Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Thanks ChrisK, You saved my day.
On Tuesday, October 23, 2012 3:23:21 PM UTC+2, ChrisK wrote:
There were a few problems here. My first example calls a zero args
function but is not formatted correctly.
If you call something like this:
th...@com.mine.PlayerImpl::callback();
It won't work. It needs the method signature and parameters separated (no
args signature doesn't imply no args last time I checked in GWT):
th...@com.mine.PlayerImpl::callback()();
Notice the additional set of brackets. Very briefly mentioned on
https://developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsJSNI
.
For the final code, I ended up passing this as a parameter from Java and
also wrapping the JS callback function so it ends up looking like this:
public PlayerImpl() {
initialiseCallbacks(this);
}
private native void initialiseCallbacks(PlayerImpl impl) /*-{
$wnd.js_callback = $entry(function() {
im...@com.mine.PlayerImpl::callback()();
});
}
I hope that helps.
On Monday, 22 October 2012 15:23:43 UTC+1, Kartik Kaipa wrote:
Hey
did you finally get this working.
I am doing the exact same thing
I pass in the instance of the object as a parameter in the function method
Could you post the working code that you have.
Would really apreciate it.
Thanks,
Kartik
On Tuesday, March 23, 2010 7:31:24 PM UTC+5:30, Olivier Monaco wrote:
ChrisK,
For instance method, you need to reference the method from the
instance like this.@ Here is my exact code that compile:
private native void installListener()
/*-{
var callback = $entry(this.
@net.antidot.gwtcommon.mvp.share.client.channel.HTML5MessageChannel::process(Lnet/
antidot/gwtcommon/mvp/share/client/channel/HTML5MessageEvent;));
$wnd.addEventListener(message, (function(callback, channel) {
return function(event) {
callback.call(channel, event);
};
})(callback, this), false);;
}-*/;
Sorry, I forgot that...
Olivier
On 23 mar, 13:58, ChrisK cknow...@gmail.com wrote:
Actually, Olivier's methods work in development mode but don't seem to
compile with this error:
Cannot make an unqualified reference to the instance method callback
I've tried the pre-assignment of this to var that and also an
argument to the JSNI method passing in my instance. I've tried both of
these with Olivier's first method as well as the second to avoid
leaks. All with the same result - working in development mode but not
when I compile.
It looks to me as though the compiler doesn't understand the call
method or the closure correctly. It looks at though it's trying to
parse the @mypackage.MyClass::MyMethod() and seeing it's an instance
method so failed (instead of looking at subsequent JavaScript). Of
course I could quite easily be doing something wrong.
Thomas - your method compiles fine so I guess I'll use that for now.
On Mar 23, 10:07 am, ChrisK cknow...@gmail.com wrote:
Ahhh ok. Sorry for the simple questions but I'm just getting my head
around all this. I also have some other methods with arguments and
have those working thanks to both of you.
On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote:
ChrisK,
On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote:
Thomas - your solution worked from 6 worked but at first I didn't
include both pairs of brackets after the function call
MyMethod but
it turns out they are required. With only one set (i.e. no
arguments),
it just doesn't work. I thought that was legal but maybe not.
Remember that @mypackage.MyClass::MyMethod() is a reference to
the
function, not a call. The parenthesis allow you to give the full
signature of the method. Java allows two methods to have the same
name
but different parameters. GWT needs the full signature to find
which
method you want to reference, even is there is only one method with
this name.
The second parenthesis are to call the method. If you forgot then,
you
just obtain the function object and do nothing with it...
Olivier
a\@a
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Thanks ChrisK,, You've done a smart job.. It is working.
On Tuesday, October 23, 2012 6:53:21 PM UTC+5:30, ChrisK wrote:
There were a few problems here. My first example calls a zero args
function but is not formatted correctly.
If you call something like this:
th...@com.mine.PlayerImpl::callback();
It won't work. It needs the method signature and parameters separated (no
args signature doesn't imply no args last time I checked in GWT):
th...@com.mine.PlayerImpl::callback()();
Notice the additional set of brackets. Very briefly mentioned on
https://developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsJSNI
.
