Array of objects - modyfing object's fields C#

Question

I've got such a problem. I'm a beginner in C#. I have an object array (various classes) and in one place of application I want to modify fields like an age or name. Construction

static Object[] prac = new Object[10];
public static void Main(string[] args)
{
    prac[0].age = 21;
}

shouts an error

'object' does not contain a definition for 'age' and no extension method 'age' accepting a first argument of type 'object' could be found

I thought that will be similiar to a Java code, but it isn't. What am I doing wrong?

Regards.

I don't think this code works in Java also, probably you mean javascript ( which is dynamic language) you need to cast from Object to the class you need... — Schwarzie2478
– Schwarzie2478, Commented Sep 16, 2014 at 9:34
Trying not to sound condescending, but I think you need to go take a tutorial in c# — DavidG
– DavidG, Commented Sep 16, 2014 at 9:34
Ow, I made a mistake. It's a Person[] prac = new Person[10]. — Box
– Box, Commented Sep 16, 2014 at 9:40

Alex Barac · Accepted Answer · 2014-09-16 09:36:10Z

2

You need to cast your member to the class type that contains the age. I'll just assume that your class name is Person and that is has a age member :

static Object[] prac = new Object[10];
public static void Main(string[] args)
{
    ((Person)prac[0]).age = 21;
}

Important to note are the brackets : (Person)prac[0] is the cast part, you cast the Object prac[0] to a Person object. The outer brackets ((Person)prac[0]) are there so that the code is taken as a Person object, instead of a regular Object.

answered Sep 16, 2014 at 9:36

Alex Barac

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1 Comment

Box Over a year ago

Yeah, that's it! My array type should be Person at all... Thanks.

walther · Accepted Answer · 2014-09-16 09:33:47Z

First you need to cast the object to the type you're intending to work with.

If you work with type object, it has only a limited amount of properties and methods. To use property age, you first need to cast it to the corresponding type that has that property. For instance something like this:

static Object[] prac = new Object[10];
public static void Main(string[] args)
{
    SpecificType myObject = prac[0] as SpecificType; // returns null if not successful
    if (myObject != null)
        myObject.age = 21;
}

HOWEVER, I'm not convinced you're doing the right thing here. I'd personally avoid type object unless absolutely there would be no other way of doing it (and that is very rare in my code). C# is a strongly-type language and by using object you're prone to errors all over the place.

ivan.mylyanyk · Accepted Answer · 2014-09-16 09:33:56Z

1

Object doesn't have property age. All Object's properties and methods are stated here.

answered Sep 16, 2014 at 9:33

ivan.mylyanyk

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Comments

Selman Genç · Accepted Answer · 2014-09-16 09:34:05Z

1

It's an array of objects and as the error message suggests, 'object' does not contain a definition for 'age'

You need to declare your array with the type that has age field or property.And the you can modify it whatever you want. For example:

class Person 
{
    public string Name { get; set; }
}

answered Sep 16, 2014 at 9:34

Selman Genç

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Tim Schmelter · Accepted Answer · 2014-09-16 09:34:21Z

1

You have to use an array of your class instead of Object which is the base type of all classes.

static MyClass[] prac = new MyClass[10];

or you have to cast it:

MyClass mc = (MyClass) prac[0];
mc.age = 21;

answered Sep 16, 2014 at 9:34

Tim Schmelter

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Comments

Hellin · Accepted Answer · 2014-09-16 09:34:52Z

0

Object is the base class for all classes in .Net.

Just cast the required value to the required typed class. Or Create a list with the right type instead of object.

answered Sep 16, 2014 at 9:34

Hellin

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