通用方法将T强制转换为对象类型

Question

I have a method that accepts a generic type of BaseViewModel. I want to get the actual object in the method.

What I tried:

public static void LogScreen<T>() where T : BaseViewModel
 {
    var viewModel = T as BaseViewModel;
 }

Answer 1

You are not passing any object into the method, only the parameter type .

To apply value correctly, You should use the syntax like:

public static void LogScreen<T>(T TArg)
    where T : BaseViewModel
{
    var viewModel = TArg; //not necessary: as BaseViewModel;
}

In this kind of code You do not really need to use generic and You might go with simplier version as:

public static void LogScreen(BaseViewModel viewModel)
{
     //already got viewModel as correct type and checked during compile for types
}

---

Note: The big advantage of using generic approach is putting there some type and then work with the type whole time (great example IEnumerable<int> ). If You would do that without generic type, You would need to use object everywhere and You would need to cast the object all the time

• Generic is advantage there as You can put anything inside.

On the other hand if You have a method, where You have only one type the only one, it is easier to go with strict parameter type (2nd approach).

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Comment of ZoharPeled - the code should be written as:

public static void LogScreen<T>(T TArg)
    where T : BaseViewModel
{
    var viewModel = TArg as BaseViewModel;
    var viewModel2 = TArg;
}

From the compiler's point of view, the type of the reference named viewModel is exactly the same as the type of the reference named viewModel2 - both are BaseViewModel , and both instances may or may not be of any type derived from BaseViewModel . Long story short, the as operator is redundant in this code. Even if you pass an instance of some class derived from BaseModelView you can only reference it as a BaseModelView in this method.