UnitsNet and WPF

Question

We are possibly about to introduce UnitsNet in our application for two reasons: Type safe computations and ability to switch between different unit systems (metric, imperial etc.) This means those types will be all over our application and also in our view models for presentation. And this is where it gets tricky. I would like the various quantities to be displayed more or less automatically in the GUI, solely by specifying the desired unit.

Since there will be a lot of those quantities it would be tiresome to always specify a type converter in the xaml file, and I'm not sure it would be possible to specify which unit to display at the same time.

So what would be a good approach to this? Writing your own user controls, using conversion attributes, or is there a better way?

Jan Paolo Go · Accepted Answer · 2017-12-16T20:50:28.853

UnitsNet quantity classes (e.g. Length, Mass, etc) have a public static ToStringDefaultUnit property which you can set to whichever Unit you want the quantity classes to be displayed as (ToString) during runtime.

For example:

Length myLength = Length.FromMeters(1);

//default Length.ToStringDefaultUnit is LengthUnit.Meter
string display1 = myLength.ToString(); //1m

Length.ToStringDefaultUnit = LengthUnit.Centimeter;
string display2 = myLength.ToString(); //100cm

Length.ToStringDefaultUnit = LengthUnit.Foot; 
string display3 = myLength.ToString(); //3.28ft

If you need different units per quantity then it would be a good idea to create new types to represent the difference. It would also be a good idea to copy how UnitsNet does the implementation to be consistent.

public struct ShortLength
{
    private Length _internalLength;
    public ShortLength(QuantityValue centimeters)
    {
        _internalLength = Length.FromCentimeters(centimeters);
    }
    public static ShortLength FromCentimeters(QuantityValue value)
    {
        return new ShortLength(value);
    }
    public static LengthUnit ToStringDefaultUnit { get; set; } = LengthUnit.Centimeter;

    public override string ToString()
    {
        return ToString(ToStringDefaultUnit);
    }

    public string ToString(LengthUnit lengthUnit)
    {
        //just copy how UnitsNet implement ToString
    }
}

One way to leverage the ToStringDefaultUnit property is to have one class that will manage the conversion for the whole app. This way, your unit conversions will not be all over the place.

public static class AppUnitSystem
{
    public static void ToMetric()
    {
        Length.ToStringDefaultUnit = LengthUnit.Meter;
        ShortLength.ToStringDefaultUnit = LengthUnit.Centimeter;

        Density.ToStringDefaultUnit = DensityUnit.KilogramPerCubicMeter;

        //TODO: other quantities...
    }

    public static void ToImperial()
    {
        Length.ToStringDefaultUnit = LengthUnit.Foot;
        ShortLength.ToStringDefaultUnit = LengthUnit.Inch;

        Density.ToStringDefaultUnit = DensityUnit.PoundPerCubicFoot;

        //TODO: other quantities...
    }
}

Ah, alright, thank you! So if you bind, let's say a textblock, to a view model property that has type Density it will automatically print that value without having specify a converter? But how would that work if you have several properties on the same view model and you would like different units on them, for example some in cm and some in m? — Olle, Dec 16 '17 at 10:46
Ok, thank you very much! One thing that remains though is text boxes for editing, preferebly with the unit beside the box. Any suggestions there? The quantities have no set properties from what I can see. — Olle, Dec 18 '17 at 16:37
I would suggest making a CustomControl that will display the value and unit. It could be similar to how a combobox displays a value and the dropdown button. I believe a CustomControl would give you the most flexibility for a value-unit use case. — Jan Paolo Go, Dec 18 '17 at 17:28

UnitsNet and WPF

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