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Signals

Signals — Object methods and callbacks

Types and Values

Includes

#include <gtk/gtk.h>

Description

The GTK+ signal system merely proxies the GLib signal system now. For future usage, direct use of the GSignal API is recommended, this avoids significant performance hits where GtkArg structures have to be converted into GValues.

What are signals?

Signals are a way to get notification when something happens and to customize object behavior according to the user's needs. Every signal is uniquely identified by a name, "class_name::signal_name", where signal_name might be something like "clicked" and class_name might be "GtkButton". Note that some other class may also define a "clicked" callback, so long as it doesn't derive from GtkButton.

When they are created, they are also assigned a unique positive integer, the signal id (1 is the first signal id- 0 is used to flag an error). Each is also tied to an array of types that describes the prototype of the function pointer(s) (handlers) you may connect to the signal. Finally, every signal has a default handler that is given by a function pointer in its class structure: it is run by default whenever the signal is emitted. (It is possible that a signal will be emitted and a user-defined handler will prevent the default handler from being run.)

Signals are used by everyone, but they are only created on a per class basis -- so you should not call call gtk_signal_new() unless you are writing a new GtkObject type. However, if you want to make a new signal for an existing type, you may use gtk_object_class_user_signal_new() to create a signal that doesn't correspond to a class's builtin methods.


How are signals used?

There are two basic actions in the signal handling game. If you want notification of an event, you must connect a function pointer and a data pointer to that signal; the data pointer will be passed as the last argument to the function (so long as you are using the default marshalling functions). You will receive a connection id, a unique positive integer corresponding to that attachment.

Functions that want to notify the user of certain actions, emit signals.


Basic Terminology

signal

A class method, e.g. GtkButton::clicked. More precisely it is a unique class-branch/signal-name pair. This means you may not define a signal handler for a class which derives from GtkButton that is called clicked, but it is okay to share signals names if they are separate in the class tree.

default handler

The object's internal method which is invoked when the signal is emitted.

user-defined handler

A function pointer and data connected to a signal (for a particular object).

There are really two types: those which are connected normally, and those which are connected by one of the connect_after functions. The connect_after handlers are always run after the default handler.

Many toolkits refer to these as callbacks.

emission

the whole process of emitting a signal, including the invocation of all the different handler types mentioned above.

signal id

The unique positive (nonzero) integer used to identify a signal. It can be used instead of a name to many functions for a slight performance improvement.

connection id

The unique positive (nonzero) integer used to identify the connection of a user-defined handler to a signal. Notice that it is allowed to connect the same function-pointer/user-data pair twice, so there is no guarantee that a function-pointer/user-data maps to a unique connection id.


A brief note on how they work.

The functions responsible for translating an array of GtkArgs to your C compiler's normal semantics are called Marshallers. They are identified by gtk_marshal_return_value__parameter_list() for example a C function returning a gboolean and taking a gint can be invoked by using gtk_marshal_BOOL__INT(). Not all possibly combinations of return/params are available, of course, so if you are writing a GtkObject with parameters you might have to write a marshaller.

Functions

gtk_signal_new ()

guint
gtk_signal_new (const gchar *name,
                GtkSignalRunType signal_flags,
                GType object_type,
                guint function_offset,
                GSignalCMarshaller marshaller,
                GType return_val,
                guint n_args,
                ...);

gtk_signal_new is deprecated and should not be used in newly-written code.

Use g_signal_new() instead.

Creates a new signal type. (This is usually done in the class initializer.)

Parameters

name

the event name for the signal, e.g. "clicked".

 

signal_flags

a combination of GTK_RUN flags specifying detail of when the default handler is to be invoked. You should at least specify GTK_RUN_FIRST or GTK_RUN_LAST.

 

object_type

the type of object this signal pertains to. It will also pertain to derivers of this type automatically.

 

function_offset

How many bytes the function pointer is in the class structure for this type. Used to invoke a class method generically.

