Trying to set a maximum row count with a data-bound DataGridView

Question

I have a DataGridView in my applicaiton, but I want to limit it to 20 rows only, however because it is data-bound, I get the InvalidOperationException. Through research I have come across virtual mode, but this looks incredibly confusing for a starter like me. Furthermore, I have seen people say setting the DGV.DataSource = null; to solve the problem, but this doesn't work for me.

I basically, click a button, and then the DataGridView populates with information. The only work around I have in place, is limiting the user to enter only 20 instances of my object. Then they have to delete one in order to enter another.

Is there any way I can set a maximum row limit with a data-bound DataGridView?

EDIT

In my separate class file (objectStorage.cs) I have this

public class objectStorage: IComparable<objectStorage>
{
    public string objID { get; set; }
    public string objName { get; set; }
    public string objDescription { get; set; }


    public static List<objectStorage> objArray = new List<objectStorage>();
}

Then in my form where I add a new object (addObj.cs) I have this:

private void objCreationBtn_Click(object sender, EventArgs e)
    {
         objectStorage.objArray.Add(new objectStorage
         {
            objID = objIDValueTxt.Text,
            objName = objNameRTB.Text,
            objDescription = objDescRTB.Text,
         });

    }

Then In my main form I have the DGV (Where I assigned the data source to objectStorage in the GUI, and thus created a binding source) which I have created a method to show the objects, like this in a button press:

private void displayObjBtn_Click(object sender, EventArgs e)
{
        showObjects();
}

private void showObjects()
    {

       objectStorageBindingSource.DataSource = null;

       objectStorageBindingSource.DataSource = objectStorage.objArray; 
    }

This works completely okay, but obviously includes no limit to the row count, and I cannot do this because of the data-bound problem.

Answer 1

Caveat

In the long run, this is not the approach you should take, but I provide this as a pragmatic answer given that the question is quite specific to your approach and lacking in some surrounding details (which will eventually mean the question will be closed).

It also makes the assumption that "virtual mode" operation is not what you are after (as per the linked duplicate question, which provides an answer).

Please preface the remainder of the answer with the above in mind.

---

Limiting rows at the source

Further to our discussion in the comments, and without seeing what the code currently looks like, I would suggest something straightforward.

The DataGridView will be on a Form, which will have a code-behind file. In this file, we want to make the amendments necessary to limit the list to 20 items:

using System.Linq;
using System.Collections.Generic;

public class MyForm : Form
{
    // Event handler for the Forms Load event
    public void MyForm_OnLoad(object sender, EventArgs e)
    {
        // Take 20 items from whatever source you are currently using in the DGV.
        List<MyDataBoundItem> items = objectStorage.Items.Take(20).ToList();

        dataGridView1.DataSource = items;
    }
}

A binding list isn't always required, a List<T> can be used but it will be readonly I think, whereas a BindingList<T> supports adding and removing rows.

Also remember to remove the designer-lead solution, as they will interfere with each other.

The DataGridView control, if memory serves, does not provide a mechanism for enforcing maximum rows. You will have to handle cases where the user is trying to add a new row and is at the maximum, assuming the grid allows for adding rows. Other user input scenarios may need manual intervention.

---

A brief note on patterns

As to the brief mention of a "view model", disregard this for now. It is a term borrowed from one of a few standard UI patterns for separating handling of a UI into testable chunks. It is a more advanced topic that you should read up on when you've gone through a little of the pain of non-patterned UI coding :-)

For future delectation, search for "MVC", "MVP", and "MVVM".