PicoSettings

This is an example how to use PicoMQTT together with the ESP32 Preferences library for retrieving and changing configuration values backed by non-volatile storage.

Example

An instance of this class associates an MQTT server with a Preferences namespace, exporting variables in this namespace to topics like preferences/<namespace>/<variable>

// keep variables under the "testns" namespace:
PicoSettings settings(mqtt, "testns");

// this variable will appear under the topic preferences/testns/bar
PicoSettings::Setting<int> bar(settings, "bar", 42);

Setting a new value via assignment

To permanently change a Settings variable, just assign its value - the new value will be recorded in NVS:

bar = 4711;

On next reboot, bar will be set to 4711.

Setting a value via MQTT

To change the value of the bar setting, publish a new value to preferences/testns/bar.

The new value will be stored permanently in NVS, hence will retain the new value after a reboot.

Inspecting values via MQTT

For conveniently making all variables and their values visible via MQTT, periodically call settings.publish() .

Getting a value

A Setting can be used like a variable of the underlying type, for example:

Serial.printf("bar = %d\n", bar);

Resetting all variables to their compile-time defaults

To reset all variables in a namespace to their compile-time defaults, use the defaults() method:

setting.defaults();

After reboot, bar will again have the value 42.

Resetting all variables in a namespace via MQTT

To achieve the same effect via MQTT, publish any value to the special topic preferences/<namespace>/reset .

With this example, the reset topic would be preferences/testns/reset .

Value change notification

A value change callback may be associate with a setting, to cause some action in user code.

Example using a lambda:

PicoSettings::Setting<bool> flag(settings, "flag", true, [] {
    log_i("flag=%d", flag.get());
});

Example using a callback function:

void on_fparam_change(void) {
    log_i("fparam changed to %f, default value: %f",
          fparam.get(), fparam.get_default());
}

PicoSettings::Setting<float> fparam(settings, "fparam", 2.718, on_fparam_change);

Initialisation

To make the persisted values of PicoSettings available, call the begin() method:

PicoSettings settings(mqtt, "testns");
PicoSettings::Setting<int> bar(settings, "bar", 42);

void setup() {
    settings.begin();
    // print the persisted value of bar
    Serial.printf("bar = %d\n", bar.get());
}

This will fire the initial value change callback, subscribe settings for updates via the preferences/<namespace>/<name> topic, and register a preferences/<namespace>/reset topic.

Writing any value to this reset topic will wipe that namespace, and revert all values to compile-time defaults.

Publishing PicoSettings

To publish all variables in a namespace with their current values, call the publish() method.