 

marshaller

the function to translate between an array of GtkArgs and the native calling convention. Usually they are identified just by the type of arguments they take: for example, gtk_marshal_BOOL__STRING() describes a marshaller which takes a string and returns a boolean value.

 

return_val

the type of return value, or GTK_TYPE_NONE for a signal without a return value.

 

n_args

the number of parameter the handlers may take.

 

Returns

the signal id.


gtk_signal_newv ()

guint
gtk_signal_newv (const gchar *name,
                 GtkSignalRunType signal_flags,
                 GType object_type,
                 guint function_offset,
                 GSignalCMarshaller marshaller,
                 GType return_val,
                 guint n_args,
                 GType *args);

gtk_signal_newv is deprecated and should not be used in newly-written code.

Use g_signal_newv() instead.

Creates a new signal type. (This is usually done in a class initializer.)

This function take the types as an array, instead of a list following the arguments. Otherwise the same as gtk_signal_new().

Parameters

name

the name of the signal to create.

 

signal_flags

see gtk_signal_new().

 

object_type

the type of GtkObject to associate the signal with.

 

function_offset

how many bytes the function pointer is in the class structure for this type.

 

return_val

the type of the return value, or GTK_TYPE_NONE if you don't want a return value.

 

n_args

the number of parameters to the user-defined handlers.

 

args

an array of GtkTypes, describing the prototype to the callbacks.

 

Returns

the signal id.


gtk_signal_lookup()

#define             gtk_signal_lookup(name,object_type)

gtk_signal_lookup is deprecated and should not be used in newly-written code.

Use g_signal_lookup() instead.

Given the name of the signal and the type of object it connects to, get the signal's identifying integer. Emitting the signal by number is somewhat faster than using the name each time.

It also tries the ancestors of the given type.

Parameters

name

the signal's name, e.g. clicked.

 

object_type

the type that the signal operates on, e.g. GTK_TYPE_BUTTON.

 

Returns

the signal's identifying number, or 0 if no signal was found.


gtk_signal_name()

#define             gtk_signal_name(signal_id)

gtk_signal_name is deprecated and should not be used in newly-written code.

Use g_signal_name() instead.

Given the signal's identifier, finds its name.

Two different signals may have the same name, if they have differing types.

Parameters

signal_id

the signal's identifying number.

 

Returns

the signal name, or NULL if the signal number was invalid.


gtk_signal_emit ()

void
gtk_signal_emit (GtkObject *object,
                 guint signal_id,
                 ...);

gtk_signal_emit is deprecated and should not be used in newly-written code.

Use g_signal_emit() instead.

Emits a signal. This causes the default handler and user-defined handlers to be run.

Here is what gtk_signal_emit() does:

1. Calls the default handler and the user-connected handlers. The default handler will be called first if GTK_RUN_FIRST is set, and last if GTK_RUN_LAST is set.

2. Calls all handlers connected with the "after" flag set.

Parameters

object

the object that emits the signal.

 

signal_id

the signal identifier.

 

gtk_signal_emit_by_name ()

void
gtk_signal_emit_by_name (GtkObject *object,
                         const gchar *name,
                         ...);

gtk_signal_emit_by_name is deprecated and should not be used in newly-written code.

Use g_signal_emit_by_name() instead.

Emits a signal. This causes the default handler and user-connected handlers to be run.

Parameters

object

the object that emits the signal.

 

name

the name of the signal.

 

gtk_signal_emitv ()

void
gtk_signal_emitv (GtkObject *object,
                  guint signal_id,
                  GtkArg *args);

gtk_signal_emitv is deprecated and should not be used in newly-written code.

Use g_signal_emitv() instead.

Emits a signal. This causes the default handler and user-connected handlers to be run. This differs from gtk_signal_emit() by taking an array of GtkArgs instead of using C's varargs mechanism.

Parameters

object

the object to emit the signal to.

