I am using one activity all fragment approach. Now I have a fragment A and when I go to fragment B I replace A in container with B with
.replace(R.id.master_fragment_container_above_toolbar, fragment)
.addToBackStack("")
.commit();
As you can see, I have added fragment to backStack. But now when I press back on device, it re-instantiates the fragment A and thus takes time to go back.
Is there another way to do it? I don't want to use add(), if I add multiple fragments to container, it will take up a lot of memory.
The short answer - there's no silver bullet in your case. You'll have to use replace() and it will re-create fragment's View on going back. That's "by design".
The good news is that there're a few tricks you can do to make it less dramatic for UX.
Cache whatever you can. If you load content from web - write it into the local SQLite db. And fill the screen from Local Storage while refreshing the data from the server.
In onCreateView() avoid re-creating Adapters once they are already exist. If user is getting back to FragmentA from the FragmentB, FragmentA will recreate its View. But it doesn't mean, that local variables are null at this point. So I do it like this:
public class FeedFragment extends Fragment {
private FeedAdapter adapter;
......
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = initialize(inflater, container, R.layout.fragment_with_recyclerview);
....
if (adapter == null) {
adapter = new FeedAdapter();
}
RecyclerView recyclerView = (RecyclerView)rootView.findViewById(R.id.recyclerView)
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL));
return rootView;
}
}
It matters, because filling TextViews, etc. are so fast operations, that you don't really care about it, while huge ListView or RecyclerView can be much more expensive;
Use image-caching and good image-loading tool. I'd recommend Picasso from Square. It has automatic memory and disk caching;
Try to logically decouple your app. Let's take a Gmail-style application, as an example:
It has NavigationDrawer, which is switching user through the root fragments (i.e. no need to keep navigation stack). Once you open mail-thread - it replaces the root fragment with MailThread fragment. There you can consume the content.
But once you click on "Compose email" - you are redirecting to a separate Activity - as you move from consuming content to composing content state (I.e. significant change in user's behaviour: new user scenario == new activity).
Many top developers go even further and having Activities for pretty much everything. Twitter (and it's satellite products) as an example. But personally, I prefer to keep it in balance (as opening new activity is an expensive operation from perf. point of view).
Related
I am absolutely in love with these new components Android is introducing. So, I am building a standard mobile application with solely one activity using the Navigation components and Architecture components such as a View Model as I am performing a lot of communication with my data that I stored in room.
In one of my bottom navigation tabs, I have a list that is loaded from all my data in room. So far, I have set up my RecyclerView and my adapter in the OnCreateView() (only function used in this fragment) of this list fragment and every thing shows successfully.
The problem is that every time (especially more at first view) the fragment takes a solid 10 seconds to display all the data (which is normal considering there is a lot of it).
My question: Is there a way the adapter and and RecylcerView of this specific fragment could be setup (and load all my data) in the OnCreate() of my sole activity? So that when I view the fragment for the first time, everything pops up right away.
Also, how would I go about using OnPause() of the list fragment so that when I am on another tab, the list fragment doesn't get destroyed and when we go back on it, it displays right away?
Fetch all data from room inside onCreate() method of fragment. The onDestroyView() method calls everytime you moves away from the fragment.
To prevent recreation of views inside fragment store view in a variable.
Example:
class YourFragment extends Fragment{
View rootView;
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
//fetch data from room
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState){
if(rootView == null)
rootView = inflater.inflate(R.layout.your_fragment_layout, container, false);
return rootView;
}
}
I made an activity which is simply a viewpager with a few tabs. Each tab is like a form that the user needs to fill out. When the user is done, the data from the view pager should be collected and sent back as a result. I almost have this working but for some reason the data on my first tab seems to get reset when the user gets to the third tab. I'm guessing this is due to some view recycling in the pager. Anyways, I'm wondering if there is some easy way to gather all the data from the different tabs or do I have to create some kind of tight coupling between the activity and viewpager object?
you have to use SmartFragmentStatePagerAdapter as described here "https://guides.codepath.com/android/ViewPager-with-FragmentPagerAdapter" and than need to
vpPager.setOffscreenPageLimit(3);
Your issue should be resolved. :)
A viewpager will kill off the fragment if it is 2 pages away from the current page. It then recreates it when the pager is on a page that is 1 step away from it.
