Setting List items in C# without automatic setter/getter

Question

I'm trying to make a manual setter/getter method in C#, but i'm getting the following error from the "set"-line: Error: The best overloaded method match for 'System.Collections.Generic.ListPackage.Add(Package)' has some invalid arguments

private List<Package> packages = new List<Package>();    

public List<Package> Packages
{
    set { packages.Add(value); }
    get { return packages; }
}

The `setter` is called when you use the `=` operator, this operator checks for the `assignability` from the value (on the right side), so the right side value should always be `List`, that value is held by `value` in the `setter`, when you write this `packages.Add(value)` in the setter, it is of course recoginized by the `IDE` that the `type` is invalid. (`value` should be of type `Package`). — King King, Sep 18 '13 at 11:48

Jaime Torres · Accepted Answer · 2018-09-03T16:05:18.133

6

Your code should look like this.

private var packages = new List<Package>();    

public List<Package> Packages
{
    set { packages = value; }
    get { return packages; }
}

If you're trying to use the index getter/setter for some kind of passthrough:

public int this[int key]
{
    get
    {
        return Packages[key];
    }
    set
    {
        Packages[key] = value;
    }
}

edited Sep 03 '18 at 16:05

answered Sep 18 '13 at 11:37

Jaime Torres

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dav_i · Answer 2 · 2013-09-18T11:52:58.217

3

With a getter/setter the input and output types must be the same. (hence the declaration being public List<Package> Packages { ... - it is expecting an input of List<Packages> and an output of List<Packages>.

What you are doing here is trying to get type List<Package> and set type Package. This is not allowed.

What I think you want to do is the following:

private List<Package> packages = new List<Package>();    

public List<Package> Packages
{
    // no setter
    get { return packages; }
}

Then call myObject.Packages to get all the packages and myObject.Packages.Add(package) to add.

edited Sep 18 '13 at 11:52

answered Sep 18 '13 at 11:37

dav_i

27,509
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But if i change it to set { packages.Add(Package); } i get "Package is a "type" but is used as a variable" – Mads K Sep 18 '13 at 11:39
@MadsK I think you misunderstand. I updated my question to try and explain it better. – dav_i Sep 18 '13 at 11:42

score 1 · Answer 3 · answered Sep 18 '13 at 11:40

1

If you really want to add value, which is a List<Package>, to packages you should use

set { packages.AddRange(value); }

Otherwise,

set { packages = value; }

answered Sep 18 '13 at 11:40

Ovidiu

1,407
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score 1 · Answer 4 · answered Sep 18 '13 at 11:47

You can not do that.

if you are trying to set an element you should...

public void addPackage(Package pack){
    packages.Add(pack);
}

usage: MyClass m= new MyClass(); m.addPackage(new Package());

if you are trying to set the collection then ...

public List<Package> Packages
{
    set { packages=value; }
    get { return packages; }
}

usage:

MyClass m= new MyClass();
m.Packages=new List<Package>();

score 0 · Answer 5 · answered Sep 18 '13 at 11:38

I think you have yourself a bit mixed up here.

The type of Packages is List<Package>. When you're calling packages.Add(value);, packages is in fact, List<Package>.

public List <Package> Packages
{
    get { return packages; }
    set { packages = value; }
}

This corrects the property.

To add an item:

Packages.Add(myPackage);

score 0 · Answer 6 · answered Sep 18 '13 at 11:49

You are trying to use the set{} method as the Add method, which it isn't. set is used to change the entire collection whereas an Add method would add an item to the collection. what has been stated in other answers is correct... if you really want the = operator to add to the collection rather than assign a new collection, you can use AddRange() but for clarity sake, you should be overriding the = operator if that is the case.

Setting List items in C# without automatic setter/getter

6 Answers6

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