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c#asp.netasp.net-mvcasp.net-core
Colin Marks
Colin Marks

Reputation: 19

Confused on usage and meaning of 'context' in C#

I am a fresh intern who has just completed my first year of college. I took two intro to comp sci classes and have a fairly solid fundamental knowledge of Java but also basic OOP language ideas. I have never used C# before and my internship requires it. My task has been to start a MVC application that does some basic task but I am confused on the usage of 'context' in this situation. I am using Microsoft Virtual Studio with the ASP.NET MVC blank template. Here is where I find 'context' to be used. I am mainly confused on how or why it is being used in this method. 

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.Use

        app.Run(async (context) =>
        {
            await context.Response.WriteAsync("Hello World!");
        });
    }

Upvotes: 1

Views: 784

Answers (1)

Tim
Tim

Reputation: 6060

This code

app.Run(async (context) =>
    {
        await context.Response.WriteAsync("Hello World!");
    });

Tells ASP.NET Core to "Run" a middleware. Running a middleware means, given an HttpContext, read the request and write the result-- as opposed to "using" a middleware which means the middleware might execute or might defer execution to the next middeware in the chain. This is specific to ASP.NET Core, not C#.

The app.Run() method expects a delegate in the form of an async function that takes a single HttpContext parameter. The lamda expression (context)=> { } is shorthand for an anonymous function with a single parameter named context. The C# compiler recognizes the type of context based on the expected prototype. You might write that code like this:

app.Run(helloWorldHandler);
...

private async Task helloWorldHandler(HttpContext context) {
   await context.Response.WriteAsync("Hello World!");
}

Upvotes: 1

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