Passing Events in Angular 6+ - A Guide to Scroll Interactions Between Components

Описание: Learn how to effectively manage events and implement scrolling behaviors between parent and child components in Angular 6+ . This guide provides a clear solution to common issues faced during event handling.
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This video is based on the question https://stackoverflow.com/q/68864920/ asked by the user 'beanic' ( https://stackoverflow.com/u/10652694/ ) and on the answer https://stackoverflow.com/a/68866519/ provided by the user 'Lukasz Gawrys' ( https://stackoverflow.com/u/15025918/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Challenge: Passing Events Between Components in Angular 6+

When working with Angular, you may find yourself needing to link functionalities between components. This often arises when a child component requires to trigger an action in its parent component, such as scrolling. Imagine you have a main component that holds a nested child component. The child component has buttons that, when clicked, should scroll to specific areas within the main component.

In this guide, we'll explore how to address a common problem faced when passing events in Angular 6+ . You might encounter errors when trying to scroll to a form in the main component from a button in the child component. Let's break down the solution into simple steps to ensure smooth interaction between these components.

The Scenario

For context, here's the setup:

Main Component: Contains a nested child component and a form.

Child Component: Holds two buttons:

Button 1: Scrolls to a form in the main component.

Button 2: Scrolls to content within the child component itself.

The issue arises when the application runs into errors such as:

Cannot read property 'emit' of undefined

Cannot read property 'viewportScroller' of undefined

These errors typically indicate a misuse of event handling, particularly how the EventEmitter is utilized.

The Solution: Streamlining Event Emission

Step 1: Adjust the EventEmitter

First, we need to make the event emitter's purpose clearer and more functional. Here’s how to correctly define it in the child component:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Update the Button Handler

Next, we will change the method that handles the scroll action triggered by Button 1. Instead of using event.target, which does not point to the correct component, modify the method to directly call the emitter:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Modify the Parent Component's HTML

In your main component's HTML, you will need to update how the child component’s event is listened to. The syntax will look like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Define the Scroll Method in the Main Component

In the main component's TypeScript file, redefine the scroll method to match the new setup that does not require a parameter since we're just listening for the event:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following these steps, you ensure that your components communicate effectively without running into the mentioned errors. The changes streamline how events are emitted and handled in Angular, allowing for smooth scrolling transitions based on user interactions.

Key Takeaways:

Use Clear Naming Conventions: Name your event emitters based on their purpose for clarity.

Directly Emit Events from the Component: Avoid using event.target in the context of event emissions.

Update Parent Component to Listen Correctly: Ensure the parent component is set to respond to the events emitted by the child.

By mastering how to handle events fluidly between components, you'll enhance the user experience and functionality of your Angular applications.