[SOLVED] In the MVP pattern, is the presenter responsible for formatting numbers to percent?

In the MVP pattern, is the presenter responsible for formatting numbers to percent?

So the presenter calls the model to get some data.

That data is returned as a DTO with no formatting.

Let's say the data is simply a decimal .12

Does the presenter then format the number to a percent?

view.Amount = Math.Round(dto.Amount * 100, 2) + "%";

Or is it the views responsibility?

public decimal Amount 
{
    set 
    {
        txtAmount.Text = Math.Round(dto.Amount * 100, 2) + "%";
    }
}

Solution

I do not use C# and WebFormsMvp, but I think your question is pretty much related to common MVP architecture. Let me explain it out of WebFormsMvp scope. The only responsiblity of a P should be mediating between a M and a V (in terms of how to "pass" the M data to the V and vice versa), and the V is responsible for how the data is represented to the user.

Consider the following scenario: you decide to drop the txtAmount field (let's consider it's just a text label or input, etc) in favor of a certain kind of progress bars or simple charts. If you passed "normalized" number values before (as they come from your M in your case) -- you still can replace your amount view as you wish, as they are supposed to accept a raw number value.

public interface IView {
    decimal Amount { set; }
}

Compare the above to:

public interface IView {
    // How to apply a string to a chart as a data item?
    string Amount { set; }
}

For the latter, you'd be face to face with "string to decimal" problem for the Amount property requiring to rework your string IView.Amount back to decimal IView.Amount (or even worse: parsing the percentaged value dropping the % sign and so on right in an IView instance to make it a number again even not knowing the original number type: was it a decimal or an integer?)

You might also consider percents as a V for humans: 42% in a percentage view or 420‰ in a promille view is still 0.42 in the model.