# Hello, World desktop app

Let's put together a simple "hello world" desktop application to get acquainted with Dioxus. 

In this chapter, we'll cover:

- Starting a new Dioxus project with Cargo
- Adding Dioxus as a dependency
- Launching our first component as the app root

### A new project with Cargo

First, let's start a new project. Rust has the concept of executables and libraries. Executables have a `main.rs` and libraries have `lib.rs`. A project may have both. Our `hello world` will be an executable - we expect our app to launch when we run it! Cargo provides this for us:

```shell
$ cargo new --bin hello-dioxus
```

Now, we can `cd` into our project and poke around:

```shell
$ cd hello-dioxus
$ tree
.
├── Cargo.toml
├── .git
├── .gitignore
└── src
    └── main.rs
```

We are greeted with a pre-initialized git repository, our code folder (`src`) and our project file (`Cargo.toml`).

Our `src` folder holds our code. Our `main.rs` file holds our `fn main` which will be executed when our app is ran.

```shell
$ more src/main.rs
```

```rust
fn main() {
    println!("Hello, world!");
}
```

Right now, whenever our app is launched, "Hello world" will be echoed to the terminal.

```shell
$ cargo run
   Compiling hello-dioxus v0.1.0
    Finished dev [unoptimized + debuginfo] target(s) in 0.41s
     Running `target/debug/hello-dioxus`
Hello, world!
```

Our `Cargo.toml` file holds our dependencies and project flags.

```shell
$ cat Cargo.toml
```

```toml
[package]
name = "hello-dioxus"
version = "0.1.0"
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

```

### Adding Dioxus as a dependency

To use the Dioxus library, we'll want to add the most recent version of `Dioxus` to our crate. If you have `cargo edit` installed, simply call:

```shell
$ cargo add dioxus --features desktop
```

It's very important to add `dioxus` with the `desktop` feature for this example. The `dioxus` crate is a batteries-include crate that combines a bunch of utility crates together, ensuring compatibility of the most important parts of the ecosystem. Under the hood, the `dioxus` crate configures various renderers, hooks, debug tooling, and more. The `desktop` feature ensures the we only depend on the smallest set of required crates to compile and render.

If you plan to develop extensions for the `Dioxus` ecosystem, please use the `dioxus` crate with the `core` feature to limit the amount of dependencies your project brings in.

### Our first app

Now, let's edit our `main.rs` file:

```rust
use dioxus::prelude::*;


fn main() {
    dioxus::desktop::launch(App);
}

fn App(cx: Scope) -> Element {
    cx.render(rsx! (
        div { "Hello, world!" }
    ))
}
```

At this point, you could call `cargo run` and be greeted with a simple `Hello, World!` screen:

![hello world](images/helloworld.png)

### Dissecting our example

The `use` statement at the top of our app imports everything from the the `prelude` module. `use`-ing the prelude imports the right traits, types, and macros needed for working with Dioxus.

```rust
use dioxus::prelude::*;
```

This initialization code launches a Tokio runtime on a helper thread where your code will run. Then, the WebView renderer will be launched on the main-thread. Due to platform requirements, the main thread is blocked by your app's event loop.

```rust
fn main() {
    dioxus::desktop::launch(App);
}
```

Finally, our app. Every component in Dioxus is a function that takes in `Context` and `Props` and returns an `Element`.

```rust
fn App(cx: Scope) -> Element {
    cx.render(rsx! {
        div { "Hello, world!" }
    })    
}
```

Writing `fn App(cx: Scope) -> Element {` might become tedious. Rust will also let you write functions as static closures, but these types of Components cannot have props that borrow data.

```rust
static App: Component<()> = |cx| cx.render(rsx!(div { "Hello, world!" }));
```

### What is this `Context` object?

Coming from React, the `Context` object might be confusing. In React, you'll want to store data between renders with hooks. However, hooks rely on global variables which make them difficult to integrate in multi-tenant systems like server-rendering. 

In Dioxus, you are given an explicit `Context` object to control how the component renders and stores data. The `Context` object provides a handful of useful APIs for features like suspense, rendering, and more.

## Moving on

Congrats! You've built your first desktop application with Dioxus. Next, we're going to learn about the basics of building interactive user interfaces.