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JsonReader provides a simple, cursor-based API for parsing a JSON DOM.

It is similar, in spirit, to the XML Reader API.

Using JsonReader

g_autoptr(JsonParser) parser = json_parser_new ();

// str is defined elsewhere
json_parser_load_from_data (parser, str, -1, NULL);

g_autoptr(JsonReader) reader = json_reader_new (json_parser_get_root (parser));

json_reader_read_member (reader, "url");
const char *url = json_reader_get_string_value (reader);
json_reader_end_member (reader);

json_reader_read_member (reader, "size");
json_reader_read_element (reader, 0);
int width = json_reader_get_int_value (reader);
json_reader_end_element (reader);
json_reader_read_element (reader, 1);
int height = json_reader_get_int_value (reader);
json_reader_end_element (reader);
json_reader_end_member (reader);

Error handling

In case of error, JsonReader will be set in an error state; all subsequent calls will simply be ignored until a function that resets the error state is called, e.g.:

// ask for the 7th element; if the element does not exist, the
// reader will be put in an error state
json_reader_read_element (reader, 6);

// in case of error, this will return NULL, otherwise it will
// return the value of the element
str = json_reader_get_string_value (value);

// this function resets the error state if any was set
json_reader_end_element (reader);

If you want to detect the error state as soon as possible, you can use [methodJson.Reader.get_error]:

// like the example above, but in this case we print out the
// error immediately
if (!json_reader_read_element (reader, 6))
{
const GError *error = json_reader_get_error (reader);
g_print ("Unable to read the element: %s", error->message);
}

Hierarchy

Index

Constructors

Properties

gTypeInstance: TypeInstance
root: Json.Node

The root of the JSON tree that the reader should read.

$gtype: GType<Reader>
name: string

Methods

  • Creates a binding between source_property on source and target_property on target.

    Whenever the source_property is changed the target_property is updated using the same value. For instance:

      g_object_bind_property (action, "active", widget, "sensitive", 0);
    

    Will result in the "sensitive" property of the widget #GObject instance to be updated with the same value of the "active" property of the action #GObject instance.

    If flags contains %G_BINDING_BIDIRECTIONAL then the binding will be mutual: if target_property on target changes then the source_property on source will be updated as well.

    The binding will automatically be removed when either the source or the target instances are finalized. To remove the binding without affecting the source and the target you can just call g_object_unref() on the returned #GBinding instance.

    Removing the binding by calling g_object_unref() on it must only be done if the binding, source and target are only used from a single thread and it is clear that both source and target outlive the binding. Especially it is not safe to rely on this if the binding, source or target can be finalized from different threads. Keep another reference to the binding and use g_binding_unbind() instead to be on the safe side.

    A #GObject can have multiple bindings.

    Parameters

    • sourceProperty: string

      the property on source to bind

    • target: GObject.Object

      the target #GObject

    • targetProperty: string

      the property on target to bind

    • flags: BindingFlags

      flags to pass to #GBinding

    Returns Binding

  • Creates a binding between source_property on source and target_property on target, allowing you to set the transformation functions to be used by the binding.

    This function is the language bindings friendly version of g_object_bind_property_full(), using #GClosures instead of function pointers.

    Parameters

    • sourceProperty: string

      the property on source to bind

    • target: GObject.Object

      the target #GObject

    • targetProperty: string

      the property on target to bind

    • flags: BindingFlags

      flags to pass to #GBinding

    • transformTo: TClosure<any, any>

      a #GClosure wrapping the transformation function from the source to the target, or %NULL to use the default

    • transformFrom: TClosure<any, any>

      a #GClosure wrapping the transformation function from the target to the source, or %NULL to use the default

    Returns Binding

  • connect(sigName: "notify::root", callback: ((...args: any[]) => void)): number
  • connect(sigName: string, callback: ((...args: any[]) => void)): number
  • Parameters

    • sigName: "notify::root"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns number

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns number

  • countElements(): number
  • Counts the elements of the current position, if the reader is positioned on an array.

    In case of failure, the reader is set to an error state.

    Returns number

  • countMembers(): number
  • Counts the members of the current position, if the reader is positioned on an object.

    In case of failure, the reader is set to an error state.

    Returns number

  • emit(sigName: "notify::root", ...args: any[]): void
  • emit(sigName: string, ...args: any[]): void
  • endElement(): void
  • Moves the cursor back to the previous node after being positioned inside an array.

    This function resets the error state of the reader, if any was set.

    Returns void

  • endMember(): void
  • Moves the cursor back to the previous node after being positioned inside an object.

    This function resets the error state of the reader, if any was set.

    Returns void

  • forceFloating(): void
  • This function is intended for #GObject implementations to re-enforce a [floating][floating-ref] object reference. Doing this is seldom required: all #GInitiallyUnowneds are created with a floating reference which usually just needs to be sunken by calling g_object_ref_sink().

