DataTable扩展方法C＃

Question

I have a method to perform operation in Datatable.

public DataTable SetColumnsOrder(DataTable table, String[] columnNames)
    {
        int columnIndex = 0;
        foreach (var columnName in columnNames)
        {
            if (table.Columns.Contains(columnName))
            {
                table.Columns[columnName].SetOrdinal(columnIndex);
                columnIndex++;
            }
        } return table;
    }

To access this method I need to do like this

dt = SetColumnsOrder(dt,colNames);

Instead of doing like this, how to create a function to call it like below in c#

dt.SetColumnOrder(colNames);

where the function should take dt as input to perform operations and store back in same dt.

Answer 1

You would need to use an extension method like so:

public static class DataTableExtensions
{
    public static DataTable SetColumnsOrder(this DataTable table, string[] columnNames)
    {
        int columnIndex = 0;
        foreach (var columnName in columnNames)
        {
            if (table.Columns.Contains(columnName))
            {
                table.Columns[columnName].SetOrdinal(columnIndex);
                columnIndex++;
            }
        }
        return table;
    }
}

Usage would be:

dt.SetColumnsOrder(columnNames);

And since you're modifying the DataTable, which is a reference type. You can use void as the return type and just access the sorted dt variable

Answer 2

First of all, you don't need to return the same DataTable that you pass in. You could change your method signature to:

public void SetColumnsOrder(DataTable table, String[] columnNames)

and remove the return , and it would still work the same (obviously you'd call it like SetColumnsOrder(dt,colNames); instead of dt = SetColumnsOrder(dt,colNames); . And you should do that, because it's less confusing design.

Then, in order to call it as an extension method, just change the signature again, to:

public static void SetColumnsOrder(this DataTable table, String[] columnNames)

And now you can use it like dt.SetColumnOrder(colNames); .

Answer 3

Change your signature from

public DataTable SetColumnsOrder(DataTable table, String[] columnNames)

to

public static DataTable SetColumnsOrder(this DataTable table, String[] columnNames)