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How to update selected item when bottom navigation switch to Navigation Rail

I have a Bottom-Navigation in portrait Mode and a Navigation-Rail-View in landscape mode.
How can I update the selected item when the device is rotated?
I tried it with savedInstanceState, with override theonSaveInstanceState and onRestoreInstanceState.
But because I use savedInstanceState for other things too, overide the two above methods cause crash.

Eventually I found a solution.
But before that, I should mention that a better title for this question could be: How to share selection item between the BottomNavigation and NavigationRail.
Ok, solution:
Just replace setSelectedItemId with getMenu().getItem(itemIndex).setChecked(true)
Example:
Use:
bottomNavigationView.getMenu().getItem(indexOfItem2).setChecked(true);
Instead of:
bottomNavigationView.setSelectedItemId(R.id.item2);

try this
navigationRailView.setSelected(false);

How should I structure bottom navigation in Android coming from iOS background?

Some background:
Coming from an iOS background, using UITabbarController is very common and straight forward. Each Tab in the tab controller will change the current view to another UIViewController, and each of these UIViewControllers can have its own NavigationController (which kind of acts as a back stack). So whenever I switch tab, I would resume to the state where I left off.
Now I want to implement the same thing in Android, but it seems like the use of ViewController is different in Android. After digging around, I read that instead of using Activity like UIViewController, I should use Activity to act more like NavigationController, and use Fragments (which is deprecated)
to act as UIViewController instead.
However my question is:
Should I be implementing multiple Activities for Bottom Navigation? When I click on each item in the Bottom Navigation should I use an Intent to change Activity? Because from my understanding, using Intent to change Activity will add the new Activity to an Activity back stack, which would prevent me from switching back to whichever Activity I want. If someone could, Please tell me what is the "right" way (if there is one) to structure Bottom Navigation. Thank you all in advance.

You can use fragments as UIs, And Use a BottomNavigationView in your activity or you can use some libraries.
Here is a library for better customization: https://github.com/ittianyu/BottomNavigationViewEx
Native Method:
https://medium.com/#hitherejoe/exploring-the-android-design-support-library-bottom-navigation-drawer-548de699e8e0

In Android you should use Viewpager, tablayout and Fragments. Just search for its tutorials. there are lots of them on internet

How to change app theme from ordinary "Blank Activity" to "Master/Detail Flow"

I have an application that works on the basic theme "Blank Activity" and what i would like to do is to change it to a "Master/Detail Flow" theme. I do know that this will make my application work on android SDK 11 + (android 3.0 Honeycomb +), that is OK with me. The issue is i don't know where to start from, what are the basic steps to make this BIG conversion? I couldn't find any example to help me out with this issue. What should i be looking for. i am sure this has been done, can you at least please give me some pointer on how to do this?
my Application is not that complicated it uses activities, async tasks, DB, custom lists,... it is very basic. I use the custom list to display data and when i click on it it displays much more details, so I thought what better way to do this in a more professorial matter than the "Master/Detail Flow". If you have any tutorial regarding the "Master/Detail Flow" that you can hook me up with that might help.

I have an application that works on the basic theme "Blank Activity"
and what i would like to do is to change it to a Master/Detail Flow"
theme.
I think a change of the application flow would be more appropriate then a change of theme. Two obvious questions that would appear are why do you suddenly want to make this change and are sure your app makes sense in a master/detail flow? The answer would most likely be positive but you should answer them nonetheless.
I do know that this will make my application work on android SDK 11 +
(android 3.0 Honeycomb +), that is OK with me
I don't see why you're app couldn't run on versions below with the new master/detail stuff.
The issue is i don't know where to start from, what are the basic
steps to make this BIG conversion? I couldn't find any example to help
me out with this issue. What should i be looking for. i am sure this
has been done, can you at least please give me some pointer on how to
do this?
You haven't provided details about how is your app implemented. The change would revolve around fragments so a BIG question would be if the current single pane version is built using the fragments framework.
If your app is built using fragments then making the change shouldn't be too hard. You'd need to:
establish which parts(fragments) should be combined in an activity(from your old ones) to make the master/detail(when the space would allow it)
change the multi pane activity to accommodate the new fragment(s). This should be easy to do but it would depend on the size of the features exposed by each of those fragments.
modify the rest of the activities(for when the app will not run in the multi pane mode), this would be small changes as the activities would mainly remain as the current version
If your app isn't built using fragments, then what I said above still applies but you'd need to also actually make the required fragments wrapping whatever functionality your app has. This would most likely result in a big code refactoring.

