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Actually, the type of b is the problem:
override def buttonPressed(b: Button): Unit = action
or even
override def buttonPressed(b: Button) = action
instead of
override def buttonPressed(b: PushButton): Unit = action
is what you want.
Clint Gilbert wrote:
> This is getting off-topic, but it's something I actually know a tiny bit
> about.
>
> The compiler is complaining (I think) because you're not actually
> overriding buttonPressed. This can happen when type inference goes a
> little astray, especially with methods that return Unit. Naming
> buttonPressed's param 'b' shouldn't be a problem. I'd try explicitly
> specifying the return type, like
>
> def pressedDo (aB: PushButton, action: Unit) = {
> aB.getButtonPressListeners.add(new ButtonPressListener {
> override def buttonPressed(b: PushButton): Unit = action
> })
> }
>
> There are also inference rule that take effect regarding the = in
>
> def foo(...) = { }
>
> vs def foo(...) { }
>
> The latter (I believe) is assumed to return Unit, but I always add the =
> just to be sure. (/Programming Scala/ by Odersky, Venners, and Spoon
> explains things like this very, very well.)
>
> Additionally, you probably want something like this:
>
> def pressedDo (aB: PushButton, action: => Unit) = {
> aB.getButtonPressListeners.add(new ButtonPressListener {
> override def buttonPressed(b: PushButton) = action
> })
> }
>
> Note the new type of the 'action' param. It's now "a function that
> takes no params and returns Unit", instead of an actual value of type
> Unit. This is an easy way to have lazily-evaluated parameters.
>
> Due to some neat syntactic sugar for writing anonymous functions of this
> type, if you split the parameter list for pressedDo, like
>
> def pressedDo (aB: PushButton)(action: => Unit) = {
> aB.getButtonPressListeners.add(new ButtonPressListener {
> override def buttonPressed(b: PushButton) = action
> })
> }
>
> You could call it like:
>
> pressedDo(someButton) {
> val foo = new Foo
>
> someOtherThing.doStuff(foo)
>
> //etc
> }
>
> Here the stuff in the braces becomes an anonymous function that gets
> passed to pressedDo.
>
> It's also possible to use implicit conversions (the perhaps
> tastelessly-named "Pimp-My-Library" pattern[1]) to "add" the pressedDo
> method to the Button class. Well, kind of, not really to the Button
> class, but combined with the above technique, you could make a call like
>
> val someButton: Button = ...
>
> someButton pressed {
> val foo = new Foo
>
> someOtherThing.doStuff(foo)
> }
>
> which is starting to look smooth. Implicits can get pretty black-magic
> though, so use them with care and restraint if you do.
>
> [1]: http://scala.sygneca.com/patterns/pimp-my-library
>
> Bojan Vu ini wrote:
>> Hi All,
>
>> If you are using Scala for your code then you are obliged to write listeners
>> in the following way:
>
>
>> printButton.getButtonPressListeners.add(new ButtonPressListener {
>> override def buttonPressed(b: Button) {
>> print
>> }
>> })
>
>
>> I've tried to simplify this by defining the following method:
>
>> def pressedDo (aB: PushButton, action: Unit) = {
>> aB.getButtonPressListeners.add(new ButtonPressListener {
>> override def buttonPressed(b: PushButton) { action }})
>> }
>
>
>> and than invoking the method in this way (example)
>
>> pressedDo(printButton, print)
>
>
>> however, this results in a compiler error:
>
>
>> error: object creation impossible, since method buttonPressed in trait
>> ButtonPressListener of type (x$1: org.apache.pivot.wtk.Button)Unit is not
>> defined
>> aB.getButtonPressListeners.add(new ButtonPressListener {
>
>
>> I'm not a programming language specialist, and in addition a Scala novice,
>> but I'm puzzled why putting boilerplate code in a separate method is not
>> working??
>
>> Best regards,
>> Bojan
>
>
>> Dr. Bojan Vu ini
>> President, Ma-CAD<http://www.ma-cad.com/>
>> [email protected]<mailto:[email protected]>
>> IM: bvucinic (Skype)
>> http://fr.linkedin.com/in/bvucinic
>
>> Maintenance Concept Adjustment & Design 31, rue Chanzy
>> Paris, Ile de France 75011 France
>> Work: +33 (6) 14 15 36 70
>> Mobile: +33 (6) 14 15 36 70
>> Fax: +33 (1) 53 01 38 28
>> See who we know in common<http://www.linkedin.com/e/wwk/4839994/> Want
>> a signature like this?<http://www.linkedin.com/e/sig/4839994/>
>
>
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