generic-callbacks.md

description	This guide will show you how you can declare a generic callback thanks to Codeware's reflection.

Generic callbacks

Requirements

You need Codeware (Nexus | Wiki) to use the following classes. It provides a Reflection module which is exactly what we need to make our callback in a generic way.

How to

We will declare two classes: Callback to use with methods of a class, and StaticCallback to use with static methods of a class.

Callback

Declaration

public class Callback extends DelayCallback {
  private let m_target: wref<IScriptable>;
  private let m_fn: CName;
  private let m_data: array<Variant>;

  public static func Create(target: wref<IScriptable>,
                            fn: CName,
                            opt data: array<Variant>) -> ref<Callback> {
    let self = new Callback();
    self.m_target = target;
    self.m_fn = fn;
    self.m_data = data;
    return self;
  }

  public func Call() -> Variant {
    if !IsDefined(this.m_target) {
      return null;
    }

    return Reflection.GetClassOf(ToVariant(this.m_target))
                     .GetFunction(this.m_fn)
                     .Call(this.m_target, this.m_data);
  }

  public func Call(data: array<Variant>) -> Variant {
    if !IsDefined(this.m_target) {
      return null;
    }

    let args = this.m_data;
    for item in data {
      ArrayPush(args, item);
    }

    return Reflection.GetClassOf(ToVariant(this.m_target))
                     .GetFunction(this.m_fn)
                     .Call(this.m_target, args);
  }
}

We declare Callback which inherits DelayCallback. This way we can use Callback if we need it as-is, and we can also use it with DelaySystem.

We implement the method Call() which is expected by DelaySystem / DelayCallback. If we want to use it without DelaySystem, we simply need to call Call() when we want to execute a callback by ourself.

We return the result of the callback method as a Variant. User can convert the value by knowing the return type in advance, using FromVariant.

{% hint style="info" %} We declare an override of the Call method with an array of Variant. It allows to execute the callback and pass arguments in addition of the optional arguments defined when creating the callback (using Create). {% endhint %}

Example

public class MyService extends ScriptableService {

  // ...

  public cb func OnSessionReady(event: ref<GameSessionEvent>) {
    if event.IsPreGame() {
      return;
    }
    let delaySystem = GameInstance.GetDelaySystem(GetGameInstance());
    let callback = Callback.Create(this, n"OnPlay", [42]);
    let delay: Float = 1.0; // seconds

    delaySystem.DelayCallback(callback, delay, false);
    // callback.Call(["More"]);
  }

  // [cb] is required to make function a callback.
  // [arg] is an optional argument which can be passed when calling [Callback.Create].
  // [arg2] is an additional argument when executing Call yourself.
  private cb func OnPlay(arg: Int32 /*, arg2: String */) {
    FTLog(s"arg: \(arg)"); // print 42
    // do stuff after [delay] s.
    
    // FTLog(s"arg2: \(arg2)"); // print More
  }

}

StaticCallback

Declaration

public class StaticCallback extends DelayCallback {
  private let m_fn: CName;
  private let m_data: array<Variant>;

  public static func Create(fn: CName, opt data: array<Variant>) -> ref<StaticCallback> {
    let self = new StaticCallback();
    self.m_fn = fn;
    self.m_data = data;
    return self;
  }

  public func Call() -> Variant {
    return Reflection.GetGlobalFunction(this.m_fn)
                     .Call(this.m_data);
  }

  public func Call(data: array<Variant>) -> Variant {
    let args = this.m_data;
    for item in data {
      ArrayPush(args, item);
    }
    return Reflection.GetGlobalFunction(this.m_fn)
                     .Call(args);
  }
}

This looks like Callback, we still inherits DelayCallback to be compatible with DelaySystem. But this time we only need a function's name.

{% hint style="warning" %} Static methods of a class are registered as global functions. You'll need to use this syntax: n"ModuleName.ClassName::MethodName". Method must be declared with keyword cb. ModuleName is optional. {% endhint %}

Example

This shows how it looks like when declaring in a custom module MyModule. It is not mandatory and you can declare it in the global scope.

module MyModule

public class MyService extends ScriptableService {

  // ...

  public cb func OnSessionReady(event: ref<GameSessionEvent>) {
    if event.IsPreGame() {
      return;
    }
    let delaySystem = GameInstance.GetDelaySystem(GetGameInstance());
    let callback = StaticCallback.Create(n"MyModule.MyService::OnPlay", [n"Choom"]);
    let delay: Float = 1.0; // seconds

    delaySystem.DelayCallback(callback, delay, false);
    // callback.Call(["More"]);
  }

  // [cb] is required to make function a callback.
  // [name] is an optional argument which can be passed when calling [StaticCallback.Create].
  // [eg] is an additional argument when executing Call yourself.
  private static cb func OnPlay(name: CName /*, eg: String */) {
    FTLog(s"name: \(name)"); // print Choom
    // do stuff after [delay] s.

    //FTLog(s"e.g. \(eg)"); // print More
  }

}