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Is that any Next function for a foreach in KeyValuePair?

Is that any Next function for a foreach in KeyValuePair ?
foreach (KeyValuePair<string, List<class>> KPV in dic )
{ }
or the only solution is using the traditional for loop with counter

Read MSDN Dictionary Class:
Represents a collection of keys and values.
While iterating through the dictionary, you work with KeyValuePair Structure, which represents a pair of key (here string) and value (here List<T>). So if the intention is to loop through List<T> in each pair, you need to access KeyValuePair.Value Property:
foreach (KeyValuePair<string, List<object>> KPV in dic)
{
foreach (object v in KPV.Value)
{
}
}
Also I replaced List<class> with List<object>, as definitely class is not a possible name for a type.
If each KeyValuePair.Key Property value is not important you may iterate through Dictionary.Values Property:
foreach (List<object> values in dic.Values)
{
foreach (object v in values)
{
}
}

KeyValuePair<TKey, TValue> objects can be enumerated if they are inside a Dictionary<TKey, TValue> object.
Inside a Dictionary you can use the Dictionary.Enumerator structure, which exposes the Dictionary.Enumerator.MoveNext() method, which may be the "Next" function you are looking for.
It would be nice if you can tell us what you intend to do inside that foreach code block.

The best way to use dictionary items as we use the advantages of List

I want to get use of dictionary items like I do in List generic class,
e.g;
foreach(item in ItemList)
{
item.BlaBla;
}
But in dictionary there s no chance, like e method above...
Dictionary<string, HtmlInputImage> smartPenImageDictionary;
I mean I got to know the key item for the dictionary item.. but what I want, I want to travel from beginning of the list till the end..

I am not absolutely sure what you want to achieve but here are the common things you can do with a dictionary.
IDictionary<Int32, String> dictionary = new Dictionary<Int32, String>();
// Iterate over all key value pairs.
foreach (KeyValuePair<Int32, String> keyValuePair in dictionary)
{
Int32 key = keyValuePair.Key;
String value = keyValuePair.Value;
}
// Iterate over all keys.
foreach (Int32 key in dictionary.Keys)
{
// Get the value by key.
String value = dictionary[key];
}
// Iterate over all values.
foreach (String value in dictionary.Values)
{
}

Iterating over a dictionary results in KeyValuePair<>s. Simply access the Key and Value members of the appropriate variable.

Something like this:
foreach (KeyValuePair<string, HtmlInputImage> kvp in smartPenImageDictionary)
{
Console.WriteLine("Value " + kvp.Value);
}

A dictionary doesn't have a "beginning" and "end" - it's unordered.
However, you can iterate over the keys or the values:
foreach (string key in smartPenImageDictionary.Keys)
{
...
}
foreach (HtmlInputImage image in smartPenImageDictionary.Values)
{
...
}
or key/value pairs:
foreach (KeyValuePair<string, HtmlInputImage> pair in smartPenImageDictionary)
{
string key = pair.Key;
HtmlInputImage image = pair.Value;
...
}
(Or course var makes the last case rather nicer.)

I assume you want them in order, the same way an IList<T> provides. As far as I know there is no order guaranteed for a Dictionary<Tkey,TValue>, so you'll need to
mydictionary.ToList();
However as you add and remove items, or even call this again it may change. One solution is to write your own Collection that has a custom indexer you can use.

testing for one item in dictionary<k,v>

I'm using VS 2005 fx2.0.
If I know my Dictionary contains only 1 item how do I get to it?
Thanks,
rod

The only way (with framework 2.0) is to iterate over it with foreach.
Or make a method that do that, like:
public static T GetFirstElementOrDefault<T>(IEnumerable<T> values)
{
T value = default(T);
foreach(T val in values)
{
value = val;
break;
}
return value;
}
It works with all IEnumerable and in your case T is KeyValuePair

Make sure you have using System.Linq;. The below command will get the key value pair of the dictionary
var item = Dictionary<k,v>.Single();
var key = item.Key;
var value =item.Value;

Graviton is correct but to be a bit safer (in the event that there is more than one item) you could do this:
yourDictionary.First();
And to be even safer you could do this (in the event that the dictionary was empty as well):
yourDictionary.FirstOrDefault();

Just iterate over all elements of Dictionary (in this case only one)
foreach (KeyValuePair<v, k> keyValue in dictionary)
{
}

dictionary.SingleOrDefault();

How to iterate over a dictionary?

