How do I create a permanent field calculation in an AGOL feature layer?

[AshleyThornton]

I have create a map to use in Collector for ArcGIS for the fire department. After using it they have a request: Once they input values for Field A and Field B, they want Field C to calculate a solution using Fields A and B.

I have used the calculate field function in AGOL (ex. Field C = Field A + Field B). However, the field will not 'remember' this calculation. I want the field calculation to stay in that field so that each time I or another user opens the map and inputs the data for A and B, it will auto-populate the value for C.  Is there a way to NOT have to run a field calculation each time I open the map?

[PayneTodd]

In dashboards I was able to hack the table view and display a calculated expression.  The key was to add a field that was not being displayed in the table (like OBJECTID) Then update the label in the Header  section for me it was updated to STATUS.  Then in the Values section return a calculation for the status as the display text.  DEFINATELY A HACK.  It would be nice to add a calculated field to the hosted feature layer directly, kinda like a computed column in SQL. or perhaps in a view of the layer.

OBJECTID: {

      displayText : alarmStatus,

      textColor: 'Red',

      backgroundColor: alarmColor,

      textAlign: 'right',

      iconName: '',

      iconAlign: '',

      iconColor: '',

      iconOutlineColor: ''

    },

[Michael_Stead]

This is an old post, but I do not understand why it doesn't have the answer, so I will add it... maybe I am misreading the question.

1. Add the field you want to populate to your layer (if it doesnt exist)

2. Open the layer in the webmap being used to add new features and select the layer from the layers panel on the left

3. go to Configure Editing on the right and then to Forms

4. convert popup or add whatever fields you would like

5. Configure each field you have added, for the field you would like to autopopulate make it read-only and at the bottom in Calculated Expression hit the little gear and New Expression

6. rename the expression what you want and write it. I often generate a unique ID based on the user and time stamp using the expression: 

Replace(( Concatenate([ GetUser($layer).fullName, Day(Now()), Month(Now()),Year(Now()),Hour(Now()),Minute(Now()),Second(Now())],'_')),' ', '_')

You can also do geoprocessing operations, like pull a field from the nearest associated layer or populate with a distance to a certain type of feature.. lots of possibilities