Question

Can someone shed some light on how Unity automatically does dependency graph resolution? I am not looking for the code of the algorithm, but just a simple explanation, and maybe some sort of example or analogy.

Answer 1

Unity is an extensible library, so how it does its dependency resolution can be customized and changed. The default build plans however look like the following:

1. Start build up on the type requested
2. Look for the longest constructor on the type
3. Go to (1.) for each constructor parameter type
4. Create instance using resulting objects
5. Look for all public properties marked with [DependencyAttribute]
6. Go to (1.) for each property type
7. Set property values to resulting objects
8. Return created object

The build up of an object can be thought of in multiple stages. This MSDN link nicely sums up the various stages and what is performed by default at each stage: UnityBuildStage