[SOLVED] Bevy system could not access system parameter ResMut<Events<event>>

Bevy system could not access system parameter ResMut<Events<event>>

I am trying to learn bevy but I run into a wierd dead end. When I try to insert a cuntom event into a system variables, the game crashes at start. I am perhaps missing some detail?

The code:

use bevy::prelude::*;
fn main() {
    let mut app = App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Update, dummy)
        .run();
}
#[derive(Event)]
struct Score;
fn dummy(
    mut events: EventWriter<Score>,
){}

cargo.toml:

[package]
name = "bevy_playground"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.15.3"

error:

dummy could not access system parameter ResMut<Events<Score>>

full output:

C:/Users/fanda/.cargo/bin/cargo.exe run --color=always --package bevy_playground --bin bevy_playground --profile dev
warning: unused variable: `app`
 --> src\main.rs:3:13
  |
3 |     let mut app = App::new()
  |             ^^^ help: if this is intentional, prefix it with an underscore: `_app`
  |
warning: variable does not need to be mutable
 --> src\main.rs:3:9
  |
3 |     let mut app = App::new()
  |         ----^^^
  |         |
  |         help: remove this `mut`
  |
  = note: `#[warn(unused_mut)]` on by default

warning: `bevy_playground` (bin "bevy_playground") generated 2 warnings (run `cargo fix --bin "bevy_playground"` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.27s
     Running `target\debug\bevy_playground.exe`
2025-03-05T16:31:03.441833Z  INFO bevy_diagnostic::system_information_diagnostics_plugin::internal: SystemInfo { os: "Windows 11 Home", kernel: "26100", cpu: "", core_count: "12", memory: "31.6 GiB" }
2025-03-05T16:31:03.643666Z  INFO bevy_render::renderer: AdapterInfo { name: "Qualcomm(R) Adreno(TM) X1-85 GPU", vendor: 20803, device: 909329200, device_type: Integrat
edGpu, driver: "Qualcomm Technologies Inc. Adreno Vulkan Driver", driver_info: "Driver Build: , , 1698055923\nDate: 10/23/2023\nCompiler Version: E031.47.15.00\nDriver Branch: \n", backend: Vulkan }
2025-03-05T16:31:04.249683Z  INFO bevy_winit::system: Creating new window "App" (0v1#4294967296)
thread 'main' panicked at C:\Users\fanda\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bevy_ecs-0.15.3\src\system\function_system.rs:216:28:
bevy_playground::dummy could not access system parameter ResMut<Events<Score>>
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!
error: process didn't exit successfully: `target\debug\bevy_playground.exe` (exit code: 101)

Process finished with exit code 101

Solution

Ok, so it turns out that I didn't add the event to the app:

.add_event::<Score>()

Note for devs: You should deffinitely add this to the event docs: https://docs.rs/bevy/latest/bevy/ecs/event/struct.EventWriter.html