CODEWITHSUNDEEP
c#castingienumerable
chanti
chanti

Reputation: 95

System.InvalidCastException with iennumrable cast

why I see System.InvalidCastException for the below code?

object[] obj = new object[5];
obj[0] = 1;
obj[0] = 2;
obj[0] = 3;
obj[0] = 4;
obj[0] = 5;
var exc = obj.Cast<string>().ToList();

Unable to cast object of type System.Int32 to type System. String.

Upvotes: 1

Views: 61

Answers (1)

pinkfloydx33
pinkfloydx33

Reputation: 12799

You have two problems:

  1. You make the assumption that int can be directly cast to string (in cannot)
  2. You assume that if #1 was valid, that Cast<T> would then perform that cast (it won't)

To get passed the first problem, you can simply project the source using Select and call ToString in the selector function (I make the assumption below that you didn't intend to assign all five values to index 0 but actually meant to populate the array in full):

var obj = new object[] { 1, 2, 3, 4, 5 };
var result = obj.Select(c => c.ToString()).ToList();

Alternatively you could use Convert.ToString:

var obj = new object[] { 1, 2, 3, 4, 5 };
var result = obj.Select(c => Convert.ToString(c)).ToList();

Both of these remove the "need" for Cast<> and solve problem #2 in the process.

It's important to note that even if there was an implicit or explicit conversion from int to string, that Cast<int> would not perform the cast. This is because the function relies on a generic cast which does not invoke conversion operators. The source objects must be the same type as the generic argument. Cast is used for non-generic IEnumerable collections that existed pre-Linq allowing you to convert to an IEnumerable<T> to enable using LINQ operations. For example (broken into parts):

DataTable dt = GetDataTable();
DataRowCollection drc = dt.Rows;
IEnumerable<DataRow> idr = drc.Cast<DataRow>();
var result = idr.Select(dr => GetDataFromDataRow(dr)).ToList();

Upvotes: 1

Related Questions