GstChildProxy

## GstChildProxy GstChildProxy — Interface for multi child elements. |

## Synopsis

    #include <gst/gst.h>

                        GstChildProxy;
    struct              GstChildProxyInterface;
    guint               gst_child_proxy_get_children_count  (GstChildProxy *parent);
    GObject *           gst_child_proxy_get_child_by_name   (GstChildProxy *parent,
                                                             const gchar *name);
    GObject *           gst_child_proxy_get_child_by_index  (GstChildProxy *parent,
                                                             guint index);
    gboolean            gst_child_proxy_lookup              (GstChildProxy *object,
                                                             const gchar *name,
                                                             GObject **target,
                                                             GParamSpec **pspec);
    void                gst_child_proxy_get_property        (GstChildProxy *object,
                                                             const gchar *name,
                                                             GValue *value);
    void                gst_child_proxy_get_valist          (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             va_list var_args);
    void                gst_child_proxy_get                 (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             ...);
    void                gst_child_proxy_set_property        (GstChildProxy *object,
                                                             const gchar *name,
                                                             const GValue *value);
    void                gst_child_proxy_set_valist          (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             va_list var_args);
    void                gst_child_proxy_set                 (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             ...);
    void                gst_child_proxy_child_added         (GstChildProxy *parent,
                                                             GObject *child,
                                                             const gchar *name);
    void                gst_child_proxy_child_removed       (GstChildProxy *parent,
                                                             GObject *child,
                                                             const gchar *name);

## Object Hierarchy

      GInterface
       +----GstChildProxy

## Prerequisites

GstChildProxy requires GObject.

## Known Implementations

GstChildProxy is implemented by GstBin and GstPipeline.

## Signals

      "child-added"                                    : Run First
      "child-removed"                                  : Run First

## Description

This interface abstracts handling of property sets for elements with children. Imagine elements such as mixers or polyphonic generators. They all have multiple GstPad or some kind of voice objects. Another use case are container elements like GstBin. The element implementing the interface acts as a parent for those child objects.

By implementing this interface the child properties can be accessed from the parent element by using `gst_child_proxy_get()` and `gst_child_proxy_set()`.

Property names are written as "child-name::property-name". The whole naming scheme is recursive. Thus "child1::child2::property" is valid too, if "child1" and "child2" implement the GstChildProxy interface.

## Details

### GstChildProxy

    typedef struct _GstChildProxy GstChildProxy;

Opaque GstChildProxy data structure.

### struct GstChildProxyInterface

    struct GstChildProxyInterface {
      GTypeInterface parent;

      /* methods */
      GObject * (*get_child_by_name)  (GstChildProxy * parent, const gchar * name);
      GObject * (*get_child_by_index) (GstChildProxy * parent, guint index);
      guint     (*get_children_count) (GstChildProxy * parent);
    };

GstChildProxy interface.

GTypeInterface `parent`; | parent interface type.
`get_child_by_name` () | virtual method to fetch the child by name
`get_child_by_index` () | virtual method to fetch the child by index
`get_children_count` () | virtual method to get the children count

### gst_child_proxy_get_children_count ()

    guint               gst_child_proxy_get_children_count  (GstChildProxy *parent);

Gets the number of child objects this parent contains.

`parent` : | the parent object
Returns : | the number of child objects MT safe.

### gst_child_proxy_get_child_by_name ()

    GObject *           gst_child_proxy_get_child_by_name   (GstChildProxy *parent,
                                                             const gchar *name);

Looks up a child element by the given name.

This virtual method has a default implementation that uses GstObject together with `gst_object_get_name()`. If the interface is to be used with GObjects, this methods needs to be overridden.

`parent` : | the parent object to get the child from
`name` : | the childs name
Returns : | the child object or `NULL` if not found. Unref after usage. MT safe. [transfer full]

### gst_child_proxy_get_child_by_index ()

    GObject *           gst_child_proxy_get_child_by_index  (GstChildProxy *parent,
                                                             guint index);

Fetches a child by its number.

