ios - 使用writeToFile保存文件

Question

因此，我发现了使用writeToFile保存数组以稍后检索它的一个小问题。我正在使用:

        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                             NSUserDomainMask, YES);
        if ([paths count] > 0)
        {
            NSString *arrayPath = [[paths objectAtIndex:0]
                         stringByAppendingPathComponent:@"array.out"];

            [finalSavedArray writeToFile:arrayPath atomically:YES];
            [[NSUserDefaults standardUserDefaults] setObject:arrayPath forKey:@"SavedArrayPath"];
            [[NSUserDefaults standardUserDefaults] synchronize];
        }

将“finalSavedArray”另存为文件，然后使用以下方法检索此数组:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
        NSLog(@"File path: %@",[[NSUserDefaults standardUserDefaults] objectForKey:@"SavedArrayPath"]);
        NSMutableArray *savedArray = [NSMutableArray arrayWithContentsOfFile:[[NSUserDefaults standardUserDefaults] objectForKey:@"SavedArrayPath"]];
        dispatch_sync(dispatch_get_main_queue(), ^{
            NSLog(@"SAVED ARRAY:%@",savedArray);
        });

    });

当我在保存文件后不久访问文件时，此方法工作正常，但是当我重新启动应用程序时，数组显示为空，并且在保存的目录中似乎找不到。从一点阅读看来，此文件目录应该是相对的，因为每次打开应用程序时，此文件目录我现在都会更改，但是我还无法弄清楚如何更改代码为了将其保存到相对目录。任何帮助将不胜感激 :)

Answer 1

应用程序的路径可以更改。绝对不要存储文件的绝对路径。在您的情况下，只需存储相对于Documents文件夹的路径。

当您要读取文件时，请从NSUserDefaults读取相对路径，然后像编写文件一样重新构建完整路径。

写入文件:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
if ([paths count] > 0)
{
    NSString *arrayPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"array.out"];

    [finalSavedArray writeToFile:arrayPath atomically:YES];
    [[NSUserDefaults standardUserDefaults] setObject:[arrayPath lastPathComponent] forKey:@"SavedArrayPath"];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

读取文件:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *filename = [[NSUserDefaults standardUserDefaults] objectForKey:@"SavedArrayPath"];
    NSString *path = [[paths objectAtIndex:0] stringByAppendingPathComponent:filename];
    NSMutableArray *savedArray = [NSMutableArray arrayWithContentsOfFile:path];
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"SAVED ARRAY:%@",savedArray);
    });

});