将数组内容写入文件

Question

我整天都在努力使用这里的答案,但我找不到适合我的解决方案,所以我想我会寻求帮助:

我有一个从实体中提取的对象数组.

我想要做的就是将对象写入文件.

到目前为止我想出的是:

    NSLog(@" Exported Records: %i", [exportArray count]); 
    // the count here is 4 records.
    //Each record has about 8 elements. 
//I'm just trying to get this working with the first two elements right now

        NSString *writeString = nil;
        NSError *error = nil;
        int i = 0;
        NSString *key = nil;
        NSString *tempString = nil;
        for (i=0; i<[exportArray count]; i++)
        {
            tempString = [tempString stringByAppendingString: @" \n "];

            for (int j=0; j<3; j++)
            {
                if (j == 0)
                {
                    key = [[exportArray objectAtIndex:i]  valueForKey:@"title"];
                    //[NSString stringWithFormat:tempString2, [[exportArray objectAtIndex:i]  valueForKey:@"title"]];
                }
                if (j == 1)
                {
                    key = [[exportArray objectAtIndex:i]  valueForKey:@"username"];
                    //[NSString stringWithFormat:tempString2, [[exportArray objectAtIndex:i]  valueForKey:@"username"]];
                }
                writeString = [NSString stringWithFormat:tempString, key];
            }
        }

        // Write to the file
        [writeString writeToFile:dataFile atomically:YES
                    encoding:NSUTF8StringEncoding error:&error];
        if (error)
        {
            NSLog(@"%@", error);
        }

现在,我得到的是最后一项,所以我要覆盖字符串.但是,必须有一个更好的方法来实现这一目标.如果这里有另一个答案符合我的问题,请告诉我,或者请发布一些想法.

UPDATE

当我记录exportArray时,我得到了这个:

"<ItemEntity: 0x1ddf6560> (entity: ItemEntity; id: 0x1ddf46d0 <x-coredata://78FBC4A5-AE1A-4344-98AB-978126457D96/ItemEntity/p2> ; data: <fault>)",
    "<ItemEntity: 0x1ddf6800> (entity: ItemEntity; id: 0x1ddf46e0 <x-coredata://78FBC4A5-AE1A-4344-98AB-978126457D96/ItemEntity/p2051> ; data: <fault>)",
    "<ItemEntity: 0x1ddf6860> (entity: ItemEntity; id: 0x1ddf45d0 <x-coredata://78FBC4A5-AE1A-4344-98AB-978126457D96/ItemEntity/p3075> ; data: <fault>)",
    "<ItemEntity: 0x1ddf68c0> (entity: ItemEntity; id: 0x1ddf45e0 <x-coredata://78FBC4A5-AE1A-4344-98AB-978126457D96/ItemEntity/p5124> ; data: <fault>)"
)

当我记录实际值时:

NSLog(@" Exported titles: %@", [exportArray valueForKey:@"title"]);
NSLog(@" Exported usernames: %@", [exportArray valueForKey:@"username"]);

我得到了正确的结果.我只是不知道如何将这些和其他属性联系在一起..

  Exported titles: (
    1,
    2,
    4,
    6
)
  Exported usernames: (
    ellis,
    david,
    bea,
    ian
)

Answer 1

如果您刚NSDictionaries进入阵列,则可以使用writeToFile:atomically:哪种.plist格式保存文件(比CSV更容易阅读).

查看Apple Docs for NSArray,并详细了解plist.

所以你最终会得到:

[exportArray writeToFile:fileName atomically:YES];

编辑:您无法将核心数据对象保存到文件.所以你想要做的是创建一个只包含你想要的数据的临时数组,然后将其写入文件.

NSMutableArray* arrayToSave = [NSMutableArray arrayWithCapacity:exportArray.count];
[exportArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSDictionary* exportDict = [NSDictionary dictionaryWithObjectsAndKeys:
                                [obj objectForKey:@"username"], @"username",
                                [obj objectForKey:@"title"], @"title", nil];
    [arrayToSave addObject:exportDict];
}];

[arrayToSave writeToFile:fileName atomically:YES];

Answer 2

用这个,

[exportArray writeToFile:dataFile atomically:YES];

NSArray有writeToFile:这样做的方法.请查看此处的文档.如果数组中没有自定义对象,这可以正常工作.

如果您只想保存标题或用户名(即使它在数组中有自定义对象),您可以这样做:

NSArray *array1 = [exportArray valueForKey:@"title"];
[array1 writeToFile:dataFile atomically:YES];

要么

NSArray *array2 = [exportArray valueForKey:@"username"];
[array2 writeToFile:dataFile atomically:YES];