我如何错误地使用System.Uri和MakeRelativeUri（..）方法？

Question

Update:

I added the missing two variables to the repo code blush Sincere appologies about that - I was rushing out to pick up the kids and missed it when i quickly reviewed the post.

---

When i call the .NET framework's MakeRelativeUri(...) method and the pass in a Uri which contains a file path .. and the file path has spaces in it .. then there's a great disturbance in the Force, as if millions of voices suddenly cried out in terror, and were suddenly silenced.

Here's my repo code. Appologies for this being an MSTest repo and not something a bit nicer like NUnit or XUnit.

[TestMethod]
public void SadPanda()
{
    // Arrange.
    var outputPath =
        @"C:\Users\AAAAAAA.BBBBB\Documents\Visual Studio 2010\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\___sa.bundle.#.css";

    var sourcePath =
        @"C:\Users\AAAAAAA.BBBBB\Documents\Visual Studio 2010\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\home.css";
    var sourcePathJussy =
        @"C:\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\home.css";

    // Added missing 2x vars *blush*    
    var sourceUri = new Uri(Path.GetDirectoryName(sourcePath) + "/", UriKind.Absolute);
    var outputUri = new Uri(Path.GetDirectoryName(outputPath) + "/", UriKind.Absolute);

    var relativePath = "../images/home-feature-bg.png";
    var resolvedSourcePath = new Uri(sourceUri + relativePath, true);

    // Act. 
    var resolvedOutput = outputUri.MakeRelativeUri(resolvedSourcePath);     

    // Assert.
    Assert.IsTrue(resolvedOutput.Contains("XWing")); // :~(
}

Now if you look at the output it is something evil with the real path of the location, etc.

Now if we remove the SPACES from the paths, it now works :)

[TestMethod]
public void DoubleRaindbowUnicorns()
{
    // Arrange.
    var outputPath =
        @"C:\Users\AAAAAAA.BBBBB\Documents\Visual Studio 2010\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\___sa.bundle.#.css";

    var sourcePath =
        @"C:\Users\AAAAAAA.BBBBB\Documents\Visual Studio 2010\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\home.css";
    var sourcePathJussy =
        @"C:\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\home.css";

    outputPath = outputPath.Replace(" ", "-");
    sourcePath = sourcePath.Replace(" ", "-");

    // Added missing 2x vars *blush*
    var sourceUri = new Uri(Path.GetDirectoryName(sourcePath) + "/", UriKind.Absolute);
    var outputUri = new Uri(Path.GetDirectoryName(outputPath) + "/", UriKind.Absolute);

    var relativePath = "../images/home-feature-bg.png";
    var resolvedSourcePath = new Uri(sourceUri + relativePath, true);

    // Act. 
    var resolvedOutput = outputUri.MakeRelativeUri(resolvedSourcePath);     

    // Assert.
    Assert.IsFalse(resolvedOutput.Contains("XWing")); // Here yee! Woot, say I!
}

the output of this image resource is ../images/home-feature-bg.png (which by fluke is the same as it's source path) .. and not the really long evil string.

Yes / no ?

Update 2:

Renamed the subject (to better reflect the answer).

Answer 1

You need to use the System.IO.Path.Combine() function. What's happening here is you are using a URI class which cannot contain spaces, which would require the %20 if it were a path for HTML.

Answer 2

I think you are misunderstanding the purpose of the MakeRelativeUri() function. It is supposed to be called on one absolute URI taking in another in order to return the relative URI which represents how to arrive at the second resource in context of the first.

Example:

var cssFileUri = new Uri(@"C:\Temp\Spaces in this path\foo.css");
var imageFileUri = new Uri(@"C:\Temp\Images\bar.png");

var relativeUri = cssFileUri.MakeRelative(imageFileUri);
// The value of relativeUri is "../Images/bar.png"

So you can see how the relativeUri value gets us to the "bar.png" file from "foo.css".

In your example you'd pass in your CSS file path and a path to the image to get the value you have in relativePath .

In order to "undo" that (find the full path of an image in relation to a given CSS file) you construct a new Uri object:

var relativeImageUri = @"..\Image Folder\bar.png";
var cssFileUri = new Uri(@"C:\Some Path\Other Folder\foo.css");

var absoluteImageUri = new Uri(cssFileUri, relativeImageUri);
// The value of absoluteImageUri is "file:///C:/Some Path/Image Folder/bar.png"

So in order to find the resolvedOutput from your sample code:

var outputPath =  @"C:\Users\AAAAAAA.BBBBB\Documents\Visual Studio 2010 Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\___sa.bundle.#.css";

var sourcePath = @"C:\Users\AAAAAAA.BBBBB\Documents\Visual Studio 2010\Projects\XWing\Code\CCCCCCCCCCC.XWing.Application.Web\content\shared\css\home.css";

var relativePath = "../images/home-feature-bg.png";

var outputUriBase = new Uri(outputPath);
var resolvedOutput = new Uri(outputUriBase, relativePath);

You can now use the resolvedOutput Uri object to access the "home-feature-bg.png" image relative to the output path.

All these handle spaces in the path without error.

Answer 3

The

uriInstance.MakeRelativeUri() 

method seems to be corrupt. The resulting Uri will show escaped characters when called with ToString(), eg %20 for an empty space. Other Uri instances don't do so, not even relative ones.

I wanted to use it for creating relative paths by subtracting the root path from a full path, then store a string from it in a DB

var baseUri = new Uri("http://myserver/pics")
var fullUri = new Uri("http://myserver/pics/myself/smile a.jpg")

var madeRelativeUri = baseUri.MakeRelativeUri(fullUri)

  // madeRelativeUri.ToString() = "myself/smile%20a.jpg"

var manualRelativeUri = new Uri(@"myself/smile b", UriKind.Relative)

  // manualRelativeUri.ToString() = "myself/smile b.jpg" // no escape