12.03.2011 0:31, David Williams пишет:
Does Java do certain things asynchronously then? I was thinking that
things were done in a serial fashion but perhaps that is not the case.
ProgressDialog.show is asynchronous, just like may other UI operations.
Normally, this works, because the Android UI toolkit, just like many
others (and not just for Java) is built around the "event loop" or
"message loop" concept. The main thread runs in an infinite loop for
processing messages, one at a time. Each message is a small task: this
can include, for example, showing a dialog, redrawing a view, calling
one of the application's callback methods.
Your code:
- Called by Android in onCreate
- Calls setContentView
- Calls ProgressDialog.show
- Fetches stuff from the Internet
- Returns from onCreate
All of the above happens on the UI thread, which waits for your onCreate
to return before proceeding to the next message (== "small task").
What your code in onCreate should do:
- Call setContentView
- Call ProgressDialog.show
- Start an asynchronous operation to fetch stuff from the Internet
- Return from onCreate
- [ Android processes queued-up operations: draws your activity, shows
the dialog ]
The asynchronous fetch then should:
- Run on its own thread;
- When done, "tell" the application to hide the progress dialog and proceed.
Hopefully, it starts to make more sense as you read through the links
I've provided.
This is probably the easiest way to implement asynchronous operations:
http://developer.android.com/reference/android/os/AsyncTask.html
--
Kostya Vasilyev -- http://kmansoft.wordpress.com
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