Return more than one object

Question

I have a method that checks through a list of items and returns the item if the conditions in the method are met. The problem is that sometimes I have more than one item that needs to be returned to be drawn on the screen. So if I have 2 or 3 items that need to be drawn, only the first one is. This may be a problem with my draw code but I'm not sure yet.

foreach(Item i in List)
{
    if conditions are met
    {
        return i

Is there a way to check for more than one item being returned in this method?

As soon as the return statement is hit, the function ends. So your code would only ever return one item if it finds it. You probably want to have a seperate list of matches you find, and then return that. — Abbath, Oct 09 '14 at 03:11
So instead of returning the item, I would just add it to a list and draw from that list? — Christian Frantz, Oct 09 '14 at 03:12
Yes just create a new list at the start of the function, and for every match you find add to it. After you have finished iterating through the orginal list, return the list of matches. You should also check later on that the list being returned is not empty. — Abbath, Oct 09 '14 at 03:13

score 8 · Accepted Answer · edited May 23 '17 at 11:49

8

Why not use LINQ?

// return an enumerable
return items.Where( item => item.SomeCondition );

Or

// execute once and store in a list
return items.Where( item => item.SomeCondition ).ToList();

There's an important difference between these two examples. The first returns an IEnumerable that can be used to iterate over the list. The second example iterates through the items once and stores them in a list.

This is also a candidate for yield. Like the first example, this returns IEnumerable<T>.

foreach( var item in items )
{
    if( conditions ){
         yield return item;
    }
}

edited May 23 '17 at 11:49

Community

1
1

answered Oct 09 '14 at 03:18

Tim M.

53,671
14
120
163

1

+1 but i'd suggest that if OP is new to C#, stick to the basics of LINQ & collections before learning about `yield` :) – Robert Levy Oct 09 '14 at 03:26
@RobertLevy - definitely agree. I also added a little info on deferred execution that can cause subtle bugs if not understood. – Tim M. Oct 09 '14 at 03:42
I'll have to look into using yield. I've never seen it before – Christian Frantz Oct 09 '14 at 03:47

score 1 · Answer 2 · answered Oct 09 '14 at 03:14

You can do something like this by returning a list of items meeting the condition:

List<YourItemType> itemsMeetingCondition = new List<YourItemType>();
foreach(Item i in List)
{
    if( conditions are met)
    {
        itemsMeetingCondition.Add(i);
    }
}
return itemsMeetingCondition;

score 0 · Answer 3 · answered Oct 09 '14 at 03:14

First way is to make a class with 2 or more properties.

Here would be a return class:

public class ColorSelection
    {
        public string ColorCode { get; set; }
        public bool IsBold { get; set; }

    }

In your code you would return this at some point.

The second way is used if they are all the same type. You would return a List<string> for example.

score 0 · Answer 4 · answered Oct 09 '14 at 03:20

You can use the yield keyword and return IEnumerable instead:

Yield interacts with the foreach-loop. It is a contextual keyword: yield is a keyword only in certain statements. It allows each iteration in a foreach-loop be generated only when needed. In this way it can improve performance.

http://www.dotnetperls.com/yield

public IEnumerable<Item> GetItems()
{
    foreach(Item i in List)
    {
        if conditions are met
        {
            yield return i;
        }
    }
}

Return more than one object

4 Answers4