在 DataGridView 中读取 CSV 文件

Question

I want to read a csv-file into a Datagridview. I would like to have a class and a function which reads the csv like this one:

class Import
{
    public DataTable readCSV(string filePath)
    {            
        DataTable dt = new DataTable();
        using (StreamReader sr = new StreamReader(filePath))
        {
            string strLine = sr.ReadLine();     

            string[] strArray = strLine.Split(';');

            foreach (string value in strArray)
            {
                dt.Columns.Add(value.Trim());
            } 
            DataRow dr = dt.NewRow();

            while (sr.Peek() >= 0)
            {
                strLine = sr.ReadLine();
                strArray = strLine.Split(';');
                dt.Rows.Add(strArray);
            }
        }
        return dt;
     }   
}

and call it:

Import imp = new Import();

DataTable table = imp.readCSV(filePath);
foreach(DataRow row in table.Rows)
{
 dataGridView.Rows.Add(row);
}

Result of this is-> rows are created but there is no data in the cells !!

Answer 1

First solution using a litle bit of linq

public DataTable readCSV(string filePath)
{
    var dt = new DataTable();
    // Creating the columns
    File.ReadLines(filePath).Take(1)
        .SelectMany(x => x.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries))
        .ToList()
        .ForEach(x => dt.Columns.Add(x.Trim()));

    // Adding the rows
    File.ReadLines(filePath).Skip(1)
        .Select(x => x.Split(';'))
        .ToList()
        .ForEach(line => dt.Rows.Add(line));
    return dt;
}

Below another version using foreach loop

public DataTable readCSV(string filePath)
{
    var dt = new DataTable();
    // Creating the columns
    foreach(var headerLine in File.ReadLines(filePath).Take(1))
    {
        foreach(var headerItem in headerLine.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries))
        {
            dt.Columns.Add(headerItem.Trim());
        }
    }

    // Adding the rows
    foreach(var line in File.ReadLines(filePath).Skip(1))
    {
        dt.Rows.Add(x.Split(';'));
    }
    return dt;
}

First we use the File.ReadLines, that returns an IEnumerable that is a colletion of lines. We use Take(1), to get just the first row, that should be the header, and then we use SelectMany that will transform the array of string returned from the Split method in a single list, so we call ToList and we can now use ForEach method to add Columns in DataTable.

To add the rows, we still use File.ReadLines, but now we Skip(1), this skip the header line, now we are going to use Select, to create a Collection<Collection<string>> , then again call ToList, and finally call ForEach to add the row in DataTable. File.ReadLines is available in .NET 4.0.

Obs.: File.ReadLines doesn't read all lines, it returns a IEnumerable, and lines are lazy evaluated, so just the first line will be loaded two times.

See the MSDN remarks

The ReadLines and ReadAllLines methods differ as follows: When you use ReadLines, you can start enumerating the collection of strings before the whole collection is returned; when you use ReadAllLines, you must wait for the whole array of strings be returned before you can access the array. Therefore, when you are working with very large files, ReadLines can be more efficient.

You can use the ReadLines method to do the following:

Perform LINQ to Objects queries on a file to obtain a filtered set of its lines.

Write the returned collection of lines to a file with the File.WriteAllLines(String, IEnumerable) method, or append them to an existing file with the File.AppendAllLines(String, IEnumerable) method.

Create an immediately populated instance of a collection that takes an IEnumerable collection of strings for its constructor, such as a IList or a Queue.

This method uses UTF8 for the encoding value.

If you still have any doubt look this answer: What is the difference between File.ReadLines() and File.ReadAllLines()?

