Recently, the landscape of development has shifted, making it seem easier than ever to implement Mendix widgets through vibe coding. The allure is strong: just sit back, relax, and ask an AI to generate the code. After some trial and error, you might indeed find yourself with a working widget and a decent UI. Sounds very nice, right?

However, this apparent simplicity can be deceptive. While AI can undoubtedly accelerate the initial scaffolding, a critical truth remains: you still need to know the system. Without that foundational understanding, relying solely on AI-generated code can quickly become akin to blindly copying solutions from Stack Overflow without truly grasping the underlying principles.

Developing widgets for Mendix comes with its own unique set of challenges, requiring thoughtful decisions that impact both the development process and the long-term success of your application. From choosing the right architecture to handling data and optimizing performance, each decision comes with its own set of trade-offs.

By exploring the different approaches available and understanding their implications, you can make more informed choices and create widgets that are both powerful and scalable. Let’s dive deeper into the nuances of Mendix widget development.

Widget architecture – Making the right choice

When building a widget for Mendix, start with an architecture decision to determine the best approach. Your options depend largely on the widget’s complexity, and you’ll need to consider:

• A combination of widgets and Mendix components
• Container widgets
• Multiple widgets
• Loader widget approach

The first approach that comes to mind is creating one widget for the entire component. While this is simple for basic components, it becomes more challenging when the component is complex and includes multiple interactive actions.

Let’s explore this using a Todo List widget as an example. I’m going to discuss three different approaches for implementing the same widget.

Approach 1: Single widget as the list container

In this approach, you include the data source as part of the Todo List widget settings. The widget handles the rendering of the entire list, giving you complete control over the view. For example, you can render items vertically, horizontally, or as cards with custom layouts that aren’t possible with standard Mendix list components.

However, you’ll need to handle all list-related challenges within the widget, including but not limited to pagination, sorting, filtering, and lazy loading behavior. This means implementing these features from scratch rather than leveraging Mendix’s built-in optimizations.

Data handling complexity

The next significant challenge is handling actions and data updates. Since the data source is read-only, you cannot directly modify a Todo item. Instead, you need a dummy attribute to pass changes through microflows. This creates several implementation challenges:

Update operations

For simple operations like deleting an item or toggling a Todo’s status, you can implement separate actions. However, for more complex updates, you must either pass all changes to a single microflow or create separate microflows for each update action (toggle status, change title, change due date, change priority, etc.).

Performance considerations

When dealing with large datasets, you must implement your own pagination logic. This includes managing page size, handling scroll events for infinite scrolling, and ensuring smooth performance when users navigate through thousands of items.

Memory management

Since you’re handling the entire dataset within the widget, you need to be mindful of memory usage, especially on mobile devices or when dealing with large lists. Using pagination will mitigate the issue.

Action variables

From version 10.21.0 and above, it is possible to use action variables which makes the implementation easier than before. In earlier versions, the MF behind an action couldn’t have any parameters, and the MF had to retrieve the value of the dummy objects itself.

Configuration complexity

These additional settings make the widget setup more challenging for Mendix developers, requiring a solid understanding of several key configurations. Developers must learn how to configure dummy objects for data passing, create appropriate microflows for different actions, and ensure proper error handling to account for failed operations. Additionally, maintaining data consistency when multiple users are editing the same items demands extra care and planning.

Advantages

Complete rendering control
Widget has full control over list rendering (cards, vertical, horizontal layouts, custom animations, drag-and-drop interfaces).

Advanced filtering and sorting
The Widget can implement complex sorting algorithms, multi-column sorting, and advanced filtering options that go beyond standard Mendix capabilities.

Consistent styling
Easier to maintain styling consistency across the entire component since everything is contained within one widget.

Custom interactions
Can implement advanced user interactions like bulk operations, keyboard shortcuts, and complex selection patterns.

Disadvantages

Monolithic complexity
Creates a monolithic structure with increased complexity within the widget code, making it harder to maintain and debug.

Performance implementation burden
Requires significant effort to implement pagination, sorting, filtering, and lazy loading behavior efficiently.

Styling integration challenges
More difficult to align widget styling with the app’s overall design system and theme changes.

Complex setup requirements
Complex setup for Mendix developers, requiring dummy objects, multiple microflows, and an understanding of the widget’s internal data flow.

Testing complexity
Harder to test individual features since everything is tightly coupled within one component.

Approach 2: List item widget

Another option is to leverage Mendix’s built-in list components, such as the Gallery widget, List View, or Data Grid. In this case, you only build the item widget and use it within the list container provided by Mendix.
This approach fundamentally separates concerns between different components. The Mendix list widget handles all the complex list management tasks: pagination, lazy loading, sorting, and filtering. Since these controls and patterns are familiar to Mendix developers, setup becomes significantly easier and follows established patterns.

