Calling .NET Methods With and Without Async
Let's say that you have an asynchronous method -- a method that looks something like this one that returns a Customer
object wrapped inside a Task
object:
public async Task<Customer> GetCustomerById(string custId) {
You can call this method with or without the await
keyword. The syntax with the await
keyword looks like this:
Customer cust = await GetCustomerById("A123");
Using the await
keyword launches the method (and any code that follows it in the calling method) on a separate thread. When the method finishes running, the Customer
object is pulled from the Task
object and, in this case, stuffed into the cust
variable.
The syntax without the await
keyword looks like this:
Task<Customer> cust = GetCustomerById("A123");
With this syntax, you get back the Task
object that manages the GetCustomerById
method ... and that's it. You can now treat this cust
variable as you would any other object: pass it to other methods, return it from the method with this code, store it in a global variable, and so on. When you're ready to run the Task
in the cust
variable, you can do asynchronously by calling the cust
variable's Start
method.
This code will start the GetCustomerById
method running but go right on to the next line of code following the Start
method:
cust.Start();
Alternatively, you can retrieve the Customer
object returned by the method synchronously by reading the cust
variable's Result
property.
This code will cause processing to stop dead on this line of code until the GetCustomerById
method managed by the Task
object returns a Customer
object:
Customer custResult = cust.Result;
There's more that you can with a Task
object than just call the Start
method and read the Result
property (in fact, you'll probably use them together). But my point is that it's worth remembering that if you want the Task
object associated with your async method, you can have it.
Posted by Peter Vogel on 10/17/2019