I've seen a few different ways to iterate over a dictionary in C#. Is there a standard way?

foreach(KeyValuePair<string, string> entry in myDictionary)
{
// do something with entry.Value or entry.Key
}

If you are trying to use a generic Dictionary in C# like you would use an associative array in another language:
foreach(var item in myDictionary)
{
foo(item.Key);
bar(item.Value);
}
Or, if you only need to iterate over the collection of keys, use
foreach(var item in myDictionary.Keys)
{
foo(item);
}
And lastly, if you're only interested in the values:
foreach(var item in myDictionary.Values)
{
foo(item);
}
(Take note that the var keyword is an optional C# 3.0 and above feature, you could also use the exact type of your keys/values here)

In some cases you may need a counter that may be provided by for-loop implementation. For that, LINQ provides ElementAt which enables the following:
for (int index = 0; index < dictionary.Count; index++) {
var item = dictionary.ElementAt(index);
var itemKey = item.Key;
var itemValue = item.Value;
}

Depends on whether you're after the keys or the values...
From the MSDN Dictionary(TKey, TValue) Class description:
// When you use foreach to enumerate dictionary elements,
// the elements are retrieved as KeyValuePair objects.
Console.WriteLine();
foreach( KeyValuePair<string, string> kvp in openWith )
{
Console.WriteLine("Key = {0}, Value = {1}",
kvp.Key, kvp.Value);
}
// To get the values alone, use the Values property.
Dictionary<string, string>.ValueCollection valueColl =
openWith.Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console.WriteLine();
foreach( string s in valueColl )
{
Console.WriteLine("Value = {0}", s);
}
// To get the keys alone, use the Keys property.
Dictionary<string, string>.KeyCollection keyColl =
openWith.Keys;
// The elements of the KeyCollection are strongly typed
// with the type that was specified for dictionary keys.
Console.WriteLine();
foreach( string s in keyColl )
{
Console.WriteLine("Key = {0}", s);
}

Generally, asking for "the best way" without a specific context is like asking
what is the best color?
One the one hand, there are many colors and there's no best color. It depends on the need and often on taste, too.
On the other hand, there are many ways to iterate over a Dictionary in C# and there's no best way. It depends on the need and often on taste, too.
Most straightforward way
foreach (var kvp in items)
{
// key is kvp.Key
doStuff(kvp.Value)
}
If you need only the value (allows to call it item, more readable than kvp.Value).
foreach (var item in items.Values)
{
doStuff(item)
}
If you need a specific sort order
Generally, beginners are surprised about order of enumeration of a Dictionary.
LINQ provides a concise syntax that allows to specify order (and many other things), e.g.:
foreach (var kvp in items.OrderBy(kvp => kvp.Key))
{
// key is kvp.Key
doStuff(kvp.Value)
}
Again you might only need the value. LINQ also provides a concise solution to:
iterate directly on the value (allows to call it item, more readable than kvp.Value)
but sorted by the keys
Here it is:
foreach (var item in items.OrderBy(kvp => kvp.Key).Select(kvp => kvp.Value))
{
doStuff(item)
}
There are many more real-world use case you can do from these examples.
If you don't need a specific order, just stick to the "most straightforward way" (see above)!

