Nsryjdtyk

this should be easy but I havent quite figured it out yet:

I have a list of my custom type Mp3ObjectSmall.
This is basically a list containing mp3s with the URI on the phone, the artist and the song name. This is the type:

public class MP3objectSmall

{

    public string SongName { get; set; }

    public string ArtistName { get; set; }

    public string Mp3Uri { get; set; }

}

This list contains about 700 items, each with a different song.

Now, for my recycler view, I need to be able to for instance click on the letter "x" in my app and then have a function return an int with first item in above list containing an "x" as a song name.

Even if I had say 100 song names that all begin with the letter "x" I need to just be returned the first item's position.

How do I find the first string of a member of a custom type list that starts with a certain letter?

If anythin is unclear, just comment on it!

Thank you :-)

What I have tried so far:

        if (letter != "0") // scroll to top when it is 0, so nothing needs to be done here 

        {

            foreach(MP3objectSmall o in Mp3ObjectSmall)

            {

                if (letter.Equals(o.SongName.StartsWith(letter)))

                {



                }



            }

        }

Use Linq. The simple example for your case.

Also, check Lambda Expressions

var list = new List<MP3objectSmall>();

var s1 = new MP3objectSmall { SongName = "abc" };

var s2 = new MP3objectSmall { SongName = "def" };

var s3 = new MP3objectSmall { SongName = "xyz" };

var s4 = new MP3objectSmall { SongName = "xxx" };



list.Add(s1);

list.Add(s2);

list.Add(s3);

list.Add(s4);



var filteredList = list.Where(i => i.SongName.StartsWith("x")).ToList();



foreach(var item in filteredList)

{

    Console.WriteLine(item.SongName);

}

• 
  list.Where will filter the list based on the provided condition


• 
  i => i.SongName is a lambda expression which allows accessing the object properties.


• 
  StartsWithprovides a way to find/filter the string which starts with specifi character

Remember to import these namespaces

using System.Collections.Generic;

using System.Linq;

Also, use FirstOrDefault as the question is to fetch the first element after filters.

I think you are looking for FindIndex:

var indexOfFirstSongThatStartsWithX = Mp3ObjectSmall

    .FindIndex(s => s.SongName.StartsWith("x"));

This will return the index of the first item in the list where the SongName property starts with an x.

If you want the item itself, you can use Find the same way:

var firstSongThatStartsWithX = Mp3ObjectSmall

    .Find(s => s.SongName.StartsWith("x"));

This will return the first item where the SongName property starts with an x.

Another solution: https://dotnetfiddle.net/RzH5li

public static void Main()

{



    List<MP3objectSmall> songs = new List<MP3objectSmall>();



    songs.Add(new MP3objectSmall(){SongName ="a"});

    songs.Add(new MP3objectSmall(){SongName ="b"});

    songs.Add(new MP3objectSmall(){SongName ="x"});

    songs.Add(new MP3objectSmall(){SongName ="z"});



    string letter = "x";



    MP3objectSmall  firstSong = songs.FirstOrDefault(x => x.SongName.ToLowerInvariant().StartsWith(letter));



    if(firstSong != null)

    {

        int index = songs.IndexOf(firstSong);

        Console.WriteLine(index);

    }

}

I think you are missing the List<> variable itself.

For example, assumed you have a similar code:

var songList = /* some function returning a List object like: List<MP3objectSmall> */;

You could then do some List filtering:

int desiredIndex = songList.FindIndex(file => file.SongName.StartWith(letter));

Your index is then in the variable desiredIndex