Here is a tutorial about the Master/Detail template in Android - An Android Master/Detail Flow Tutorial.
As far as I understand your application is up and running - so I'm not sure whether it is worth it to try rewriting it, unless you are experiencing some problems of course. :)
In general the master/details flow requires the following steps:
Implement a ListFragment showing basic information of your items
Implement a Fragment showing detailed information about a particular item
Make an xml layout file for large devices (located in layout-sw600dp folder for example). In this layout you have to put both your fragments.
Write a general version of this layout file (i.e. file with the same name but located in the layout folder), which contains only the ListFragment.
Let your activity handle onItemClick event from the ListFragment. Each time an item is clicked, you have to check if the activity is showing both fragments or only the ListFragment. If both are visible, you have to notify the details fragment that new item is selected so it can show its data. Otherwise you have to create new details fragment (you reuse it of course), pass it some information about the selected item (so it can show the item's data) and replace the ListFragment with the new one.
That a basic overview, but it should be enough to give you some idea about this flow. If you need any more details - just let me know. :)

Master/detail flow and blank activity is not same as you want to change by only changing app theme or app base theme. It will be better, if you first design master/detail flow template using UI fragments, then according integrate you blank activity with the master template making necessary changes. And for master/detail flow tutorial just google it, you will find lots of example there.

Here are some links from developer.android.com fragment-ui and adaptui
These are some guidelines about fragments but they are told using a master/Detail app.
Also dont forget to checkout the news reader app provided as sample in the second link.

If you have a recent version of the Android SDK, you should be able to create a new Android application and during that process you can elect to have the wizard create a Master/Detail Flow app for you. It will create a basic working app so that you can look through the code and understand the necessary parts.
Then, depending on how simple your app is, you may want to move all your present code to the new application or vise versa.
Macro changes that will happen:
Change all your current Activities to extend Fragment instead.
You will have to create a FragmentActivity to call your Fragments. This will basically be the boilerplate code, with just the names of your Fragments added to it.
Don't forget to double check your Manifest!
In your converted Fragments that previously extended Activity:
Everywhere you needed a Context, switch that with getActivty() (or create a global variable so that it is only called once)
Change onCreate() to
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
mView = inflater.inflate(R.layout.fragment_signals, container, false);
setHasOptionsMenu(true); // Add if you want to display a Menu
// Your initiation code here
return mView;
}
If you have a menu, change it to
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.activity_main, menu);
super.onCreateOptionsMenu(menu, inflater);
}
And that's it for basic applications. When you first change Activities to Fragments, there will be many errors. But, they are all easy to fix.

Google Maps API v2 for Android using FEATURE_ACTION_BAR_OVERLAY

I was viewing a different question Google Maps Android API v2 - Interactive InfoWindow (like in original android google maps) and as you can see he's using the requestFeature(Window.FEATURE_ACTION_BAR_OVERLAY); to make the map v2 use the full screen. I tried this but the my location button is partially covered by the action bar on mine unlike his. Does anyone know how to move it down slightly?
Thanks!

Unfortunately you don't have any control over this button. Obviously, you can search for this button id in android sources and change layout params manually from the code, but I definitely wouldn't do that.
This button is super easy to implement yourself. So I recommend to disable built-in "locate me" button and implement your own which will be positioned right below the action bar.
To disable it use:
googleMap.setMyLocationEnabled(false);
New button onClick method content:
googleMap.animateCamera(CameraUpdateFactory.newLatLng(new LatLng(googleMap.getMyLocation().getLatitude(),
googleMap.getMyLocation().getLongitude())));

You can just get the view by its id and re-set the top margin Apparently the id is always 2, but this isn't documented and your app will break when/if the id ever changes. Like Pavel said, it's safer to make your own location button and wire it up.
Unfortunately, calling ActionBar.getHeight() in your onCreate will always return 0 since layout hasn't finished. The way to get the real heigh is by using a listener on the ViewTreeObserver:
mainLayout.getViewTreeObserver().addOnGlobalLayoutListener(
new ViewTreeObserver.OnGlobalLayoutListener() {
public void onGlobalLayout() {
int actionBarHeight = getActionBar().getHeight();
// TODO: set margin of views dependent on actionbar height
// remove the listener
mainLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this);
}
}
}

Android custom title bar, does not work with android:label from manifest

I have a custom title bar that I would like to apply to all my activities. I have searched online and found a few ways of doing that however I have ran into a problem.
It seems that despite the fact I have a TextView in my titlebar with id #android:/title, Android will not use the value defined in the manifest in android:label for each activity.
I tried also calling setTitle(R.string.myTitle) but it still will not render it! If I manually put some text in my TextView in the xml it shows up fine.
How can I have a custom title bar that is linked and makes Android use my manifest values for labels? I do not want to lose the setTitle() or the XML attributes functionality.
Thanks.

Try using #android:id/title instead of #android:/title.