= Chapter 20 Notes =

Title: '''Async and File I/O'''

== Summary ==

So much ado about Labels and the text in them.

=== Programming Concepts Summary ===

 1. AlertCallbacks - 626
 1. AlertLambdas - 630
 1. AlertAwait - 630 (All three of these accomplish the same thing)
 1. NothingAlert 632 Even Simpler version of the previous 3. Compare the OnButtonClick Methods

Saving Settings:

 1. SaveProgramSettings - 635 (See codebehind for on 637-638 for async code. ASK THE QUESTION POSED ON 638 Is... reentrant?)

Delay using a task:

 1. TaskDelayClock - 639 (Every 250 milliseconds, the code in the while loop runs to give the Label the current time, but also to randomly change its font size and its location within the AbsoluteLayout)

File IO:

 1. TextFileTryout - 643 (Dependency Service - You know like the padding thing... 1. Interface on p. 643, Implementation in iOS platform 630-644. Read 645 leadup to UWP project! Read 646 leadup to code! Run it with a view of the XAML/CodeBehind...) THIS IS NOT ASYNC!!! Move on to next
 1. TextFileAsync - 653 (Section intro has important hightlighted subjects, especially related to nuget. New IFileHelper starts on 654-655. Read 655 bottom and fall along for a while... crosses over into a new section: keeping it in the background.) 
  1. 664 Don't block on the UI thread!!! Read it. 

Async with scientific computing:

 1. MandelbrotSet - 666-667
 1. MandelbrotProgress - 694 The progress bar usage.
 1. MandelbrotCancellation - 677 how to cancel a long running worker thread.
 1. MandelbrotXF - 680 MVVM version that includes the first M, V, VM all together.

Asynchronous programming model (APM) to Task-based asynchronous pattern (TAP) --> Web actions. 

 1. ApmToTap - 701 robust method to access web pages.