    Returns void

  • freezeNotify(): void
  • Increases the freeze count on object. If the freeze count is non-zero, the emission of "notify" signals on object is stopped. The signals are queued until the freeze count is decreased to zero. Duplicate notifications are squashed so that at most one #GObject::notify signal is emitted for each property modified while the object is frozen.

    This is necessary for accessors that modify multiple properties to prevent premature notification while the object is still being modified.

    Returns void

  • getBooleanValue(): boolean
  • Retrieves the boolean value of the current position of the reader.

    See also: [methodJson.Reader.get_value]

    Returns boolean

  • getData(key?: string): object
  • Gets a named field from the objects table of associations (see g_object_set_data()).

    Parameters

    • Optional key: string

      name of the key for that association

    Returns object

  • getDoubleValue(): number
  • Retrieves the floating point value of the current position of the reader.

    See also: [methodJson.Reader.get_value]

    Returns number

  • getIntValue(): number
  • Retrieves the integer value of the current position of the reader.

    See also: [methodJson.Reader.get_value]

    Returns number

  • getMemberName(): string
  • Retrieves the name of the current member.

    In case of failure, the reader is set to an error state.

    Returns string

  • getNullValue(): boolean
  • Checks whether the value of the current position of the reader is null.

    See also: [methodJson.Reader.get_value]

    Returns boolean

  • getProperty(propertyName?: string, value?: any): void
  • Gets a property of an object.

    The value can be:

    • an empty #GValue initialized by %G_VALUE_INIT, which will be automatically initialized with the expected type of the property (since GLib 2.60)
    • a #GValue initialized with the expected type of the property
    • a #GValue initialized with a type to which the expected type of the property can be transformed

    In general, a copy is made of the property contents and the caller is responsible for freeing the memory by calling g_value_unset().

    Note that g_object_get_property() is really intended for language bindings, g_object_get() is much more convenient for C programming.

    Parameters

    • Optional propertyName: string

      the name of the property to get

    • Optional value: any

      return location for the property value

    Returns void

  • getQdata(quark: number): object
  • This function gets back user data pointers stored via g_object_set_qdata().

    Parameters

    • quark: number

      A #GQuark, naming the user data pointer

    Returns object

  • getStringValue(): string
  • Retrieves the string value of the current position of the reader.

    See also: [methodJson.Reader.get_value]

    Returns string

  • Retrieves the value node at the current position of the reader.

    If the current position does not contain a scalar value, the reader is set to an error state.

    Returns Json.Node

  • getv(names: string[], values: any[]): void
  • Gets n_properties properties for an object. Obtained properties will be set to values. All properties must be valid. Warnings will be emitted and undefined behaviour may result if invalid properties are passed in.

    Parameters

    • names: string[]

      the names of each property to get

    • values: any[]

      the values of each property to get

    Returns void

  • isArray(): boolean
  • Checks whether the reader is currently on an array.

    Returns boolean

  • isFloating(): boolean
  • isObject(): boolean
  • Checks whether the reader is currently on an object.

    Returns boolean

  • isValue(): boolean
  • Checks whether the reader is currently on a value.

    Returns boolean

  • listMembers(): string[]
  • Retrieves a list of member names from the current position, if the reader is positioned on an object.

    In case of failure, the reader is set to an error state.

    Returns string[]

  • notify(propertyName: string): void
  • Emits a "notify" signal for the property property_name on object.

    When possible, eg. when signaling a property change from within the class that registered the property, you should use g_object_notify_by_pspec() instead.

    Note that emission of the notify signal may be blocked with g_object_freeze_notify(). In this case, the signal emissions are queued and will be emitted (in reverse order) when g_object_thaw_notify() is called.

    Parameters

    • propertyName: string

      the name of a property installed on the class of object.

    Returns void

  • Emits a "notify" signal for the property specified by pspec on object.

    This function omits the property name lookup, hence it is faster than g_object_notify().

    One way to avoid using g_object_notify() from within the class that registered the properties, and using g_object_notify_by_pspec() instead, is to store the GParamSpec used with g_object_class_install_property() inside a static array, e.g.:

      enum
    {
    PROP_0,
    PROP_FOO,
    PROP_LAST
    };

    static GParamSpec *properties[PROP_LAST];

    static void
    my_object_class_init (MyObjectClass *klass)
    {
    properties[PROP_FOO] = g_param_spec_int ("foo", "Foo", "The foo",
    0, 100,
    50,
    G_PARAM_READWRITE);
    g_object_class_install_property (gobject_class,
    PROP_FOO,
    properties[PROP_FOO]);
    }

    and then notify a change on the "foo" property with:

      g_object_notify_by_pspec (self, properties[PROP_FOO]);
    

    Parameters

    • pspec: ParamSpec

      the #GParamSpec of a property installed on the class of object.

