iphone - 给定文件和目录生成相对路径的 Objective-C 代码

Question

给定一个文件路径和一个目录路径作为 NSStrings，有没有人有 Objective-C 代码来生成文件相对于目录的路径？

例如，给定目录 /tmp/foo 和文件 /tmp/bar/test.txt，代码应该生成 ../bar/test.txt.

我知道 Python，至少，有一个方法可以做到这一点:os.path.relpath .

Answer 1

与其继续为我为什么需要这个辩护，我决定只写它并分享。我基于 Python 的 os.path.relpath 在 http://mail.python.org/pipermail/python-list/2009-August/1215220.html 的实现。

@implementation NSString (Paths)

- (NSString*)stringWithPathRelativeTo:(NSString*)anchorPath {
    NSArray *pathComponents = [self pathComponents];
    NSArray *anchorComponents = [anchorPath pathComponents];

    NSInteger componentsInCommon = MIN([pathComponents count], [anchorComponents count]);
    for (NSInteger i = 0, n = componentsInCommon; i < n; i++) {
        if (![[pathComponents objectAtIndex:i] isEqualToString:[anchorComponents objectAtIndex:i]]) {
            componentsInCommon = i;
            break;
        }
    }

    NSUInteger numberOfParentComponents = [anchorComponents count] - componentsInCommon;
    NSUInteger numberOfPathComponents = [pathComponents count] - componentsInCommon;

    NSMutableArray *relativeComponents = [NSMutableArray arrayWithCapacity:
                                          numberOfParentComponents + numberOfPathComponents];
    for (NSInteger i = 0; i < numberOfParentComponents; i++) {
        [relativeComponents addObject:@".."];
    }
    [relativeComponents addObjectsFromArray:
     [pathComponents subarrayWithRange:NSMakeRange(componentsInCommon, numberOfPathComponents)]];
    return [NSString pathWithComponents:relativeComponents];
}

@end

请注意，在某些情况下这无法正确处理。它恰好可以处理我需要的所有情况。这是我用来验证正确性的简单单元测试:

@implementation NSStringPathsTests

- (void)testRelativePaths {
    STAssertEqualObjects([@"/a" stringWithPathRelativeTo:@"/"], @"a", @"");
    STAssertEqualObjects([@"a/b" stringWithPathRelativeTo:@"a"], @"b", @"");
    STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a"], @"b/c", @"");
    STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a/b"], @"c", @"");
    STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a/d"], @"../b/c", @"");
    STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a/d/e"], @"../../b/c", @"");
    STAssertEqualObjects([@"/a/b/c" stringWithPathRelativeTo:@"/d/e/f"], @"../../../a/b/c", @"");
}

@end