If the item contains a metadata value for key.
Checks if a value exists for a metadata key and retrieves the #GVariantType for that key.
the name of the metadata
a location for a #GVariantType or null
true if self contains metadata named key and value_type is set to the value's #GVariantType. Otherwise false and value_type is unchanged.
If the item contains a metadata value for key.
Checks if a value exists for a metadata key and retrieves the #GVariantType for that key.