文件相关

读文件头签名：xxd -l 128

文件在 App 内打开后，会自动放在 Documents/Inbox 文件夹下。

[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
[NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) firstObject];
NSTemporaryDirectory()

Info.plist

UIFileSharingEnabled: If you set this key to YES, your app can share files with the user. Place the files in a Documents folder located in the app’s home directiory. The default value is NO.

UISupportsDocumentBrowser: To allow other apps to open and edit the files stored in your app’s Documents folder, set this key to YES. This key also lets users set the app’s default save location in Settings.

LSSupportsOpeningDocumentsInPlace: A Boolean value indicating whether the app may open the original document from a file provider, rather than a copy of the document.

NSExtensionFileProviderSupportsEnumeration: A Boolean value that indicates whether a File Provider extension enumerates its content.

自动重命名文件

/// 传入一个文件路径，如果该路径下的文件不存在，则返回它本身；如果已存在，那么会自动重命名文件名，返回一个不冲突的文件路径。
/// @param filePath 文件路径
+ (NSString *)autoRenamePath:(NSString *)filePath {
    NSFileManager *manager = [NSFileManager defaultManager];
    NSString *fileName = [[filePath lastPathComponent] stringByDeletingPathExtension]; // 例如“PDF_0707”
    NSString *directory = [filePath stringByDeletingLastPathComponent]; // 目录
    NSUInteger numOfFiles = [manager contentsOfDirectoryAtPath:directory error:nil].count;
    // 如果“PDF_0707”存在，就在后面自动追加数字后缀
    NSUInteger counter = 0; // 计数器
    NSString *newName = [fileName copy];
    while ([manager fileExistsAtPath:filePath]) {
        ++counter;
        if (counter > numOfFiles + 1) {
            break; // 循环的次数不大于目录下的文件个数+1
        }
        newName = [NSString stringWithFormat:@"%@(%@)", fileName, @(counter)]; // 例如“PDF_0707(1)”
        NSString *extension = [filePath pathExtension];
        filePath = [[directory stringByAppendingPathComponent:newName] stringByAppendingPathExtension:extension];
        // 不会一直循环下去，因为用户每天导出的文件数是有限的，0707 这个日期下的 PDF 文件大多数情况下也就几个
        // 因此随着计数器的增加，一定会找到一个可以用的数字，例如“PDF_0707(99)”，就是可用的文件路径
    }
    return filePath;
}

文件大小格式化字符串

+ (NSString *)displayStringWithFileSize:(NSUInteger)fileSize {
    if (fileSize >= 1024 * 1024) {
        return [NSString stringWithFormat:@"%.2fMB", fileSize / 1024 / 1024];
    } else if (fileSize >= 1024) {
        return [NSString stringWithFormat:@"%.2fKB", fileSize / 1024];
    } else {
        return [NSString stringWithFormat:@"%.2fB", fileSize];
    }
}