I'd like to add an event handler in my C++ code.
I followed document in firebreath.org (Callback from Scripts):
FB::JSObjectPtr doc = m_host->getDOMDocument()->getJSObject();
doc->Invoke("addEventListener", FB::variant_list_of("load", FB::make_callback(this, &mine::foo)));
but seeing following error:
/home/dq/manager/mine.cpp: In member function ‘void mine::init()’:
/home/dq/manager/mine.cpp:284:119: error: no matching function for call to ‘variant_list_of(const char [5], FB::JSAPIPtr)’
/home/dq/manager/mine.cpp:284:119: note: candidates are:
/usr/include/firebreath/ScriptingCore/variant_list.h:122:5: note: FB::detail::VariantListInserter FB::variant_list_of(FB::variant)
/usr/include/firebreath/ScriptingCore/variant_list.h:122:5: note: candidate expects 1 argument, 2 provided
/usr/include/firebreath/ScriptingCore/variant_list.h:128:5: note: FB::VariantList FB::variant_list_of()
/usr/include/firebreath/ScriptingCore/variant_list.h:128:5: note: candidate expects 0 arguments, 2 provided
In file included from /home/deqing/manager/mine.h:51:0,
from /home/deqing/manager/mine.cpp:37:
/usr/include/firebreath/ScriptingCore/JSCallback.h: In function ‘FB::JSAPIPtr FB::make_callback(const T&, F, bool) [with T = mine*, F = void (mine::*)(), FB::JSAPIPtr = boost::shared_ptr<FB::JSAPI>]’:
/home/dq/manager/mine.cpp:284:118: instantiated from here
/usr/include/firebreath/ScriptingCore/JSCallback.h:47:107: error: request for member ‘get’ in ‘instance’, which is of non-class type ‘mine* const’
/usr/include/firebreath/ScriptingCore/JSCallback.h:49:97: error: request for member ‘get’ in ‘instance’, which is of non-class type ‘mine* const’
make[2]: *** [CMakeFiles/mine.dir/manager/mine.cpp.o] Error 1
make[1]: *** [CMakeFiles/mine.dir/all] Error 2
make: *** [all] Error 2
Looking into the implementation of make_callback(), I tried following instead:
FB::JSObjectPtr doc = m_host->getDOMDocument()->getJSObject();
doc->Invoke("addEventListener", FB::variant_list_of("load")(FB::JSAPIPtr(new FB::JSCallback(FB::make_method(this, &mine::foo)))));
Compile passed this time, but my function - mine::foo() is not called with document.load()
By using "Inspect Element" in chrome, in "Event Listeners" I can see a new listener is added for "load". However, the listenerBody is a <JSAPI-Auto Javascript Object>.
I'm afraid this is why mine::foo() is not called, Javascript don't know how to call it because it is not a function, only an object.
Any one know how to get this done?
Another way that I can think of is:
Register a custom event handler
Fire the custom event on init
I'd like to use something like:
registerEventMethod("myevent", &mine::foo);
so that when myevent is fired, mine::foo() can be called.
The question here is, mine::foo is not a JSObjectPtr, so this snippet of code wouldn't work.
What is the proper way to use registerEventMethod() in this case?
registerEventObject was really never intended to be called manually; it is used by the internal implementations of addEventListener and attachEvent. The purpose is to attach javascript handlers to events in the plugin.
I would recommend you use something like boost's signals and slots to implement your own c++-side event system; FireBreath's stuff was never intended to solve that problem. On the other hand, if you wanted to look at it it would probably be possible to extend FireBreath's functionality to support that and I have it on very good authority that the gatekeeper for FireBreath would probably entertain a pull request to that end. =]
Related
I want to pass to function object, const of type MouseEvent.CLICK and function to trigger. In my case:
my class Assistant:
public static function addEventListenerTo(obj:Object, MouseEventConst:String, functinToTrigger:Function) {
obj.addEventListener(MouseEventConst, functinToTrigger:Function);
}
and my class Engine which invokes
Assistant.addEventListenerTo(deck,"MouseEvent.CLICK",showObject);
Please give me advice how to make it work. Thanks.
In the code you provide there is one compiler error (the one Tahir Ahmed pointed to in his second comment).
Fixing this by removing the second :Function in the first code block:
public static function addEventListenerTo
(obj:Object, MouseEventConst:String, functinToTrigger:Function)
{
obj.addEventListener(MouseEventConst, functinToTrigger);
}
will let the code compile. (I wrapped the Method signature to avoid the scrollbar, this is not required to make it compile.)
The other major problem is a configuration error (or maybe a typo): the one about MouseEvent.CLICK. (the one Tahir Ahmed pointed to in his first comment)
Looking at the documentation it is defined to have the value "click" (a String literal following the AS3 convention of the lowercase constant name). So to pass it to your method you can either put in a reference to the constant by writing MouseEvent.CLICK (without the "s around it) or reach the same goal with passing its value by writing "click".
As using the reference will prevent mistyping because the compiler checks it, the first approach should be preferred.