For the final code, I ended up passing this as a parameter from Java and
also wrapping the JS callback function so it ends up looking like this:
public PlayerImpl() {
initialiseCallbacks(this);
}
private native void initialiseCallbacks(PlayerImpl impl) /*-{
$wnd.js_callback = $entry(function() {
im...@com.mine.PlayerImpl::callback()();
});
}
I hope that helps.
On Monday, 22 October 2012 15:23:43 UTC+1, Kartik Kaipa wrote:
Hey
did you finally get this working.
I am doing the exact same thing
I pass in the instance of the object as a parameter in the function method
Could you post the working code that you have.
Would really apreciate it.
Thanks,
Kartik
On Tuesday, March 23, 2010 7:31:24 PM UTC+5:30, Olivier Monaco wrote:
ChrisK,
For instance method, you need to reference the method from the
instance like this.@ Here is my exact code that compile:
private native void installListener()
/*-{
var callback = $entry(this.
@net.antidot.gwtcommon.mvp.share.client.channel.HTML5MessageChannel::process(Lnet/
antidot/gwtcommon/mvp/share/client/channel/HTML5MessageEvent;));
$wnd.addEventListener(message, (function(callback, channel) {
return function(event) {
callback.call(channel, event);
};
})(callback, this), false);;
}-*/;
Sorry, I forgot that...
Olivier
On 23 mar, 13:58, ChrisK cknow...@gmail.com wrote:
Actually, Olivier's methods work in development mode but don't seem to
compile with this error:
Cannot make an unqualified reference to the instance method callback
I've tried the pre-assignment of this to var that and also an
argument to the JSNI method passing in my instance. I've tried both of
these with Olivier's first method as well as the second to avoid
leaks. All with the same result - working in development mode but not
when I compile.
It looks to me as though the compiler doesn't understand the call
method or the closure correctly. It looks at though it's trying to
parse the @mypackage.MyClass::MyMethod() and seeing it's an instance
method so failed (instead of looking at subsequent JavaScript). Of
course I could quite easily be doing something wrong.
Thomas - your method compiles fine so I guess I'll use that for now.
On Mar 23, 10:07 am, ChrisK cknow...@gmail.com wrote:
Ahhh ok. Sorry for the simple questions but I'm just getting my head
around all this. I also have some other methods with arguments and
have those working thanks to both of you.
On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote:
ChrisK,
On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote:
Thomas - your solution worked from 6 worked but at first I didn't
include both pairs of brackets after the function call
MyMethod but
it turns out they are required. With only one set (i.e. no
arguments),
it just doesn't work. I thought that was legal but maybe not.
Remember that @mypackage.MyClass::MyMethod() is a reference to
the
function, not a call. The parenthesis allow you to give the full
signature of the method. Java allows two methods to have the same
name
but different parameters. GWT needs the full signature to find
which
method you want to reference, even is there is only one method with
this name.
The second parenthesis are to call the method. If you forgot then,
you
just obtain the function object and do nothing with it...
Olivier
a\@a
--
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
There were a few problems here. My first example calls a zero args function
but is not formatted correctly.
If you call something like this:
th...@com.mine.PlayerImpl::callback();
It won't work. It needs the method signature and parameters separated (no
args signature doesn't imply no args last time I checked in GWT):
th...@com.mine.PlayerImpl::callback()();
Notice the additional set of brackets. Very briefly mentioned on
https://developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsJSNI.
For the final code, I ended up passing this as a parameter from Java and
also wrapping the JS callback function so it ends up looking like this:
public PlayerImpl() {
initialiseCallbacks(this);
}
private native void initialiseCallbacks(PlayerImpl impl) /*-{
$wnd.js_callback = $entry(function() {
im...@com.mine.PlayerImpl::callback()();
});
}
I hope that helps.
On Monday, 22 October 2012 15:23:43 UTC+1, Kartik Kaipa wrote:
Hey
did you finally get this working.
I am doing the exact same thing
I pass in the instance of the object as a parameter in the function method
Could you post the working code that you have.
Would really apreciate it.
Thanks,
Kartik
On Tuesday, March 23, 2010 7:31:24 PM UTC+5:30, Olivier Monaco wrote:
ChrisK,
For instance method, you need to reference the method from the
instance like this.@ Here is my exact code that compile:
private native void installListener()
/*-{
var callback = $entry(this.
