Android learning notes

Creating Views Dynamically

var textViewAppContext = new TextView(getApplicationContext() /* also "this" if you want to do activity */)
// set some stuff on the textView

layout.addView(textViewAppContext)

Context

• a handle to the android system

  • Resources layouts, strings, images
  • System services (LayouteInflator, SharedPreferences...)
  • Launching Activities
  • Access Databases
  • Etc...

• Typical Subclasses

  • Activity
  • Application
  • Service

• Activity Context only lasts as long as it's alive

  • if you hold a reference to it you could cause a memory leak because it won't allow the Activity to garbage collect

• Application lasts forever? getApplicationContext()

• Often you pass "this"?

ViewPager

• ViewPager → Controlls the actually swiping between views

• ViewPager gets it's content from a PagerAdapter

• 1 View per page → Pager Adapter

• A Fragment for each page → FragmentPagerAdapter (for fragments)

  • this keeps each page in memory, which can be expensive if you have a lot

• FragmentStatePagerAdapter

  • Destory & Recreate fragments

ViewPager2 is the one I should use

ViewModel

learned from: https://www.youtube.com/watch?v=5qlIPTDE274

View Models survive "Configuration Changes"

Rotating a phone basically tears down your activity and re-creates it

this clears out all local state

ViewModels survive therefore don't have this problem

Also they have a better separation of concerns

• ViewModel: holds UI data (Login form state, etc...)
• Activity: Displays the ViewModel's UI centric data
• Repository: API for saving/loading app data

WARNING: these do not save their state if the process closes down, onSaveInstanceState does

LiveData

A class that will broadcast changes to data (create reactive data)

• Android fundimentials
• Android