So calling the Method should look like this:
Assistant.addEventListenerTo(deck, MouseEvent.CLICK, showObject);
If you want to know why your version didn't work you should read a simple introduction to AS3 Events and EventDispatchers. As a short hint: if deck would dispatch an Event that has its type property set to "MouseEvent.CLICK" your listener would get fired.
While you are at it, you could improve the quality of your code by to major things:
the first one is about avoiding getting runtime Errors and prefering compile time errors: Not every instance of type Object has a method called addEventListener. In your current code, when you pass an instance to Assistant.addEventListenerTo as first parameter, that doesn't have this method (e.g. {} or an instance of type Array), the error will get thrown while your swf is displayed and it might stop displaying anything and might show an error message to the user.
If the type of the parameter is IEventDispatcher instead, the compiler will already tell you that you passed an incompatible instance.
The second one is about names and conventions, which helps other developers to read your code (an having more fun helping you).
what you called MouseEventConst is called an event type in AS3, which provides a better name for a parameter, as it being a String nobody stops anybody from passing contants of other event types like Event
the functionToTrigger is what is called a listener (or event listener)
the first letter of parameter names should be lower case
So if I would have written the static method it would look like this:
import flash.events.*;
public class Assistent{
public static function addEventListenerTo
(dispatcher:IEventDispatcher, eventType:String, listener:Function)
{
dispatcher.addEventListener(eventType, listener);
}
}
I was testing Jakobs patch on the Sortables Class and this line this.reset() gave me a Uncaught TypeError: undefined is not a function.
I don't understand why since the Class has a method reset.
So my solution was to a var self = this; inside the same end: method (here), and called self.reset(); in the same line as I had this.reset(); before. Worked good. Why?
Then just to check (I suspected already) I did a console.log(this == self) and gave false.
Why does using self work but not this?
Fiddle
In javascript the this keyword change accordingly with the execution context
in global code this refer to the global object
inside eval the scope is the same as the calling context one, if no context provided then is the same as above
in all the case below if the this argument passed to .bind .call or .apply is not an object (or null) this will be the global object
when using a function which has been binded to a specific object using .bind then this refers to the this argument passed to bind, the function is now permabinded.
when running a function the context is provided from the caller, if before the function call operator () there is a dot(.) or a [] operator then this refers to the part on the left of such operator, unless the function is permabinded to something else or we are using .call or .apply if so this refers to the this argument unless the function was previously permabinded;
if before the function call operator () there neither the . nor the [] operators then this will refer to the global object (unless the function stores the result of the .bind function)
when running a constructor function (basically when using new) this refers to the object we are creating
now when using the use strict directive things changes a bit, mostly instead of the global object when the context is not given this will be null, but not in all the cases.
I rarely use "use strict" so I just suggest to try it by yourself when in need.
now, what happens when a function is cached inside a variable like this:
var cache = 'A.foo'
if that you lose the context in which the original function was stored, so in this case foo will not be anymore a property on the instance A and when you run it using
cache()
the context will be evaluated using the rules I wrote above in this case the this will refer to the global object.
The semantics of "this" in Javascript are not what is expected by OO programmers. The symbol "this" refers to the dynamic/runtime calling context, not the lexicographic context. For example, if you have an object A with "method" and then do B.method = A.method; B.method(); then the context is now B and that is what this will point to. The difference becomes very apparent in "handler" type situations where the calling context is usually the object with the handler installed.
Your solution using self is sound.
kentaromiura's answer is absolutely right.
That said, mootools provides function.bind() as a way to decide what this will refer inside of your function. this means that if you simply do this :
var destroy = function () {
`bind() [...]
this.reset();
}.bind(this);
it will work as you intended (that is, this will be the same inside of destroy() and outside).
Now, a lot of coders will balk at fiddling with the context, with good reason as it is very difficult to read and maintain. But here you have it and I think bind() is a very nifty trick of mootools.
I have just started a new version of my Crysis Wars Server Side Modification called InfinityX. For better management, I have put the functions inside tables as it looks neater and I can group functions together (like Core.PlayerHandle:GetIp(player)), but I have ran into a problem.
The problem is that the specified method to get the players' name, player:GetName() is being seen as an invalid method, when the method actually is completely valid.
I would like to know if using the below structure is causing a problem and if so, how to fix it. This is the first time I've used this structure for functions, but it is already proving easier than the old method I was using.
The Code:
Event =
{
PlayerConnect = function(player)
Msg.All:CenteredConsole("$4Event$8 (Connect)$9: $3"..player:GetName().." on channel "..player.actor:GetChannel());
System.LogAlways(Default.Tag.."Incoming Connect on Channel "..player.actor:GetChannel());
Event:Log("Connect", player);
end;
};
The below code works when I bypass the function and put the code directly where it's needed:
Msg.All:CenteredConsole("$4Event$8 (Connect)$9: $3"..player:GetName().." on channel "..player.actor:GetChannel());
System.LogAlways(Default.Tag.."Incoming Connect on Channel "..player.actor:GetChannel());
The Error:
[Warning] [Lua Error] infinityx/main/core.events.lua:23: attempt to call method 'GetName' (a nil value)
PlayerConnect, (infinityx/main/core.events.lua: 23)
ConnectScript, (infinityx/main/core.main.lua: 52)
OnClientEnteredGame, (scripts/gamerules/instantaction.lua: 511)
(null) (scripts/gamerules/teaminstantaction.lua: 520)
Any clarification would be appreciated.