You should move your form data into your activity/fragment that is holding the viewpager and use fragment listeners to update your data accordingly
For example, you could use a fragment listener like below to pass the data to/from the containing activity
public interface MyFragmentListener{
void saveMyFormData(MyFormData formData);
MyFormData getFormData();
}
private MyFragmentListener mListener;
//initialise fragment listener in onAttach (or elsewhere)
private void initFormView(){
MyFormData data = mListener.getFormData();
//do stuff with data
}
private void saveData(){
mListener.saveMyFormData(myFormDataObject);
}
I'm a beginner in Android, so I apologize for the mistakes and I'd appreciate any constructive criticism.
I'm writing a basic application with a ListView of images, and when the user clicks on an item in the list, I want to display that image in a ViewPager, where the user can swipe back and forth to browse the whole list of images. Afterwards when the user presses the back button, I want to switch back to the ListView.
I manage the business logic in the MainActivity, which uses MainActivityFragment for the ListView and ImageHolderFragment for ViewPager.
The simplified code so far is as follows:
#Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mListItems = new ArrayList<>();
mListItemAdapter = new ListItemAdapter(this, R.layout.list_item, R.id.list_item_name, mListItems);
mListView = (ListView) findViewById(R.id.list_view_content);
mListView.setAdapter(mListItemAdapter);
mDeletedListItems = new ArrayList<>();
mViewPager = (ViewPager) getLayoutInflater().inflate(R.layout.image_display, null, true);
mImageAdapter = new ImageAdapter(getSupportFragmentManager(), mListItems);
mViewPager.setAdapter(mImageAdapter);
mViewPager.setOffscreenPageLimit(3);
mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mViewPager.setCurrentItem(position);
setContentView(mViewPager); // TODO: this is very wrong!
}
});
loadImages();
noContentText = (TextView) findViewById(R.id.no_content_text);
if (mListItems.isEmpty()) {
noContentText.setText(R.string.no_images);
} else {
mImageAdapter.notifyDataSetChanged();
}
}
Although this does work to some extent, meaning that it manages to display the ViewPager when an item in the list is clicked, there are two things about it ringing the alarm bells:
I've read that calling setContentView() for the second time in the same class is pretty much a sin. Nobody explained me why.
The back button doesn't work in this case. When it's pressed, the application is terminated instead of going back to the list view. I believe this is connected to the first point.
I would appreciate any help, explanations if my idea is completely wrong, and if my case is hopeless, I'd like to see a successful combination of ListView and ViewPager with transitions between each other.
Your activity already has R.layout.activity_main set as content view, which rightly displays the list view - that's what the responsibility of this activity is as you defined it. If we want to change what's shown on the screen, we should use a different instance of a building block (activity or fragment) to display the view pager images.
To say the least, imagine if you wanted to change the view to a third piece of functionality or UI, or a fourth... it would be a nightmare to maintain, extend and test as you're not separating functionality into manageable units. Fields that are needed in one view are mixed with those needed in another, your class file would grow larger and larger as each view brings its click listeners, callbacks, etc., you'd also have to override the back button so it does what you want - it's just not how the Android framework was designed to help you. And what if you wanted to re-use UI components in different contexts whilst tapping in to the framework's activity lifecycle callbacks? That's why fragments were introduced.
In your case, the list view could continue to run in your MainActivity and in your click listener, onItemClick you could start a new activity that will hold a viewPager:
Intent i = new Intent(MainActivity.this, MyLargePhotoActivityPager.class);
i.putExtra(KEY_POSITION, position);
// pass the data too
startActivityForResult(i, REQUEST_CODE);
Notice how you could pass the position to this activity as an int extra, in order for that second activity to nicely set the viewPager to the position that the user clicked on. I'll let you discover how to build the second activity and put the ViewPager there. You also get back button functionality assuming your launch modes are set accordingly, if needed. One thing to note is that when you do come back to the list View, you'd probably want to scroll to the position from the view pager, which is why you could supply that back as a result via a request code. The returned position can be supplied back to the list view.
Alternatively, you could use the same activity but have two fragments (see the link further above) and have an equivalent outcome. In fact, one of your fragments could store the list view, and the second fragment could be a fullscreen DialogFragment that stores a viewPager, like a photo gallery (some details here).
Hope this helps.
I've read that calling setContentView() for the second time in the
same class is pretty much a sin. Nobody explained me why.
Well, you kind of get an idea as to why.
When you use setContentView() to display another 'screen' you do no have a proper back stack.
You also keep references to Views (like mListView) that are not visible anymore and are therefore kind of 'useless' after you setContentView() for the second time.
Also keep in mind orientation changes or your app going to the background - you'll have to keep track of the state that your Activity was in which is way more complicated than it has to be if you have one Activity that does two different things.