Second solution using CsvHelper package

First, install this nuget package

PM> Install-Package CsvHelper 

For a given CSV, we should create a class to represent it

CSV File

Name;Age;Birthdate;Working
Alberto Monteiro;25;01/01/1990;true
Other Person;5;01/01/2010;false

The class model is

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public DateTime Birthdate { get; set; }
    public bool Working { get; set; }
}

Now lets use CsvReader to build the DataTable

public DataTable readCSV(string filePath)
{
    var dt = new DataTable();

    var csv = new CsvReader(new StreamReader(filePath));
    // Creating the columns
    typeof(Person).GetProperties().Select(p => p.Name).ToList().ForEach(x => dt.Columns.Add(x));

    // Adding the rows
    csv.GetRecords<Person>().ToList.ForEach(line => dt.Rows.Add(line.Name, line.Age, line.Birthdate, line.Working));
    return dt;
}

To create columns in DataTable e use a bit of reflection, and then use the method GetRecords to add rows in DataTabble

Answer 2

using Microsoft.VisualBasic.FileIO;

I would suggest the following. It should have the advantage at least that ';'in a field will be correctly handled, and it is not constrained to a particular csv format.

public class CsvImport
{
    public static DataTable NewDataTable(string fileName, string delimiters, bool firstRowContainsFieldNames = true)
    {
        DataTable result = new DataTable();

        using (TextFieldParser tfp = new TextFieldParser(fileName))
        {
            tfp.SetDelimiters(delimiters); 

            // Get Some Column Names
            if (!tfp.EndOfData)
            {
                string[] fields = tfp.ReadFields();

                for (int i = 0; i < fields.Count(); i++)
                {
                    if (firstRowContainsFieldNames)
                        result.Columns.Add(fields[i]);
                    else 
                        result.Columns.Add("Col" + i);
                }

                // If first line is data then add it
                if (!firstRowContainsFieldNames)
                    result.Rows.Add(fields); 
            }

            // Get Remaining Rows
            while (!tfp.EndOfData) 
                result.Rows.Add(tfp.ReadFields());
        }

        return result;
    } 
}

Answer 3

CsvHelper's Author build functionality in library. Code became simply:

using (var reader = new StreamReader("path\\to\\file.csv"))
using (var csv = new CsvReader(reader, CultureInfo.CurrentCulture))
{
    // Do any configuration to `CsvReader` before creating CsvDataReader.
    using (var dr = new CsvDataReader(csv))
    {        
        var dt = new DataTable();
        dt.Load(dr);
    }
}

CultureInfo.CurrentCulture is used to determine the default delimiter and needs if you want to read csv saved by Excel.

Answer 4

I had the same problem but I found a way to use @Alberto Monteiro 's Answer in my own way...

My CSV file does not have a "First-Line-Column-Header", I personally didn't put them there for some reasons, So this is the file sample

1,john doe,j.doe,john.doe@company.net
2,jane doe,j.doe,jane.doe@company.net

So you got the idea right ?

Now in I am going to add the Columns manually to the DataTable . And also I am going to use Tasks to do it asynchronously. and just simply using a foreach loop adding the values into the DataTable.Rows using the following function:

public Task<DataTable> ImportFromCSVFileAsync(string filePath)
{
    return Task.Run(() =>
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Index");
        dt.Columns.Add("Full Name");
        dt.Columns.Add("User Name");
        dt.Columns.Add("Email Address");

        // splitting the values using Split() command 
        foreach(var srLine in File.ReadAllLines(filePath))
        {
            dt.Rows.Add(srLine.Split(','));
        }
        return dt;
    });
}

Now to call the function I simply ButtonClick to do the job

private async void ImportToGrid_STRBTN_Click(object sender, EventArgs e)
{
   // Handling UI objects
   // Best idea for me was to put everything a Panel and Disable it while waiting
   // and after the job is done Enabling it
   // and using a toolstrip docked to bottom outside of the panel to show progress using a 
   // progressBar and setting its style to Marquee

   panel1.Enabled = false;
   progressbar1.Visible = true;
   try
   {
      DataTable dt = await ImportFromCSVFileAsync(@"c:\myfile.txt");
      if (dt.Rows.Count > 0)
      {
         Datagridview1.DataSource = null; // To clear the previous data before adding the new ones
         Datagridview1.DataSource = dt;
      }
   }
   catch (Exception ex)
   {
      MessagBox.Show(ex.Message, "Error");
   }

   progressbar1.Visible = false;
   panel1.Enabled = true;

}