What does Handler do

 * <p>There are two main uses for a Handler: (1) to schedule messages and
 * runnables to be executed at some point in the future; and (2) to enqueue
 * an action to be performed on a different thread than your own.
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  • Schedule message and runnable execution at some point in the future (passing messages)
  • Queue and execute operations in different threads (thread switching is often used when a child thread notifies the UI thread to update the UI, provided the Handler holds a mainLooper).

How to use Handler

Handler source code analysis

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