C# 7.0 introduced Deconstructors and if you are using .NET Core 2.0+ Application, the struct KeyValuePair<> already include a Deconstruct() for you. So you can do:
var dic = new Dictionary<int, string>() { { 1, "One" }, { 2, "Two" }, { 3, "Three" } };
foreach (var (key, value) in dic) {
Console.WriteLine($"Item [{key}] = {value}");
}
//Or
foreach (var (_, value) in dic) {
Console.WriteLine($"Item [NO_ID] = {value}");
}
//Or
foreach ((int key, string value) in dic) {
Console.WriteLine($"Item [{key}] = {value}");
}

I would say foreach is the standard way, though it obviously depends on what you're looking for
foreach(var kvp in my_dictionary) {
...
}
Is that what you're looking for?

You can also try this on big dictionaries for multithreaded processing.
dictionary
.AsParallel()
.ForAll(pair =>
{
// Process pair.Key and pair.Value here
});

I appreciate this question has already had a lot of responses but I wanted to throw in a little research.
Iterating over a dictionary can be rather slow when compared with iterating over something like an array. In my tests an iteration over an array took 0.015003 seconds whereas an iteration over a dictionary (with the same number of elements) took 0.0365073 seconds that's 2.4 times as long! Although I have seen much bigger differences. For comparison a List was somewhere in between at 0.00215043 seconds.
However, that is like comparing apples and oranges. My point is that iterating over dictionaries is slow.
Dictionaries are optimised for lookups, so with that in mind I've created two methods. One simply does a foreach, the other iterates the keys then looks up.
public static string Normal(Dictionary<string, string> dictionary)
{
string value;
int count = 0;
foreach (var kvp in dictionary)
{
value = kvp.Value;
count++;
}
return "Normal";
}
This one loads the keys and iterates over them instead (I did also try pulling the keys into a string[] but the difference was negligible.
public static string Keys(Dictionary<string, string> dictionary)
{
string value;
int count = 0;
foreach (var key in dictionary.Keys)
{
value = dictionary[key];
count++;
}
return "Keys";
}
With this example the normal foreach test took 0.0310062 and the keys version took 0.2205441. Loading all the keys and iterating over all the lookups is clearly a LOT slower!
For a final test I've performed my iteration ten times to see if there are any benefits to using the keys here (by this point I was just curious):
Here's the RunTest method if that helps you visualise what's going on.
private static string RunTest<T>(T dictionary, Func<T, string> function)
{
DateTime start = DateTime.Now;
string name = null;
for (int i = 0; i < 10; i++)
{
name = function(dictionary);
}
DateTime end = DateTime.Now;
var duration = end.Subtract(start);
return string.Format("{0} took {1} seconds", name, duration.TotalSeconds);
}
Here the normal foreach run took 0.2820564 seconds (around ten times longer than a single iteration took - as you'd expect). The iteration over the keys took 2.2249449 seconds.
Edited To Add:
Reading some of the other answers made me question what would happen if I used Dictionary instead of Dictionary. In this example the array took 0.0120024 seconds, the list 0.0185037 seconds and the dictionary 0.0465093 seconds. It's reasonable to expect that the data type makes a difference on how much slower the dictionary is.
What are my Conclusions?
Avoid iterating over a dictionary if you can, they are substantially slower than iterating over an array with the same data in it.
If you do choose to iterate over a dictionary don't try to be too clever, although slower you could do a lot worse than using the standard foreach method.

As already pointed out on this answer, KeyValuePair<TKey, TValue> implements a Deconstruct method starting on .NET Core 2.0, .NET Standard 2.1 and .NET Framework 5.0 (preview).
With this, it's possible to iterate through a dictionary in a KeyValuePair agnostic way:
var dictionary = new Dictionary<int, string>();
// ...
foreach (var (key, value) in dictionary)
{
// ...
}

There are plenty of options. My personal favorite is by KeyValuePair
Dictionary<string, object> myDictionary = new Dictionary<string, object>();
// Populate your dictionary here
foreach (KeyValuePair<string,object> kvp in myDictionary)
{
// Do some interesting things
}
You can also use the Keys and Values Collections

