KeyValuePair VS DictionaryEntry

Posted 2020-07-31 楊柳

There are some difference between KeyValuePair which is the generic version and DictionaryEntry which is non generic version. 

1. KeyValuePair < T,T > is for iterating through Dictionary < T,T >. This is the .Net 2 way of doing things.
2. DictionaryEntry is for iterating through HashTables. This is the .Net 1 way of doing things.
3. KeyValuePair<TKey,TValue> is used in place of DictionaryEntry because it is generic.

The advantage of using a KeyValuePair<TKey,TValue> is that we can give the compiler more information about what is in our dictionary. Esp. the data type

Dictionary<string, int> dict = new Dictionary<string, int>();
foreach (KeyValuePair<string, int> item in dict) {
  int i = item.Value;
}

Hashtable hashtable = new Hashtable();
foreach (DictionaryEntry item in hashtable) {
  // Cast required because compiler doesn‘t know it‘s a <string, int> pair.
  int i = (int) item.Value;
}