iPhone - 数据库读取方法和内存泄漏答案

【问题标题】：iPhone - database reading method and memory leaksiPhone - 数据库读取方法和内存泄漏
【发布时间】：2011-02-10 04:59:31
【问题描述】：

在我的应用程序（一个 RSS 阅读器）中，我遇到了无法修复的内存泄漏，因为我无法理解它们的来源。这是 Instruments 指出的代码。

-(void) readArticlesFromDatabase {



[self setDatabaseInfo];

 sqlite3 *database;

 articles = [[NSMutableArray alloc] init];

 if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {
  const char *sqlStatement = "select * from articles";
  if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
   while(sqlite3_step(compiledStatement) == SQLITE_ROW) {

    NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];
    NSString *aDate = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)];
    NSString *aUrl = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 3)];
    NSString *aCategory = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 4)];
    NSString *aAuthor = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 5)];
    NSString *aSummary = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 6)];
    NSMutableString *aContent = [NSMutableString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 7)];
    NSString *aNbrComments = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 8)];
    NSString *aCommentsLink = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 9)];
    NSString *aPermalink = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 11)];

    [aContent replaceCharactersInRange: [aContent rangeOfString: @"http://www.mywebsite.com/img/action-on.gif"] withString: @"hellocoton-action-on.gif"];
    [aContent replaceCharactersInRange: [aContent rangeOfString: @"hhttp://www.mywebsite.com/img/action-on-h.gif"] withString: @"hellocoton-action-on-h.gif"];
    [aContent replaceCharactersInRange: [aContent rangeOfString: @"hthttp://www.mywebsite.com/img/hellocoton.gif"] withString: @"hellocoton-hellocoton.gif"];

    NSString *imageURLBrut = [self parseArticleForImages:aContent];    
    NSString *imageURLCache = [imageURLBrut stringByReplacingOccurrencesOfString:@":" withString:@"_"];
    imageURLCache = [imageURLCache stringByReplacingOccurrencesOfString:@"/" withString:@"_"];
    imageURLCache = [imageURLCache stringByReplacingOccurrencesOfString:@" " withString:@"_"];

    NSString *uniquePath = [tmp stringByAppendingPathComponent: imageURLCache];
    if([[NSFileManager defaultManager] fileExistsAtPath: uniquePath]) {
     imageURLCache = [@"../tmp/" stringByAppendingString: imageURLCache];
     [aContent replaceCharactersInRange: [aContent rangeOfString: imageURLBrut ] withString: imageURLCache];
    }

    Article *article = [[Article alloc] initWithName:aName date:aDate url:aUrl category:aCategory author:aAuthor summary:aSummary content:aContent commentsNbr:aNbrComments commentsLink:aCommentsLink commentsRSS:@"" enclosure:aPermalink enclosure2:@"" enclosure3:@""];

    [articles addObject:article];

    article = nil;
    [article release];
   }
  }
  sqlite3_finalize(compiledStatement);

 }
 sqlite3_close(database);
}

我有很多“文章”泄露，并且 NSString 与这些使用匹配：

[NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, X)];

我尝试了很多不同的代码，但总是有这些漏洞。有人有什么想法可以帮助我吗？

【问题讨论】：

标签： iphone database nsstring memory-leaks

【解决方案1】：

您泄露文章是因为：

article = nil;
[article release];

你为什么试图释放 nil？

只需将行设置文章删除为零，不需要。鉴于上述示例，该代码中可能存在更多问题。

【讨论】：

感谢您的回答。我试图添加这个，因为我已经在这一点上工作了很长时间，并且我正在寻找它。正如您所说，问题并非来自那一点（根据仪器，它不会改变任何东西（有或没有））。您说该代码中还有很多问题，您知道为什么这些行会造成泄漏吗： NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];感谢您的宝贵时间和帮助。
删除分配为 nil 将阻止您的泄漏文章。
您还泄漏了数组“articles”，应该在方法结束时释放它。如果要将其保留为实例变量，则应使用属性赋值。
即使没有“article = nil;”，它仍然会泄漏“article”。关于数组“articles”我稍后使用它，我需要保留它，所以我在dealloc中释放它。

【解决方案2】：

我最近几天一直在跟踪这个问题，下面为我解决了这个问题。

为您的文章 NSObject 添加一个 dealloc 方法并释放所有字符串。然后在您的 readArticlesFromDatabase 方法中首先发布文章，然后执行您的 init。

【讨论】：

【解决方案3】：

我终于自己找到了部分解决方案。

我的错误是将“文章”数组初始化为我的函数。事实上，每次我调用我的函数时，我都会丢失这个数组中以前的数据。现在我在启动过程中初始化了“articles”数组，我只是在我的函数中删除了它的内容：

- (void)applicationDidFinishLaunching:(UIApplication *)application {
       // My Code
       articles = [[NSMutableArray alloc] init];
       // My Code
}

然后

-(void) readArticlesFromDatabase {

    [self setDatabaseInfo];
    sqlite3 *database;

    [articles removeAllObjects];

    if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {
        const char *sqlStatement = "select * from articles";
        sqlite3_stmt *compiledStatement;
        if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
            while(sqlite3_step(compiledStatement) == SQLITE_ROW) {

                NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];
                NSString *aDate = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)];
                NSString *aUrl = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 3)];
                NSString *aCategory = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 4)];
                NSString *aAuthor = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 5)];
                NSString *aSummary = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 6)];
                NSMutableString *aContent = [NSMutableString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 7)];
                NSString *aNbrComments = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 8)];
                NSString *aCommentsLink = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 9)];
                NSString *aPermalink = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 11)];

                [aContent stringByReplacingOccurrencesOfString: @"http://www.mywebsite.com/img/action-on.gif" withString: @"hellocoton-action-on.gif"];
                [aContent stringByReplacingOccurrencesOfString: @"http://www.mywebsite.com/img/action-on-h.gif" withString: @"hellocoton-action-on-h.gif"];
                [aContent stringByReplacingOccurrencesOfString: @"http://www.mywebsite.com/img/hellocoton.gif" withString: @"hellocoton-hellocoton.gif"];

                NSString *imageURLBrut = [self parseArticleForImages:aContent]; 
                NSString *imageURLCache = [imageURLBrut stringByReplacingOccurrencesOfString:@":" withString:@"_"];
                [imageURLCache stringByReplacingOccurrencesOfString:@"/" withString:@"_"];
                [imageURLCache stringByReplacingOccurrencesOfString:@" " withString:@"_"];

                NSString *uniquePath = [tmp stringByAppendingPathComponent: imageURLCache];
                if([[NSFileManager defaultManager] fileExistsAtPath: uniquePath]) {
                    imageURLCache = [@"../tmp/" stringByAppendingString: imageURLCache];
                    [aContent replaceCharactersInRange: [aContent rangeOfString: imageURLBrut ] withString: imageURLCache];
                }

                Article *article = [[Article alloc] initWithName:aName date:aDate url:aUrl category:aCategory author:aAuthor summary:aSummary content:aContent commentsNbr:aNbrComments commentsLink:aCommentsLink commentsRSS:@"" enclosure:aPermalink enclosure2:@"" enclosure3:@""];

                [articles addObject:article];

                [article release];
            }
        }
        sqlite3_finalize(compiledStatement);
    }
    sqlite3_close(database);
}

现在我必须关注由 [articles removeAllObjects] 引起的“文章”泄漏。如果我不删除所有对象，我没有任何泄漏，但如果我这样做，我有泄漏。任何想法？如何在不泄漏这些文章对象的情况下清空数组？

【讨论】：

当你说“NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];”时，aName 必须被释放。否则会引发内存泄漏。