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How do you handle multiple event sources and subscribers in event aggregator pattern in MVVM?

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Event aggregator pattern is a popular way to implement communication between loosely coupled components in model-view-viewmodel (MVVM) architecture. It allows multiple event sources to publish messages to a central mediator, which then distributes them to the interested subscribers. This reduces the complexity and dependency of the components and makes the code more maintainable and testable. But how do you handle multiple event sources and subscribers in event aggregator pattern in MVVM? In this article, we will explore some best practices and tips to make your event aggregation more efficient and robust.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian |…
Mayursinh Parmar

Dreaming of the perfect app? Let's make it real || Android || Java || Kotlin || Jetpack compose || Ktor || Dart ||…

1 Define clear and consistent event contracts

One of the key aspects of event aggregator pattern is to define clear and consistent event contracts, which are the types and data of the messages that are exchanged between the event sources and subscribers. Event contracts should be simple, descriptive, and relevant to the domain of the application. They should also follow the principle of least privilege, which means they should only expose the minimum information needed by the subscribers. By defining clear and consistent event contracts, you can avoid confusion, duplication, and ambiguity in your event aggregation.

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Mayursinh Parmar

Dreaming of the perfect app? Let's make it real || Android || Java || Kotlin || Jetpack compose || Ktor || Dart || Flutter || Dev-blogger
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Clearly define the type of event being communicated. This could be a class, interface, or data structure representing the event. Specify any data associated with the event. Define the properties or fields that convey relevant information about the event. Include metadata if necessary, such as timestamps, event identifiers, or other contextual information that helps in understanding the event.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian | BFSI | Aviation | E-Commerce | Healthcare | Telecom | Fintech | Analytic Thinker
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Clear and consistent event contracts are essential in the MVVM pattern to ensure that the communication between components is robust and maintainable. By adhering to the principle of least privilege, the system's security posture is improved, reducing the risk of exposing sensitive data. Furthermore, well-defined contracts facilitate easier refactoring and testing, as the boundaries and expectations of each interaction are well understood. This approach also aids in the scalability of the application as new event types or subscribers can be added with minimal impact on existing functionality.

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2 Use dependency injection to register and resolve event aggregator

Another important aspect of event aggregator pattern is to use dependency injection to register and resolve the event aggregator instance. Dependency injection is a technique that allows you to inject dependencies, such as services, repositories, or other components, into your classes, instead of creating them inside the classes. This makes your classes more loosely coupled, testable, and flexible. By using dependency injection, you can register the event aggregator as a singleton service, which means there is only one instance of it throughout the application. You can then resolve the event aggregator in your event sources and subscribers, and use it to publish or subscribe to events.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian | BFSI | Aviation | E-Commerce | Healthcare | Telecom | Fintech | Analytic Thinker
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Incorporating dependency injection for the event aggregator in MVVM not only streamlines event management but also aligns with the principle of inversion of control, enhancing modularity. By treating the event aggregator as a shared resource, akin to a communication bus, we ensure a consistent mechanism for event handling across different components, which is crucial for maintaining a scalable and maintainable codebase. This approach also simplifies unit testing by allowing mock implementations of the event aggregator to be injected, thereby isolating components for more focused tests.

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3 Use weak references or unsubscribe to avoid memory leaks

One of the potential pitfalls of event aggregator pattern is memory leaks, which occur when objects are not properly disposed or garbage collected, and consume memory unnecessarily. Memory leaks can happen when you use strong references to subscribe to events, which means the event aggregator holds a reference to the subscriber object, and prevents it from being garbage collected, even if it is no longer needed. To avoid memory leaks, you can use weak references, which do not prevent garbage collection, or unsubscribe from events when the subscriber object is disposed or deactivated.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian | BFSI | Aviation | E-Commerce | Healthcare | Telecom | Fintech | Analytic Thinker
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Handling multiple event sources and subscribers in the event aggregator pattern within MVVM is crucial for efficient memory management. One common issue is memory leaks, where objects linger and use up unnecessary memory. This happens when strong references are used for event subscriptions, causing the event aggregator to hold onto subscriber objects even when they're no longer needed. To prevent this, consider using weak references or actively unsubscribing from events. Weak references don't hinder garbage collection, allowing unused objects to be properly disposed of and avoiding memory leaks. It's a simple yet vital practice for maintaining the health of your mobile application.

