Moving and vanishing lines of code; trouble with Eclipse's XML Editor
After some tests, I have found that the option "Automatically format the XML edited by the visual layout editor" (in Preferences | Android | Editors) might be the culprit here.
With my tests, I've found that changing a property (such as the layout_gravity) while in Graphical Layout design mode always screw up the visual display of the file when I go back to the XML (text) mode when this option is ON but that I have no problem when it's off.
If you want to format the XML upon your return from the Graphical Layout design mode, simply use the shortcut Ctrl+Shift+F. Also, I didn't see any problem with using the option "Format on Save"; even when I use it in the Graphical Layout mode; so you can use Ctrl+S instead while you're still in the Graphical Layout mode to both save and format your XML.
I've tried other editors options like "Show range indicator" or "Use characters to show changes in vertical ruler" but I didn't see any difference in behavior with activating or de-activating these options.
Finally, to correct the visual display of the file when it's corrupt; I found that using the shortcut: Ctrl+A, Ctrl+C, Ctrl+V is a little easier than closing/reopening the file. This is equivalent to making a Select All, Copy, Paste; effectively copying the whole XML file over itself.
This bug is (finally) fixed in ADT 21. The fix is now available in ADT 21 Preview 9, posted a few minutes ago, here: https://android-review.googlesource.com/#/c/44936/1
The reason you get weird visual artifacts is that if a file contains broken DOS line endings (multiple carriage returns without a newline for each carriage return), Eclipse gets very confused. That's Eclipse issue https://bugs.eclipse.org/bugs/show_bug.cgi?id=375421 .
There are two parts to the fix:(1) First, ADT was fixed such that it no longer introduces these \r\r sequences into the document. This makes sure that you don't get new documents which triggers the weird editing behavior, but it does not retroactively fix older documents with these line endings, so if you open them, you still get weird editing behavior.
(2) Second, there's a new lint check which looks for broken line endings in documents. This runs incrementally, so if you edit an XML file which has this problem, ADT will add an error marker for this problem -- along with a quickfix to perform surgery on the document to fix it.
In short:Get ADT 21 Preview 9; run Lint on your projects and look for any complaints about files containing broken line endings, and if it finds any, apply the quickfix. From now on, further edits with the layout editor should keep the files consistently formatted.
FYI, the relevant fix is here: https://android-review.googlesource.com/#/c/44936/
Instructions for easily updating SDK Tools and the Eclipse ADT plugin are here: http://tools.android.com/preview-channel
-- Tor(from the Android tools team)