将数组内容写入文件 [英] Writing array contents to a file
问题描述
我整天都在使用这里的答案来解决这个问题,但我找不到适合我的解决方案,所以我想我会寻求帮助:
I've struggled with this all day using answers from here, but I cannot find a solution that is working for me, so I thought I'd ask for help:
我有一个从实体中提取的对象数组.
I have an array of objects that I've extracted from an entity.
我想做的就是将对象写入文件.
All I want to do is to write the objects to a file.
到目前为止我想出的是:
What I've come up with so far is this:
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,我只得到最后一项,所以我要覆盖字符串.但是,必须有更好的方法来实现这一点.如果这里有其他答案与我的问题相符,请告诉我,或者请发表一些想法.
Right now, all I'm getting the the last item, so I'm overwriting the string. But, there must be a better method to achieve this. Please let me know if there is another answer here matches my question, or please, post some ideas.
更新
当我记录 exportArray 时,我得到这个:
When I log the exportArray, I get this:
"<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..
I get correct results. I just don't know how to tie these and the other attributes together..
Exported titles: (
1,
2,
4,
6
)
Exported usernames: (
ellis,
david,
bea,
ian
)
推荐答案
如果你的数组中只有 NSDictionaries
,你可以使用 writeToFile:atomically:
这将节省.plist
格式的文件(比 CSV 更容易阅读).
If you just have NSDictionaries
in your array, you can use writeToFile:atomically:
which will save a file in .plist
format (which is much easier to read than a CSV).
查看 Apple 文档用于 NSArray,以及关于 plist 的好文章.
Check out the Apple Docs for NSArray, and a good write up on plists.
所以你最终会得到:
[exportArray writeToFile:fileName atomically:YES];
<小时>
您无法将核心数据对象保存到文件中.因此,您要做的是创建一个仅包含您想要的数据的临时数组,然后将其写入文件.
You cannot save a core data object to a file. So what you want to do is create an interim array with just the data you want, then write that to the file.
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];
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