Leveraging Mendix’s built-in optimizations

By using Mendix’s native list components, you automatically benefit from:

• Optimized data retrieval: Mendix automatically implements efficient data retrieval patterns, including the Retrieve & Aggregate optimization that reduces database queries when you only need counts rather than full datasets.
• Built-in pagination: Native pagination handling with configurable page sizes, reducing server load and improving client-side performance.
• Lazy loading: Automatic lazy loading of data as users scroll, preventing unnecessary data retrieval and improving initial page load times.
• Caching mechanisms: Mendix implements intelligent caching strategies that reduce redundant server requests.

Simplified data management

For adding new items, you can handle this outside the widget by displaying a pop-up page, a modal, or navigation to a separate form. This approach provides several benefits:

• Familiar patterns: Mendix developers can use standard page layouts, form validations, and styling approaches they already know.
• Access control: Easier to implement role-based access control using Mendix’s built-in security features.
• Form validation: Can leverage Mendix’s validation framework and error handling mechanisms.
• Responsive design: Automatically benefits from Mendix’s responsive design capabilities.

Editable data handling

In this approach, Todo items become editable (depending on the user’s object access permissions). Within the widget, implementing update logic becomes significantly simpler:

• Direct object manipulation: Can directly modify object attributes without requiring dummy objects.
• Simplified microflows: The microflow for changes is straightforward—it only needs to commit the object without requiring additional dummy parameters for operations.
• Real-time updates: Changes can be reflected immediately in the UI without complex state management.
• Validation integration: Can leverage Mendix’s built-in validation rules and error handling.

Advantages

Simplified maintenance
Significantly simpler widget maintenance with reduced code complexity and fewer potential failure points

Standard performance patterns
Uses proven, optimized practices for pagination, sorting, filtering, and lazy loading that are continuously improved by Mendix

Design system integration
Easier alignment of widget styling with the app’s design system, automatic theme support, and consistent user experience

Developer-friendly setup
Simplified setup for Mendix developers—no need for extra dummy objects, complex microflow configurations, or understanding of internal widget data flows

Proven scalability
Benefits from Mendix’s tested and optimized list handling capabilities that scale well with large datasets

Accessibility compliance
Automatically inherits Mendix’s accessibility features and compliance with web standards

Disadvantages

Limited rendering control
Reduced control over list rendering options (limited to Mendix’s built-in layout options)

Customization Constraints
Cannot implement highly custom interactions or layouts that go beyond Mendix’s standard capabilities

Advanced Feature Limitations
May not support advanced features like complex drag-and-drop, custom sorting algorithms, or unique interaction patterns

Approach 3: Multiple widgets

The third option involves building multiple interconnected widgets: a container widget that renders the list of items and one or more item widgets that render individual Todo items. This approach is particularly valuable when you need functionality not available in Mendix’s built-in list components, such as advanced drag-and-drop capabilities, custom layout algorithms, or complex inter-item interactions.

This approach also facilitates better planning and iterative development. You can decide which parts require custom widgets and which can utilize Mendix’s built-in components. As you iterate on features, you can replace components as needed without rebuilding the entire system.

Scalability and reusability benefits

In our Todo example, if we build the container widget, we can reuse the item widget from our second approach above. Then, within the container widget, we can add advanced functionality like:

• Advanced drag-and-drop: Multi-directional dragging, drop zones with visual feedback, and complex reordering logic
• Custom layout algorithms: Masonry layouts, dynamic sizing based on content, or algorithmic positioning
• Bulk operations: Multi-select capabilities, batch editing, and complex selection patterns
• Real-time collaboration: Live updates when multiple users are editing the same list
• Advanced filtering: Custom filter interfaces, saved filter presets, and complex query builders

The multi-widget approach provides better scalability and separation of concerns. However, you must consider increased implementation complexity to make components truly reusable and generic.
Without proper abstraction and design, reusability becomes limited, and maintenance becomes more challenging.

Implementation complexity considerations

Additionally, there are significant challenges when multiple widget instances on the same page need to communicate with each other:

• State synchronization: Ensuring all widgets stay in sync when data changes
• Event coordination: Managing complex event chains between widgets
• Performance optimization: Preventing unnecessary re-renders and data fetches
• Error handling: Gracefully handling failures in one widget without affecting others
• Droppable area configuration: Implementing preview mode in the widget to preview the droppable area in Studio Pro

State management challenges

Signaling and state management between widgets

One of the most significant complexities with multiple widgets is inter-widget communication and state management. When widgets need awareness of each other’s state—for example, when a user drags an item from one column to another in a Kanban board—you need a robust communication mechanism. One widget must hide the item while another displays it, all while maintaining data consistency and providing smooth user feedback.
This requires sophisticated data flow and synchronization between widgets, which isn’t straightforward and demands specific implementation techniques and careful consideration of edge cases.