 

signal_id

the signal identifier.

 

args

an array of GtkArgs, one for each parameter, followed by one which is a pointer to the return type.

 

gtk_signal_emitv_by_name ()

void
gtk_signal_emitv_by_name (GtkObject *object,
                          const gchar *name,
                          GtkArg *args);

gtk_signal_emitv_by_name is deprecated and should not be used in newly-written code.

Use g_signal_emitv() and g_signal_lookup() instead.

Emits a signal by name. This causes the default handler and user-connected handlers to be run. This differs from gtk_signal_emit() by taking an array of GtkArgs instead of using C's varargs mechanism.

Parameters

object

the object to emit the signal to.

 

name

the name of the signal.

 

args

an array of GtkArgs, one for each parameter, followed by one which is a pointer to the return type.

 

gtk_signal_emit_stop()

#define             gtk_signal_emit_stop(object,signal_id)

gtk_signal_emit_stop is deprecated and should not be used in newly-written code.

Use g_signal_stop_emission() instead.

This function aborts a signal's current emission.

It will prevent the default method from running, if the signal was GTK_RUN_LAST and you connected normally (i.e. without the "after" flag).

It will print a warning if used on a signal which isn't being emitted.

Parameters

object

the object whose signal handlers you wish to stop.

 

signal_id

the signal identifier, as returned by g_signal_lookup().

 

gtk_signal_emit_stop_by_name ()

void
gtk_signal_emit_stop_by_name (GtkObject *object,
                              const gchar *name);

gtk_signal_emit_stop_by_name is deprecated and should not be used in newly-written code.

Use g_signal_stop_emission_by_name() instead.

This function aborts a signal's current emission.

It is just like gtk_signal_emit_stop() except it will lookup the signal id for you.

Parameters

object

the object whose signal handlers you wish to stop.

 

name

the name of the signal you wish to stop.

 

gtk_signal_connect()

#define             gtk_signal_connect(object,name,func,func_data)

gtk_signal_connect is deprecated and should not be used in newly-written code.

Use g_signal_connect() instead.

Attaches a function pointer and user data to a signal for a particular object.

The GtkSignalFunction takes a GtkObject as its first parameter. It will be the same object as the one you're connecting the hook to. The func_data will be passed as the last parameter to the hook.

All else being equal, signal handlers are invoked in the order connected (see gtk_signal_emit() for the other details of which order things are called in).

Here is how one passes an integer as user data, for when you just want to specify a constant int as parameter to your function:

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static void button_clicked_int (GtkButton* button, gpointer func_data)
{
    g_print ("button pressed: %d\n", GPOINTER_TO_INT (func_data));
}
/* By calling this function, you will make the g_print above
 * execute, printing the number passed as `to_print'. */
static void attach_print_signal (GtkButton* button, gint to_print)
{
    gtk_signal_connect (GTK_OBJECT (button), "clicked",
        GTK_SIGNAL_FUNC (button_clicked_int),
        GINT_TO_POINTER (to_print));
}

Parameters

object

the object associated with the signal, e.g. if a button is getting pressed, this is that button.

 

name

name of the signal.

 

func

function pointer to attach to the signal.

 

func_data

value to pass as to your function (through the marshaller).

 

Returns

the connection id.


gtk_signal_connect_after()

#define             gtk_signal_connect_after(object,name,func,func_data)

gtk_signal_connect_after is deprecated and should not be used in newly-written code.

Use g_signal_connect_after() instead.

Attaches a function pointer and user data to a signal so that this handler will be called after the other handlers.

Parameters

object

the object associated with the signal.

 

name

name of the signal.

 

func

function pointer to attach to the signal.

 

func_data

value to pass as to your function (through the marshaller).

 

Returns

the unique identifier for this attachment: the connection id.


gtk_signal_connect_object()

#define             gtk_signal_connect_object(object,name,func,slot_object)

gtk_signal_connect_object is deprecated and should not be used in newly-written code.

