问题
Should you get data via a cursor and fill in the data on the screen, such as setting the window title, in onStart() or onResume()?
onStart() would seem the logical place because after onStart() the Activity can already be displayed, albeit in the background. Notably I was having a problem with a managed dialog that made me rethink this. If the user rotates the screen while the dialog is still open, onCreateDialog() and onPrepareDialog() are called between onStart() and onResume(). If the dialog needs to be based on the data you need to have the data before onResume().
If I'm correct about onStart() then why does the Notepad example give a bad example by doing it in onResume()? See http://developer.android.com/resources/samples/NotePad/src/com/example/android/notepad/NoteEditor.html NoteEditor.java line 176 (title = mCursor.getString...).
Also, what if my Activity launches another Actvity/Dialog that changes the data my cursor is tracking. Even in the simplest case, does that mean that I have to manually update my previous screen (a listener for a dialog in the main activity), or alternatively that I have to register a ContentObserver, since I'm no longer updating the data in onResume() (though I could update it twice of course)?
I know it's a basic question but the dialog only recently, to my surprise, made me realize this.
回答1:
To answer your question about NoteEditor, simply take a look at the lines above the one you cite and you'll see...
// Requery in case something changed while paused (such as the title)
mCursor.requery();
The comment seems to explain it all. Although I haven't gone through the NotePad example myself, it appears the author(s) are building in the ability to recover from changes whilst the NoteEditor is paused (and then resumed).
As GSree explains (whilst I was typing this), there isn't a right or wrong answer and it simply depends on what needs to be done at which point of the Activity life-cycle.
回答2:
Again the solution depends on what suits you.
If you want the cursor to be pre-populated once per application (and not bothered about any change, then you can do it in onCreate(). This method will be recalled only if the app process is killed and app is reinitiated.
If you want the cursor to be prepopulated everytime the visible lifetime starts (most cases a service/broadcast is calling your activity, you should use onStart()
If you want the cursor to be prepopulated for every foreground lifecyle of activity, you should use onResume(). So if you have a dialog box or another subactivity modifying some information and hence you want to reload the cursor, it is best you do so in onResume(). The downside for this method is everytime the activity comes in foreground the cursor is reloaded.
Hope this makes it clear
来源：https://stackoverflow.com/questions/4636797/android-lifecycle-fill-in-data-in-activity-in-onstart-or-onresume