With .NET Framework 4.7 one can use decomposition
var fruits = new Dictionary<string, int>();
...
foreach (var (fruit, number) in fruits)
{
Console.WriteLine(fruit + ": " + number);
}
To make this code work on lower C# versions, add System.ValueTuple NuGet package and write somewhere
public static class MyExtensions
{
public static void Deconstruct<T1, T2>(this KeyValuePair<T1, T2> tuple,
out T1 key, out T2 value)
{
key = tuple.Key;
value = tuple.Value;
}
}

As of C# 7, you can deconstruct objects into variables. I believe this to be the best way to iterate over a dictionary.
Example:
Create an extension method on KeyValuePair<TKey, TVal> that deconstructs it:
public static void Deconstruct<TKey, TVal>(this KeyValuePair<TKey, TVal> pair, out TKey key, out TVal value)
{
key = pair.Key;
value = pair.Value;
}
Iterate over any Dictionary<TKey, TVal> in the following manner
// Dictionary can be of any types, just using 'int' and 'string' as examples.
Dictionary<int, string> dict = new Dictionary<int, string>();
// Deconstructor gets called here.
foreach (var (key, value) in dict)
{
Console.WriteLine($"{key} : {value}");
}

foreach is fastest and if you only iterate over ___.Values, it is also faster

Using C# 7, add this extension method to any project of your solution:
public static class IDictionaryExtensions
{
public static IEnumerable<(TKey, TValue)> Tuples<TKey, TValue>(
this IDictionary<TKey, TValue> dict)
{
foreach (KeyValuePair<TKey, TValue> kvp in dict)
yield return (kvp.Key, kvp.Value);
}
}
And use this simple syntax
foreach (var(id, value) in dict.Tuples())
{
// your code using 'id' and 'value'
}
Or this one, if you prefer
foreach ((string id, object value) in dict.Tuples())
{
// your code using 'id' and 'value'
}
In place of the traditional
foreach (KeyValuePair<string, object> kvp in dict)
{
string id = kvp.Key;
object value = kvp.Value;
// your code using 'id' and 'value'
}
The extension method transforms the KeyValuePair of your IDictionary<TKey, TValue> into a strongly typed tuple, allowing you to use this new comfortable syntax.
It converts -just- the required dictionary entries to tuples, so it does NOT converts the whole dictionary to tuples, so there are no performance concerns related to that.
There is a only minor cost calling the extension method for creating a tuple in comparison with using the KeyValuePair directly, which should NOT be an issue if you are assigning the KeyValuePair's properties Key and Value to new loop variables anyway.
In practice, this new syntax suits very well for most cases, except for low-level ultra-high performance scenarios, where you still have the option to simply not use it on that specific spot.
Check this out: MSDN Blog - New features in C# 7

Simplest form to iterate a dictionary:
foreach(var item in myDictionary)
{
Console.WriteLine(item.Key);
Console.WriteLine(item.Value);
}

I found this method in the documentation for the DictionaryBase class on MSDN:
foreach (DictionaryEntry de in myDictionary)
{
//Do some stuff with de.Value or de.Key
}
This was the only one I was able to get functioning correctly in a class that inherited from the DictionaryBase.

Sometimes if you only needs the values to be enumerated, use the dictionary's value collection:
foreach(var value in dictionary.Values)
{
// do something with entry.Value only
}
Reported by this post which states it is the fastest method:
http://alexpinsker.blogspot.hk/2010/02/c-fastest-way-to-iterate-over.html

I know this is a very old question, but I created some extension methods that might be useful:
public static void ForEach<T, U>(this Dictionary<T, U> d, Action<KeyValuePair<T, U>> a)
{
foreach (KeyValuePair<T, U> p in d) { a(p); }
}
public static void ForEach<T, U>(this Dictionary<T, U>.KeyCollection k, Action<T> a)
{
foreach (T t in k) { a(t); }
}
public static void ForEach<T, U>(this Dictionary<T, U>.ValueCollection v, Action<U> a)
{
foreach (U u in v) { a(u); }
}
This way I can write code like this:
myDictionary.ForEach(pair => Console.Write($"key: {pair.Key}, value: {pair.Value}"));
myDictionary.Keys.ForEach(key => Console.Write(key););
myDictionary.Values.ForEach(value => Console.Write(value););

