When I was trying to use foreach loop with classes or a value type I was doing it like that
foreach(int item in items)
{
//rest of the code
}
However when I tried to loop the Dictionary like that
foreach(Dictionary<TKey,TValue> item in dictionaryobject)
{
//compile error
}
I got a compile error so I must use KeyValuePair<int, string>
foreach(KeyValuePair<int,string> item in dictionaryobject)
{
//code
}
Why must I use KeyValuePair instead of the Dictionary?
3
Why must I use KeyValuePair instead of the Dictionary?
Because KeyValuePair<TKey, TValue> is what the enumerator of GetEnumerator yields for each item in the dictionary. A Dictionary<TKey, TValue> implements IEnumerable(Of KeyValuePair(Of TKey, TValue)) and that interface needs to be implemented for foreach, so GetEnumerator is called when you use a foreach. See: Make a Visual C# class usable in a foreach statement
If you have a List<int> each int is enumerated, but in case of a dictionary you want the pair of key and value.
Regarding:
foreach(int item in items)
Assuming items is e.g. a List<int> (or similar), it makes sense to use int item in a for-each loop, because each entry in the collection is an int.
But in this line:
foreach(Dictionary<TKey,TValue> item in dictionaryobject)
Assuming dictionaryobject is a Dictionary, each element is not a Dictionary<TKey,TValue>.
Therefore the 2 lines are not correlated.
The correlative version is indeed:
foreach(KeyValuePair<int,string> item in dictionaryobject)
Because each element in a Dictionary is a KeyValuePair<int,string>.
2
Your dictionary is dictionaryobject. when iterating over it, each iteration provides a pair of key and value, not another dictionary – hence, the KeyValuePair<int,string>.