为什么 NSMutableArray 有重复的对象？

Question

我有一些代码可以创建一个字符串并将该字符串添加到一个可变数组中。代码如下：

    ExportBookData *abe = [[ExportBookData alloc] initWithCategory:@"ABE"];
    abe.builtFileList = [[NSMutableDictionary alloc] initWithCapacity: 2];
    abe.exportData = [NSMutableArray array];  

        for(int i = 0; i < booksArray.count; i++)  {
        [tabString setString: @""];  //   clear it...
        [tabString appendString:[NSString stringWithFormat:@"%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t"
                                 "%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\n",

                                 [[booksArray objectAtIndex:i] sku],
                                 [[booksArray objectAtIndex:i] title],
                                 [[booksArray objectAtIndex:i] author],
                                 [[booksArray objectAtIndex:i] illustrator],
                                 [[booksArray objectAtIndex:i] price],
                                 [(Books *)[booksArray objectAtIndex:i] quantity],
                                 @"Book",  //  book type
                                 [[booksArray objectAtIndex:i] bookDescription],
                                 [[booksArray objectAtIndex:i] binding],
                                 [[booksArray objectAtIndex:i] bookCondition],
                                 [[booksArray objectAtIndex:i] pubName],
                                 [[booksArray objectAtIndex:i]pubLocation ],
                                 [[booksArray objectAtIndex:i] pubYear],
                                 [[booksArray objectAtIndex:i] isbn],
                                 [[booksArray objectAtIndex:i] primaryCatalog],
                                 @"",@"",  //  seller catalogs  secondary and third catalog entries (not used)
                                 @"",  //  ABE category    <----- TODO
                                 [[booksArray objectAtIndex:i] keywords],
                                 [[booksArray objectAtIndex:i] jacket],
                                 [[booksArray objectAtIndex:i] edition],
                                 [[booksArray objectAtIndex:i] printing],
                                 [[booksArray objectAtIndex:i] signedBy],
                                 [[booksArray objectAtIndex:i]volume],
                                 [[booksArray objectAtIndex:i] bookSize],
                                 @""  //  image url
                                 ]];

        NSLog(@"\n\ntabString: %@",tabString);

        [abe.exportData addObject: tabString];  //  add to array

        NSLog(@"\n\nexportData: %@", abe.exportData);  //  <-------------- overwritten with last entry, so all entries are the same  TODO
    }

booksArray 是一个 NSMutableArray，它通过读取 CoreData 存储来填充； exportData 也是一个 NSMutableArray。 booksArray 中的数据有效，计数为 2； tabString 中的数据也是有效的，包含 booksArray 中的正确行。线

[abe.exportData addObject: tabString];

与 booksArray 中的最后一条记录重复。这是日志方法的输出：

---->booksArray.count: 2

tabString: 120  Women Who Run With The Wolves:  Myths And Stories Of The Wild Woman Archetype   Clarissa Pinkola Estes      2.1 1   Book        Hardcover       Ballantine Books        1992    0345377443                      Like New        (null)              

exportData: (
"120\tWomen Who Run With The Wolves:  Myths And Stories Of The Wild Woman Archetype\tClarissa Pinkola Estes\t\t2.1\t1\tBook\t\tHardcover\t\tBallantine Books\t\t1992\t0345377443\t\t\t\t\t\tLike New\t\t(null)\t\t\t\t\n"
)

tabString: 121  Colossus: The Secrets Of Bletchley Park's Code-breaking Computers   B. Jack Copeland        35  1   Book        Paperback (Reprint)     Oxford University Press, USA        2010    9780199578146                       No Dust Jacket      (null)              

exportData: (
"121\tColossus: The Secrets Of Bletchley Park's Code-breaking Computers\tB. Jack Copeland\t\t35\t1\tBook\t\tPaperback (Reprint)\t\tOxford University Press, USA\t\t2010\t9780199578146\t\t\t\t\t\tNo Dust Jacket\t\t(null)\t\t\t\t\n",
"121\tColossus: The Secrets Of Bletchley Park's Code-breaking Computers\tB. Jack Copeland\t\t35\t1\tBook\t\tPaperback (Reprint)\t\tOxford University Press, USA\t\t2010\t9780199578146\t\t\t\t\t\tNo Dust Jacket\t\t(null)\t\t\t\t\n"
)

我已经看了好几个小时（Google，SO），从我在其他问题的答案中看到的情况来看，我所做的一切都是正确的，我看不出是什么原因造成的。帮助将不胜感激。标清

Answer 1

您的tabString 似乎是您尝试反复使用的NSMutableString。那是行不通的。您最终多次将相同的可变字符串添加到数组中。只需将stringWithFormat 分配给普通的本地NSString。

为什么要一遍又一遍地打电话给[booksArray objectAtIndex:i]？获取对象一次。更好的是，在循环中使用快速枚举。

for (YourBookClass *book in booksArray) {
    NSString *tabString = [NSString stringWithFormat:@"%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t"
                             "%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\t%@\n",
       book.sku,
       book.title,
       // and all of the rest of the properties
       ]];

    [abe.exportData addObject:tabString];
}

另外请注意，如果任何值包含制表符或换行符，您的代码将生成无效的 CSV 文件。这些值需要用引号括起来。