    Returns void

  • off(sigName: "notify::root", callback: ((...args: any[]) => void)): EventEmitter
  • off(sigName: string, callback: ((...args: any[]) => void)): EventEmitter
  • Parameters

    • sigName: "notify::root"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns EventEmitter

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    Returns EventEmitter

  • on(sigName: "notify::root", callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • on(sigName: string, callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • Parameters

    • sigName: "notify::root"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • once(sigName: "notify::root", callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • once(sigName: string, callback: ((...args: any[]) => void), after?: boolean): EventEmitter
  • Parameters

    • sigName: "notify::root"
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • Parameters

    • sigName: string
    • callback: ((...args: any[]) => void)
        • (...args: any[]): void
        • Parameters

          • Rest ...args: any[]

          Returns void

    • Optional after: boolean

    Returns EventEmitter

  • readElement(index: number): boolean
  • Advances the cursor of the reader to the element of the array or the member of the object at the given position.

    You can use [methodJson.Reader.get_value] and its wrapper functions to retrieve the value of the element; for instance, the following code will read the first element of the array at the current cursor position:

    json_reader_read_element (reader, 0);
    int_value = json_reader_get_int_value (reader);

    After reading the value, you should call [methodJson.Reader.end_element] to reposition the cursor inside the reader, e.g.:

    const char *str_value = NULL;

    json_reader_read_element (reader, 1);
    str_value = json_reader_get_string_value (reader);
    json_reader_end_element (reader);

    json_reader_read_element (reader, 2);
    str_value = json_reader_get_string_value (reader);
    json_reader_end_element (reader);

    If the reader is not currently on an array or an object, or if the index is bigger than the size of the array or the object, the reader will be put in an error state until [methodJson.Reader.end_element] is called. This means that, if used conditionally, [methodJson.Reader.end_element] must be called on all branches:

    ```c if (!json_reader_read_element (reader, 1)) { g_propagate_error (error, json_reader_get_error (reader)); json_reader_end_element (reader); return FALSE; } else { const char *str_value = json_reader_get_string_value (reader); json_reader_end_element (reader);

    // use str_value

    return TRUE;

    } ```c

    Parameters

    • index: number

      the index of the element

    Returns boolean

  • readMember(memberName: string): boolean
  • Advances the cursor of the reader to the member_name of the object at the current position.

    You can use [methodJson.Reader.get_value] and its wrapper functions to retrieve the value of the member; for instance:

    json_reader_read_member (reader, "width");
    width = json_reader_get_int_value (reader);

    After reading the value, json_reader_end_member() should be called to reposition the cursor inside the reader, e.g.:

    json_reader_read_member (reader, "author");
    author = json_reader_get_string_value (reader);
    json_reader_end_member (reader);

    json_reader_read_member (reader, "title");
    title = json_reader_get_string_value (reader);
    json_reader_end_member (reader);

    If the reader is not currently on an object, or if the member_name is not defined in the object, the reader will be put in an error state until [methodJson.Reader.end_member] is called. This means that if used conditionally, [methodJson.Reader.end_member] must be called on all branches:

    if (!json_reader_read_member (reader, "title"))
    {
    g_propagate_error (error, json_reader_get_error (reader));
    json_reader_end_member (reader);
    return FALSE;
    }
    else
    {
    const char *str_value = json_reader_get_string_value (reader);
    json_reader_end_member (reader);

    // use str_value

    return TRUE;
    }

    Parameters

    • memberName: string

      the name of the member to read

    Returns boolean

  • Increases the reference count of object.

    Since GLib 2.56, if GLIB_VERSION_MAX_ALLOWED is 2.56 or greater, the type of object will be propagated to the return type (using the GCC typeof() extension), so any casting the caller needs to do on the return type must be explicit.

    Returns GObject.Object

  • Increase the reference count of object, and possibly remove the [floating][floating-ref] reference, if object has a floating reference.

    In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

    Since GLib 2.56, the type of object will be propagated to the return type under the same conditions as for g_object_ref().

    Returns GObject.Object

  • runDispose(): void
  • Releases all references to other objects. This can be used to break reference cycles.

    This function should only be called from object system implementations.

    Returns void

  • setData(key: string, data?: object): void
  • Each object carries around a table of associations from strings to pointers. This function lets you set an association.

    If the object already had an association with that name, the old association will be destroyed.

    Internally, the key is converted to a #GQuark using g_quark_from_string(). This means a copy of key is kept permanently (even after object has been finalized) — so it is recommended to only use a small, bounded set of values for key in your program, to avoid the #GQuark storage growing unbounded.

