C# inherit from Dictionary, iterate over KeyValuePairs
I have a class that inherits from Dictionary<string, string> . Within an instance method, I want to iterate over all KeyValuePair<string, string> 's. I've tried doing the following:
foreach (KeyValuePair<string, string> pair in base)
But this fails with the following error:
Use of keyword 'base' is not valid in this context
How can I iterate over the KeyValuePair<string, string> 's in an instance method in a class that derives from Dictionary<string, string> ?
Edit: I found I can do the following:
var enumerator = base.GetEnumerator();
while (enumerator.MoveNext())
{
KeyValuePair<string, string> pair = enumerator.Current;
}
However, I would still like to know if there's a way to do this via a foreach loop.
Edit: thanks for the advice about not inheriting from Dictionary<string, string> . I'm instead implementing System.Collections.IEnumerable, ICollection<KeyValuePair<string, string>>, IEnumerable<KeyValuePair<string, string>>, IDictionary<string, string> .
First, deriving from the .NET collection classes is generally ill-advised because they don't offer virtual methods for calls not inherited from object . This can result in bugs when passing your derived collection in via a base-class reference somewhere. You are better off implementing the IDictionary<T,TKey> interface and aggregating a Dictionary<,> inside your implementation - to which you then forward the appropriate calls.
That aside, in your specific case, what you want to do is:
foreach( KeyValuePair<string,string> pair in this ) { /* code here */ }
The base keyword is primarily used to access specific members of your base class. That's not what you're doing here - you are attempting to iterate over the items of a particular instance ... which is simply the this reference.
I agree with JaredPar's comment that this isn't a great idea. You probably don't want to publicly expose all of the methods of Dictionary to the outside world, so just make the Dictionary a private member variable and then provide your own interface to it.
With that said, the way to do what you're trying to do is:
foreach (KeyValuePair<string, string> pair in this)
Encapsulate Dictionary<string, string> as a composed field inside custom class MyDictionary and implement a custom IEnumerable and IEnumerator (or variations thereof) for MyDictionary (or make a method that implements handy C# yield keyword to produce the items)...
Eg
class MyDictionary : IEnumerable<KeyValuePair<string,string>> {
Dictionary<string, string> _dict;
IEnumerator<KeyValuePair<string,string>> GetEnumerator() {
return new MyEnum(this); // use your enumerator
// OR simply forget your own implementation and
return _dict.GetEnumerator();
}
class MyEnum : IEnumerator<KeyValuePair<string,string>> {
internal MyEnum(MyDictionary dict) {
//... dict
}
// implemented methods (.MoveNext, .Reset, .Current)...
This maintains encapsulation of extraneous methods. And you can still iterate over you instances like so from inside or outside :
// from outside
MyDictionary mdict = new MyDictionary();
foreach (KeyValuePair<string, string> kvp in mdict)
//...
// from inside, assuming: this == MyDictionary instance)
public void MyDictionaryMethod() {
foreach (KeyValuePair<string, string> kvp in this)
//...