If you want to use a for loop, you can do as below:
var keyList=new List<string>(dictionary.Keys);
for (int i = 0; i < keyList.Count; i++)
{
var key= keyList[i];
var value = dictionary[key];
}

I will take the advantage of .NET 4.0+ and provide an updated answer to the originally accepted one:
foreach(var entry in MyDic)
{
// do something with entry.Value or entry.Key
}

If say, you want to iterate over the values collection by default, I believe you can implement IEnumerable<>, Where T is the type of the values object in the dictionary, and "this" is a Dictionary.
public new IEnumerator<T> GetEnumerator()
{
return this.Values.GetEnumerator();
}

The standard way to iterate over a Dictionary, according to official documentation on MSDN is:
foreach (DictionaryEntry entry in myDictionary)
{
//Read entry.Key and entry.Value here
}

I wrote an extension to loop over a dictionary.
public static class DictionaryExtension
{
public static void ForEach<T1, T2>(this Dictionary<T1, T2> dictionary, Action<T1, T2> action) {
foreach(KeyValuePair<T1, T2> keyValue in dictionary) {
action(keyValue.Key, keyValue.Value);
}
}
}
Then you can call
myDictionary.ForEach((x,y) => Console.WriteLine(x + " - " + y));

Dictionary< TKey, TValue > It is a generic collection class in c# and it stores the data in the key value format.Key must be unique and it can not be null whereas value can be duplicate and null.As each item in the dictionary is treated as KeyValuePair< TKey, TValue > structure representing a key and its value. and hence we should take the element type KeyValuePair< TKey, TValue> during the iteration of element.Below is the example.
Dictionary<int, string> dict = new Dictionary<int, string>();
dict.Add(1,"One");
dict.Add(2,"Two");
dict.Add(3,"Three");
foreach (KeyValuePair<int, string> item in dict)
{
Console.WriteLine("Key: {0}, Value: {1}", item.Key, item.Value);
}

The best answer is of course: Think, if you could use a more appropriate data structure than a dictionary if you plan to iterate over it- as Vikas Gupta mentioned already in the (beginning of the) discussion under the question. But that discussion as this whole thread still lacks surprisingly good alternatives. One is:
SortedList<string, string> x = new SortedList<string, string>();
x.Add("key1", "value1");
x.Add("key2", "value2");
x["key3"] = "value3";
foreach( KeyValuePair<string, string> kvPair in x )
Console.WriteLine($"{kvPair.Key}, {kvPair.Value}");
Why it could be argued a code smell of iterating over a dictionary (e.g. by foreach(KeyValuePair<,>) ?
A basic principle of Clean Coding:
"Express intent!"
Robert C. Martin writes in "Clean Code": "Choosing names that reveal intent". Obviously naming alone is too weak. "Express (reveal) intent with every coding decision" expresses it better.
A related principle is "Principle of least surprise" (=Principle of Least Astonishment).
Why this is related to iterating over a dictionary? Choosing a dictionary expresses the intent of choosing a data structure which was made for primarily finding data by key. Nowadays there are so much alternatives in .NET, if you want to iterate through key/value pairs that you could choose something else.
Moreover: If you iterate over something, you have to reveal something about how the items are (to be) ordered and expected to be ordered!
Although the known implementations of Dictionary sort the key collection in the order of the items added-
AFAIK, Dictionary has no assured specification about ordering (has it?).
But what are the alternatives?
TLDR:
SortedList: If your collection is not getting too large, a simple solution would be to use SortedList<,> which gives you also full indexing of key/value pairs.
Microsoft has a long article about mentioning and explaining fitting collections:
Keyed collection
To mention the most important: KeyedCollection<,> and SortedDictionary<,> .
SortedDictionary<,> is a bit faster than SortedList for only inserting if it gets large, but lacks indexing and is needed only if O(log n) for inserting is preferenced over other operations. If you really need O(1) for inserting and accept slower iterating in exchange, you have to stay with simple Dictionary<,>.
Obviously there is no data structure which is the fastest for every possible operation..
Additionally there is ImmutableSortedDictionary<,>.
And if one data structure is not exactly what you need, then derivate from Dictionary<,> or even from the new ConcurrentDictionary<,> and add explicit iteration/sorting functions!

