How to inject constructor argument from config file with Unity

Question

Imagine we have a class

public class MyClass
{
    private string _val;
    public MyClass(string val) 
    {
         _val = val;
    }
}

and app.config (or web.config)

<appSettings>
    <add key="value" value="some value" />
</appSettings>

Is there way to register type MyClass in Unity container and point Unity to inject value for val constructor parameter from config file?

possible duplicate of In Unity config, how to pass connectionString to a constructor? — Mark Seemann
– Mark Seemann, Commented Nov 18, 2011 at 20:24

Ethan Wu · Accepted Answer · 2017-04-04 02:19:28Z

10

it is very easy.

C# Code:

var container = new UnityContainer();
container.LoadConfiguration();
MyClass mc = container.Resolve<MyClass>();

Configuration file:

<unity xmlns="http://schemas.microsoft.com/practices/2010/unity">    
 <container>
  <register type="[namespace].MyClass, [assembly-name]" 
    mapTo="[namespace].MyClass, [assembly-name]">
    <constructor>
      <param name="val" value="Ethan Woo"/>
    </constructor>
  </register>
</container>

edited Apr 4, 2017 at 2:19

answered Nov 22, 2011 at 6:17

Ethan Wu

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5 Comments

brentlightsey Over a year ago

Where is the reference to the appSetting named "value" in this configuration file?

Ethan Wu Over a year ago

<param name="val" value="Ethan Woo"/> : "value" attribute here.

User.Anonymous Over a year ago

There is no reference to a config files. Then how to map config file or just from <app key> ?

Ethan Wu Over a year ago

"Configuration file" here means app.config for win/console app, and web.config for iis hosting application e.g. web, wcf... container.LoadConfiguration(); will automatically load the configuration accordingly.

User.Anonymous Over a year ago

You don't aswer the question. This answer concerns about a key/value from web.config to Unity constructor and not how to define Unity constructor in web.config.

Daniel Lemke · Accepted Answer · 2015-05-18 10:07:24Z

Quite an old post but I thought the following information could be helpful in case that it's not a value for a native type but a complex data type instead:

<configuration>

  <configsections>
    <section name="unity" type="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection, Microsoft.Practices.Unity.Configuration">
    </section>
  </configsections>

  <unity xmlns="http://schemas.microsoft.com/practices/2010/unity">

    <alias alias="IRepository" type="UnityTest.IRepository, UnityTest">
      <alias alias="Repository" type="UnityTest.Repository, UnityTest">

        <container>
          <register mapto="Repository" type="IRepository">

            <register name="MyClass" type="UnityTest.MyClass, UnityTest">
              <constructor>
                <param name="repository" type="IRepository">
                <dependency name="IRepository">

                </dependency>
              </constructor>
            </register>

          </register>
        </container>

      </alias>
    </alias>
  </unity>

</configuration>

A bit more detailed described here: http://postlabs.blogspot.com/2015/05/injecting-non-native-data-type-via.html

Andrew McLachlan · Accepted Answer · 2017-08-21 07:38:49Z

7

If you are using XML config you can do this by defining an extension that handles AppSettings as Unity parameters, see http://www.neovolve.com/2010/04/23/appsetting-parameter-injection-in-unity-2/.

Alternatively, if you are doing C# configuration you can use an injection constructor as follows...

var container = new UnityContainer();
container.RegisterType<MyClass>(
    new InjectionConstructor(
       InjectionParameter<string>(ConfigurationManager.AppSettings["value"])));

The reason to use the AppSettings value rather than the string directly in the XML config is that it centralises all the paramter values into AppSettings and simplifies migrations between environments.

edited Aug 21, 2017 at 7:38

Andrew McLachlan

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answered Oct 27, 2014 at 10:05

Paul Hatcher

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2 Comments

Mou Over a year ago

why RegisterType<MyClass, MyClass>() register type function specify two name of same class?

Paul Hatcher Over a year ago

The original XML registration says type, mapTo with the same type in both so I was reproducing that. For the fluent registration, you are correct you don't need the second value; typically however you you have RegisterType<IMyInterface, MyClass>

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