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Part 4 — State and Data [Mutable Fields]
In this part, you will learn how to change the values of state and data fields. And how they can be used in the application.
Remember the Part 6 State Machine?
Let me remind you: in the example from Part 6,
we wrote the timer value in the
state.timerValue field.
Then we did not change the state value while the program was running.But what if we want to change the value of the timer?
For these purposes, we have
two types of fields available:- 1.state — for storing lightweight values
- 2.data — for storing heavyweight values
In order to use mutable fields while the application is running:
- 1.All required fields must be initialized before calling
app.run - 2.Fields keys must be written in
CamelCaseregister - 3.
datafields can't read the values of widgets, so for widgets you need to usestate
src/main.py (partially)
def main():
data = {}
state = {}
# initialize required fields here
state['timerValue'] = 0
data['timeLeft'] = None
app.run(data=data, state=state)
To
get or set field, we need to refer to the api of the application.
Here's a simple example:src/main.py (partially)
app = sly.AppService()
app_api = app.public_api
logger = sly.logger
@app.callback('start_timer')
def start_timer(api: sly.Api, task_id, context, state, app_logger):
timer_value = app_api.app.get_field(task_id=task_id,
field='state.timerValue') # getting field
...
app_api.app.set_field(task_id=task_id,
field='data.timeLeft',
payload=0) # setting field
Let's run the app and take a look at our improved timer!
State and Data