`parent` : | the parent object to get the child from
`index` : | the childs position in the child list
Returns : | the child object or `NULL` if not found (index too high). Unref after usage. MT safe. [transfer full]

### gst_child_proxy_lookup ()

    gboolean            gst_child_proxy_lookup              (GstChildProxy *object,
                                                             const gchar *name,
                                                             GObject **target,
                                                             GParamSpec **pspec);

Looks up which object and GParamSpec would be effected by the given `name`.

MT safe.

`childproxy` : | child proxy object to lookup the property in
`name` : | name of the property to look up
`target` : | pointer to a GObject that takes the real object to set property on. [out][allow-none][transfer full]
`pspec` : | pointer to take the GParamSpec describing the property. [out][allow-none][transfer none]
Returns : | TRUE if `target` and `pspec` could be found. FALSE otherwise. In that case the values for `pspec` and `target` are not modified. Unref `target` after usage. For plain GObjects `target` is the same as `object`.

### gst_child_proxy_get_property ()

    void                gst_child_proxy_get_property        (GstChildProxy *object,
                                                             const gchar *name,
                                                             GValue *value);

Gets a single property using the GstChildProxy mechanism. You are responsible for freeing it by calling `g_value_unset()`

`object` : | object to query
`name` : | name of the property
`value` : | a GValue that should take the result. [out caller-allocates]

### gst_child_proxy_get_valist ()

    void                gst_child_proxy_get_valist          (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             va_list var_args);

Gets properties of the parent object and its children.

`object` : | the object to query
`first_property_name` : | name of the first property to get
`var_args` : | return location for the first property, followed optionally by more name/return location pairs, followed by NULL

### gst_child_proxy_get ()

    void                gst_child_proxy_get                 (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             ...);

Gets properties of the parent object and its children.

`object` : | the parent object
`first_property_name` : | name of the first property to get
`...` : | return location for the first property, followed optionally by more name/return location pairs, followed by NULL

### gst_child_proxy_set_property ()

    void                gst_child_proxy_set_property        (GstChildProxy *object,
                                                             const gchar *name,
                                                             const GValue *value);

Sets a single property using the GstChildProxy mechanism.

`object` : | the parent object
`name` : | name of the property to set
`value` : | new GValue for the property

### gst_child_proxy_set_valist ()

    void                gst_child_proxy_set_valist          (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             va_list var_args);

Sets properties of the parent object and its children.

`object` : | the parent object
`first_property_name` : | name of the first property to set
`var_args` : | value for the first property, followed optionally by more name/value pairs, followed by NULL

### gst_child_proxy_set ()

    void                gst_child_proxy_set                 (GstChildProxy *object,
                                                             const gchar *first_property_name,
                                                             ...);

Sets properties of the parent object and its children.

`object` : | the parent object
`first_property_name` : | name of the first property to set
`...` : | value for the first property, followed optionally by more name/value pairs, followed by NULL

### gst_child_proxy_child_added ()

    void                gst_child_proxy_child_added         (GstChildProxy *parent,
                                                             GObject *child,
                                                             const gchar *name);

Emits the "child-added" signal.

`parent` : | the parent object
`child` : | the newly added child
`name` : | the name of the new child

### gst_child_proxy_child_removed ()

    void                gst_child_proxy_child_removed       (GstChildProxy *parent,
                                                             GObject *child,
                                                             const gchar *name);

Emits the "child-removed" signal.

`parent` : | the parent object
`child` : | the removed child
`name` : | the name of the old child

## Signal Details

### The `"child-added"` signal

    void                user_function                      (GstChildProxy *child_proxy,
                                                            GObject       *object,
                                                            gchar         *name,
                                                            gpointer       user_data)        : Run First

Will be emitted after the `object` was added to the `child_proxy`.

`child_proxy` : | the GstChildProxy
`object` : | the GObject that was added
`name` : | the name of the new child
`user_data` : | user data set when the signal handler was connected.

### The `"child-removed"` signal

    void                user_function                      (GstChildProxy *child_proxy,
                                                            GObject       *object,
                                                            gchar         *name,
                                                            gpointer       user_data)        : Run First

Will be emitted after the `object` was removed from the `child_proxy`.

`child_proxy` : | the GstChildProxy
`object` : | the GObject that was removed
`name` : | the name of the old child
`user_data` : | user data set when the signal handler was connected.

## See Also

GstBin