Watching for File Changes in ASP .NET Core

This is the eighth of a new series of posts on ASP .NET Core. In this post, we’ll learn how to use the .NET CLI file watcher tool during development and debugging.

ASPNETCoreLogo-300x267

Before You Begin

Before you begin, take a look at the sample code project on GitHub:

AspNetCoreWatcher on GitHub: https://github.com/shahedc/AspNetCoreWatcher

Specifically, look at the history of CalcController to see how the Sum() method has been updated to accept doubles and not just ints, when summing up two numbers.

Github link: before the change
Github link: after the change

Debugging while Running

Initially, we have a Sum() method that looks like this:

 [Route("[action]")]
 public ActionResult<string> Sum(
    [FromQuery(Name = "num1")] int num1,
    [FromQuery(Name = "num2")] int num2)
 {
    var sum = (num1 + num2).ToString();
    return $"The sum of numbers {num1} and {num2} is {sum}.";
 }

We can run the web app from the command line using dotnet run:

> dotnet run

This allows us to access the Web API via a web browser to add 2 numbers, e.g. 3 and 4 for num1 and num2.

https://localhost:5001/api/calc/Sum?num1=3&num2=4

However, we get an error if we try to pass in numbers with decimal points, e.g. 3 and 4.4 for num1 and num2.

https://localhost:5001/api/calc/Sum?num1=3&num2=4.4

To fix the error, we can change the input parameters to expect doubles instead of ints.

 [Route("[action]")]
 public ActionResult<string> Sum(
 [FromQuery(Name = "num1")] double num1,
 [FromQuery(Name = "num2")] double num2)
 {
 var sum = (num1 + num2).ToString();
 return $"The sum of numbers {num1} and {num2} is {sum}.";
 }

If you try to refresh the browser, you should still get the same old error message. You would have to restart the app just to see the new changes. Don’t fret… there’s an easy way to get around this!