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4 Use asynchronous and thread-safe methods to handle events

Another potential challenge of event aggregator pattern is concurrency, which occurs when multiple threads or tasks access or modify the same data or resources simultaneously. Concurrency can cause race conditions, deadlocks, or inconsistent results, and affect the performance and reliability of your application. To handle concurrency, you can use asynchronous and thread-safe methods to publish and subscribe to events. Asynchronous methods allow you to execute tasks without blocking the main thread, and improve the responsiveness and scalability of your application. Thread-safe methods ensure that only one thread or task can access or modify a shared resource at a time, and prevent data corruption or inconsistency.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian | BFSI | Aviation | E-Commerce | Healthcare | Telecom | Fintech | Analytic Thinker
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Concurrency issues in the event aggregator pattern can be mitigated by leveraging modern programming languages' built-in concurrency mechanisms, such as async/await in C# or JavaScript, which simplify asynchronous programming. Additionally, employing thread-safe collections and synchronization primitives like mutexes or semaphores can prevent race conditions. It's crucial to design the system with concurrency in mind from the outset, as retrofitting concurrency controls into an existing design can be challenging and error-prone.

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5 Use filters or topics to manage event granularity

One of the optional features of event aggregator pattern is to use filters or topics to manage the granularity of events. Filters or topics are criteria or categories that allow you to specify which events you are interested in or not interested in. For example, you can use filters or topics to subscribe to events from a specific source, type, or data. By using filters or topics, you can reduce the noise and overhead of receiving irrelevant or redundant events, and improve the performance and usability of your event aggregation.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian | BFSI | Aviation | E-Commerce | Healthcare | Telecom | Fintech | Analytic Thinker
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When leading mobile app development with the event aggregator pattern in MVVM, consider using filters or topics. These act like categories for events, letting you choose specific sources, types, or data. Imagine it as sorting your inbox – you only want emails about a certain project. This not only declutters your app but also boosts performance by avoiding unnecessary events. It's like tuning in to the channels you care about, making your event aggregation more efficient and user-friendly.

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6 Use unit tests and logging to debug and monitor events

One of the final tips for event aggregator pattern is to use unit tests and logging to debug and monitor events. Unit tests are methods that verify the functionality and quality of your code, and detect errors or bugs. Logging is a technique that records the activities and events of your application, and provides information or traces for debugging or monitoring purposes. By using unit tests and logging, you can ensure that your event aggregation works as expected, and identify and resolve any issues or problems that may arise.

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Shweta Jain

27k+ ???? @Linkedin | Technical Architect - Mobility | Mobile Application | Android | iOS | React Native | Appian | BFSI | Aviation | E-Commerce | Healthcare | Telecom | Fintech | Analytic Thinker
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In the world of Mobile App Development, juggling multiple event sources and subscribers in the Event Aggregator pattern of MVVM can get tricky. Here's a helpful tip: embrace unit tests and logging. Unit tests are like your app's personal detectives, making sure everything runs smoothly and catching any sneaky bugs. Logging, on the other hand, is like a diary for your app, keeping a record of what's happening. By using unit tests, you can be sure that all the parts of your app are playing nice together. If something goes wrong, these tests will point you straight to the issue. Logging helps you keep an eye on your app's activities. If there's a hiccup, the logs will spill the beans on what went wrong.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How do you handle multiple event sources and subscribers in event aggregator pattern in MVVM?

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1 Define clear and consistent event contracts

2 Use dependency injection to register and resolve event aggregator

3 Use weak references or unsubscribe to avoid memory leaks

4 Use asynchronous and thread-safe methods to handle events

5 Use filters or topics to manage event granularity

6 Use unit tests and logging to debug and monitor events

7 Here’s what else to consider

Model-view-viewmodel (MVVM)

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