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Copyright (C) 2024, Axis Communications AB, Lund, Sweden. All Rights Reserved.

ACAP application using parameters

This example shows how to handle system-wide and application-defined parameters using the AXParameter library. Emphasis has been put on the use of callback functions and some of the limitations they impose.

Project structure

The files for building the application are organized in the following structure.

axparameter
├── app
│   ├── axparameter.c
│   ├── LICENSE
│   ├── Makefile
│   └── manifest.json
├── Dockerfile
└── README.md
  • app/axparameter.c - Application source code.
  • app/LICENSE - List of all open source licensed source code distributed with the application.
  • app/Makefile - Build and link instructions for the application.
  • app/manifest.json - Definition of the application and its configuration, including predefined parameters.
  • Dockerfile - Assembles an image containing the ACAP SDK toolchain and builds the application using it.
  • README.md - Step by step instructions on how to run the example.

Program structure and behavior

In the paramConfig section of manifest.json, two parameters have been defined; IsCustomized and BackupValue. These will exist on the device as soon as the application has been installed, even before any application code has run, and can be accessed using VAPIX calls to param.cgi.

Since BackupValue is tagged with the control word hidden, it will not show up in the application's Settings dialog, but IsCustomized will be shown there as a checkbox.

Immediately upon startup, the application reads a system property using ax_parameter_get(). By specifying a qualified parameter name like Properties.System.SerialNumber, it is possible to read parameters that do not belong to this application.

Before entering the main loop, the program uses ax_parameter_register_callback() to subscribe to parameter changes through a callback to parameter_changed(). This callback will drive the behavior for the rest of the application's life time.

parameter_changed() will get called immediately when a parameter is modified through VAPIX or GUI. It will receive the name and the new value of the modified parameter, but it must not make any calls to the AXParameter library itself. In order to work around this limitation, g_timeout_add_seconds() is used to schedule a call monitor_parameters() one second later.

monitor_parameters() will use the AXParameter library to solve its tasks. It inspects the values of all parameters, before performing one of two actions:

  • If IsCustomized is yes it will, if necessary, use ax_parameter_add() to add parameter CustomValue and give it the current value stored in BackupValue.
  • If IsCustomized is no it will, if necessary, store the current value of CustomValue in BackupValue and then use ax_parameter_remove() to remove parameter CustomValue.

Whenever CustomValue is added or removed at runtime, this also controls whether the input field for CustomValue is shown in the application's Settings dialog or not. However, the user also needs to reload the Apps page in order to see or get rid of the field in the Settings dialog.

Build the application

Standing in your working directory run the following commands:

Note

Depending on the network you are connected to, you may need to add proxy settings. The file that needs these settings is: ~/.docker/config.json. For reference please see https://docs.docker.com/network/proxy and a script for Axis devices in the ACAP documentation.

docker build --tag <APP_IMAGE> --build-arg ARCH=<ARCH> .
  • <APP_IMAGE> is the name to tag the image with, e.g., axparameter:1.0
  • <ARCH> is the SDK architecture, armv7hf or aarch64.

Copy the result from the container image to a local directory build:

docker cp $(docker create <APP_IMAGE>):/opt/app ./build

The build directory contains the build artifacts, where the ACAP application is found with suffix .eap, depending on which SDK architecture that was chosen, one of these files should be found:

  • axparameter_1_0_0_aarch64.eap
  • axparameter_1_0_0_armv7hf.eap

Install and start the application

Browse to the application page of the Axis device:

http://<AXIS_DEVICE_IP>/index.html#apps
  • Click on the tab Apps in the device GUI
  • Enable Allow unsigned apps toggle
  • Click (+ Add app) button to upload the application file
  • Browse to the newly built ACAP application, depending on architecture:
    • axparameter_1_0_0_aarch64.eap
    • axparameter_1_0_0_armv7hf.eap
  • Click Install
  • Run the application by enabling the Start switch

Expected output

The application log can be found by either

  • Browsing to http://<AXIS_DEVICE_IP>/axis-cgi/admin/systemlog.cgi?appname=axparameter.
  • Browsing to the Apps page and select App log.

Initially, the log will show the device serial number, read from the system parameters.

[ INFO    ] axparameter[1234567]: SerialNumber: 'BA9876543210'

Open the Settings dialog, check the Is customized checkbox, and click Save. The log immediately shows:

[ INFO    ] axparameter[1234567]: IsCustomized was changed to 'yes' just now

Followed one second later by:

[ INFO    ] axparameter[1234567]: IsCustomized was changed to 'yes' one second ago
[ INFO    ] axparameter[1234567]: App has a parameter named BackupValue
[ INFO    ] axparameter[1234567]: App has a parameter named IsCustomized
[ INFO    ] axparameter[1234567]: Parameter CustomValue was not found
[ INFO    ] axparameter[1234567]: The parameter CustomValue was added, but won't be visible in the Settings page until the Apps page is reloaded.
[ INFO    ] axparameter[1234567]: Custom value: 'restored from backup'

Note that the order of these messages will vary. The order above is the order that they are written by the application.

Reload the Apps page and open the Settings dialog. It will now show a field Custom value with the value "restored from backup". Change it to "my customization" and click Save.

The log immediately shows:

[ INFO    ] axparameter[1234567]: CustomValue was changed to 'my customization' just now

Followed one second later by:

[ INFO    ] axparameter[1234567]: CustomValue was changed to 'my customization' one second ago
[ INFO    ] axparameter[1234567]: App has a parameter named BackupValue
[ INFO    ] axparameter[1234567]: App has a parameter named CustomValue
[ INFO    ] axparameter[1234567]: App has a parameter named IsCustomized
[ INFO    ] axparameter[1234567]: Parameter CustomValue was found
[ INFO    ] axparameter[1234567]: Custom value: 'my customization'

Open the Settings dialog, uncheck the Is customized checkbox, and click Save. The log immediately shows:

[ INFO    ] axparameter[1234567]: IsCustomized was changed to 'no' just now

Followed one second later by:

[ INFO    ] axparameter[1234567]: IsCustomized was changed to 'no' one second ago
[ INFO    ] axparameter[1234567]: App has a parameter named BackupValue
[ INFO    ] axparameter[1234567]: App has a parameter named CustomValue
[ INFO    ] axparameter[1234567]: App has a parameter named IsCustomized
[ INFO    ] axparameter[1234567]: Parameter CustomValue was found
[ INFO    ] axparameter[1234567]: The parameter CustomValue was removed, but will be visible in the Settings page until the Apps page is reloaded.
[ INFO    ] axparameter[1234567]: Not customized

Reload the Apps page and open the Settings dialog. The field Custom value is now gone. Check the Is customized checkbox, and click Save.

The log immediately shows:

[ INFO    ] axparameter[1234567]: IsCustomized was changed to 'yes' just now

Followed one second later by:

[ INFO    ] axparameter[1234567]: IsCustomized was changed to 'yes' one second ago
[ INFO    ] axparameter[1234567]: App has a parameter named BackupValue
[ INFO    ] axparameter[1234567]: App has a parameter named IsCustomized
[ INFO    ] axparameter[1234567]: Parameter CustomValue was not found
[ INFO    ] axparameter[1234567]: Custom value: 'my customization'
[ INFO    ] axparameter[1234567]: The parameter CustomValue was added, but won't be visible in the Settings page until the Apps page is reloaded.

Reload the Apps page and open the Settings dialog. The field Custom value is back again, with the value "my customization" restored from the backup.

License

Apache License 2.0