@net.antidot.gwtcommon.mvp.share.client.channel.HTML5MessageChannel::process(Lnet/
antidot/gwtcommon/mvp/share/client/channel/HTML5MessageEvent;));
$wnd.addEventListener(message, (function(callback, channel) {
return function(event) {
callback.call(channel, event);
};
})(callback, this), false);;
}-*/;
Sorry, I forgot that...
Olivier
On 23 mar, 13:58, ChrisK cknow...@gmail.com wrote:
Actually, Olivier's methods work in development mode but don't seem to
compile with this error:
Cannot make an unqualified reference to the instance method callback
I've tried the pre-assignment of this to var that and also an
argument to the JSNI method passing in my instance. I've tried both of
these with Olivier's first method as well as the second to avoid
leaks. All with the same result - working in development mode but not
when I compile.
It looks to me as though the compiler doesn't understand the call
method or the closure correctly. It looks at though it's trying to
parse the @mypackage.MyClass::MyMethod() and seeing it's an instance
method so failed (instead of looking at subsequent JavaScript). Of
course I could quite easily be doing something wrong.
Thomas - your method compiles fine so I guess I'll use that for now.
On Mar 23, 10:07 am, ChrisK cknow...@gmail.com wrote:
Ahhh ok. Sorry for the simple questions but I'm just getting my head
around all this. I also have some other methods with arguments and
have those working thanks to both of you.
On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote:
ChrisK,
On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote:
Thomas - your solution worked from 6 worked but at first I didn't
include both pairs of brackets after the function call MyMethod
but
it turns out they are required. With only one set (i.e. no
arguments),
it just doesn't work. I thought that was legal but maybe not.
Remember that @mypackage.MyClass::MyMethod() is a reference to the
function, not a call. The parenthesis allow you to give the full
signature of the method. Java allows two methods to have the same
name
but different parameters. GWT needs the full signature to find
which
method you want to reference, even is there is only one method with
this name.
The second parenthesis are to call the method. If you forgot then,
you
just obtain the function object and do nothing with it...
Olivier
a\@a
--
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Hey
did you finally get this working.
I am doing the exact same thing
I pass in the instance of the object as a parameter in the function method
Could you post the working code that you have.
Would really apreciate it.
Thanks,
Kartik
On Tuesday, March 23, 2010 7:31:24 PM UTC+5:30, Olivier Monaco wrote:
ChrisK,
For instance method, you need to reference the method from the
instance like this.@ Here is my exact code that compile:
private native void installListener()
/*-{
var callback = $entry(this.
@net.antidot.gwtcommon.mvp.share.client.channel.HTML5MessageChannel::process(Lnet/
antidot/gwtcommon/mvp/share/client/channel/HTML5MessageEvent;));
$wnd.addEventListener(message, (function(callback, channel) {
return function(event) {
callback.call(channel, event);
};
})(callback, this), false);;
}-*/;
Sorry, I forgot that...
Olivier
On 23 mar, 13:58, ChrisK cknow...@gmail.com wrote:
Actually, Olivier's methods work in development mode but don't seem to
compile with this error:
Cannot make an unqualified reference to the instance method callback
I've tried the pre-assignment of this to var that and also an
argument to the JSNI method passing in my instance. I've tried both of
these with Olivier's first method as well as the second to avoid
leaks. All with the same result - working in development mode but not
when I compile.
It looks to me as though the compiler doesn't understand the call
method or the closure correctly. It looks at though it's trying to
parse the @mypackage.MyClass::MyMethod() and seeing it's an instance
method so failed (instead of looking at subsequent JavaScript). Of
course I could quite easily be doing something wrong.
Thomas - your method compiles fine so I guess I'll use that for now.
On Mar 23, 10:07 am, ChrisK cknow...@gmail.com wrote:
Ahhh ok. Sorry for the simple questions but I'm just getting my head
around all this. I also have some other methods with arguments and
have those working thanks to both of you.
On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote:
ChrisK,
On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote:
Thomas - your solution worked from 6 worked but at first I didn't
include both pairs of brackets after the function call MyMethod
but
it turns out they are required. With only one set (i.e. no
arguments),
it just doesn't work. I thought that was legal but maybe not.
