Add objects to an empty list

Question

I'm new to C#, so this question might be an easy one. However I did not find any solution yet.

Description of the problem:

I want to create and empty array [4] of lists [length not know]. Later on I will read out four different channels and fill the list with objects created beforehand.

What I did so far

class objChannel 
{
    private int channel;
    public objChannel(int inputChannel)
    {
        channel = inputChannel;
    }

    public int Channel {get {return channel;}}
}

List<objChannel>[] listChannel = new List<objChannel>[4];

listChannel[1].Add(objChannel(1));

This does not work because of an null error.

Right now I have a work around like this:

List<objChannel>[] listChannel = {new List<objChannel> { new objChannel(1) },
                                  new List<objChannel> { new objChannel(2) },
                                  new List<objChannel> { new objChannel(3) },
                                  new List<objChannel> { new objChannel(4) }};

However, this will give me non-empty list.

First you have to instantiate `listChannel[1]` and then you can call the instance method `Add`. — Habib, Jun 14 '16 at 17:07
You want a _single_ container of `objChannel` or you want a _container of containers_ of `objChannel`?? — Khalil Khalaf, Jun 14 '16 at 17:07

Jared Wilkin · Accepted Answer · 2016-06-14T18:02:27.063

4

when you initialize your array of lists, you need to create empty lists as well like:

List<objChannel>[] listChannel = {new List<objChannel>(), new List<objChannel>(), new List<objChannel> (), new List<objChannel> ()};

or

for(int i = 0; i<4; i++)
{
    listChannel[i] = new List<objChannel>();
}

edited Jun 14 '16 at 18:02

answered Jun 14 '16 at 17:09

Jared Wilkin

231
3
12

Is there an option to do that with even less code? I have to do a similar things which has 17 objChannels. I would like to avoid to write `new List()` so often. – alias_paj Jun 14 '16 at 17:49
yes, after creating the listChannel array, use a for loop to create new List objects, see updated answer – Jared Wilkin Jun 14 '16 at 18:00
Thanks. I thought there was some secret code I just don't know yet. Seems to be that I just have to do it the `for loop` or `while` way. – alias_paj Jun 14 '16 at 21:54

score 2 · Answer 2 · answered Jun 14 '16 at 17:09

2

The reason your first code is failing is because you have to instantiate the listChannel[1] and then you can only call the instance method like:

listChannel[1] = new List<objChannel>();
listChannel[1].Add(new objChannel(1));

The other point to note is that the array index starts with 0 and not 1. (Although not sure if that use in the question was intentional).

answered Jun 14 '16 at 17:09

Habib

219,104
29
407
436

Thanks @Habib for the fast reply. That works. Now I have the following `List[] listChannel = new List[4]; listChannel[0] = new List(); listChannel[1] = new List(); listChannel[2] = new List(); listChannel[3] = new List();` – alias_paj Jun 14 '16 at 17:18

Add objects to an empty list

2 Answers2