HasValue and != null

Nullable type of C# allows nullable values, which can be valid values ​​or null. There are two common ways to check if a nullable value has been assigned:

Nullable.HasValue

HasValue property of Nullable indicates whether the value has been assigned. It returns a boolean value, true if the value is non-null, and false if the value is null.

Nullable != null

This expression also checks whether the nullable value is non-null. It uses the equal sign operator to compare null values ​​with null.

Equivalence in compilation

compiler optimizes these checks by replacing the != null comparison with a call to HasValue . This means there is no significant difference in performance or functionality between the two approaches.

Preferences

HasValue and != null is purely based on readability and preference. Some developers prefer the clarity of HasValue , while others find the concise != null is easier to read.

Example

int? a = null;

// 使用 HasValue
if (a.HasValue)
{
    // ...
}

// 使用 != null
if (a != null)
{
    // ...
}

In short, HasValue and != null are both effective ways to check non-null nullable values ​​in C#. The compiler optimizes these checks to have equivalent behavior, making choices a question of developer preferences and code readability.