Part 3 — APP Handlers [Handle Events and Errors]

In this part, we will introduce you to app handlers and tell you what they are for.

Table of contents

1. Handle HTML events

2. Dialog window instead of an error

3. Results

Step 1 — Handle HTML events

How do I make the IU buttons work? It's very simple. In the HTML file, I will create a button that invokes the command on click:

src/gui.html (partially)

<div>
	<el-button
		type="success"
	    	@click="command('normal_handler')">
        		Call normal handler
	 </el-button>
</div>

In Python code I will handle this command using callback handler

src/main.py (partially)

@app.callback('normal_handler')
def normal_handler(api: sly.Api, task_id, context, state, app_logger):

This callback is triggered if the command name matches the name of the callback parameter. Arguments that come to the input:

• api — api the object of the user who called the callback

• task_id — app task_id

• context — information about the environment in which the application is running

• state — state of all widgets in Python dict format

• app_logger — sly_logger with task_id

Step 2 — Dialog window instead of an error

Sometimes we want the application not to crash after an error occurs. Therefore, we can use app.ignore_errors_and_show_dialog_window() handler:

src/main.py (partially)

@app.callback('error_handler')
@app.ignore_errors_and_show_dialog_window()
def error_handler(api: sly.Api, task_id, context, state, app_logger):
    logger.info('normal handler called')
    raise SystemError('there could be an error message here')

Step 3 — Results

App Handlers