Refactoring to avoid the use of dynamic

Question

Based on the answer to my question on StackOverflow, I have ended up with the following code:

public class ColumnDataBuilder<T>
{
 public abstract class MyListViewColumnData
 {
 public string Name { get; protected set; }
 public int Width { get; protected set; }
 public ColumnType Type { get; protected set; }
 public delegate TOUT FormatData<out TOUT>(T dataIn);
 protected abstract dynamic GetData(T dataRow);
 public string GetDataString(T dataRow)
 {
 dynamic data = GetData(dataRow);
 switch (Type)
 {
 case ColumnType.String:
 case ColumnType.Integer:
 case ColumnType.Decimal:
 return data.ToString();
 case ColumnType.Date:
 return data.ToShortDateString();
 case ColumnType.Currency:
 return data.ToString("c");
 break;
 case ColumnType.Boolean:
 var b = (bool)data;
 if (b) return "Y";
 else return "N";
 default:
 throw new ArgumentOutOfRangeException();
 }
 }
 }
 public class MyListViewColumnData<TOUT> : MyListViewColumnData
 {
 public MyListViewColumnData(string name, int width, ColumnType type, FormatData<TOUT> dataFormater)
 {
 DataFormatter = x => dataFormater(x); // Per https://stackoverflow.com/a/1906850/298754
 Type = type;
 Width = width;
 Name = name;
 }
 public Func<T, TOUT> DataFormatter { get; protected set; }
 protected override dynamic GetData(T dataRow)
 {
 return DataFormatter(dataRow);
 }
 }
 }

This is called from a factory method (in ColumnDataBuilder) as

public MyListViewColumnData Create<TOUT>(string name, int width, ColumnType type, MyListViewColumnData.FormatData<TOUT> dataFormater)
{
 return new MyListViewColumnData<TOUT>(name, width, type, dataFormater);
}
public MyListViewColumnData Create(string name, int width, MyListViewColumnData.FormatData<DateTime> dataFormater)
{
 return new MyListViewColumnData<DateTime>(name, width, ColumnType.Date, dataFormater);
}
...

That, in turn, is called from my code as:

builder.Create("Date", 40, x => x.createdDate);

and

private ListViewItem CreateListViewItem<TDATA>(IEnumerable<ColumnDataBuilder<TDATA>.MyListViewColumnData> columns, TDATA rowData)
{
 var item = new ListViewItem();
 foreach (var col in columns)
 {
 item.SubItems.Add(col.GetDataString(rowData));
 }
 item.SubItems.RemoveAt(0); // We generate an extra SubItem for some reason.
 return item;
}

How can I refactor this so that I'm not using dynamic, but still preserve the syntax as it currently exists in the code?

• Bobson: Alternatively, if this is a proper use for dynamic, that'd be good to know too... but I'm pretty sure it isn't.
• Jeff Vanzella: Where does T come from?
• almaz: Your public abstract class MyListViewColumnData has no generic parameters while it has delegate TOUT FormatData<out TOUT>(T dataIn) declared. Please make sure you post a compilable code here
• Bobson: @JeffVanzella - Good catch. I missed copying the class declaration. Edited it in.
• Bobson: @almaz - I think this will now compile. If it doesn't, I'll go back and post a larger block, but I am trying to keep it down to the relevant portions.

Answer 1

I don't think you need MyListViewColumnData class there, I would replace it with interface and move the GetDataString implementation to MyListViewColumnData<TOut>. And you don't need dynamic here, just use object instead (yes, it will use boxing for most cases except strings, but it's more efficient than dynamics).

public class ColumnDataBuilder<T>
{
 public interface IMyListViewColumnData
 {
 string Name { get; }
 int Width { get; }
 ColumnType Type { get; }
 string GetDataString(T dataRow);
 }
 public delegate TOut FormatData<out TOut>(T dataIn);
 public class MyListViewColumnData<TOut> : IMyListViewColumnData
 {
 public string Name { get; private set; }
 public int Width { get; private set; }
 public ColumnType Type { get; private set; }
 private readonly FormatData<TOut> _dataFormatter;
 public MyListViewColumnData(string name, int width, ColumnType type, FormatData<TOut> dataFormater)
 {
 _dataFormatter = dataFormater;
 Type = type;
 Width = width;
 Name = name;
 }
 public string GetDataString(T dataRow)
 {
 object data = _dataFormatter(dataRow);
 switch (Type)
 {
 case ColumnType.String:
 case ColumnType.Integer:
 case ColumnType.Decimal:
 return data.ToString();
 case ColumnType.Date:
 return ((DateTime)data).ToShortDateString();
 case ColumnType.Currency:
 return ((decimal)data).ToString("c");
 case ColumnType.Boolean:
 return (bool)data ? "Y" : "N";
 default:
 throw new ArgumentOutOfRangeException();
 }
 }
 }
 public IMyListViewColumnData Create<TOut>(string name, int width, ColumnType type, FormatData<TOut> dataFormater)
 {
 return new MyListViewColumnData<TOut>(name, width, type, dataFormater);
 }
 public IMyListViewColumnData Create(string name, int width, FormatData<DateTime> dataFormater)
 {
 return new MyListViewColumnData<DateTime>(name, width, ColumnType.Date, dataFormater);
 }
}
public enum ColumnType
{
 String,
 Integer,
 Decimal,
 Date,
 Currency,
 Boolean
}

Update In comments it was asked if you can extract interface for ColumnDataBuilder. Of course you can :), and the easiest way would be to use "Extract interface" refactoring from ReSharper :). If you still don't use it you'll have to do that manually (move the IMyListViewColumnData and FormatData<TOut> declarations out of ColumnDataBuilder<T> first):

public interface IColumnDataBuilder<Tin>
{
 IMyListViewColumnData Create<TOut>(string name, int width, ColumnType type, FormatData<TOut> dataFormater);
 IMyListViewColumnData Create(string name, int width, FormatData<DateTime> dataFormater);
}

• Bobson: Just a followup: Is there any way to extract an interface of ColumnDataBuilder<>, so that I can store it without knowing the type? Or is that asking too much of the compiler?
• almaz: @Bobson see updated answer
• Bobson: I'm not sure that addresses the goal, though. I have another class (the ListView subclass which this is handling the data for), which could have any datatype for Tin there. And I can't make it generic for other reasons, or this would be a lot simpler. So what type do I make that property? Or could I leave off the <Tin> and get this scenario working?
• almaz: you should have told how you want it to work first :). If you want to write a general logic that doesn't know about specific types upfront in may be a good idea just to stop using generics... At what time ListView gets to know the type T? Where is the code that calls ColumnDataBuilder<T>.Create located? Does that code know about specific types? It's probably better to open a new question since we've moved quite far from original one...
• Bobson: Fair enough - I hadn't thought that far ahead when I asked this question. While I was waiting for an answer, I realized I needed to separate column creation from attaching the data. I'll see if I can formulate a new question, and then I'll link it here.