C# What Layer to start with

Ok 2 questions here.

I am creating a c# application from a vb6 application. I will be using a business logic layer, a da开发者_如何学运维ta layer, presentation layer, and data layer.

What layer should I start with since the database is already in place?

2nd question. If I code a new app would I start with this same layer?

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Which layer to start with is a hard thing to talk about abstractly. It does vary depending on what type of application you are discussing, the size of said application, and the general interdependencies.

If I understand your question correctly it sounds like you are considering writing (say) the entire data layer before moving on to the business layer.

Why start with any one layer? If you writing an application (either from scratch or as a port of an existing app) then why wouldn't you divide that app up into stories and tackel it in more of a feature oriented fashion?

By doing this you will have parts of a functional app that you can prototype with much quicker. This will also allow you to spot design problems in all layers much quicker, as you are not only writing the layers but also consuming them.

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I generally prefer starting with the UI. The UI is the point of customer interaction, and so drives the requirements for the rest of the layers.

In some cases, there's some core bit of logic that's really key, and it's a good idea to start there. But generally, I find the UI is the best place to start.