string
is an alias in C# for System.String
.
So technically, there is no difference. It's like int
vs. System.Int32
.
As far as guidelines, it's generally recommended to use string
any time you're referring to an object.
e.g.
string place = "world";
Likewise, I think it's generally recommended to use String
if you need to refer specifically to the class.
e.g.
string greet = String.Format("Hello {0}!", place);
This is the style that Microsoft tends to use in their examples.
It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.
There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:
// File1.cs
using System;
namespace Outer.Inner
{
class Foo
{
static void Bar()
{
double d = Math.PI;
}
}
}
Now imagine that someone adds another file (File2.cs) to the project that looks like this:
// File2.cs
namespace Outer
{
class Math
{
}
}
The compiler searches Outer
before looking at those using
directives outside the namespace, so it finds Outer.Math
instead of System.Math
. Unfortunately (or perhaps fortunately?), Outer.Math
has no PI
member, so File1 is now broken.
This changes if you put the using
inside your namespace declaration, as follows:
// File1b.cs
namespace Outer.Inner
{
using System;
class Foo
{
static void Bar()
{
double d = Math.PI;
}
}
}
Now the compiler searches System
before searching Outer
, finds System.Math
, and all is well.
Some would argue that Math
might be a bad name for a user-defined class, since there's already one in System
; the point here is just that there is a difference, and it affects the maintainability of your code.
It's also interesting to note what happens if Foo
is in namespace Outer
, rather than Outer.Inner
. In that case, adding Outer.Math
in File2 breaks File1 regardless of where the using
goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using
directive.
Best Answer
first of all - indeed, it's not allowed by design, to install and ClickOnce app as admin: http://msdn.microsoft.com/en-us/library/142dbbz4(v=vs.90).aspx
take a look at this post: http://antscode.blogspot.ca/2011/02/running-clickonce-application-as.html - it explains how to run ClickOnce app as admin. BUT - it have to say that I have walked this path - and I did not have much luck with it. I had numerous troubles with this approach (trying to run ClickOnce app with admin privileges). As far as I recall, the biggest problem was auto-update was not working properly. Not to mention that non-admin users might need to enter admin credentials all the time.
So my advise would be to rethink your logic, and encapsulate the piece you need to be done as admin in a separate EXE file - and make it very clear for a user that when he clicks THAT button, UAC prompt will show up (probably by addin "shield" icon to the button). And in that button_click event do something like this:
this approach worked very well for me. The key here is this:
it runs your EXE with admin right - so UAC prompt will be displayed at that moment. Another nice consequence here is that users might not run this particular piece of logic each time they are using the app - and therefore they won't be annoyed by the prompt when they do not need it.