R – Castle Windsor: suppress exceptions thrown by Resolve()

castle-windsornet

When resolving a component which the Windsor container cannot find, an exception is thrown.

StructureMap has a TryGetInstance method, which returns null of it can't find the requested component.

Does Castle Windsor has something like this? Or am I forced to catch these exceptions (I don't like that, because of the performance overhead of throwing and catching exceptions).

Thanks in advance,

Remco

Best Answer

You can check if the MicroKernel has an instance of the component registered before calling the Resolve method of the Windsor container.

Something like the following should work.

if ( windsor.Kernel.HasComponent( componentType ) )
{
    return windsor.Resolve( componentType );
}

return null;

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C# – Catch multiple exceptions at once

Catch System.Exception and switch on the types

catch (Exception ex)            
{                
    if (ex is FormatException || ex is OverflowException)
    {
        WebId = Guid.Empty;
        return;
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    throw;
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In Castle Windsor 3, override an existing component registration in a unit test

There are two things that you have to do to create an overriding instance:

Assign it a unique name
Call the IsDefault method

So to get the example to work:

this.WindsorContainer.Register(
                             Component.For<IMediaPlayerProxyFactory>()
                                      .Instance(mockMediaPlayerProxyFactory)
                                      .IsDefault()
                                      .Named("OverridingFactory")
                          );

Because I plan to use this overriding patten in many tests, I've created my own extension method:

public static class TestWindsorExtensions
{
    public static ComponentRegistration<T> OverridesExistingRegistration<T>(this ComponentRegistration<T> componentRegistration) where T : class
    {
        return componentRegistration
                            .Named(Guid.NewGuid().ToString())
                            .IsDefault();
    }
}

Now the example can be simplified to:

this.WindsorContainer.Register(
                             Component.For<IMediaPlayerProxyFactory>()
                                      .Instance(mockMediaPlayerProxyFactory)
                                      .OverridesExistingRegistration()
                          );

Later Edit

Version 3.1 introduces the IsFallback method. If I register all my initial components with IsFallback, then any new registrations will automatically override these initial registrations. I would have gone down that path if the functionality was available at the time.

https://github.com/castleproject/Windsor/blob/master/docs/whats-new-3.1.md#fallback-components

Best Answer

Related Solutions

C# – Catch multiple exceptions at once

In Castle Windsor 3, override an existing component registration in a unit test

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