


Can I Assign a List of Derived Class Objects to a Base Class List in C#?
Feb 02, 2025 am 05:31 AM
For example, consider the following code:
In this code, the list of the Giraffe object is assigned to the list referenced by Animal. However, this assignment failed during compilation due to the problem of coordination.
class Animal { } class Giraffe : Animal { } static void Main(string[] args) { List<Giraffe> giraffes = new List<Giraffe>(); List<Animal> animals = giraffes; // 編譯時(shí)錯(cuò)誤 }
<變> Cooperation and non -variability
C #'s generic types can be coordinated or unchanged. Coordination allows base class references to reference the derived class objects, while non -degeneration prevents such assignments. For the list, the default behavior is non -variability, which means that list cannot be assigned to list
.
In order to solve this problem, there are several solutions:
<式> Explicit conversion:The following code can be used to display list
to list- :
-
However, it is not recommended to use this explicit conversion, because if the conversion is invalid, it may cause runtime errors.
List<Animal> animals = (List<Animal>)giraffes; // 不推薦,可能導(dǎo)致運(yùn)行時(shí)錯(cuò)誤You can use the list
.Convertall method to convert List
to List- by providing LAMBDA expressions that convert each element. For example:
-
<現(xiàn)> Implement the iCovariant interface
List<Animal> animals = giraffes.ConvertAll(g => (Animal)g);It can be explicitly specified to specify the collaborative change of generic types through custom interfaces. By implementing the icovariant
- interface, the class can allow the object to use the generic type of genetic class to reference the assignment. (Note:
- does not exist in C#, the actual solution is to use , because list itself does not support the coordination.) Change.
Which method to choose depends on the specific situation and the requirements for the robustness of the code. ICovariant<out T>
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