Stateful components like
their state in the socket's
assigns. In Surface, those assigns are called
In order to declare a data assign, you must use the
data name, type, options
name- is the name of the assign.
type- an atom defining the type of the assign. See all available types in section "Components Basics > Types available".
options- a keyword list of options for additional customization.
default- defines a default value for the assign.
values- the list or range of values suggested for the assign.
values!- the list or range of all possible values for the assign. Unlike
values, this option enforces validation of the default value against the given list.
from_context- sets the value to the one stored in the context under the given key.
In the following example, we create a simple
Counter component that has its state
defined by a single assign named
count. You can use the
+ buttons to
decrement/increment the counter's value.
datamacro is available in both stateful and stateless components. It allows you to define intermediary assigns in the
updatefunction of the component that computes values based on one or several properties.
Note: Since we defined a default value for
count, we don't need to implement the
mount/1callback to initialize it. All
dataassigns with default values will be automatically initialized by Surface. That means if you need some
datato be initialized, you need to add a default value, even if it's
nil. If you do not add a default value, the
datais not initialized.