ASP.Net EditorFor with custom expression

Question

The built-in EditorFor does only work with member access expressions.

But in one scenario, I need to multiply the value with 100 and have that inside a text box. That is because the value represents a percentage and the user should be able to input 27 which is internally stored as 0.27. For this it would be nice to have something like EditorFor(m => m.MyValue * 100).

Is there any equivalent for that?

IMHO that would not only be very hard to implement, it would also be very wrong. Conversion of input values is not a responsibility of the View layer. Also, maintaining view code on ASP.NET MVC is already hard enough, please avoid placing C# code in there as much as you can. — rsenna
– rsenna, Commented Jan 2, 2014 at 12:42

volpav · Accepted Answer · 2014-01-02 11:55:44Z

1

Just add something like MyValueAsPercentage to your view model:

public class MyDataModel
{
    public double MyValue { get; set; }
}

// ...

public class MyViewModel
{
    public double MyValueAsPercentage { get; set; }

    public MyViewModel(MyDataModel dataModel)
    {
        this.MyValueAsPercentage = dataModel.MyValue * 100;
    }

    public MyDataModel ToDataModel()
    {
        return new MyDataModel() { MyValue = MyValueAsPercentage / 100 };
    }
}

Now you can use the same member access expression over your view model:

Html.EditorFor(m => m.MyValueAsPercentage)

Hope this helps.

answered Jan 2, 2014 at 11:55

volpav

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4 Comments

wertzui Over a year ago

This is my current approach, but i would like to know if it is possible without a dummy property.

volpav Over a year ago

@wertzui Well, the ModelMetadata.FromLambdaExpression which is used internally, only understands expressions of type "member access", "array index" and "indexer".

wertzui Over a year ago

I thought that maybe someone came up with something like EditorForCustomExpression(), like someone already came up with EditorForMany() to implement custom templates with Lists.

volpav Over a year ago

@wertzui Sure, you can make a custom version, but in this case you'd at least need to initialize model metadata "your own way". It seems to me like a little bit of an overhead considering what you're trying to achieve. Personally, I don't see why having a special view model property is a bad approach since the view model is basically a version of your data entry "tuned" for viewing/editing.

stann1 · Accepted Answer · 2014-01-02 12:45:24Z

1

You can try adding an attribute to your property

[DisplayFormat(DataFormatString = "{0:P2}", ApplyFormatInEditMode = true)]
    public decimal MyValueASPercentage { get; set; }

Now a value of 0.27 will appear as 27 % on your page. Hope that helps

answered Jan 2, 2014 at 12:45

stann1

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2 Comments

volpav Over a year ago

Wow, that looks neat but will MyValueAsPercentage have 0.27 when I type 27% or will it be 27?

wertzui Over a year ago

I need it without the '%'-sign. Additionally I'm looking for a solution without having to modify the model.

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