Use g_signal_connect_swapped() instead.

This function is for registering a callback that will call another object's callback. That is, instead of passing the object which is responsible for the event as the first parameter of the callback, it is switched with the user data (so the object which emits the signal will be the last parameter, which is where the user data usually is).

This is useful for passing a standard function in as a callback. For example, if you wanted a button's press to gtk_widget_show() some widget, you could write:

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gtk_signal_connect_object (button, "clicked", gtk_widget_show, window);

Parameters

object

the object which emits the signal.

 

name

the name of the signal.

 

func

the function to callback.

 

slot_object

the object to pass as the first parameter to func. (Though it pretends to take an object, you can really pass any gpointer as the slot_object .)

 

Returns

the connection id.


gtk_signal_connect_object_after()

#define             gtk_signal_connect_object_after(object,name,func,slot_object)

gtk_signal_connect_object_after is deprecated and should not be used in newly-written code.

Use g_signal_connect_data() instead, passing G_CONNECT_AFTER|G_CONNECT_SWAPPED as connect_flags .

Attaches a signal hook to a signal, passing in an alternate object as the first parameter, and guaranteeing that the default handler and all normal handlers are called first.

Parameters

object

the object associated with the signal.

 

name

name of the signal.

 

func

function pointer to attach to the signal.

 

slot_object

the object to pass as the first parameter to func.

 

Returns

the connection id.


gtk_signal_connect_full ()

gulong
gtk_signal_connect_full (GtkObject *object,
                         const gchar *name,
                         GCallback func,
                         GtkCallbackMarshal unsupported,
                         gpointer data,
                         GDestroyNotify destroy_func,
                         gint object_signal,
                         gint after);

gtk_signal_connect_full is deprecated and should not be used in newly-written code.

Use g_signal_connect_data() instead.

Attaches a function pointer and user data to a signal with more control.

Parameters

object

the object which emits the signal. For example, a button in the button press signal.

 

name

the name of the signal.

 

func

function pointer to attach to the signal.

 

data

the user data associated with the function.

 

destroy_func

function to call when this particular hook is disconnected.

 

object_signal

whether this is an object signal-- basically an "object signal" is one that wants its user_data and object fields switched, which is useful for calling functions which operate on another object primarily.

 

after

whether to invoke the user-defined handler after the signal, or to let the signal's default behavior preside (i.e. depending on GTK_RUN_FIRST and GTK_RUN_LAST).

 

Returns

the connection id.


gtk_signal_connect_while_alive ()

void
gtk_signal_connect_while_alive (GtkObject *object,
                                const gchar *name,
                                GCallback func,
                                gpointer func_data,
                                GtkObject *alive_object);

gtk_signal_connect_while_alive is deprecated and should not be used in newly-written code.

Use g_signal_connect_object() instead.

Attaches a function pointer and another GtkObject to a signal.

This function takes an object whose "destroy" signal should be trapped. That way, you don't have to clean up the signal handler when you destroy the object. It is a little less efficient though.

(Instead you may call gtk_signal_disconnect_by_data(), if you want to explicitly delete all attachments to this object. This is perhaps not recommended since it could be confused with an integer masquerading as a pointer (through GINT_TO_POINTER()).)

Parameters

object

the object that emits the signal.

 

name

name of the signal.

 

func

function pointer to attach to the signal.

 

func_data

pointer to pass to func.

 

alive_object

object whose death should cause the handler connection to be destroyed.

 

gtk_signal_connect_object_while_alive ()

void
gtk_signal_connect_object_while_alive (GtkObject *object,
                                       const gchar *name,
                                       GCallback func,
                                       GtkObject *alive_object);

gtk_signal_connect_object_while_alive is deprecated and should not be used in newly-written code.

Use g_signal_connect_object() instead, passing G_CONNECT_SWAPPED as connect_flags .

These signal connectors are for signals which refer to objects, so they must not be called after the object is deleted.

