Determine if an object is an array of any type, and access the array length

Question

I have an overridden method that has an object parameter. I am determining if this is an array, and then want to determine its length:

public override bool IsValid(object value)
{
    Type type = value.GetType();
    if (type.IsArray)
    {
        return ((object[]) value).Length > 0;
    }
    else
    {
        return false;
    }
}

The problem is if value is an int[], it errors when I try to cast to an object[]. Is there any way to handle this cast so it will work with any type of array?

Possible duplicate of C# Reflection : how to get an array values & length? — Fredou
– Fredou, Commented Oct 22, 2015 at 15:15
Be careful using the term "generic" as it's means something specific in C#, though you can do this in a generic way. — DavidG
– DavidG, Commented Oct 22, 2015 at 15:15
You need to make a new array. Value type arrays can't be cast to object[], because all the values need to be boxed. All that aside, what you're doing seems like a code smell; are you sure you can't just accept an Array as the parameter? — user1726343
– user1726343, Commented Oct 22, 2015 at 15:16
Are you able to modify the method you are overriding or are you stuck with this method signature? — DavidG
– DavidG, Commented Oct 22, 2015 at 15:18
Not all you code paths return a value. What do you return if value is not an array? — Matt Burland
– Matt Burland, Commented Oct 22, 2015 at 15:20

Michael Liu · Accepted Answer · 2015-10-22 15:19:58Z

14

Cast value to the base System.Array class:

return ((Array) value).Length > 0

By using the as operator, you can simplify your code further:

public static bool IsValid(object value)
{
    Array array = value as Array;
    return array != null && array.Length > 0;
}

Note: This will return true for multidimensional arrays such as new int[10, 10]. If you want to return false in this case, add a check for array.Rank == 1.

edited Oct 22, 2015 at 15:19

answered Oct 22, 2015 at 15:14

Michael Liu

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2 Comments

Matt Burland Over a year ago

Using as you should at least check for array == null.

Michael Liu Over a year ago

@MattBurland: Thanks. Fixed.

user1726343 · Accepted Answer · 2015-10-22 15:29:40Z

1

An alternative approach that avoids having to interrogate the type in your validation method is to use dynamic dispatch:

// Default overload
public static bool IsValid(object value) 
{ return false; }

// If it's an array
public static bool IsValid(Array value)
{
    return value.Length > 0;
}

...

bool isValid = IsValid((dynamic)obj); // Will call the overload corresponding to type of obj

answered Oct 22, 2015 at 15:29

user1726343

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