GtkAda Reference Manual - Package Glib.Properties.Creation

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# Package Glib.Properties.Creation

This package provides all the required subprograms to create and manipulate new properties associated with new widget types.

You do not have to be familiar with this package in order to use properties. See Glib.Object instead, that provides the minimal subprograms to get and set properties.

This package is only intended for writers of new widgets. You will need this function to create new properties.

Each object in gtk+ has a set of so-called properties. These are attributes that can be accessed, and possibly modified, by names. They provide introspection, that is an object can specify which properties it knows about, which can be modified,..., and thus provide a huge support for special applications like GUI-Builders that need to act on any kind of widgets, even those it doesn't know about yet.

However, for efficiency reasons, the properties are only names, and are not the only way to modify attributes of objects. It is often more efficient to use the alternate method, as documented in the GtkAda documentation for each property.

Another interesting feature of properties is that every time a property is modified, a signal "property_changed" or "notify" is emitted, and it is thus easy to keep track of attributes in objects.

- Glib.Properties.Creation Types
- Glib.Properties.Creation Subprograms

## Types

    type Enum_Class is new Glib.C_Proxy;
    type Enum_Value is new Glib.C_Proxy;
    type Flags_Class is new Glib.C_Proxy;
    type Flags_Int_Value is mod Glib.Gint'Last;
    type Flags_Value is new Glib.C_Proxy;
    type Get_Property_Handler is access procedure
    type Param_Spec_Boolean is new Param_Spec;
    type Param_Spec_Boxed is new Param_Spec;
    type Param_Spec_Char is new Param_Spec;
    type Param_Spec_Double is new Param_Spec;
    type Param_Spec_Enum is new Param_Spec;
    type Param_Spec_Flags is new Param_Spec;
    type Param_Spec_Float is new Param_Spec;
    type Param_Spec_Int is new Param_Spec;
    type Param_Spec_Long is new Param_Spec;
    type Param_Spec_Object is new Param_Spec;
    type Param_Spec_Param is new Param_Spec;
    type Param_Spec_Pointer is new Param_Spec;
    type Param_Spec_String is new Param_Spec;
    type Param_Spec_Uchar is new Param_Spec;
    type Param_Spec_Uint is new Param_Spec;
    type Param_Spec_Ulong is new Param_Spec;
    type Param_Spec_Unichar is new Param_Spec;
    type Property_Id is new Guint;
    type Set_Property_Handler is access procedure