    Parameters

    • key: string

      name of the key

    • Optional data: object

      data to associate with that key

    Returns void

  • setProperty(propertyName: string, value?: any): void
  • Sets a property on an object.

    Parameters

    • propertyName: string

      the name of the property to set

    • Optional value: any

      the value

    Returns void

  • Sets the root node of the JSON tree to be read by reader.

    The reader will take a copy of the node.

    Parameters

    Returns void

  • stealData(key?: string): object
  • Remove a specified datum from the object's data associations, without invoking the association's destroy handler.

    Parameters

    • Optional key: string

      name of the key

    Returns object

  • stealQdata(quark: number): object
  • This function gets back user data pointers stored via g_object_set_qdata() and removes the data from object without invoking its destroy() function (if any was set). Usually, calling this function is only required to update user data pointers with a destroy notifier, for example:

    void
    object_add_to_user_list (GObject *object,
    const gchar *new_string)
    {
    // the quark, naming the object data
    GQuark quark_string_list = g_quark_from_static_string ("my-string-list");
    // retrieve the old string list
    GList *list = g_object_steal_qdata (object, quark_string_list);

    // prepend new string
    list = g_list_prepend (list, g_strdup (new_string));
    // this changed 'list', so we need to set it again
    g_object_set_qdata_full (object, quark_string_list, list, free_string_list);
    }
    static void
    free_string_list (gpointer data)
    {
    GList *node, *list = data;

    for (node = list; node; node = node->next)
    g_free (node->data);
    g_list_free (list);
    }

    Using g_object_get_qdata() in the above example, instead of g_object_steal_qdata() would have left the destroy function set, and thus the partial string list would have been freed upon g_object_set_qdata_full().

    Parameters

    • quark: number

      A #GQuark, naming the user data pointer

    Returns object

  • thawNotify(): void
  • Reverts the effect of a previous call to g_object_freeze_notify(). The freeze count is decreased on object and when it reaches zero, queued "notify" signals are emitted.

    Duplicate notifications for each property are squashed so that at most one #GObject::notify signal is emitted for each property, in the reverse order in which they have been queued.

    It is an error to call this function when the freeze count is zero.

    Returns void

  • unref(): void
  • Decreases the reference count of object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed).

    If the pointer to the #GObject may be reused in future (for example, if it is an instance variable of another object), it is recommended to clear the pointer to %NULL rather than retain a dangling pointer to a potentially invalid #GObject instance. Use g_clear_object() for this.

    Returns void

  • watchClosure(closure: TClosure<any, any>): void
  • This function essentially limits the life time of the closure to the life time of the object. That is, when the object is finalized, the closure is invalidated by calling g_closure_invalidate() on it, in order to prevent invocations of the closure with a finalized (nonexisting) object. Also, g_object_ref() and g_object_unref() are added as marshal guards to the closure, to ensure that an extra reference count is held on object during invocation of the closure. Usually, this function will be called on closures that use this object as closure data.

    Parameters

    • closure: TClosure<any, any>

      #GClosure to watch

    Returns void

  • compatControl(what: number, data: object): number
  • Find the #GParamSpec with the given name for an interface. Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().

    Parameters

    • gIface: TypeInterface

      any interface vtable for the interface, or the default vtable for the interface

    • propertyName: string

      name of a property to look up.

    Returns ParamSpec

  • Add a property to an interface; this is only useful for interfaces that are added to GObject-derived types. Adding a property to an interface forces all objects classes with that interface to have a compatible property. The compatible property could be a newly created #GParamSpec, but normally g_object_class_override_property() will be used so that the object class only needs to provide an implementation and inherits the property description, default value, bounds, and so forth from the interface property.

    This function is meant to be called from the interface's default vtable initialization function (the class_init member of #GTypeInfo.) It must not be called after after class_init has been called for any object types implementing this interface.

    If pspec is a floating reference, it will be consumed.

    Parameters

    • gIface: TypeInterface

      any interface vtable for the interface, or the default vtable for the interface.

    • pspec: ParamSpec

      the #GParamSpec for the new property

    Returns void

  • Lists the properties of an interface.Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().

    Parameters

    • gIface: TypeInterface

      any interface vtable for the interface, or the default vtable for the interface

    Returns ParamSpec[]

  • Creates a new reader.

    You can use this object to read the contents of the JSON tree starting from the given node.

    Parameters

    Returns Reader

  • Creates a new instance of a #GObject subtype and sets its properties.

    Construction parameters (see %G_PARAM_CONSTRUCT, %G_PARAM_CONSTRUCT_ONLY) which are not explicitly specified are set to their default values.

    Parameters

    • objectType: GType<unknown>

      the type id of the #GObject subtype to instantiate

    • parameters: GObject.Parameter[]

      an array of #GParameter

    Returns GObject.Object

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