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