How Can I Check if a C# Object is a Nullable Value Type?

C# object nullability check

In C#, it is crucial to distinguish between nullable and non-nullable objects. This article focuses on how to determine whether an object is nullable, focusing on value types rather than reference types.

Implementation method:

The following code snippet demonstrates one way to check whether an object is a nullable value type:

bool IsNullableValueType(object o)
{
    if (o == null) return true; // 显而易见的情况
    Type type = o.GetType(); // 修正此处，使用 o.GetType() 获取对象的实际类型
    if (!type.IsValueType) return true; // 引用类型
    if (Nullable.GetUnderlyingType(type) != null) return true; // Nullable<T>
    return false; // 值类型
}

Code explanation:

This method checks three situations:

• Null object: If o is null, it is itself nullable.
• Reference types: If o is a reference type (not a value type), it is considered nullable.
• Nullable value type: The Nullable.GetUnderlyingType method checks whether the type of o is of type Nullable<t></t>. o is a nullable value type if it returns a non-null type.

Handling boxed objects:

However, this method may fail if o is a boxed value type. This problem can be overcome using generics:

static bool IsNullable<T>(T obj)
{
    if (obj == null) return true; // 显而易见的情况
    Type type = typeof(T);
    if (!type.IsValueType) return true; // 引用类型
    if (Nullable.GetUnderlyingType(type) != null) return true; // Nullable<T>
    return false; // 值类型
}

By using generics, this modified method can infer the type of T from the object passed in, which works even if o has been boxed.

More resources:

For more information about nullable types in C#, see Microsoft's documentation: https://www.php.cn/link/55298ec38b13c613ce8ffe0f1d928ed2

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