C# static readonly vs constant variables

I wondered about the differences between these the other day and here's what I found.

I am comparing constants to static readonly class fields because they are used in the same way.

At a high level, constants are obviously dealt with at compile-time, while static readonly fields are set at the time they are evaluated at run-time. The fact that constant values are subsituted by the compiler means that any library/assembly which references the constant value will need to be recompiled if the constant value changes. Libraries referencing a static readonly field will reference the field and not the value, thus they will pick up any change in the field without the need for recompilation. So constants 0 - static readonly 1 in the area of maintainability.

Static readonly fields are able to hold reference types whereas constants will only support value types plus the special .NET ones string and null.

Finally, readonly fields can be set wherever and however the developer chooses meaning they can be lazy-loaded, and they can contain calculated values. A use for this that I found was when I was developing a system which could potentially use multiple databases. I needed the maximum permissible date from Oracle and Sql Server. Based on application configuration I was able to calculate this at runtime and still store the value in a static readonly field in the static Constants class along with regular constant values.

So, it appears that constants should be used when it is very unlikely that the value will ever change, or if no external apps/libs will be using the constant. Static readonly fields should be used when run-time calculation is required, or if it external consumers are a factor.

References

Static readonly versus constants

how to patch uxtheme.dll on windows xp (to use unsigned themes)

Having the ability to use custom (non-Microsoft) XP/2003 themes is highly recommended. It makes life a lot more fun. It's not hard to do but I thought I'd explain it again since it wasn't trivial.

1. Download the correct version of uxtheme.dll. This site has pretty much all of them.
2. Unzip and store the patched file in somewhere like c:\temp. Note it will be the same size as your existing file.
3. You might want to force a system restore point if you're really paranoid.
4. You won't be able to copy the patched file over this one since Windows doesn't all this.
5. You will need this program: Replacer. Download the STABLE version.
6. Replacer will do the hard work with making windows let go of the uxtheme.dll file and allowing you to copy over it. Just in case, make a backup yourself - rename c:\windows\system32\uxtheme.dll to uxtheme.dll.old.
7. Unzip Replacer to somwehre like c:\temp\replacer
8. Before running it, I found that you have to remove all the sources that Windows can use to overwrite the patched file. Do a search (Start Menu -> Search) for *uxtheme* while making sure that hidden and system files are visible in explorer, and are selected in Advanced Options in Search.
9. There will be matching files in c:\windows\system32\dllcache, and probably in c:\i386. Just rename these (not copy) to uxtheme.dll.old.
8. Now run Replacer (replacer.cmd)
9. Drag the existing file c:\windows\system32\uxtheme.dll into the command window. Hit enter.
10. Drag the new file from c:\temp into the command window.
11. Hit enter. And then type Y.
12. Check that the file date and size of c:\windows\system32\uxtheme.dll matches that of the one from c:\temp.
13. Reboot.
14. Grab a theme from customize.org. Download it and unzip to c:\windows\resources\themes, making sure to select 'extract subfolders'.
15. Right click on the Windows desktop.
16. Click on Appearance. Under windows and buttons you should see your new theme listed!

[Books of the Month] CLR via C#, Headfirst Design Patterns

CLR via C#
by Jeffrey Richter

This is the one i'm reading at the moment. So far it's great! Richter's style is conversational while still precise. The passion he has for software development is clearly evident in his writing. I find that each topic is explained in the way that someone might do if they were helping you out at work. They start simple, and then progress to the advanced features. The examples are decent and "real-world" which is nice, since it can often be hard to see how object graphs made up of cars can apply to your actual code.

Head First Design Patterns
by Elisabeth Freeman et al

This is an excellent book! It reminds me of fun educational books I read before the age of 10. And why should a software development text be boring!? To contradict my statement above, they use example class hierarchies made up of things like ducks, with interfaces like flyable and quackable. However, the depth of the examples surpass the silliness and the examples present poignant issues to do with implementing object design concepts properly.

More to come..

Followup to Visual Studio debugger issues on a UNC share

a.k.a. 'I want to develop .NET projects on a remote drive!'

Will not be too detailed - doing this from memory.

1. Ensure the site's .webinfo or .csproj file contains the path to the HTTP path to the UNC share.
e.g. You have it on \\192.168.1.2\w$\dev\projects, where the webroot is pointing to \dev
The path in the above files should be http://192.168.1.2/projects/

2. Open up your .NET security configuration tool (in control panel). This should work for 1.1. and 2.0.

3. Go to Runtime Security Policy; Code Trust.

4. Under Local Intranet, add a new code group.

5. Call it dev server or whatever.

6. Select URL, and enter file://192.168.1.2/w$/dev/projects/*

7. Select Full Trust.

8. Save, and be sure to RESTART visual studio.

9. Success will be evident if VS doesn't complain about the project existing in a non-trusted area.

Leave me a comment if you need any more info/help.

SQL Server 2000: Column values as arguments to table-valued functions

Short answer - impossible. Apparently the issue has been fixed in 2005.

So basically in sql 2000, you can't do this:

SELECT email
FROM [tb_Email]
WHERE
@job_type IN (SELECT * FROM [dbo].[CsvToIntTable](job_type))

where tb_Email.job_type is a field containing data like '1,2,3,4'
and CsvToIntTable returns this data separated into rows.

The server will return an error like so:
'job_type' is not a recognized OPTIMIZER LOCK HINTS option.

Bugger!