C# Keywords Tutorial – Part 6: await

C# is a modern programming language that has gained widespread popularity among developers due to its simplicity, readability, and robustness. One of the features that makes C# stand out is its ability to handle asynchronous programming, which allows developers to write more efficient and responsive applications. The keyword “await” plays a crucial role in this process.

In this blog post, we will explore the “await” keyword in C# and demonstrate how it can be used in practical scenarios with code examples.

What is the “await” keyword in C#?

The “await” keyword is used to wait for a task to complete asynchronously in C#. When we mark a method with the “async” keyword, it returns a Task or Task<T> object, which represents an asynchronous operation. We can then use the “await” keyword to pause the execution of the method until the asynchronous operation completes.

Here is an example of how the “await” keyword can be used to pause the execution of a method:

async Task<string> GetDataAsync()
{
? ? // Perform an asynchronous operation
? ? await Task.Delay(1000);


? ? // Return a string value
? ? return "Data fetched successfully";
}        

In this example, the “GetDataAsync” method is marked as async and returns a Task<string> object. The method contains an asynchronous operation, which is simulated by calling the “Task.Delay” method with a delay of one second. The “await” keyword is used to pause the execution of the method until the delay completes. Once the delay completes, the method returns the string value “Data fetched successfully”.

Code Examples

Let’s explore some practical scenarios where the “await” keyword can be used in C#.

1. Reading a file asynchronously

In this example, we will read a file asynchronously and return its content as a string.

async Task<string> ReadFileAsync(string filePath)
{
? ? using (var reader = new StreamReader(filePath))
? ? {
? ? ? ? // Pause the execution of the method until the file is read
? ? ? ? return await reader.ReadToEndAsync();
? ? }
}        

In this code snippet, we are using the “StreamReader” class to read a file asynchronously. The “using” statement ensures that the “StreamReader” object is disposed of correctly after it is used. The “ReadToEndAsync” method reads the entire contents of the file and returns them as a string. We use the “await” keyword to pause the execution of the method until the file is read.

1. Making HTTP requests asynchronously

In this example, we will make an HTTP request asynchronously and return the response as a string.

async Task<string> MakeRequestAsync(string url)
{
? ? using (var client = new HttpClient())
? ? {
? ? ? ? // Pause the execution of the method until the HTTP request is completed
? ? ? ? var response = await client.GetAsync(url);


? ? ? ? // Read the content of the response asynchronously and return it as a string
? ? ? ? return await response.Content.ReadAsStringAsync();
? ? }
}        

In this code snippet, we are using the “HttpClient” class to make an HTTP request asynchronously. The “using” statement ensures that the “HttpClient” object is disposed of correctly after it is used. The “GetAsync” method sends an HTTP GET request to the specified URL and returns a “HttpResponseMessage” object. We use the “await” keyword to pause the execution of the method until the request is completed. Once the request is completed, we use the “ReadAsStringAsync” method to read the content of the response asynchronously and return it as a string.