tempString];
            [tempString release];
        }
        else {
            [tempArray addObject:@"<empty>"];
        }

        NSMutableString *detail = nil;

        for (int j=0; j<[lableNameArray count]; j++) 
        {
             detail = [[ NSMutableString alloc]initWithString:@"_________________"];
            NSMutableString *key = [[NSMutableString alloc]initWithFormat:@"%@",[lableNameArray objectAtIndex:j]];
            NSString *checkNull=[[subArray1 objectAtIndex:i] valueForKey:key];
           [key release];

            if(checkNull != (NSString *)[NSNull null] && checkNull.length > 0)
            {
                NSString *decodedString4 = [NSString stringWithUTF8String:[checkNull cStringUsingEncoding:[NSString defaultCStringEncoding]]];
                [detail setString:[NSString stringWithFormat:@"%@\n%@ : %@ ",detail,[lableNameArray objectAtIndex:j],decodedString4]];
            } 
              [detailTextArray addObject:detail]; 
              [detail release];              
        }   


    }
    [subArray1 release];
    [newArray release];

UPDATE : Please do read comments in the code and reply back so that things could be improved.

    NSMutableString *subQuery =[ [NSMutableString alloc] initWithFormat:@"SELECT %@ FROM tbl_lang WHERE glossary = '%@'",append1,glossaryName];
   //*****NOTE THIS POINT ----> please make returnExecuteQuery's returned array autorelease if it is not.  
   NSArray *subArray1 = [[self returnExecuteQuery:subQuery] mutableCopy] ;
    [subArray addObjectsFromArray:subArray1];

    [subQuery release]; 
    NSMutableString *columnQuery ==[ [NSMutableString alloc] initWithFormat:@"select AutoID,%@ from tbl_lang where glossary='%@'",lblshortName.text,glossaryName];
    //*****NOTE THIS POINT ----> please make returnExecuteQuery's returned array autorelease if it is not.  
    NSArray *newArray =[[self returnExecuteQuery:columnQuery] mutableCopy] ;
    [langArray addObjectsFromArray:newArray];
    [columnQuery relese];
    NSMutableArray *tempArray = [[NSMutableArray alloc] init];

    for (int i=0; i<[newArray count]; i++) {
        NSMutableString *tempKey = [[NSMutableString  alloc]initWithFormat:@"%@",lblshortName.text]];


        NSString *cellText = [[newArray objectAtIndex:i] valueForKey:tempKey];
        [tempKey release];

        if (cellText != (NSString *)[NSNull null] && ![cellText isEqualToString:@""] ) {
            NSString *decodedString3 = [NSString stringWithUTF8String:[cellText cStringUsingEncoding:[NSString defaultCStringEncoding]]];
            NSMutableString *tempString  = [[NSMutableString alloc] initWithFormat:@"%@ : %@",lblshortName.text, decodedString3]];

            [tempArray addObject:tempString];
            [tempString release];
        }
        else {
            [tempArray addObject:@"<empty>"];
        }

        NSMutableString *detail =  [[ NSMutableString alloc]initWithString:@"_________________"];

        for (int j=0; j<[lableNameArray count]; j++) 
        {

            NSMutableString *key = [[NSMutableString alloc]initWithFormat:@"%@",[lableNameArray objectAtIndex:j]];
            NSString *checkNull=[[subArray1 objectAtIndex:i] valueForKey:key]; //also here if you note you are using subArray1 not subArray?
           [key release];

            if(checkNull != (NSString *)[NSNull null] && checkNull.length > 0)
            {
                NSString *decodedString4 = [NSString stringWithUTF8String:[checkNull cStringUsingEncoding:[NSString defaultCStringEncoding]]];
                [detail setString:[NSString stringWithFormat:@"%@\n%@ : %@ ",detail,[lableNameArray objectAtIndex:j],decodedString4]];
               break;//I am not sure why you are checking this condition but assume that you want to get NOT NULL VALUE and  add it to array?
            } 

        }   
        [detailTextArray addObject:detail]; 
        [detail release];              

    }
    [subArray1 release];
    [newArray release];

UPDATE 2:

if(checkNull != (NSString *)[NSNull null] && checkNull.length > 0)
            {
                NSString *decodedString4 = [NSString stringWithUTF8String:[checkNull cStringUsingEncoding:[NSString defaultCStringEncoding]]];
                [detail appendFormat:@"%@\n%@ : %@ ",detail,[lableNameArray objectAtIndex:j],decodedString4]];

            }

Thanks,

Answer 3

You could start by releasing your tempArray once done with it (after the loops).

Often, the higher levels leaks are hidden in the flood of lower level ones (ie a container leaking causes all its content to be leaked as well), which might be the case for your string.

Using mutableCopy] autorelease]; is fine by the way.