Making Custom DataGridViewCell ReadOnly

I am making several custom DataGridViewCell classes to handle various cases in my C# application. One of the custom classes is associated with read-only data, so I'm attempting to make the cell itself read-only.

I initially tried setting the ReadOnly property in the constructor, but doing so causes an InvalidOperationException: "ReadOnly property of a cell cannot be set before it is added to a row."

Which method should I override (i.e., which method add开发者_如何转开发s the cell to the row), so that I can set the ReadOnly property?

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It looks like the way to get the desired behavior (prohibiting the user from editing the data in the cell) is to override the EditType property in the DataGridViewCell sub-class:

    public override Type EditType
    {
        get
        {
            return null;
        }
    }

This keeps the cell from displaying an edit control, consequently making the cell read-only.