Effective Interface Organization in C# Layered Applications

Learn how to structure interfaces in your C# WPF application without causing circular references and versioning issues, providing a seamless integration experience.
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This video is based on the question https://stackoverflow.com/q/66067519/ asked by the user 'Hey Mikey' ( https://stackoverflow.com/u/12704975/ ) and on the answer https://stackoverflow.com/a/66067543/ provided by the user 'Peter Dongan' ( https://stackoverflow.com/u/1658168/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Where Do Interfaces Go in C# Layered Applications?

When building a layered application in C# , especially with technologies like WPF, developers often encounter questions about the best practices for organizing their code. One common issue is where to place interfaces, particularly when you want to keep your application flexible and maintainable. In this post, we will address a question raised by our community regarding the mechanics of interface organization in C# applications.

The Problem at Hand

As described by our reader, Mike, he is developing a C# WPF application that will initially use IBM iSeries data and later connect to Oracle data through a web service. To ensure that the application is modular and testable, he planned to use interfaces. However, he faces a challenge:

Circular References: If he defines interfaces within the view layer, it leads to circular dependencies. The data source needs references from the view for the interface, while the view needs the data source for dependency injection.

Version Control: Maintaining separate versions of interfaces across different projects can become cumbersome and lead to potential inconsistencies.

Proposed Solution: A Separate Project for Interfaces

The best solution to avoid these complications is quite straightforward. Here’s how you can effectively organize interfaces in your C# application:

1. Create a Separate Project for Interfaces

Designate a New Project: Start by creating a dedicated project specifically for your interfaces. This could be named something like MyApp.Interfaces.

Reference the Project: In each of your data source implementations and view model projects, include a reference to this new interfaces project.

2. Benefits of a Separate Interfaces Project

By placing your interfaces in a separate project, you can reap several benefits:

Decoupling: This approach decouples your data sources from the view, eliminating circular references and making it easier to manage dependencies.

Centralized Management: All interfaces will be in one location, simplifying version control and making updates easier as your application evolves.

Improved Testing: Having interfaces allows for better testing; you can easily swap out implementations in tests without altering the rest of your code base.

3. Implementation Steps

To implement this solution, follow these steps:

Create the Interfaces Project:

Set up a new class library project in your solution.

Add the necessary interfaces that define your data access methods based on the required operations for both data sources.

Referencing the Interfaces:

In your data source projects, reference the interfaces project.

In your view models, similarly, include a reference to the interfaces project to ensure access to the defined contracts.

Implement the Interfaces:

In each of your data source projects, implement the interfaces you defined. Each data source can now have its own data mapping logic while adhering to the common interface contract.

Conclusion

Organizing your interfaces in a separate project is an effective strategy to tackle the issue of circular dependencies and maintainabilit. This method not only streamlines your application structure but also enhances its testability and flexibility. Don't let interface management become a bottleneck—implement these practices to boost your development experience!

If you have any questions or thoughts about this approach, feel free to share in the comments below.

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