Package eu.webtoolkit.jwt

Class JSignal2<A1,A2>

java.lang.Object
eu.webtoolkit.jwt.AbstractSignal
eu.webtoolkit.jwt.AbstractEventSignal
eu.webtoolkit.jwt.AbstractJSignal
eu.webtoolkit.jwt.JSignal2<A1,A2>
public abstract class JSignal2<A1,A2> extends AbstractJSignal
A signal to relay JavaScript to Java calls, passing 2 arguments.

The signal is identified by a unique name within the scope of a WObject, or a unique global name (when declaring the signal in your WApplication).

The argument types A1 and A2 must be a String, WString, or a wrapper class of one of the Java primitive types. Values of the corresponding JavaScript types can be passed to the JavaScript call.

Note that this is an abstract class. To create a JSignal, you should specialize this class, but you do not need to specialize any method. The reason for this is to circumvent limitations in Java to obtain introspection in the types of the arguments, and provide suitable marshaling of data from JavaScript to Java. The easiest way to instantiate an object of this class is: 

   JSignal2<String, Integer> pingSignal = new JSignal2<String, Integer>(this, "pingSignal") { };

Example code: 

 class MyWidget extends WCompositeWidget
 {
     public MyWidget() {
         doSome = new JSignal2<String, Integer>(this, "doSome") { };
          ...
     }

     JSignal<String, Integer> doSome() { return doSome; }

     private JSignal2<String, Integer> doSome;
 }

The following JavaScript statement will emit the signal for a DOM element element that corresponds to a widget of class MyWidget: 

  Wt.emit(element, 'dosome', 'foo', 42);

The element can be a DOM element, or the object ID of a WObject, or the constant 'Wt' which is an alias for WApplication's id.

You can use the methods createCall(String arg1, String arg2) to let the signal itself generate this JavaScript call for you: 

   doSome_.createCall("'foo'", "42");

The JavaScript generated by createCall(String arg1, String arg2) is possibly affected by every connect or disconnect to the signal. In practice, you will use this class internally within a widget and call createCall(String arg1, String arg2) only after you connected internal slots to signal.

It is also possible to propagate an original JavaScript event as a last argument, of type WMouseEvent or WKeyEvent. In that case, the second argument in Wt.emit() must be an object which indicates also the JavaScript event and event target.

Consider a signal declaration: 

  JSignal2<String, Integer, WMouseEvent> doSome();

Then, the following would be a suitable JavaScript call: 

  Wt.emit(Wt, {name: 'dosome', event: event, eventObject: object}, 'foo', 42);

  • Constructor Details

    • JSignal2

      public JSignal2(WObject sender, String name)
      Creates a signal.
      Parameters:
      sender - the object that will be identified as the sender for this signal.
      name - the signal name (must be unique for each sender)

  • Method Details

    • addListener

      public AbstractSignal.Connection addListener(WObject listenerOwner, Signal2.Listener<A1,A2> listener)
      Adds a listener for this signal.

      Each listener will be triggered whenever the signal is triggered.

      Parameters:
      listenerOwner - the enclosing object for a listener implemented using an (anonymous) inner class
      listener - the listener
      Returns:
      a connection object that may be used to control the connection
      See Also:

    • getListenerCount

      protected int getListenerCount()
      Description copied from class: AbstractSignal
      Returns the number of connected listeners.
      Overrides:
      getListenerCount in class AbstractEventSignal
      Returns:
      the number of connected listeners.

    • removeListener

      public void removeListener(Signal2.Listener<A1,A2> listener)
      Removes a listener.
      Parameters:
      listener - a listener that was previously added

    • trigger

      public void trigger(A1 arg1, A2 arg2)
      Triggers the signal.

      The arguments are passed to the listeners.

      Parameters:
      arg1 - Argument 1
      arg2 - Argument 2

    • createCall

      public String createCall(String arg1, String arg2)
      Returns a JavaScript statement that triggers this signal.

      You can use this to trigger the signal from within generated JavaScript code.

      Parameters:
      arg1 - JavaScript argument 1.
      arg2 - JavaScript argument 2.

    • addListener

      public AbstractSignal.Connection addListener(WObject listenerOwner, Signal.Listener listener)
      Description copied from class: AbstractSignal
      Adds a listener for this signal.

      Each listener will be notified when the signal is triggered.

      An owner object may be passed when the listener is implemented using an (anonymous) inner class. In that case the owner object should be the enclosing object of the listener object, and this is used to bind the lifetime of the listener. To avoid the owner object from not being garbage collected when it is no longer used, only the owner object will add a reference to the listener, while the signal will use a weak reference.

      This avoids the most common reason for memory leaks in Java implementations of the Observer pattern: the owner object will not get garbage collected because of the (anonymous) listener object having a reference to it, even if the receiver object is no longer referenced from anywhere. When the owner object is not null, the listener is stored using a strong reference in the owner object, and using a weak reference in the signal.

      Specified by:
      addListener in class AbstractSignal
      Parameters:
      listenerOwner - if not null, the enclosing object for a listener implemented using an inner class
      listener - the listener
      Returns:
      a connection object that may be used to control the connection

    • removeListener

      public void removeListener(Signal.Listener listener)
      Description copied from class: AbstractSignal
      Removes a listener.

      Specified by:
      removeListener in class AbstractSignal
      Parameters:
      listener - a listener that was previously added.

    • getArgumentCount

      protected int getArgumentCount()
      Description copied from class: AbstractSignal
      Returns the number of parameters (excluding an 'event').
      Specified by:
      getArgumentCount in class AbstractSignal