var dictionary = new Dictionary<string, int>
{
{ "Key", 12 }
};
var aggregateObjectCollection = dictionary.Select(
entry => new AggregateObject(entry.Key, entry.Value));

Just wanted to add my 2 cent, as the most answers relate to foreach-loop.
Please, take a look at the following code:
Dictionary<String, Double> myProductPrices = new Dictionary<String, Double>();
//Add some entries to the dictionary
myProductPrices.ToList().ForEach(kvP =>
{
kvP.Value *= 1.15;
Console.Writeline(String.Format("Product '{0}' has a new price: {1} $", kvp.Key, kvP.Value));
});
Altought this adds a additional call of '.ToList()', there might be a slight performance-improvement (as pointed out here foreach vs someList.Foreach(){}),
espacially when working with large Dictionaries and running in parallel is no option / won't have an effect at all.
Also, please note that you wont be able to assign values to the 'Value' property inside a foreach-loop. On the other hand, you will be able to manipulate the 'Key' as well, possibly getting you into trouble at runtime.
When you just want to "read" Keys and Values, you might also use IEnumerable.Select().
var newProductPrices = myProductPrices.Select(kvp => new { Name = kvp.Key, Price = kvp.Value * 1.15 } );

in addition to the highest ranking posts where there is a discussion between using
foreach(KeyValuePair<string, string> entry in myDictionary)
{
// do something with entry.Value or entry.Key
}
or
foreach(var entry in myDictionary)
{
// do something with entry.Value or entry.Key
}
most complete is the following because you can see the dictionary type from the initialization, kvp is KeyValuePair
var myDictionary = new Dictionary<string, string>(x);//fill dictionary with x
foreach(var kvp in myDictionary)//iterate over dictionary
{
// do something with kvp.Value or kvp.Key
}

In C# .NET 2.0, what's an easy way to do a foreach in reverse?

Lets say I have a Dictionary object:
Dictionary myDictionary<int, SomeObject> = new Dictionary<string, SomeObject>();
Now I want to iterate through the dictionary in reverse order. I can't use a simple for loop because I don't know the keys of the dictionary. A foreach is easy:
foreach (SomeObject object in myDictionary.Values)
{
// Do stuff to object
}
But how can I perform this in reverse?

A dictionary or any other form of hashtable has no ordering. So what you are trying to do is pointless :)

I'd use a SortedList instead of a dictionary. You can still access it by Key, but you can access it by index as well.
SortedList sCol = new SortedList();
sCol.Add("bee", "Some extended string matching bee");
sCol.Add("ay", "value matching ay");
sCol.Add("cee", "Just a standard cee");
// Go through it backwards.
for (int i = sCol.Count - 1; i >=0 ; i--)
Console.WriteLine("sCol[" + i.ToString() + "] = " + sCol.GetByIndex(i));
// Reference By Key
foreach (string i in sCol.Keys)
Console.WriteLine("sCol[" + i + "] = " + sCol[i]);
// Enumerate all values
foreach (string i in sCol.Values)
Console.WriteLine(i);
It's worth noting that a sorted list stores key/value pairs sorted by key only.