## Subprograms

    procedure Unref
      (Param              :        Param_Spec);
| Decrement the reference counter. If it reaches 0, the memory is freed.
### Enum classes
gtk+, a C library, has a whole system to describe its enumeration types, similar to what is available from the start in Ada ('Image and 'Value for instance). All enumerations are represented internally as Enum_Classes. However, there is no easy conversion between such an enum class and a GtkAda enumeration type. Most of the time, this has no impact on your work, since you know what type you need to use when calling an Ada function. However, you will need to manipulate these enumeration classes when interfacing with ParamSpecs and dealing with properties.
    function Get_Value
      (Klass              :        Enum_Class;
       Value              :        Glib.Gint)
       return Enum_Value;
| Return the value in Klass that is Value (equivalent of 'Val in Ada)
    function Nth_Value
      (Klass              :        Enum_Class;
       Nth                :        Glib.Guint)
       return Enum_Value;
| Return the Nth-th value in Klass, or null if there is no such value.
    function Value
      (Val                :        Enum_Value)
       return Glib.Gint;
| Return the numeric value for a specific enumeration. Use the matching Ada type and 'Val to convert it to a valid Ada enumeration
    function Name
      (Val                :        Enum_Value)
       return String;
| Return the name of Val. This is the equivalent of 'Image in Ada.
    function Nick
      (Val                :        Enum_Value)
       return String;
| Return a displayable string for Val.
    function Register_Static_Enum
      (Name               :        String;
       Values             :        Interfaces.C.Strings.chars_ptr_array)
       return Glib.GType;
| Create a new enumeration class from a list of valid values. Values must be freed by the caller.
    function Enum_Class_From_Type
      (Typ                :        Glib.GType)
       return Enum_Class;
| Return the enumeration class corresponding to a type
### Flags classes
These are very similar to Enum Classes. However, the actual value of an instance of this type is a combination of a set of flags, rather than one single enumeration value. For instance, a Gdk_Event_Mask is a Flags_Class
    function Nth_Value
      (Klass              :        Flags_Class;
       Nth                :        Glib.Guint)
       return Flags_Value;
| Return the Nth-th value in Klass, or null if there is no such value.
    function Value
      (Val                :        Flags_Value)
       return Flags_Int_Value;
| Return the numeric value for a specific enumeration. Use the matching Ada type and 'Val to convert it to a valid Ada enumeration
    function Name
      (Val                :        Flags_Value)
       return String;
| Return the name of Val. This is the equivalent of 'Image in Ada.
    function Nick
      (Val                :        Flags_Value)
       return String;
| Return a displayable string for Val.
### ParamSpec
    function Pspec_Name
      (Param              :        Param_Spec)
       return String;
| Return the name of the property. This is the internal string representing the property. It Should probably not be displayed on
    function Nick_Name
      (Param              :        Param_Spec)
       return String;
| Return the nickname of the property. This is a string that can be displayed to represent the property, and is more user-friendly than the result of Name.
    function Flags
      (Param              :        Param_Spec)
       return Param_Flags;
| Return the flags for the property
    function Description
      (Param              :        Param_Spec)
       return String;
| Return the description (ie the help string) for Param
    function Value_Type
      (Param              :        Param_Spec)
       return Glib.GType;
| Return the type of param
    procedure Set_Value_Type
      (Param              :        Param_Spec;
       Typ                :        Glib.GType);
| Override the type of param. You should only use this function when creating new Param_Spec types based on existing types. You should not change the type if you haven't created param yourself.
    function Get_Qdata
      (Param              :        Param_Spec;
       Quark              :        GQuark)
       return Glib.C_Proxy;
| Return the user data set for Param
    procedure Set_Qdata
      (Param              :        Param_Spec;
       Quark              :        GQuark;
       Data               :        Glib.C_Proxy;
       Destroy            :        G_Destroy_Notify := null);
| Associate some named data with Param. Destroy is called when Param is destroyed.
    function Minimum
      (Param              :        Param_Spec_Char)
       return Glib.Gint8;
    function Default
      (Param              :        Param_Spec_Char)
       return Glib.Gint8;
    function Minimum
      (Param              :        Param_Spec_Uchar)
       return Glib.Guint8;
    function Default
      (Param              :        Param_Spec_Uchar)
       return Glib.Guint8;
    function Default
      (Param              :        Param_Spec_Boolean)
       return Boolean;
    function Minimum
      (Param              :        Param_Spec_Int)
       return Glib.Gint;
    function Default
      (Param              :        Param_Spec_Int)
       return Glib.Gint;
    function Minimum
      (Param              :        Param_Spec_Uint)
       return Glib.Guint;
    function Default
      (Param              :        Param_Spec_Uint)
       return Glib.Guint;
    function Minimum
      (Param              :        Param_Spec_Long)
       return Glib.Glong;
    function Default
      (Param              :        Param_Spec_Long)
       return Glib.Glong;
    function Minimum
      (Param              :        Param_Spec_Ulong)
       return Glib.Gulong;
    function Default
      (Param              :        Param_Spec_Ulong)
       return Glib.Gulong;
    function Default
      (Param              :        Param_Spec_Unichar)
       return Gunichar;
    function Enumeration
      (Param              :        Param_Spec_Enum)
       return Enum_Class;
    function Gnew_Enum
      (Name, Nick, Blurb  :        String;
       Enum_Type          :        GType;
       Default            :        Gint := 0;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
| See Glib.Properties.Creation.Register_Static_Enum on how to create Enum_Type
    function Flags_Enumeration
      (Param              :        Param_Spec_Flags)
       return Flags_Class;
    function Gnew_Flags
      (Name, Nick, Blurb  :        String;
       Flags_Type         :        Glib.GType;
       Default            :        Guint;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
    function Minimum
      (Param              :        Param_Spec_Float)
       return Gfloat;
    function Default
      (Param              :        Param_Spec_Float)
       return Gfloat;
    function Gnew_Float
      (Name, Nick, Blurb  :        String;
       Minimum, Maximum, Default  :        Glib.Gfloat;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
    function Minimum
      (Param              :        Param_Spec_Double)
       return Gdouble;
    function Default
      (Param              :        Param_Spec_Double)
       return Gdouble;
    function Gnew_Double
      (Name, Nick, Blurb  :        String;
       Minimum, Maximum, Default  :        Glib.Gdouble;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
    function Default
      (Param              :        Param_Spec_String)
       return String;
    function Cset_Nth
      (Param              :        Param_Spec_String)
       return String;
    function Ensure_Non_Null
      (Param              :        Param_Spec_String)
       return Boolean;
    function Gnew_Param
      (Name, Nick, Blurb  :        String;
       Param_Type         :        Glib.GType;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
    function Gnew_Boxed
      (Name, Nick, Blurb  :        String;
       Boxed_Type         :        Glib.GType;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
    function Gnew_Pointer
      (Name, Nick, Blurb  :        String;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
    function Gnew_Object
      (Name, Nick, Blurb  :        String;
       Object_Type        :        Glib.GType;
       Flags              :        Param_Flags
                           := Param_Readable or Param_Writable)
       return Param_Spec;
### Creating new properties
There are several things that need to be done when creating a property. For one thing, you need to create the string that represents the property. This is the only item that needs to go in the specifications of your page. You then need to describe the type of the property, and the values it allows. This is very simple for simple types, and a generic packages is provided to handle the more complex enumeration-based properties. Your widget needs to define two handlers, Set_Property_Handler and Get_Property_Handler, that are called every time the user accesses the value of a property through a call to Glib.Object.Set_Property or Glib.Object.Get_Property. For efficiency reasons, a property is also associated with an integer value, that you must provide when creating the property. This value is completely free, and is passed to the two handlers described above. The two handlers manipulate Glib.Values.GValue values, so that they can get and return various types.
    procedure Set_Properties_Handlers
      (Class_Record       :        Glib.Object.GObject_Class;
       Set_Property       :        Set_Property_Handler;
       Get_Property       :        Get_Property_Handler);
| Set the two functions used to set and retrieve properties. You should never call this function on the class record of the standard gtk+ widgets, since this will break their behavior. You should first create a new class record through Initialize_Class_Record, and then use the returned Class_Record as a parameter to this subprogram. You cannot pass null to either of the two parameters, or you won't be able to install new properties afterwards
    procedure Install_Property
      (Class_Record       :        Glib.Object.GObject_Class;
       Prop_Id            :        Property_Id;
       Property_Spec      :        Param_Spec);
| Adds a new property to Class_Record. You should use this function only on class records you have created yourself, not on one of the standard widgets. Prop_Id is the internal representation for properties, that will be passed to the Set_Property and Get_Property_Handlers (see above) to set and retrieve the value of a property. Property_Spec should be the result of one of the GNew_* subprograms for Param_Spec, and this defines the type of the property.

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