Data flow patterns

For multiple widgets, data provision works similarly to single widgets, but you need to establish reliable patterns for passing data between widgets. You might use a container widget that holds child widgets, but there are important limitations to understand.

While React developers might assume they can pass props from parent to child components, this isn’t possible in Mendix pluggable widgets. If you render another widget inside a parent widget, the Mendix runtime will override any props you pass with data from the widget settings configured in Studio Pro. This means you cannot dynamically pass data through the component tree as you would in a typical React application.

Alternative communication methods

Instead, you need alternative methods to share data between widgets:

Shared attributes:

• Write to an attribute in one widget that another widget can read
• When the attribute changes, the second widget automatically re-renders because its props have changed
• Provides automatic reactivity, but can lead to performance issues with frequent updates
• Best for simple state sharing, like selected items or filter values

React context:

• React 18 introduced context for state management (previously requiring third-party libraries like Redux)
• Since all Mendix widgets on a page are rendered by the same React DOM, context can be shared between them
• You can create a context provider in one widget and consume it in others
• Ideal for complex state management and avoiding prop drilling
• Requires careful setup to prevent memory leaks and ensure proper cleanup

Post message API:

• This established mechanism uses the window.postMessage API to send events across the page
• Widgets can subscribe to these events regardless of their position, even across iframes
• Provides loose coupling between widgets but requires careful event naming and payload structure
• Best for one-way communication and event broadcasting
• Can work across different pages or even different applications

Styling challenges

Styling becomes significantly more complex with multiple widgets. When you have CSS stylesheets in one widget that you want to access from other widgets, you need to carefully plan your styling architecture:

Shared repository structure:

• Use a larger repository structure that both widgets can access
• Implement a build process that can share common styles
• Requires coordination between widget development teams
• Can lead to version synchronization challenges

Design system integration:

• Move styling out of the widget entirely and make it the responsibility of your design system
• Use classes from the design system in the widget and document the design system styling as an indirect dependency
• Provides better consistency but requires a mature design system
• May limit customization options for individual widgets

Module-based publishing:

• Publish your widget as a module rather than a standalone widget
• This allows for exporting CSS files that can be shared between widgets
• Provides more flexibility but complicates the publishing and distribution process
• Requires understanding of Mendix module development patterns

Setup complexity and developer experience

For Mendix developers, setting up multiple widgets is significantly more challenging than configuring a single widget. The complexity manifests in several ways:

Configuration dependencies:

• With one widget, developers have a straightforward data source configuration
• With multiple widgets, they must understand and follow the specific pattern used in your development
• Incorrect configuration can lead to broken functionality or poor performance

Data structure requirements:

• Multiple widgets often require specific data structures and relationships
• Developers must understand how widgets communicate and what data each widget expects
• Documentation becomes critical for successful implementation

Deployment coordination:

• All related widgets must be deployed together to ensure compatibility
• Version mismatches between widgets can cause runtime errors
• Requires careful release management and testing procedures

Debugging complexity:

• Issues can span multiple widgets, making debugging more challenging
• Developers need to understand the entire widget ecosystem to troubleshoot problems
• Requires comprehensive logging and error handling across all widgets

Performance considerations

Multiple widgets also introduce performance considerations that don’t exist with single widgets:

• Render coordination: Multiple widgets re-rendering simultaneously can cause performance bottlenecks
• Memory management: Each widget maintains its own state, potentially leading to increased memory usage
• Network optimization: Multiple widgets making simultaneous API calls can overwhelm the server
• Event handling: Complex event chains between widgets can create performance issues if not properly optimized

Despite these challenges, the multiple widget approach can be extremely powerful when implemented correctly. It provides the flexibility to create sophisticated user interfaces while maintaining code modularity and reusability. The key is to carefully plan the architecture upfront and establish clear patterns for communication, styling, and data management.

Examples of all three approaches

For comparison, I have implemented three Todo List showcase widgets using all the above approaches. The code is generated mainly by Vibe coding using Copilot. I prompted the requirements and expected functionality, then iterated over them to get the expected result. Note that these repositories are just showcase examples and have not passed quality controls to be used in production.

• Approach one code example: https://github.com/MeisamMahdian/showcase-todolist-single-widget
• Approach two code example: https://github.com/MeisamMahdian/showcase-todolist-single-item
• Approach three code example: https://github.com/MeisamMahdian/showcase-todolist-container-widget

Ultimately, I hope this article has provided you with a clearer understanding of Mendix widget architecture, demonstrating why a comprehensive grasp of the platform, beyond mere code generation, is truly indispensable for crafting exceptional custom solutions.