Unlike gtk_signal_connect_while_alive(), this swaps the object and user data, making it suitable for use with functions which primarily operate on the user data.

This function acts just like gtk_signal_connect_object() except it traps the "destroy" signal to prevent you from having to clean up the handler.

Parameters

object

the object associated with the signal.

 

name

name of the signal.

 

func

function pointer to attach to the signal.

 

alive_object

the user data, which must be an object, whose destruction should signal the removal of this signal.

 

gtk_signal_disconnect()

#define             gtk_signal_disconnect(object,handler_id)

gtk_signal_disconnect is deprecated and should not be used in newly-written code.

Use g_signal_handler_disconnect() instead.

Destroys a user-defined handler connection.

Parameters

object

the object which the handler pertains to.

 

handler_id

the connection id.

 

gtk_signal_disconnect_by_func()

#define             gtk_signal_disconnect_by_func(object,func,data)

gtk_signal_disconnect_by_func is deprecated and should not be used in newly-written code.

Use g_signal_handlers_disconnect_by_func() instead.

Destroys all connections for a particular object, with the given function-pointer and user-data.

Parameters

object

the object which emits the signal.

 

func

the function pointer to search for.

 

data

the user data to search for.

 

gtk_signal_disconnect_by_data()

#define             gtk_signal_disconnect_by_data(object,data)

gtk_signal_disconnect_by_data is deprecated and should not be used in newly-written code.

Use g_signal_handlers_disconnect_matched() instead.

Destroys all connections for a particular object, with the given user-data.

Parameters

object

the object which emits the signal.

 

data

the user data to search for.

 

gtk_signal_handler_block()

#define             gtk_signal_handler_block(object,handler_id)

gtk_signal_handler_block is deprecated and should not be used in newly-written code.

Use g_signal_handler_block() instead.

Prevents a user-defined handler from being invoked. All other signal processing will go on as normal, but this particular handler will ignore it.

Parameters

object

the object which emits the signal to block.

 

handler_id

the connection id.

 

gtk_signal_handler_block_by_func()

#define             gtk_signal_handler_block_by_func(object,func,data)

gtk_signal_handler_block_by_func is deprecated and should not be used in newly-written code.

Use g_signal_handlers_block_by_func() instead.

Prevents a user-defined handler from being invoked, by reference to the user-defined handler's function pointer and user data. (It may result in multiple hooks being blocked, if you've called connect multiple times.)

Parameters

object

the object which emits the signal to block.

 

func

the function pointer of the handler to block.

 

data

the user data of the handler to block.

 

gtk_signal_handler_block_by_data()

#define             gtk_signal_handler_block_by_data(object,data)

gtk_signal_handler_block_by_data is deprecated and should not be used in newly-written code.

Use g_signal_handlers_block_matched() instead.

Prevents all user-defined handlers with a certain user data from being invoked.

Parameters

object

the object which emits the signal we want to block.

 

data

the user data of the handlers to block.

 

gtk_signal_handler_unblock()

#define             gtk_signal_handler_unblock(object,handler_id)

gtk_signal_handler_unblock is deprecated and should not be used in newly-written code.

Use g_signal_handler_unblock() instead.

Undoes a block, by connection id. Note that undoing a block doesn't necessarily make the hook callable, because if you block a hook twice, you must unblock it twice.

Parameters

object

the object which emits the signal we want to unblock.

 

handler_id

the emission handler identifier, as returned by gtk_signal_connect(), etc.

 

gtk_signal_handler_unblock_by_func()

#define             gtk_signal_handler_unblock_by_func(object,func,data)

gtk_signal_handler_unblock_by_func is deprecated and should not be used in newly-written code.

Use g_signal_handlers_unblock_by_func() instead.

Undoes a block, by function pointer and data. Note that undoing a block doesn't necessarily make the hook callable, because if you block a hook twice, you must unblock it twice.

