ArrayTypeMismatch Exception

The ArrayTypeMismatchException is thrown when an array element location is assigned to an object whose type is not compatible.

Array covariance

The term "array covariance" sounds complicated, and it is, but it relates to how arrays of different objects can be casted back and forth.

Example

The .NET Framework supports array covariance and contravariance. These are ways to treat an array of a more derived type as an array of the less derived base class type.

class Program
{
    static void Main()
    {
        // Declares and assigns a string array.
        // ... Then implicitly casts to base class object.
        // ... Then assigns invalid element.
        string[] array1 = { "cat", "dog", "fish" };
        object[] array2 = array1;
        array2[0] = 5;
    }
}
Unhandled Exception: System.ArrayTypeMismatchException:
Attempted to access an element as a type incompatible with the array.
   at Program.Main() in ...

Array notes

All string types derive from object types. Therefore you can apply array covariance to treat the string[] as an object[] reference.

A summary

This exception is a result of the array covariance rules. The string type is derived from the object type and we can therefore use a string array as an object array type.