Access elements from a list
Monkey Forums/Monkey Programming/Access elements from a list
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| 1st time when I try to use lists. I need to access some specific elements from a List. I have this list: bouncedServerList Where I store some ids when the user is selecting an object from my game. Now I want to draw a line between these objects. A 'bounced link' How do I select a specific value from the list? |
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| A list is a chain of items in which each one points to the next one and the previous one. So you have to 'walk along' the list if you want to find anything specific. So...which item do you want? If you want to draw a line between each pair in order, for example, you could write:
Local bCurrent:Bounce
Local bPrev:Bounce
For local bounce:Bounce = Eachin bounceServerList
bPrev = bCurr
bCurr = bounce
If bPrev <> Null
DrawLine( bPrev.pos, bCurr.pos )
End
Next
That's probably nothing like what you want to do, so give us a clue ;-) |
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| Hmm, what you wrote there is quite ok but not what I am looking for. Maybe I do not understand how is working exactly so please forgive if my question is stupid: So, I have this list: bounceServerList Every time I tap on a 'server' in my game, I add the server 'ID' in that list: bouncedServerList.AddLast(s) of course if the server is already in the list I remove it: bouncedServerList.Remove(s) Now, I want to draw some yellow lines between these servers from the bounceServerList which is a list of integers. For example: 1st element in bounceServerList = 4 'server id = 4 2nd element in bounceServerList = 2 'server id = 2 3rd element in bounceServerList = 0 'server id = 0 I want to make something like DrawLine ( myServer[bounceServerList[value 1st element]].PosX, myServer[bounceServerList[value 1st element]].PosY, myServer[bounceServerList[value 1st element] + 1 ].PosX, myServer[bounceServerList[value 1st element] + 1 ].PosY ) I am trying to port my c# code from a previous XNA game. In that I used this code:
for (int x = 0; x < bouncedServers.Count - 1; x++)
{
drawLine(2, Color.Green, new Vector2(servers[bouncedServers[x]].pos.X + 32, servers[bouncedServers[x]].pos.Y + 32), new Vector2(servers[bouncedServers[x + 1]].pos.X + 32, servers[bouncedServers[x + 1]].pos.Y + 32));
}
but in C# I was able to access the value of any element from my list like that: bouncedServers[id here] Hope I was able to describe my issue. |
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ok, I played a little with your code:
Local currentBounce:Int = -1
Local previewBounce:Int = -1
For Local b = EachIn bouncedServerList
previewBounce = currentBounce
currentBounce = b
If previewBounce <> - 1
DrawLine(myServer[previewBounce].posX, myServer[previewBounce].posY, myServer[currentBounce].posX, myServer[currentBounce].posY)
EndIf
Next
and basically I obtained what I wanted.. My initial question is still up: Is there a way to obtain the value of a certain element from the list? |
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Not directly. Somebody asked the same question a few days ago, also I think looking for an equivalent to the C# function. Here is some code that will find a particular element:List< MyObject > myList = new List< MyObject > ' Populate list Local ob:MyObject Local count:Int For Local getOb:MyObject = Eachin myList If count = 5 ob = getOb Exit End count += 1 Next ' ob is the sixth object in the list, or Null if the list is shorter than six objects You could extend Monkey.List to add a function for doing this, but there's nothing there by default. It looks inefficient, but C# presumably does something similar. That said, it could be tidied up more if nodes were not hidden to derived classes by a Private access qualifier... |
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| I see. thanks for the answers. I just wanted to verify. Your initial code fits me well for now. Soon a new thread will appear to Monkey Projects sub-forum :P R. |
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| In a lot of cases I use Stack<MyObject> instead of list because of garbage concerns. With a Stack you can get an index. Instead of addLast you have push(). Stack is much closer to C#'s list, List in Monkey is close to C#'s LinkedList which people do not use that often, especially not in realtime games. Or you can just use a normal array and then you can go myArray[i] |
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| @Tibit: arrays were a good choice but I wanted to remove any element from that list easy. I didn't know about Stack.. Maybe next time! |
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| Basically you have a choice. If you want to access any element quickly, a stack or array is best. If you want to insert of remove elements quickly, a list is best. If you want to do both... some inefficiency is inevitable. |
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