Parameters

object

the object which emits the signal we want to unblock.

 

func

the function pointer to search for.

 

data

the user data to search for.

 

gtk_signal_handler_unblock_by_data()

#define             gtk_signal_handler_unblock_by_data(object,data)

gtk_signal_handler_unblock_by_data is deprecated and should not be used in newly-written code.

Use g_signal_handlers_unblock_matched() instead.

Undoes block(s), to all signals for a particular object with a particular user-data pointer

Parameters

object

the object which emits the signal we want to unblock.

 

data

the user data to search for.

 

gtk_signal_handler_pending()

#define             gtk_signal_handler_pending(object,signal_id,may_be_blocked)

gtk_signal_handler_pending is deprecated and should not be used in newly-written code.

Use g_signal_has_handler_pending() instead.

Returns a connection id corresponding to a given signal id and object.

One example of when you might use this is when the arguments to the signal are difficult to compute. A class implementor may opt to not emit the signal if no one is attached anyway, thus saving the cost of building the arguments.

Parameters

object

the object to search for the desired user-defined handler.

 

signal_id

the number of the signal to search for.

 

may_be_blocked

whether it is acceptable to return a blocked handler.

 

Returns

the connection id, if a connection was found. 0 otherwise.


gtk_signal_handler_pending_by_func()

#define             gtk_signal_handler_pending_by_func(object,signal_id,may_be_blocked,func,data)

gtk_signal_handler_pending_by_func is deprecated and should not be used in newly-written code.

Returns a connection id corresponding to a given signal id, object, function pointer and user data.

Parameters

object

the object to search for the desired handler.

 

signal_id

the number of the signal to search for.

 

may_be_blocked

whether it is acceptable to return a blocked handler.

 

func

the function pointer to search for.

 

data

the user data to search for.

 

Returns

the connection id, if a handler was found. 0 otherwise.

Types and Values

GTK_SIGNAL_OFFSET

#define GTK_SIGNAL_OFFSET	                      G_STRUCT_OFFSET

GTK_SIGNAL_OFFSET is deprecated and should not be used in newly-written code.

Use in place of offsetof(), which is used if it exists.


enum GtkSignalRunType

GtkSignalRunType is deprecated and should not be used in newly-written code.

These configure the signal's emission. They control whether the signal can be emitted recursively on an object and whether to run the default method before or after the user-defined handlers.

GTK_RUN_FIRST

Run the default handler before the connected user-defined handlers.

GTK_RUN_LAST

Run the default handler after the connected user-defined handlers. (Handlers registered as "after" always run after the default handler though)

GTK_RUN_BOTH

Run the default handler twice, once before the user-defined handlers, and once after.

GTK_RUN_NO_RECURSE

Whether to prevent a handler or hook from reemitting the signal from within itself. Attempts to emit the signal while it is running will result in the signal emission being restarted once it is done with the current processing.

You must be careful to avoid having two handlers endlessly reemitting signals, gtk_signal_n_emissions() can be helpful.

GTK_RUN_ACTION

The signal is an action you can invoke without any particular setup or cleanup. The signal is treated no differently, but some other code can determine if the signal is appropriate to delegate to user control. For example, key binding sets only allow bindings of ACTION signals to keystrokes.

GTK_RUN_NO_HOOKS

This prevents the connection of emission hooks to the signal.

Members

GTK_RUN_FIRST

   

GTK_RUN_LAST

   

GTK_RUN_BOTH

   

GTK_RUN_NO_RECURSE

   

GTK_RUN_ACTION

   

GTK_RUN_NO_HOOKS

   

gtk_signal_default_marshaller

#define gtk_signal_default_marshaller g_cclosure_marshal_VOID__VOID

gtk_signal_default_marshaller is deprecated and should not be used in newly-written code.

A marshaller that returns void and takes no extra parameters.

See Also

GtkObject

The base class for things which emit signals.

GSignal

The GLib signal system.

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