Remember that @mypackage.MyClass::MyMethod() is a reference to the
function, not a call. The parenthesis allow you to give the full
signature of the method. Java allows two methods to have the same
name
but different parameters. GWT needs the full signature to find
which
method you want to reference, even is there is only one method with
this name.
The second parenthesis are to call the method. If you forgot then,
you
just obtain the function object and do nothing with it...
Olivier
a\@a
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Hi Thomas,
The problem with memory leaks in browser is that it's sometimes hard
to understand where they come from. Here, we are writting a little
piece of code that will be transformed (replacement of @...()) and
incorporated into a more complexe code. I don't want to look at the
generated code to check if leaks are possibile. So, I always use the
syntax I give so that I'm sure there will not be any leak... It's some
type of discipline.
Using a static method to inject the code seems to me being the same
thing...
Olivier
On 23 mar, 00:07, Thomas Broyer t.bro...@gmail.com wrote:
On 22 mar, 23:42, Olivier Monaco olivier.mon...@free.fr wrote:
The call method of a JavaScript function allows you to call it with
a differente this. Then, using $wnd.js_callback.call(otherObject),
the this variable reference otherObject. So the glue is:
var that = this;
$wnd.js_callback = function() {
$entry(@mypackage.MyClass::MyMethod()).call(that);
}
When js_callback will be called, MyMethod is called on that, the
JavaScript object representing the MyClass instance. Finally, to avoid
memory leaks of closure:
$wnd.js_callback = (function(obj) {
return function() {
$entry(@mypackage.MyClass::MyMethod()).call(obj);
};
})(this);
... or more simply:
var that = this;
$wnd.js_callback = $entry(function() { that.
@mypackage.MyClass::MyMethod()(); });
(this is what I should have written previously, sorry for the buggy
code)
As for the leak, are you sure there really is one once the code is
translated into JS? would it be better if the inject method were a
static one with the instance being passed as an argument (no use of
the thiskeyword within JSNI)?
--
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Hi, thanks for the answers again!
Ok, I have some working code now! I think my issues were a combined
not understand this became the $wnd object when written how I had
it, plus not understanding what $entry actually does. Having said that
the docs on $entry could be better than the few sentences given.
Incidentally, I had some similar code where I had tried wrapping in
function() { } but hadn't gotten that working.
Olivier - your solutions worked first time for me.
Thomas - your solution worked from 6 worked but at first I didn't
include both pairs of brackets after the function call MyMethod but
it turns out they are required. With only one set (i.e. no arguments),
it just doesn't work. I thought that was legal but maybe not.
Now I just have to decide which method is best. I think I prefer
passing in the instance as a parameter of the inject method - I just
prefer the argument to be strongly typed on the Java side (being
primarily a Java developer). Olivier's code to work against memory
leaks also seems sensible to me. I have a static method which does
both of these now and works fine and think I understand the area a lot
better thanks to you two. It does seem like a lot to write just to get
a callback though! Maybe some decent examples like this would be
useful in the GWT documentation pages?
On Mar 23, 8:30 am, Olivier Monaco olivier.mon...@free.fr wrote:
Hi Thomas,
The problem with memory leaks in browser is that it's sometimes hard
to understand where they come from. Here, we are writting a little
piece of code that will be transformed (replacement of @...()) and
incorporated into a more complexe code. I don't want to look at the
generated code to check if leaks are possibile. So, I always use the
syntax I give so that I'm sure there will not be any leak... It's some
type of discipline.
Using a static method to inject the code seems to me being the same
thing...
Olivier
On 23 mar, 00:07, Thomas Broyer t.bro...@gmail.com wrote:
On 22 mar, 23:42, Olivier Monaco olivier.mon...@free.fr wrote:
The call method of a JavaScript function allows you to call it with
a differente this. Then, using $wnd.js_callback.call(otherObject),
the this variable reference otherObject. So the glue is:
var that = this;
$wnd.js_callback = function() {
$entry(@mypackage.MyClass::MyMethod()).call(that);
}
When js_callback will be called, MyMethod is called on that, the
JavaScript object representing the MyClass instance. Finally, to avoid
memory leaks of closure:
$wnd.js_callback = (function(obj) {
return function() {
$entry(@mypackage.MyClass::MyMethod()).call(obj);
};
})(this);
... or more simply:
var that = this;
$wnd.js_callback = $entry(function() { that.
