How to handle activity coming to foreground again_问答_开发者

The books I have are abysmal at explaining how to work with the lifecycle, there's a lot I'm missing that I'm hoping somebody can fill in.

My app structure is that when it's first started, it starts an activity full of legalbabble that the user has to accept. When he says 'ok', I start my main activity and then I call finish like this:

public void onClick(View view) { //as a result of "I accept"
    Intent mainIntent = new Intent(mParent, EtMain.class);
    startActivity(mainIntent); // Start the main program
    finish();
}

Then in EtMain in the onCreate method, I've got some tabs and I instantiate some classes:

super.onCreate(savedInstanceState);
setContentView(R.layout.main);

mTabHost = (TabHost)findViewById(android.R.id.tabhost);
SetupTabs.setMyTabs(mTabHost, this);

mComData = new ComFields(this); // Create the objects
mDepWx = new WxFields(this, DepArr.Departure);
mArrWx = new WxFields(this, DepArr.Arrival);
mDepVs = new DepFields(this);
mArrVs = new ArrFields(this);
mTabHost.setOnTabChangedListener(new OnTabChange开发者_JAVA技巧Listener(){
}

Questions: The 'finish' in the first fragment should terminate the legalbabble activity so it'll never be restarted, right? And the EtMain one will remain forever (until killed externally), even if my app gets pushed to the background, right?

The way it is now, when EtMain gets pushed and later brought to the foreground (by tapping on the icon), it goes through the legalbabble screen as though it's a complete start - that's what I'd like to prevent - going thru the legalbabble screen again.

It would seem that I'd want to override onRestart in the second code fragment and put something in there to restart the app, right? That's the part I'm unclear about.

My question then is what needs to be done in onRestart. Do I have to recreate all the tabs and data in the tabs and all my object instantiations? Or is the memory state of the app saved someplace and then is restored back to the state that it was in before something else was brought to the foreground in which case not much needs to be done because all the objects and listeners will still be there?

Yes after the first activity has ended you shouldn't have to view that activity again. You could also write to the shared preferences that the user has previously seen legal info.
If you're UI object creation is in the onCreate method, this should only be called once. Pausing or resuming will not call the onCreate method again.
Unless you explicitly remove your objects and tabChangedListeners in the onPause method, you should not have to touch them in the onRestart method.
Correct, the state of the app is saved automatically. You shouldn't have to touch the onRestart method.

Hope this helps!

I think the problem is that the launch activity in your manifest is the legalbabble activity, so when you click on the icon, the system launches another one. A better architecture would be to launch the legalbabble activity it from your EtMain activity in the onCreate method of the latter, using startActivityForResult. From the docs:

As a special case, if you call startActivityForResult() with a requestCode >= 0 during the initial onCreate(Bundle savedInstanceState)/onResume() of your activity, then your window will not be displayed until a result is returned back from the started activity.

When you get the result in onActivityResult, you can call finish() if the legal stuff was declined; otherwise everything will proceed normally.

This avoids the problem that the launch activity defined in your manifest finishes when the legal stuff is accepted.

EtMain will not remain forever, if the user backs out (by pressing the BACK key) the Activity will be finished (onPause, then onStop, then onDestroy will be called). In general you can ignore onRestore until you are doing something complicated.

Once the user has exited your application and re-enters (or presses the icon on the Homescreen), onCreate (followed by onStart and onResume) will be called for your first activity, so you do not need any logic in onRestart, your code in onCreate will do the setting up for you as it did the first time. Because of this your legal babble will appear again when the user starts the app after exiting unless you store a preference (in SharedPreferences or a database or file) to indicate you have already displayed it - in which case finish it straight away and start the main activity.

onRestart is only called when the application goes from the stopped state (onStop has been called but not onDestroy) to the started state (onStart is called but onResume has not yet).

For saving data - some components save their state automatically (e.g. EditTexts remember the text in them, TabHosts remember the currently selected tab etc). Some components will not. If you wish to save extra data then make use of onSaveInstanceState and onRestoreInstanceState. You should only use these methods to restore the state of your application or temporary data, not important things, e.g. the id of the resource what the user was looking at, what zoom level they were at etc. For things like contacts or actual data you should commit these changes to a database, SharedPreferences or other permanent storage (e.g. file) when onPause is called.

I recommend taking a look at the Android Activity lifecycle if you are confused. Or ask more questions!