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.

Table of contents

1. Mutable state && data fields

2. GET && SET field

3. Results

Step 1 — Mutable state && data fields

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 CamelCase register

3. data fields can't read the values of widgets, so for widgets you need to use state

src/main.py (partially)

def main():
	data = {}
	state = {}

	# initialize required fields here
	state['timerValue'] = 0
	data['timeLeft'] = None

	app.run(data=data, state=state)

Step 2 — GET && SET field

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

Step 3 — Results

Let's run the app and take a look at our improved timer!

State and Data