INQ241B - Day 15 Notes

Local Data

Recall the counting button app

page main ()
initialize
  ◳ count := 0
display
boxed
  ◳ count → post to wall
  box → set border(colors → foreground, 0.1)
  box → on tapped(handler)
    where handler() is
      ◳ count := ◳ count + 1 end
    end
  end boxed
end page

When you close and resart the app, it is back to zero
This is in part because the initilize section sets the count variable to 0 every time the app starts
So if we delete that, nothing happens
These is because by default global variables are not stored on the user’s device
They are recreated every time the app is run
Changing this is easy
Under ‘global vars’ click on the variable name and click the radio button nexted to ‘local’
Now the variable is local to the user’s device
Each device has its own local copy of the variable
Notice that the icon for the variable turned yellow

Cloud Data

If we publish and load in a different web browser, there are two different counts
If you want to share that value, click the ‘replicated’ check box
Note, with replicated data, the user must log in
Note the cloud icon at the top of the window
This replicates it across a single user’s device
Can also replicate it across all users by adding the following to the initialize section
```
cloud → switch to session(cloud data → everyone session)
```
Note that the cloud icon has changed and the variable icon has turn cyan

Collections

Recall the todo list app we created previously

page main ()
initialize
  ◳ todo list := collections
  ◳ user input := ""
display
  boxed
    box → set border(colors  → foreground, 0.1)
    box → edit("textline", ◳  user input, changehandler)
      where changehandler(text : String) is
        ◳ user input := text
      end
    end
  end boxed
  boxed
    "Add" → post to wall
    box → set border(colors → foreground, 0.1)
    box → on tapped(handler)
      where handler() is
        ◳ todo list → add(◳ user input)
      end
    end
  end boxed
  for each s in ◳ todo list do
    s → post to wall
  end for each
end page

It would be nice if it remembered things we want to do
So do the same thing as before, remove the initialization
But without the initialization it breaks, it doesn’t have a default value

Can fix this with an if statement

if ◳ todo list → is invalid then
  ◳ todo list := collections → create string collection
else do nothing end if

Make it local, but this gives an error, collections can’t be saved
To solve this need a completely different type of object, a table
Click ‘add new’, choose ‘see more options’, choose table
A table is like an Excel spread sheet, there are columns that hold data of a certain type, and rows that are entries in the table
Rename the table and add a column
Notice that the icon is yellow, by default they are local
Add to a table is a little more complicated than adding to a collection, because a table can have multiple columns
```
⌹ ToDo table → add row → thing := ◳ user input
```

To display the contents

for each ToDo in ⌹ ToDo table do
  ToDo → thing → post to wall
end for each

Activity

Activity 15