If you have .NET 3.5 you can use the .Reverse() extension method on IEnumerables. For example:
foreach (object o in myDictionary.Values.Reverse())
{
// Do stuff to object
}

Actually, in C# 2.0 you can create your own iterator that traverses a container in reverse. Then, you can use that iterator in your foreach statement. But your iterator would have to have a way of navigating the container in the first place. If it's a simple array, it could go backwards like this:
static IEnumerable<T> CreateReverseIterator<T>(IList<T> list)
{
int count = list.Count;
for (int i = count - 1; i >= 0; --i)
{
yield return list[i];
}
}
But of course you can't do that with a Dictionary as it doesn't implement IList or provides an indexer. Saying that a Dictionary does not have order is not true: of course it has order. That order can even be useful if you know what it is.
For a solution to your problem: I'd say copy the elements to an array, and use the above method to traverse it in reverse. Like this:
static void Main(string[] args)
{
Dictionary<int, string> dict = new Dictionary<int, string>();
dict[1] = "value1";
dict[2] = "value2";
dict[3] = "value3";
foreach (KeyValuePair<int, string> item in dict)
{
Console.WriteLine("Key : {0}, Value: {1}", new object[] { item.Key, item.Value });
}
string[] values = new string[dict.Values.Count];
dict.Values.CopyTo(values, 0);
foreach (string value in CreateReverseIterator(values))
{
Console.WriteLine("Value: {0}", value);
}
}
Copying your values to an array may seem like a bad idea, but depending on the type of value it's not really that bad. You might just be copying references!

I agree with #leppie, but think you deserve an answer to the question in general. It could be that you meant for the question to be in general, but accidentally picked a bad data structure. The order of the values in a dictionary should be considered implementation-specific; according to the documentation it is always the same order as the keys, but this order is unspecified as well.
Anyway, there's not a straightforward way to make foreach work in reverse. It's syntactic sugar to using the class's enumerator, and enumerators can only travel in one direction. Technically the answer could be "reverse the collection, then enumerate", but I think this is a case where you'll just have to use a "backwards" for loop:
for (int i = myCollection.Length - 1; i >= 0; i--)
{
// do something
}

If you don't have .NET 3.5 and therefore the Reverse extension method you can implement your own. I'd guess it probably generates an intermediate list (when necessary) and iterates it in reverse, something like the following:
public static IEnumerable<T> Reverse<T>(IEnumerable<T> items)
{
IList<T> list = items as IList<T>;
if (list == null) list = new List<T>(items);
for (int i = list.Count - 1; i >= 0; i-- )
{
yield return list[i];
}
}

That would be a Dictionary<int, SomeObject> myDictionary, and you would do it by:
foreach(SomeObject _object in myDictionary.Values.Reverse())
{
}

The only way I can come up with in .NET 2.0 is to first copy all the values to a List, reverse the list and then run the foreach on that list:
Dictionary<int, object> d;
List<object> tmplist;
foreach (object o in d.Values) tmplist.Add(s);
tmplist.Reverse();
foreach (object o in tmplist) {
//Do stuff
}

Literal answer:
Dictionary<int, SomeObject> myDictionary = new Dictionary<int, SomeObject>();
foreach (var pair in myDictionary.OrderByDescending(i => i.Key))
{
//Observe pair.Key
//Do stuff to pair.Value
}

If the ordering is most important, you could you a Stack and create a simple struct to store your int, Object pair.

If you want a dictionary type collection but you need to maintain the insertion order you can look into the KeyedCollection
here
It is a merger between a dictionary and a list. That way you can access elements in the collection via the key or the insertion index.
The only gotcha is if your element being stored in the collection has to have an int key. If you could change that to a string or another type (Guid Mabye). Since collection1 will be searching for the key of 1 rather than the index of 1.

A standard for loop would be best. You don't have to worry about the processing overhead of reversing the collection.

You can use the LINQ to Objects Enumerable.Reverse() function in .NET 2.0 using LinqBridge.

foreach (Sample in Samples)
try the following:
Int32 nEndingSample = Samples.Count - 1;
for (i = nEndingSample; i >= 0; i--)
{
x = Samples[i].x;
y = Samples[i].y;
}