Is there a way to check if a string is not equal to multiple different strings?
I want to validate a file uploader, by file extension. If the file extension is n开发者_运维知识库ot equal to .jpg, .jpeg, .gif, .png, .bmp then throw validation error.
Is there a way to do this without looping through each type?
Just build a collection - if it's small, just about any collection will do:
// Build the collection once (you may want a static readonly variable, for
// example).
List<string> list = new List<string> { ".jpg", ".jpeg", ".gif", ".bmp", ... };
// Later
if (list.Contains(extension))
{
...
}
That does loop over all the values of course - but for small collections, that shouldn't be too expensive. For a large collection of strings you'd want to use something like HashSet<string>
instead, which would provide a more efficient lookup.
You can use !Regex.IsMatch(extension, "^\.(jpg|jpeg|gif|png|bmp)$")
but internally somehow it will still loop
Stick the extensions in a collection, then check if the extension of your file is in that collection.
It will require a loop, but you can do this with LINQ (hides the loop)
ie:
using System.Linq;
private readonly string[] _matches = new[] { ".jpg", ".bmp", ".png", ".gif", ".bmp" };
// Assumes extension is in the format ".jpg", "bmp", so trim the
// whitespace from start and end
public bool IsMatch(string extension)
{
return _matches.Contains(extension);
}
It could also be done with Regex but I'm no regex wizz so I'll leave that to another poster :)
Use the following 2 extensions. I wrote about them in an article on CodeProject. Here you go: http://www.codeproject.com/KB/dotnet/MBGExtensionsLibrary.aspx
public static bool In<T>(this T t, IEnumerable<T> enumerable)
{
foreach (T item in enumerable)
{
if (item.Equals(t))
{ return true; }
}
return false;
}
public static bool In<T>(this T t, params T[] items)
{
foreach (T item in items)
{
if (item.Equals(t))
{ return true; }
}
return false;
}
Of course it still requires a loop, but the good thing is you don't have to do that work. It also means you don't have to write code like this:
if (myString == "val1" ||
myString == "val2" ||
myString == "val3" ||
myString == "val4" ||
myString == "val5")
{
//Do something
}
There's an answer to that on StackOverflow already. HERE But I'd suggest you take the path of constructing a list of extensions and then checking agains each one of those. Regex would be more costly than that and would internally do roughly the same.
Regular Expression.
string fx = "jpg";
if (!Regex.IsMatch(fx, "^\.?(jpg|jpeg|gif|png|bmp)$", RegexOptions.IgnoreCase))
{
}
also, to get the file extension, use
string fn= file.FileName;
if (fn.Contains("\\"))
fn= fn.Substring(fn.LastIndexOf("\\") + 1);
string fx = fn.Substring(0, fn.LastIndexOf('.'));
You can use switch statement to validate file extension:
protected bool IsValidExtension(string extension)
{
switch (extension.ToLower())
{
case ".jpg":
case ".jpeg":
case ".gif":
case ".png":
case ".bmp":
return true;
default:
return false;
}
}
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