@mypackage.MyClass::MyMethod()(); });
(this is what I should have written previously, sorry for the buggy
code)
As for the leak, are you sure there really is one once the code is
translated into JS? would it be better if the inject method were a
static one with the instance being passed as an argument (no use of
the thiskeyword within JSNI)?
--
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
ChrisK, On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote: Thomas - your solution worked from 6 worked but at first I didn't include both pairs of brackets after the function call MyMethod but it turns out they are required. With only one set (i.e. no arguments), it just doesn't work. I thought that was legal but maybe not. Remember that @mypackage.MyClass::MyMethod() is a reference to the function, not a call. The parenthesis allow you to give the full signature of the method. Java allows two methods to have the same name but different parameters. GWT needs the full signature to find which method you want to reference, even is there is only one method with this name. The second parenthesis are to call the method. If you forgot then, you just obtain the function object and do nothing with it... Olivier -- You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.
Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Ahhh ok. Sorry for the simple questions but I'm just getting my head around all this. I also have some other methods with arguments and have those working thanks to both of you. On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote: ChrisK, On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote: Thomas - your solution worked from 6 worked but at first I didn't include both pairs of brackets after the function call MyMethod but it turns out they are required. With only one set (i.e. no arguments), it just doesn't work. I thought that was legal but maybe not. Remember that @mypackage.MyClass::MyMethod() is a reference to the function, not a call. The parenthesis allow you to give the full signature of the method. Java allows two methods to have the same name but different parameters. GWT needs the full signature to find which method you want to reference, even is there is only one method with this name. The second parenthesis are to call the method. If you forgot then, you just obtain the function object and do nothing with it... Olivier -- You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.
Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Actually, Olivier's methods work in development mode but don't seem to compile with this error: Cannot make an unqualified reference to the instance method callback I've tried the pre-assignment of this to var that and also an argument to the JSNI method passing in my instance. I've tried both of these with Olivier's first method as well as the second to avoid leaks. All with the same result - working in development mode but not when I compile. It looks to me as though the compiler doesn't understand the call method or the closure correctly. It looks at though it's trying to parse the @mypackage.MyClass::MyMethod() and seeing it's an instance method so failed (instead of looking at subsequent JavaScript). Of course I could quite easily be doing something wrong. Thomas - your method compiles fine so I guess I'll use that for now. On Mar 23, 10:07 am, ChrisK cknow...@gmail.com wrote: Ahhh ok. Sorry for the simple questions but I'm just getting my head around all this. I also have some other methods with arguments and have those working thanks to both of you. On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote: ChrisK, On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote: Thomas - your solution worked from 6 worked but at first I didn't include both pairs of brackets after the function call MyMethod but it turns out they are required. With only one set (i.e. no arguments), it just doesn't work. I thought that was legal but maybe not. Remember that @mypackage.MyClass::MyMethod() is a reference to the function, not a call. The parenthesis allow you to give the full signature of the method. Java allows two methods to have the same name but different parameters. GWT needs the full signature to find which method you want to reference, even is there is only one method with this name. The second parenthesis are to call the method. If you forgot then, you just obtain the function object and do nothing with it... Olivier -- You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.
Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
ChrisK,
For instance method, you need to reference the method from the
instance like th...@ Here is my exact code that compile:
private native void installListener()
/*-{
var callback = $entry(this.
@net.antidot.gwtcommon.mvp.share.client.channel.HTML5MessageChannel::process(Lnet/
antidot/gwtcommon/mvp/share/client/channel/HTML5MessageEvent;));
$wnd.addEventListener(message, (function(callback, channel) {
return function(event) {
callback.call(channel, event);
};
})(callback, this), false);;
}-*/;
Sorry, I forgot that...
Olivier
On 23 mar, 13:58, ChrisK cknow...@gmail.com wrote:
Actually, Olivier's methods work in development mode but don't seem to
compile with this error:
Cannot make an unqualified reference to the instance method callback
I've tried the pre-assignment of this to var that and also an
argument to the JSNI method passing in my instance. I've tried both of
these with Olivier's first method as well as the second to avoid
leaks. All with the same result - working in development mode but not
when I compile.
