How Can I Reliably Check for Subclass Relationships in C# Including Self-Type Comparisons?

Reliably check subclass relationships in C#, including self-type comparisons

To determine whether a type is a subclass of another type in C#, you can use IsSubclassOf:

<code class="language-csharp">typeof(SubClass).IsSubclassOf(typeof(BaseClass)); // 返回 true</code>

However, this approach fails when checking the subclass relationship between the type and itself:

<code class="language-csharp">typeof(BaseClass).IsSubclassOf(typeof(BaseClass)); // 返回 false</code>

To work around this limitation, several options exist:

Type.IsAssignableFrom:

<code class="language-csharp">typeof(BaseClass).IsAssignableFrom(typeof(DerivedClass)); // 返回 true</code>

While this method returns true for subclasses, it also provides false positives for unrelated types, for example:

<code class="language-csharp">typeof(BaseClass).IsAssignableFrom(typeof(int[])); // 返回 true</code>

is and as (object operations):

These operators require objects rather than type objects and cannot be used to compare type definitions:

<code class="language-csharp">// 无法编译：
SubClass is BaseClass

// 无法编译：
typeof(SubClass) is typeof(BaseClass)</code>

Custom method:

In order to accurately check the subclass relationship, you can create a helper method:

<code class="language-csharp">public static bool IsSameOrSubclass(Type potentialBase, Type potentialDescendant)
{
    return potentialDescendant.IsSubclassOf(potentialBase)
        || potentialDescendant == potentialBase;
}</code>

This method correctly handles subclassing and equality comparisons.

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