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IS ONINITIALIZEDASYNC() IN BLAZOR CALLED TWICE?

Abstract: In this article, we'll explore whether the OnInitializedAsync() method
in Blazor is called twice during component initialization and discuss possible
solutions to avoid unexpected behavior.

2024-04-21 by DevCodeF1 Editors



ONINITIALIZEDASYNC() CALLED TWICE?

In Blazor, the OnInitializedAsync() lifecycle method is called twice, once
during the initial rendering of the component, and again when the component is
navigated to for the first time. This behavior is by design and is part of the
component model in Blazor. In this article, we will explore the reasons behind
this behavior and how it fits into the larger context of the Blazor component
model.


BLAZOR COMPONENT LIFECYCLE

Blazor components have a well-defined lifecycle, with various methods that are
called at different points during the lifecycle. These methods allow developers
to control the behavior of their components and to perform actions such as
setting initial state, fetching data, and handling user input. The following
diagram shows the component lifecycle in Blazor:



As we can see from the diagram, the OnInitializedAsync() method is called during
the OnInitialized phase of the component lifecycle. This phase is triggered
after the component has been rendered for the first time, and it allows
developers to perform any necessary initialization tasks, such as fetching data
from a remote API or setting the initial state of the component.


ONINITIALIZEDASYNC() CALLED TWICE

Now that we understand the component lifecycle in Blazor, let's explore why the
OnInitializedAsync() method is called twice. The reason for this behavior has to
do with how Blazor handles navigation between components. When a user navigates
to a new component, Blazor first renders the new component, and then it removes
the old component from the DOM. However, before the old component is removed,
Blazor calls the OnInitializedAsync() method one more time, giving the component
a chance to perform any necessary cleanup tasks.

This behavior is by design and is intended to ensure that components are
properly initialized and cleaned up during navigation. By calling
OnInitializedAsync() twice, Blazor ensures that components are always in a
consistent state, regardless of how they are navigated to or from.


BEST PRACTICES FOR USING ONINITIALIZEDASYNC()

When using the OnInitializedAsync() method in Blazor, it's important to keep in
mind that it may be called twice. This means that any initialization logic that
should only be run once should be placed in the OnAfterRenderAsync() method
instead. This method is called only once, after the component has been rendered
for the first time.

Additionally, any logic that depends on the component's state or properties
should be placed in the OnParametersSetAsync() method instead. This method is
called every time the component's parameters or properties change, ensuring that
the component's behavior is always up-to-date.

 * The OnInitializedAsync() method in Blazor is called twice, once during the
   initial rendering of the component, and again when the component is navigated
   to for the first time.
 * This behavior is by design and is part of the component model in Blazor.
 * The OnInitializedAsync() method should be used for any initialization tasks
   that need to be performed when the component is first rendered.
 * Any cleanup logic should be placed in the OnInitializedAsync() method as
   well, to ensure that the component is properly cleaned up during navigation.
 * Initialization logic that should only be run once should be placed in the
   OnAfterRenderAsync() method instead.
 * Logic that depends on the component's state or properties should be placed in
   the OnParametersSetAsync() method instead.


REFERENCES

 * Blazor Component Lifecycle
 * Why is OnInitializedAsync called twice in Blazor?
 * OnInitializedAsync called twice in Blazor

Tags::  Blazor C# DotNet Software Development




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