Faster way of reading csv to grid

Question

I have following in Windows Forms .NET 3.5

It works fine for csv with records less than 10,000 but is slower for records above 30,000. Input csv file can can any re

Answer 1

Instead of putting the data directly into the grid you should take a look at the VirtualMode of the DataGridView.

In your code you're doing two things at one time (read the file, fill the grid), which leads to your freezed gui. Instead you should put the grid into the virtual mode and read the file within a BackgroundWorker into a list which holds the data for the grid. The background worker can after each line read update the virtual size of the grid, which allows to already see the data while the grid is loading. By using this approach you'll getting a smooth working grid.

Below you'll find an example which just needs to be filled into a form that uses a DataGridView with two text columns, a BackgroundWorker and a Button:

public partial class FormDemo : Form
{
    private List _Elements;

    public FormDemo()
    {
        InitializeComponent();
        _Elements = new List();

        dataGridView.AllowUserToAddRows = false;
        dataGridView.AllowUserToDeleteRows = false;
        dataGridView.ReadOnly = true;
        dataGridView.VirtualMode = true;
        dataGridView.CellValueNeeded += OnDataGridViewCellValueNeeded;

        backgroundWorker.WorkerReportsProgress = true;
        backgroundWorker.DoWork += OnBackgroundWorkerDoWork;
        backgroundWorker.ProgressChanged += OnBackgroundWorkerProgressChanged;
        backgroundWorker.RunWorkerCompleted += OnBackgroundWorkerRunWorkerCompleted;
    }

    private void OnBackgroundWorkerDoWork(object sender, DoWorkEventArgs e)
    {
        var filename = (string)e.Argument;

        using (var reader = new StreamReader(filename))
        {
            string line = null;

            while ((line = reader.ReadLine()) != null)
            {
                var parts = line.Split(',');

                if (parts.Length >= 2)
                {
                    var element = new Element() { Number = parts[0], Available = parts[1] };
                    _Elements.Add(element);
                }

                if (_Elements.Count % 100 == 0)
                {
                    backgroundWorker.ReportProgress(0);
                }
            }
        }
    }

    private void OnBackgroundWorkerProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        dataGridView.RowCount = _Elements.Count;
    }

    private void OnBackgroundWorkerRunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        dataGridView.RowCount = _Elements.Count;
        button.Enabled = true;
    }

    private void OnButtonLoadClick(object sender, System.EventArgs e)
    {
        if (!backgroundWorker.IsBusy
            && DialogResult.OK == openFileDialog.ShowDialog())
        {
            button.Enabled = false;
            backgroundWorker.RunWorkerAsync(openFileDialog.FileName);
        }
    }

    private void OnDataGridViewCellValueNeeded(object sender, DataGridViewCellValueEventArgs e)
    {
        var element = _Elements[e.RowIndex];

        switch (e.ColumnIndex)
        {
            case 0:
                e.Value = element.Number;
                break;

            case 1:
                e.Value = element.Available;
                break;
        }
    }

    private class Element
    {
        public string Available { get; set; }

        public string Number { get; set; }
    }
}