It looks to me as though the compiler doesn't understand the call
method or the closure correctly. It looks at though it's trying to
parse the @mypackage.MyClass::MyMethod() and seeing it's an instance
method so failed (instead of looking at subsequent JavaScript). Of
course I could quite easily be doing something wrong.
Thomas - your method compiles fine so I guess I'll use that for now.
On Mar 23, 10:07 am, ChrisK cknow...@gmail.com wrote:
Ahhh ok. Sorry for the simple questions but I'm just getting my head
around all this. I also have some other methods with arguments and
have those working thanks to both of you.
On Mar 23, 9:56 am, Olivier Monaco olivier.mon...@free.fr wrote:
ChrisK,
On 23 mar, 10:32, ChrisK cknow...@gmail.com wrote:
Thomas - your solution worked from 6 worked but at first I didn't
include both pairs of brackets after the function call MyMethod but
it turns out they are required. With only one set (i.e. no arguments),
it just doesn't work. I thought that was legal but maybe not.
Remember that @mypackage.MyClass::MyMethod() is a reference to the
function, not a call. The parenthesis allow you to give the full
signature of the method. Java allows two methods to have the same name
but different parameters. GWT needs the full signature to find which
method you want to reference, even is there is only one method with
this name.
The second parenthesis are to call the method. If you forgot then, you
just obtain the function object and do nothing with it...
Olivier
a...@a
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
My above code got a little mangled along the way, the $entry part has (this, followed by a full stop, followed by @com.mine.PlayerImpl::callback()); -- You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.
Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
On Mar 22, 4:23 pm, ChrisK cknow...@gmail.com wrote: My above code got a little mangled along the way, the $entry part has (this, followed by a full stop, followed by @com.mine.PlayerImpl::callback()); And that's the problem: this is a special keyword and will evaluate to the this context of the calling plain JS code, whereas you'd want it to be some PlayerImpl instance. There are several ways to fix this: // evaluates this right now var that = this; // then uses that $wnd.js_callback = $entry(t...@com.mine.playerimpl::callback()); or pass the instance as an argument to the method and then use its name. But there's another bug in your code: there's no this in a static method! -- You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.
Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Thanks for the reply!
I'm not sure I understand why this evaluates to the plain JS
context. I was going off the documentation here which seems to suggest
you can use this in this way:
http://code.google.com/webtoolkit/doc/latest/DevGuideCodingBasicsJSNI.html#methods-fields
Or perhaps you just can't use it for $entry type JSNI?
Having said that, I've updated to a non-static method - silly me. I
did actually try that first but only pasted in my last attempt at
getting some working code. I have tried both of the below now with the
same stack trace as a result. Note, there are not actually any spaces
before the .@ in my code I'm just working around Google Groups
mangling it.
private native void initialiseCallbacks() /*-{
var that = this;
$wnd.js_callback =
$entry(that @com.mine.playerimpl::callback());
}-*/;
and
private native void initialiseCallbacks(PlayerImpl pl) /*-{
$wnd.js_callback = $entry(pl @com.mine.playerimpl::callback());
}-*/;
On Mar 22, 5:17 pm, Thomas Broyer t.bro...@gmail.com wrote:
On Mar 22, 4:23 pm, ChrisK cknow...@gmail.com wrote:
My above code got a little mangled along the way, the $entry part has
(this, followed by a full stop, followed by
@com.mine.PlayerImpl::callback());
And that's the problem: this is a special keyword and will evaluate
to the this context of the calling plain JS code, whereas you'd
want it to be some PlayerImpl instance.
There are several ways to fix this:
// evaluates this right now
var that = this;
// then uses that
$wnd.js_callback = $entry(t...@com.mine.playerimpl::callback());
or pass the instance as an argument to the method and then use its
name.
But there's another bug in your code: there's no this in a static
method!
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
Hi ChrisK,
You need to understand how JavaScript works.
Like in many languages, the this keyword means the current object.
The JavaScript language allows you to manipulate code as a function.
