Multiple links to single menu?

[DisasterAreaDesigns]

Let's say I have a main menu that is set up like this:

Main Menu

Button 1 Config (sub menu)
Button 2 Config (sub menu)
Buttno 3 Config (sub menu)

Then in each of the sub menus I have something like

Button 1 Menu

Button 1 Value (int)
Button 1 Color (option select)
Button 1 Name (char)

Button 2 and 3 menus are the same as button 1. I was wondering if it was possible to use a single sub menu to handle all three, my approach would be to have a menu that works on a generic set of values (value, color, name) and then we could copy the Button 1 / 2 / 3 values into that set for the menu. When the user exits the sub menu the values would be copied back to the correct place.

I understand it's very easy to make separate menus for everything, but I eventually may have dozens of these to present to the user. Making a change on one menu would require making changes on dozens of them, so I would rather just have one sub-menu to access and only keep track of the index and the values to push / pop back into their original spots.

My real question is can I fire a function upon entering and exiting a sub-menu? I know I can do this with a "button" item such as the "print" button in the Blink example, but is there a way to do something as a result of entering or exiting a sub-menu? Failing that, is there a way to know which menu we are in?

I was thinking something like:
// enter sub menu here
menuIndex = 1; // 2 for button 2, 3 for button 3
for (byte i = 0; i < 4; i++) {
menuValtoEdit[i] = menuVal[menuIndex][i]; // get values from main array and put into edit buffer
}

// exit sub menu here
menuIndex = 0; // we're no longer in the menu, just in case this is important
for (byte i = 0; i < 4; i++) {
menuVal[menuIndex][i] = menuValtoEdit[i]; // put the edited values back into the main array
}

[Spirik]

Hello there! Hopefully I will have a chance to look into it later this weekend. I think I may come up with some solution (that may or may not involve inheriting or overriding GEM classes to expose some internal methods and properties or to expand its functionality).

[Spirik]

I think I managed to implement something remotely similar to what you would like to achieve.

GEM doesn't support callbacks for entering or exiting menu pages. However similar behavior can be achieved by additional check for GEM_KEY_OK presses in a main loop and subsequent checks for current menu item index GEMPage::getCurrentMenuItemIndex() or title GEMItem::getTitle() (as in the following example).

Consider we would like to have three config menu pages with identical structure of two variables: one int number and one bool flag (this code is loosely based on GEM Basic example with encoder, so thats where test variables come from).

Variables that we would like to edit:

// Create variables
int number[] = {128, 256, 512};
bool enablePrint[] = {true, false, true};

Names of config pages and index of currently selected one:

// Config pages names
const char* configPageName[] = {"Config 0", "Config 1", "Config 2"};
byte currentConfigIndex = 0;

Then we need our proxy (or buffer) variables, that will temporarily hold values of a real ones when we enter corresponding config menu page:

// Create variables that will be editable through the menu and assign them initial values
int numberProxy = 0;
bool enablePrintProxy = false;

Create menu items for our editable proxy variables, callbacks will be used to copy values from proxy variables to the real ones upon save:

// Create two menu item objects of class GEMItem, linked to numberProxy and enablePrintProxy variables
void numberProxySaveCallback();
GEMItem menuItemInt("Number:", numberProxy, numberProxySaveCallback);
void enablePrintProxySaveCallback();
GEMItem menuItemBool("Enable print:", enablePrintProxy, enablePrintProxySaveCallback);

Create proxy config menu page:

GEMPage menuPageConfig("Config", menuPageMain); // Config submenu

Create a number of menu items linked to the same single config menu page:

// Create menu item linked to Config menu page
GEMItem menuItemMainConfig[] {
  {configPageName[0], menuPageConfig},
  {configPageName[1], menuPageConfig},
  {configPageName[2], menuPageConfig}
};

Add menu items to main menu page and config page:

void setupMenu() {
  // Add menu items to menu page
  menuPageMain
    .addMenuItem(menuItemMainConfig[0])
    .addMenuItem(menuItemMainConfig[1])
    .addMenuItem(menuItemMainConfig[2]);

  // Add menu items to Config menu page
  menuPageConfig
    .addMenuItem(menuItemInt)
    .addMenuItem(menuItemBool);
  ...
}

Then in loop() function when GEM_KEY_OK button press is detected, get title of currently selected menu item, compare it with titles of config menu pages and set currentConfigIndex variable to its index (and also update title of our proxy config menu page to reflect menu item that was pressed to access it):

...
const char* title = menu.getCurrentMenuPage()->getCurrentMenuItem()->getTitle();
for (byte i = 0; i < 3; i++) {
  if (strcmp(title, configPageName[i]) == 0) {
    currentConfigIndex = i;
  }
}
menuPageConfig.setTitle(menuItemMainConfig[currentConfigIndex].getTitle());
passValuesToProxy();
...

Lastly define callback functions that will pass values between real and proxy variables:

void passValuesToProxy() {
  numberProxy = number[currentConfigIndex];
  enablePrintProxy = enablePrint[currentConfigIndex];
}

void numberProxySaveCallback() {
  number[currentConfigIndex] = numberProxy;
}

void enablePrintProxySaveCallback() {
  enablePrint[currentConfigIndex] = enablePrintProxy;
}

Here's link to Wokwi simulator: https://wokwi.com/projects/393255597641436161
And here's gist: https://gist.github.com/Spirik/1a5fdd54f809035950a655f7daa2d9a8

Above examples use rotary encoder as an input device, but can be easily modified to use basic push-buttons (with either KeyDetector or U8g2 button press detection).

Also it is possible to go slightly different route, and create all necessary config menu pages dynamically in a loop: that will be less memory efficient than above proxy/buffer solution, but is also viable. I don't have full example of dynamic menu pages creation, however there is one for menu items: https://gist.github.com/Spirik/191fafd4095627cea7460ec47ae8a954 .

Hope that will help you in some way!

[DisasterAreaDesigns]

I think that will work great, thanks very much! The key here is the separate function that responds to the OK button so we know that we're entering a menu, and then using the getCurrentMenuPage()->getCurrentMenuItem()->getTitle() to match to the config menu names.

Thanks for your help with this!