How to Implement Async - Await in VB.Net

By: Rajesh P.S.

Using Async and Await in VB.NET allows you to write asynchronous code, making it easier to work with time-consuming operations without blocking the main thread.

How to use async/await in VB.Net

To use async/await in VB.Net, you must first mark a method as Async. This tells the compiler that the method can contain asynchronous code.
Next, you can use the Await operator to suspend execution of the method until an asynchronous task completes. The Await operator returns a Task object, which represents the asynchronous operation.
Finally, you can return control to the caller of the method. The caller will not resume execution until the asynchronous task completes.

Create an Async Method

To use Async and Await, you first need to create a method and mark it as Async. This indicates that the method can perform asynchronous operations.

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Async Function MyAsyncMethod() As Task ' Asynchronous code goes here End Function

Use Await to Call Asynchronous Operations

Inside the Async method, you can use the Await keyword to call asynchronous operations, such as Task.Run, HttpClient requests, or any other asynchronous methods. Await allows the code to continue executing without blocking the main thread until the asynchronous operation completes.

Async Function MyAsyncMethod() As Task Dim result As Integer = Await SomeAsyncOperation() ' Continue with code when SomeAsyncOperation completes. End Function Async Function SomeAsyncOperation() As Task(Of Integer) ' Simulate a time-consuming operation Await Task.Delay(1000) Return 42 End Function

In this example, SomeAsyncOperation is an asynchronous method that simulates a delay. When you Await it in MyAsyncMethod, the program will continue to execute other code while waiting for the SomeAsyncOperation to complete.

Handle Exceptions

You should handle exceptions when working with asynchronous code. You can use Try-Catch blocks to handle exceptions that might occur during an asynchronous operation:

Async Function MyAsyncMethod() As Task Try Dim result As Integer = Await SomeAsyncOperation() ' Continue with code when SomeAsyncOperation completes. Catch ex As Exception ' Handle the exception End Try End Function

Running Async Methods

When calling an Async method, you can use the Await keyword to wait for its completion. For example, if you have an Async method called MyAsyncMethod, you can call it like this:

Await MyAsyncMethod()

This ensures that the code waits for MyAsyncMethod to finish before proceeding.

Top-Level Async

In newer versions of VB.NET (Visual Studio 2022 and later), you can use top-level asynchronous code. In this case, you don't need a method to be marked as Async. You can have asynchronous code directly in a VB.NET file.

Imports System.Threading.Tasks Async Sub Main() Dim result As Integer = Await SomeAsyncOperation() ' Continue with code when SomeAsyncOperation completes. End Sub

This simplifies entry points for asynchronous code.

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Imports System Imports System.Threading.Tasks Module Program Async Sub Main() Console.WriteLine("Start of Main") Dim result As Integer = Await SomeAsyncOperation() Console.WriteLine($"Result of SomeAsyncOperation: {result}") Console.WriteLine("End of Main") End Sub Async Function SomeAsyncOperation() As Task(Of Integer) Console.WriteLine("Start of SomeAsyncOperation") ' Simulate a time-consuming operation Await Task.Delay(2000) Console.WriteLine("End of SomeAsyncOperation") Return 42 End Function End Module

In this code, we have a top-level Async Sub Main() that represents the entry point of the application. Inside Main(), we use Await to call the SomeAsyncOperation(). The SomeAsyncOperation function simulates a time-consuming operation using Task.Delay and returns a result after a delay. The program will continue executing other code while waiting for SomeAsyncOperation to complete. When SomeAsyncOperation finishes, it will display the result.

Benefits of using async/await

There are several benefits to using async/await in VB.Net:

Improved performance: Async methods can run without blocking the current thread, which can improve the performance of your application.
Improved responsiveness: Async methods allow you to perform long-running operations without freezing the UI.
Simplified code: Async/await can make your code more readable and easier to maintain.

Conclusion

Async and Await in VB.NET enable asynchronous programming by allowing you to create methods that can perform time-consuming operations without blocking the main thread, ensuring improved application responsiveness. You mark methods as "Async" and use "Await" to call asynchronous operations, allowing the program to continue executing other code while awaiting the completion of the asynchronous task.

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