This function can be affected to any variable or object member, like:
$wnd.js_callback = function() { ... }
Then, you can call your code like this:
$wnd.js_callback()
In the function body, the this variable is $wnd. If you assign the
same function to the member of another object, the this variable
will be equal to the new object.
From JSNI, @mypackage.MyClass::MyMethod() references the JavaScript
function corresponding to the MyMethod method of mypackage.MyClass.
This method can be static or not, the reference is the same (no need
of this before @... just to obtain the JavaScript function).
Calling $entry just add a function wrapper around it but it stay a
function. When you assign this function to $wnd.js_callback, the
this variable inside of the function will be $wnd. If MyMethod is
static, it's okay. If MyMethod is not static, GWT will probably cast
the $wnd to a MyClass... it's bad...
The call method of a JavaScript function allows you to call it with
a differente this. Then, using $wnd.js_callback.call(otherObject),
the this variable reference otherObject. So the glue is:
var that = this;
$wnd.js_callback = function() {
$entry(@mypackage.MyClass::MyMethod()).call(that);
}
When js_callback will be called, MyMethod is called on that, the
JavaScript object representing the MyClass instance. Finally, to avoid
memory leaks of closure:
$wnd.js_callback = (function(obj) {
return function() {
$entry(@mypackage.MyClass::MyMethod()).call(obj);
};
})(this);
And remember, for static methods it's just:
$wnd.js_callback = $entry(...);
Good luck,
Olivier
On 22 mar, 20:16, ChrisK cknow...@gmail.com wrote:
Thanks for the reply!
I'm not sure I understand why this evaluates to the plain JS
context. I was going off the documentation here which seems to suggest
you can use this in this
way:http://code.google.com/webtoolkit/doc/latest/DevGuideCodingBasicsJSNI...
Or perhaps you just can't use it for $entry type JSNI?
Having said that, I've updated to a non-static method - silly me. I
did actually try that first but only pasted in my last attempt at
getting some working code. I have tried both of the below now with the
same stack trace as a result. Note, there are not actually any spaces
before the .@ in my code I'm just working around Google Groups
mangling it.
private native void initialiseCallbacks() /*-{
var that = this;
$wnd.js_callback =
$entry(that @com.mine.playerimpl::callback());
}-*/;
and
private native void initialiseCallbacks(PlayerImpl pl) /*-{
$wnd.js_callback = $entry(pl @com.mine.playerimpl::callback());
}-*/;
On Mar 22, 5:17 pm, Thomas Broyer t.bro...@gmail.com wrote:
On Mar 22, 4:23 pm, ChrisK cknow...@gmail.com wrote:
My above code got a little mangled along the way, the $entry part has
(this, followed by a full stop, followed by
@com.mine.PlayerImpl::callback());
And that's the problem: this is a special keyword and will evaluate
to the this context of the calling plain JS code, whereas you'd
want it to be some PlayerImpl instance.
There are several ways to fix this:
// evaluates this right now
var that = this;
// then uses that
$wnd.js_callback = $entry(t...@com.mine.playerimpl::callback());
or pass the instance as an argument to the method and then use its
name.
But there's another bug in your code: there's no this in a static
method!
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Re: JavaScriptException during JSNI call: Invoking an instance method on a null instance
On 22 mar, 23:42, Olivier Monaco olivier.mon...@free.fr wrote:
The call method of a JavaScript function allows you to call it with
a differente this. Then, using $wnd.js_callback.call(otherObject),
the this variable reference otherObject. So the glue is:
var that = this;
$wnd.js_callback = function() {
$entry(@mypackage.MyClass::MyMethod()).call(that);
}
When js_callback will be called, MyMethod is called on that, the
JavaScript object representing the MyClass instance. Finally, to avoid
memory leaks of closure:
$wnd.js_callback = (function(obj) {
return function() {
$entry(@mypackage.MyClass::MyMethod()).call(obj);
};
})(this);
... or more simply:
var that = this;
$wnd.js_callback = $entry(function() { that.
@mypackage.MyClass::MyMethod()(); });
(this is what I should have written previously, sorry for the buggy
code)
As for the leak, are you sure there really is one once the code is
translated into JS? would it be better if the inject method were a
static one with the instance being passed as an argument (no use of
the thiskeyword within JSNI)?
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