Question

I have an Autofac DI Container and use constructor injection to inject configuration settings into my SampleClass. The Configuration Manager class is created as a singleInstance so the same single instance is used.

public ConfigurationManager()
{
    // Load the configuration settings
    GetConfigurationSettings();
}

public SampleClass(IConfigurationManager configurationManager)
{
    _configurationManager = configurationManager;
}

I am loading the configuration settings from a App.config file in the constructor of the configuration Manager. My problem is i am also validating the configuration settings and if they are not in the App.config file a exception is thrown, which causes the program to crash. Which means I cant handle the exception and return a response.

I am doing this the wrong way? Is there a better way to load the configuration settings Or is there a way to handle the exception being thrown.

Edit

ConfigurationManager configurationManager = new ConfigurationManager();
configurationManager.GetConfigurationSettings();
//Try catch around for the exception thrown if config settings fail

//Register the instance above with autofac
builder.Register(configurationManager()).As<IConfigurationManager>().SingleInstance();


//Old way of registering the configurationManager
builder.Register(c => new ConfigurationManager()).As<IConfigurationManager>().SingleInstance();

Answer 1

You are doing absolutely the right thing. Why? You are preventing the system from starting when the application isn’t configured correctly. The last thing you want to happen is that the system actually starts and fails later on. Fail fast! However, make sure that this exception doesn’t get lost. You could make sure the exception gets logged.

One note though. The general advice is to do as little as possible in the constructor of a type. Just store the incoming dependencies in instance variables and that’s it. This way construction of a type is really fast and can never really fail. In general, building up the dependency graph should be quick and should not fail. In your case this would not really be a problem, since you want the system to fail as soon as possible (during start-up). Still, for the sake of complying to general advice, you might want to extract this validation process outside of that type. So instead of calling GetConfigurationSettings inside that constructor, call it directly from the composition root (the code where you wire up the container) and supply the valid configuration settings object to the constructor of the ConfigurationManager. This way you -not only- make the ConfigurationManager simpler, but you can let the system fail even faster.