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# Event Bus
A module to provide eventing capabilities using pub/sub.
## API
1. `new()` - create a new `EventBus`
### Structs:
**EventBus:**
1. `publish(name string, sender voidptr, args voidptr)` - publish an event with provided
Params & name
2. `clear_all()` - clear all subscribers
3. `has_subscriber(name string)` - check if a subscriber to an event exists
**Subscriber:**
1. `subscribe(name string, handler EventHandlerFn)` - subscribe to an event
2. `subscribe_once(name string, handler EventHandlerFn)` - subscribe only once to an event
3. `subscribe_method(name string, handler EventHandlerFn, receiver voidptr)` - subscribe to
an event and also set the `receiver` as a parameter.
Since it's not yet possible to send methods as parameters, this is a workaround.
4. `is_subscribed(name string)` - check if we are subscribed to an event
5. `unsubscribe(name string)` - unsubscribe from an event
**Event Handler Signature:**
The function given to `subscribe`, `subscribe_method` and `subscribe_once` must match this:
```v oksyntax
fn cb(receiver voidptr, args voidptr, sender voidptr) {
}
// Since V can map structs to voidptr, this also works
struct ClickEvent {
x int
y int
}
// Example case where publisher sends ClickEvent as args.
fn on_press(receiver voidptr, e &ClickEvent, sender voidptr) {
println(e.x)
// your code here...
}
```
## Usage
For **usage across modules**
[check the example](https://github.com/vlang/v/tree/master/examples/eventbus).
_Note: As a general rule, you will need to **subscribe before publishing**._
**main.v**
```v oksyntax
module main
import eventbus
// initialize it globally
const (
eb = eventbus.new()
)
fn main() {
// get a mutable reference to the subscriber
mut sub := eb.subscriber
// subscribe to the 'error' event
sub.subscribe('error', on_error)
// start the work
do_work()
}
// the event handler
fn on_error(receiver voidptr, e &Error, work &Work) {
println('error occured on ${work.hours}. Error: $e.message')
}
```
**work.v**
```v oksyntax
module main
import eventbus
const eb = eventbus.new()
struct Work {
hours int
}
struct AnError {
message string
}
fn do_work() {
work := Work{20}
// get a mutable Params instance & put some data into it
error := &AnError{'Error: no internet connection.'}
// publish the event
eb.publish('error', work, error)
}
```
### Notes:
1. Each `EventBus` instance has it's own registry (i.e. there is no global event registry
so you can't just subscribe to an event wherever you are.
2. Each `EventBus` has a `Subscriber` instance which will need to be either exposed or you can make
small public helper functions specific to your module like (`onPress`, `onError`) and etc.
3. The `eventbus` module has some helpers to ease getting/setting of Params
(since V doesn't support empty interfaces yet or reflection) so use them (see usage above).
**The rationale behind separating Subscriber & Publisher:**
This is mainly for security because if publisher & subscriber are both passed around,
a client can easily publish events acting as the server.
So a client should only be able to use the Subscriber methods.
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