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State Handler

The State handler controls how the wf:state functions store and retrieve page-state variables. State variables are defined as being page-load specific. That is, a loading or reloading a page should result in an empty page state. Page state, however, is retained with postbacks, comet processes, and other asynchronous requests.

Bear in mind that the state is not a secure store. That is, page-state gets pickled and sent to the client, so anything that needs to be hidden from the client is not recommended to be stored in the state.

The default implementation of the page-state is as a simple Erlang proplist.

Behavior Functions

init(Config, State)

Initialize the state handler

• /Return Value/ - {ok, NewState}

finish(Config, State)

Clean up the handler

• /Return Value/ - {ok, NewState}

get_state(Key, DefaultValue, Config, State)

Retrieves the current value of the state variable with the identifier Key

• Key - The identifier to search for

• DefaultValue - If Key is not found, return this value instead.

• /Return Value/ - The found value associated with Key (or DefaultValue)

set_state(Key, Value, Config, State)

Stores Value in the page state with the identifier Key

• Key - The identifer to store

• Value - The value to store

• /Return Value/ - {ok, NewState}

clear(Key, Config, State)

Clears the page state value associated with Key

• Key - The identifier to delete from the page state

• /Return Value/ - {ok, NewState}

clear_all(Config, State)

Wipes out all page state variables.

• /Return Value/ - {ok, NewState}

Example

Here is the complete text of the default state handler

-module (default_state_handler).
-behaviour (state_handler).
-include_lib ("wf.hrl").
-export ([
    init/2, finish/2, get_state/4, set_state/4, clear/3, clear_all/2
]).

init(_Config, State) ->
    % Deserialize the state from domState.
    {ok, State}.

finish(_Config, State) ->
    {ok, State}.

get_state(Key, DefaultValue, _Config, State) ->
    _Value = proplists:get_value(Key, State, DefaultValue).

set_state(Key, Value, _Config, State) ->
    State1 = proplists:delete(Key, State),
    State2 = [{Key, Value}|State1],
    {ok, State2}.

clear(Key, _Config, State) ->
    State1 = proplists:delete(Key, State),
    {ok, State1}.

clear_all(Config, _State) ->
    init(Config, []).

See Also

• Handler Overview

• API: State