Advanced Power Fx & Canvas Components

Power Fx for developers

Advanced Power Fx patterns

Named formulas

Named formulas define values once and reuse them across the app. They recalculate automatically when dependencies change.

// In App.Formulas (app-level named formulas)
ActiveEmployees = Filter(Employees, Status = "Active");
TotalSalary = Sum(ActiveEmployees, Salary);
AverageAge = Average(ActiveEmployees, Age);

Why named formulas matter:

• Calculate once, use everywhere (no redundant Filter calls on every screen)
• Automatically recalculate when source data changes
• Reduce formula complexity on individual controls

Imperative vs declarative patterns

Pattern	Declarative	Imperative
Style	”What the result should be"	"What steps to take”
Keywords	Filter, Sort, Sum, Average	Set, Collect, Patch, Navigate
Where	Properties (Items, Text, Visible)	Behaviors (OnSelect, OnChange, OnStart)
Example	Filter(Orders, Status = "Open")	Collect(Cart, ThisItem); Navigate(Checkout)

Power Automate integration from canvas apps

Canvas apps can call cloud flows to perform actions the app cannot do directly — like sending emails, calling external APIs, or running long computations.

How it works:

1. Create a cloud flow with “Power Apps (V2)” trigger
2. Define input parameters the app will send
3. Define output parameters the flow will return
4. In the canvas app, call the flow: MyFlow.Run(param1, param2)
5. Handle the response: Set(varResult, MyFlow.Run(param1, param2))

Best practices:

• Use flows for operations that should not run client-side (email, external API, data processing)
• Keep flow calls asynchronous when possible (do not block the user)
• Handle errors: wrap in IfError() to catch flow failures gracefully
• Pass only the minimum data needed (not entire records)

💡 Scenario: Kai builds a submission flow integration

Kai builds a canvas app for logistics staff to submit shipment requests. When a user taps “Submit”:

1. The app calls SubmitShipment.Run(ShipmentID, DestinationCode, Priority)
2. The flow validates the destination against a reference table, calculates estimated cost, and creates a record in the Shipment table
3. The flow returns {Success: true, EstimatedCost: 450, TrackingNumber: "TRK-29381"}
4. The app displays the tracking number and cost

Why a flow? The validation requires calling an external API (shipping provider) and creating a Dataverse record with calculated fields — operations that are cleaner and more maintainable in a flow than in Power Fx formulas.

Building component libraries

Component libraries let you build reusable controls that can be shared across multiple canvas apps.

Component anatomy

Every canvas component has:

• Custom input properties — data the host app passes into the component
• Custom output properties — data the component passes back to the host app
• Custom function properties — callbacks the host app can call (e.g., Reset())
• Custom event properties — events the component can raise (e.g., OnItemSelected)

Design principles

• Single responsibility — each component does one thing well
• Configurable via properties — do not hardcode colours, labels, or data sources
• Stateless preferred — accept data through input properties, emit results through output properties
• Test independently — components should work in isolation before using them in an app

Question

What is a named formula in Power Fx?

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Answer

A named formula defines a reusable, automatically recalculating expression at the app level (in App.Formulas). Example: ActiveEmployees = Filter(Employees, Status = 'Active'). It calculates once and is available everywhere in the app without redundant formula evaluation.

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Question

How do you call a Power Automate flow from a canvas app?

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Answer

Use the flow name as a function: MyFlow.Run(parameter1, parameter2). The flow must have a 'Power Apps (V2)' trigger with defined input parameters. To capture the response: Set(varResult, MyFlow.Run(param1, param2)). Wrap in IfError() to handle failures gracefully.

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Question

What are the four types of custom properties in a canvas component?

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Answer

Input (data passed in from the host app), Output (data returned to the host app), Function (callable methods the host app can invoke, e.g., Reset), and Event (callbacks the component can raise, e.g., OnItemSelected). Together, they form the component's API.

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Knowledge Check

Kai builds a canvas app that displays a filtered list of shipments. The same filter (Status = 'Active' AND Region = varUserRegion) is used on three different screens, where varUserRegion is set from the user's profile at app start. What is the best approach to avoid redundant evaluation?

ACopy the Filter formula to each screen's gallery Items propertyBDefine a named formula in App.Formulas and reference it on each screenCUse a global variable set in App.OnStart to store the filtered collectionDCreate a Dataverse view and use that as the data source

Check Answer

Knowledge Check

A canvas app needs to send an email with an attachment when the user taps a button. The attachment is a PDF generated from form data. Where should this logic be implemented?

ADirectly in the button's OnSelect using Power Fx email functionsBIn a Power Automate cloud flow called from the button's OnSelectCIn a PCF code component embedded in the canvas appDIn a Dataverse plug-in triggered by record creation

Check Answer

🎬 Video coming soon

Next up: Troubleshoot & Optimise Apps — using Monitor and browser tools to debug issues, and optimising performance with delegation and pre-loading.