Fody And ReactiveUI

A ReactiveUI Model

If you are using ReactiveUI you binding model probably looks something like the following.

public class Person : ReactiveObject
{
    string givenNames;

    public string GivenNames
    {
        get { return givenNames; }
        set { this.RaiseAndSetIfChanged(x => x.GivenNames, value); }
    }

    string familyName;

    public string FamilyName
    {
        get { return familyName; }
        set { this.RaiseAndSetIfChanged(x => x.FamilyName, value); }
    }
}

Now this is fine. It is strong typed and supports both INotifyPropertyChanging and INotifyPropertyChanged. However using IL Weaving and Fody this code can be simplified.

How to setup Fody

Install the VSIX (Visual Studio Addin)

First off install the Fody VSIX.

Note: this is a once off per machine and only helps you configure Fody for a project. It is not required to build and the resultant project will build on other developers machines and on your build server.

Enable Fody for your proect

Select the target project and use the top level menu

Project > Fody > Configure

Leave the defaults and click OK. The project will re-load.

Note that you now have a FodyWeavers.xml file in your project.

Get some Fody Addins

If you havn't done so already install nuget

Then in your Package Manager Console type

install-package PropertyChanging.Fody
install-package PropertyChanged.Fody

This will get the PropertyChanging and PropertyChanged Fody addins

Tell Fody to use the Addins

Add the following to FodyWeavers.xml.

<?xml version="1.0" encoding="utf-8" ?>
<Weavers>
  <PropertyChanged EventInvokerNames="raisePropertyChanged"/>
  <PropertyChanging EventInvokerNames="raisePropertyChanging"/>
</Weavers>

Note the EventInvokerNames are raisePropertyChanging and raisePropertyChanged to allow the addins to detect what method to call on the base class.

Tweak your model

Now you model can look like this.

public class Person : ReactiveObject
{
    public string GivenNames { get; set; }
    public string FamilyName { get; set; }
}

What gets compiled

public class Person : ReactiveObject
{
    public string FamilyName
    {
        get { return this.<FamilyName>k__BackingField; }
        set
        {
            if (!string.Equals(this.<FamilyName>k__BackingField, value))
            {
                base.raisePropertyChanging("FamilyName");
                this.<FamilyName>k__BackingField = value;
                base.raisePropertyChanged("FamilyName");
            }
        }
    }

    public string GivenNames
    {
        get { return this.<GivenNames>k__BackingField; }
        set
        {
            if (!string.Equals(this.<GivenNames>k__BackingField, value))
            {
                base.raisePropertyChanging("GivenNames");
                this.<GivenNames>k__BackingField = value;
                base.raisePropertyChanged("GivenNames");
            }
        }
    }
}

Source code

The source for this post is available here https://github.com/SimonCropp/Experiments/tree/master/FodyReactiveUI