每行的列表框字符数限制

Question

I have a listbox in my windows form application that shows quite long texts. Since texts are so long, user have to use the horizontal slider for check the rest of text.

So, I want to limit listbox character per line. For every 50 char it should go to next row, so user won't have to use glider.

I can't put "new line" since text source is Sql Database.

My code is basically this:

listbox1.items.add(dbRead["LongText"]); // dbRead = SqlDataReader

So I have to edit listbox itself. I've checked it a bit, but didn't manage to find. I've also tried to find an event like when text is changed, for every 50 char listbox.items.add("") etc. I'm still alien to syntax.

Any suggestions ?

Answer 1

You can write an extension method( SplitByLength ) like below

var input = "I have a listbox in my windows form application that shows quite long texts. Since texts are so long, user have to use the horizontal slider for check the rest of text.\nSo, I want to limit listbox character per line. For every 50 char it should go to next row, so user won't have to use glider.";
var lines = input.SplitByLength(50).ToArray();
listBox1.Items.AddRange(lines);

---

public static partial class MyExtensions
{
    public static  IEnumerable<string> SplitByLength(this string input, int maxLen)
    {
        return Regex.Split(input, @"(.{1," + maxLen + @"})(?:\s|$)")
                    .Where(x => x.Length > 0)
                    .Select(x => x.Trim());
    }
}

----------EDIT----------

After tinstaafl's comment, an edit seems to be a must

var input = "I have a listbox in my windows form application that shows quite long texts. Since texts are so long, user have to use the horizontal slider for check the rest of text.\nSo, I want to limit listbox character per line. For every 50 char it should go to next row, so user won't have to use glider.";
input = String.Join(" ", Enumerable.Repeat(input, 100));

var t1 = Measure(10, () =>
{
    var lines = input.SplitByLength_LB(50).ToArray();
});

var t2 = Measure(10, ()=>
{
    var lines = input.SplitByLength_tinstaafl(50).ToArray();
});

---

long Measure(int n,Action action)
{
    action(); //JIT???
    var sw = Stopwatch.StartNew();
    for (int i = 0; i < n; i++)
    {
        action();
    }
    return sw.ElapsedMilliseconds;
}

---

public static partial class MyExtensions
{
    public static  IEnumerable<string> SplitByLength_LB(this string input, int maxLen)
    {
        return Regex.Split(input, @"(.{1," + maxLen + @"})(?:\s|$)")
                    .Where(x => x.Length > 0)
                    .Select(x => x.Trim());
    }

    public static IEnumerable<string> SplitByLength_tinstaafl(this string input, int maxLen)
    {
        List<string> output = new List<string>();
        while (input.Length > 0)
        {
            output.Add(new string(input.Take(maxLen).ToArray()));
            input = new string(input.Skip(maxLen).ToArray());
        }
        return output;
    }
}

And my results are different than yours: 11 ms. vs. 3384 ms. :)

Answer 2

Redid my code to take into account spaces. With variable length lines some shorter some longer than 50 characters and the line breaks adjusted for spaces, I found that the performance is very close to the same. They're both between 15 and 25 milliseconds on 1000 strings. Though regex does perform moderately faster. Here's the code I used:

public static partial class MyExtensions
{
    public static IEnumerable<string> SplitByLength_LB(this string input, int maxLen)
    {
        return Regex.Split(input, @"(.{1," + maxLen + @"})(?:\s|$)")
                    .Where(x => x.Length > 0)
                    .Select(x => x.Trim());
    }
    public static IEnumerable<string> SplitByLength_tinstaafl(this string input, int maxLen)
    {
        List<string> output = new List<string>{""};

        string[] temp = input.Split("\n ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
        for(int i = 0; i < temp.Count(); i++)
        {
            if((output.Last() + " " + temp[i]).Length > 50)
            {
                output.Add(temp[i]);
            }
            else
                output[output.Count() - 1] += " " + temp[i];
        }
        return output;
    }
        return output;
    }

The test is like this:

        Stopwatch s1 = new Stopwatch();
        List<string> source = new List<string>();
        Random rnd = new Random();
        for(int i = 0; i < 1000; i++)
        {
            var input = "I have a listbox in my windows form application that shows quite long texts. Since texts are so long, user have to use the horizontal slider for check the rest of text. So, I want to limit listbox character per line.";
            int nextbreak = rnd.Next(20, input.Length);
            source.Add(new string(input.TakeWhile((x, y) => input.IndexOf(' ', y) <= nextbreak).ToArray()));
        }
        s1.Start();
        List<string> output = new List<string>(from s in source
                                               from p in s.SplitByLength_LB(50)
                                               select p);
        s1.Stop();
        Console.WriteLine("SplitByLength_LB\t" + s1.ElapsedMilliseconds.ToString());
        s1.Reset();
        s1.Start();
        List<string> output2 = new List<string>(from s in source
                                                from p in s.SplitByLength_tinstaafl(50)
                                                select p);
        s1.Stop();
        Console.WriteLine("SplitByLength_tinstaafl\t" + s1.ElapsedMilliseconds.ToString());