Thanks :)
Well, as PlayerConnect is inside the table Event, and you are calling with a ":", add self as first arg in the function, like:
PlayerConnect = function(self, player)
Clearly, player in the first block of code is not the same as player in the second block of code. The problem must be that the caller of Event.PlayerConnect is not passing the same value.
To test that your Event.PlayerConnect function works, try this in the same place as your second block of code:
Event.PlayerConnect(player)
That should work as you expect.
So, the problem comes down to how Event.PlayerConnect is called without the second block of code. I'm not familiar with that game engine so I don't know how it is done. Perhaps reviewing the documentation and/or debugging that area would help. If you print(player) or call the equivalent log function in both cases, you should see they are different. If you can't run in a debugger, you can still get a stack trace with print(debug.traceback("Accessing player, who's value is: "..player)). If there is indeed some kind of table-based player object in both cases, you can try comparing their fields to see how they are different. You might need to write a simple dumping function to help with that.
I'm writing a simple Twitter client to play with coffeescript. I have an object literal with some functions that call each other via callbacks.
somebject =
foo: 'bar'
authenticateAndGetTweets: ->
console.log "Authorizing using oauth"
oauth = ChromeExOAuth.initBackgroundPage(this.oauthdetails)
oauth.authorize( this.afterLogin.call this )
afterLogin: ->
this.getTweets(this.pollinterval)
This code works perfectly. Edit: actually this.afterlogin should be sent as a callback above, not ran immediately, as Trevor noted below.
If, within authenticateAndGetTweets, I removed the 'call' and just ran:
oauth.authorize( this.afterLogin )
and don't use 'call', I get the following error:
Uncaught TypeError: Object [object DOMWindow] has no method 'getTweets
Which makes sense, since 'this' in afterLogin is bound to the thing that initiated the callback rather than 'someobject' my object literal.
I was wondering if there's some magic in Coffeescript I could be doing instead of 'call'. Initially I thought using the '=>' but the code will give the same error as above if '=>' is used.
So is there a way I can avoid using call? Or does coffeescript not obviate the need for it? What made '=>' not work how I expected it to?
Thanks. I'm really enjoying coffeescript so far and want to make sure I'm doing things 'the right way'.
As matyr points out in his comments, the line
oauth.authorize( this.afterLogin.call this )
doesn't cause this.afterLogin to be called as a callback by oauth.authorize; instead, it's equivalent to
oauth.authorize this.afterLogin()
Assuming that you want this.afterLogin to used as a callback by oauth.authorize, megakorre's answer gives a correct CoffeeScript idiom. An alternative approach supported by many modern JS environments, as matyr points out, would be to write
oauth.authorize( this.afterLogin.bind this )
There's no CoffeeScript shorthand for this, partly because Function::bind isn't supported by all major browsers. You could also use the bind function from a library like Underscore.js:
oauth.authorize( _.bind this.afterLogin, this )
Finally, if you were to define someobject as a class instead, you could use => to define afterLogin such that it's always bound to the instance, e.g.
class SomeClass
foo: 'bar'
authenticateAndGetTweets: ->
console.log "Authorizing using oauth"
oauth = ChromeExOAuth.initBackgroundPage(this.oauthdetails)
oauth.authorize(this.afterLogin)
afterLogin: =>
this.getTweets(this.pollinterval)
someobject = new SomeClass
you can put a lambda in the function call like so
auth.authorize(=> #afterLogin())
You have to use either the call or apply methods because they set the scope of the function (the value of this). The error results because the default scope is the window object.
I am working on some simple object-oriented code in MATLAB. I am trying to call one of my class methods with no input or output arguments in its definition.
Function definition:
function roll_dice
Function call:
obj.roll_dice;
When this is executed, MATLAB says:
??? Error using ==> roll_dice
Too many input arguments.
Error in ==> DiceSet>Diceset.Diceset at 11
obj.roll_dice;
(etc...)
Anyone have any ideas what could be causing it? Are there secret automatic arguments I'm unaware that I'm passing?
When you make the call:
obj.roll_dice;
It is actually equivalent to:
roll_dice(obj);
So obj is the "secret" automatic argument being passed to roll_dice. If you rewrite the method roll_dice to accept a single input argument (even if you don't use it), things should work correctly.
Alternatively, if you know for sure that your method roll_dice is not going to perform any operations on the class object, you can declare it to be a static method as Dan suggests.
For more information on object-oriented programming in MATLAB, here's a link to the online documentation.
I believe you can also get around this by declaring roll_dice to be a static method.