Need Hashtable and Arraylist

Question

I am trying to use someone else's C# classes in my Windows 7 Phone app. The classes use objects of type Hashtable.

The file in question has

using System.Collections;

at the top, so I'm assuming that's the Hashtable object it wants.

When I try to build my solution, I get errors that the type or namespace name 'Hashtable' could not be found, are you missing a using directive or assembly reference.

In Microsoft's documentation of Hashtable, I see it says Assembly: mscorlib

But if I try to add mscorlib via Project>Add Reference, VS says it can't add it because it is automatically referenced by the build system.

What am I missing?

Wanderoo

Answer 1

The non-generic collections, including ArrayList and HashTable, are not included in Silverlight.
These classes are hold-overs from .Net 1.0 (which didn't have generics) and should not be used in new code.

Instead, you should use the generic collections—List<T> and Dictionary<TKey, TValue>.

Achromat

Answer 2

You have a few options:

1. Change your import to using System.Collections.Generic; and change every use of a HashTable to Dictionary<> and ArrayList to List<>.

2. You might be able to get away with:

   using HashTable = System.Collections.Generic.Dictionary<object, object>;
using ArrayList = System.Collections.Generic.List<object>;
   Note that any future maintainer will hate you for doing this.

3. But it's better to refactor the code to use the generic collections properly.

4. Create a class Hashtable in a namespace System.Collections, implement IDictionary<object, object> by forwarding everything to an inner Dictionary<object, object> and implement the necessary changes in behavior (locking, missing keys, etc.); Create an ArrayList by encapsulation List<object>. (suggested by henon)

Cankerous

#2 is a horrible idea. It would work, though, except that you need fully-qualified typenames. – Achromat

@SLaks: You might not have noticed, but I have 3 ideas. Which one's horrible? Also, I'm not sure what you mean needs to be fully qualified. – Cankerous

The using statements need fully-qualified typenames, unless placed separately inside the namespace. – Achromat

SLkaks: Good point. It's almost certainly the case that code old enough to use the old collection classes would have the using list outside the namespace. – Cankerous

+1 for the abominable #2 suggestion and then pointing out that anyone looking at it in the future may well wish you eviscerated – Depilatory

Idea #4 that works very well: create a class Hashtable in a namespace System.Collections, implement IDictionary<string, object> by forwarding everything to an inner Dictionary<string, object> and implement the indexer so that it does not fail when the key is not present in the inner dict. – Decidua

Answer 3

There are different mscorlibs depending on which .NET framework you are using. If you look in the "Other Versions" dropdown on the MSDN page, you will see Hashtable is not a part of Silverlight. You will need to use a Dictionary<Object, Object> (or ideally more strongly typed keys and value types)

Orvil

Answer 4

System.Collection is a legacy of first version of .Net - no generic types.

To fix your code use Dictorany class which is a hashtable at heart, and List insted of ArrayList.

Geyser

Answer 5

It worked for me changing:

Hashtable for Dictionary<object, object>

NameValueCollection for Dictionary<object, object>

Other problem I encoutered is Encoding.ASCII is not defined either, I sorted that with a function a stackoverflow lad wrote:

public static byte[] StringToAscii(string s) {
    byte[] retval = new byte[s.Length];
    for (int ix = 0; ix < s.Length; ++ix) {
        char ch = s[ix];
        if (ch <= 0x7f) retval[ix] = (byte)ch;
        else retval[ix] = (byte)'?';
    }
    return retval;
}

credits here:

ASCIIEncoding In Windows Phone 7

So finally to return the ASCII this is what to do:

return StringToAscii(Encoding.Unicode.GetString(result.ToArray()));

Hagler