You won't be arrested for doing things like you do right now, but it's just harder to debug and keep bug free.
I'd suggest using two different Activities for the two different things that you want to do, or use one Activity and two Fragments, swapping them back and forth.
If you insist on having it all in one Activity you need to override onBackPressed() (called when the user presses the back button) and restore the first state of your Activity (setContentView() again, pretty much starting all over).
In my activity I have several fullscreen fragments, each of them downloads some data from web (using an async task) and shows them to the user. The fragments are showed one at a time.
To be more specific, each of the fragment readings some urls from a sqlite database, and fetch the content before showing them in a list, if that matters. The data loading tasks can be done in the OnCreate() function.
I would like to preload all the fragment (at least starting the downloading), when I show a splash screen. Pretty much like a viewpager preload its fragments.
I am wondering how to achieve this? I tried initialize/create all the fragments in the OnCreate() function of my activity, hoping the OnCreate() of fragments could be called earlier, but the OnCreate() and OnCreateView() function of the fragments are not called until a fragment is about to show to the user.
It sounds like you need to separate your model (the data which is downloaded) from your view (the fragments). One way to do this is to start the downloading AsyncTasks in your activity, rather than starting them in each fragment. Then when the fragments are eventually displayed they can show the data which has been downloaded (or a spinner or some other indication that the download process is still executing).
Fragment's onActivityCreated(Bundle) tells the fragment that its activity has completed its own Activity.onCreate().
So your solution to this problem is initialize or create or do your stuffs which you want to preload before fragments are created, inside your Fragment's onActivityCreated(Bundle)
see documents for fragment's lifecyle
The earliest pace you can start loading is either in a static singleton or in the Application Class
What I end up doing is the following, (1) add all the fragments into the container. So they (and their view) will be created and initialized. (2) hide those not in use and only show the one I would like the user to see. (3) use FragmentTrasaction.show()/FragmentTrasaction.hide() to manipulate the visibility instead of FragmentTrasaction.add() or FragmentTrasaction.replace().
If you following this approach, be warn that all the fragments will be cached in memory. But the benefit is the switch between fragment will be fast and efficient.
I was facing the same problem and then I used this method, suppose we are having an EditText in the fragment, then we can use codes like this
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
//this method allows you to input or instantiate fragments before showing this to an activity conidering id is "editTextEditProfileFirstName"
EditText firstName = (EditText) getActivity().findViewById(R.id.editTextEditProfileFirstName);
firstName.setText("This is my first name", TextView.BufferType.EDITABLE);
super.onViewCreated(view, savedInstanceState);
}
Normally I would use a separate activity for each "screen" I wish to display, using different XML files.
However I'm working with Dynamically loading jar files into an android application, so therefore at runtime, I am not aware of how many activities there will be, or how many screens there will be.
At the moment, using java reflection, I am able to return a list of strings from the dynamically loaded java file, and draw each list item, as a separate button onto the screen. If one of these buttons is clicked, i want to be able to load a different "screen" on the stack. So when I press back from this new screen, it goes to the previous screen that called it.
Is it possible to do this without creating a new activity and passing a new intent to it and of course making relevant changes to the android manifest file?
To use blackberry functionality as an example - Is there an equivalent in android to blackberry's push and pop screens? Where the screen ur pushing/popping, would simply extent MainScreen?
If anyone has questions, or If I've been vague, please comment and I will try my best to explain myself, any help is very much appreciated.
The Android equivalent to BB's push/pop screen is startActivity()/finish(). However, you can manage your own views in a single activity by either using a container view (such as ViewSwitcher, as #hasanghaforian suggests) or by simply calling setContentView() with a new view hierarchy whenever you want to change the screen. Be aware that when you call setContentView, any view references that you obtained by calling findViewById will be stale.
In my opinion you should use Fragment. I assume that you have some piece of code where you iterate over the strings:
for(String def : definitions) {
Fragment f = new CustomFragment();
Bundle b = new Bundle();
b.putString("STRING_DEF",def);
f.setArguments(b);
fragments.add(f);
}
in above piece of code a collection of Framents is just created. Let's look at the CustomFragment implementation:
CustomFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
String def = getArguments.getString("STRING_DEF");
//write code to create view
return view;
}
}
Now in your ListActivity you have to implement on click listener more or less like this like this
public void onListItemClick(ListView l, View v, int position, long id) {
FragmentManager fragMgr = getFragmentManager();
FragmentTransaction t = fragMgr.beginTransaction();
t.replace(R.id.id_of_view_place_holder_for_fragment,
fragments.get(position),"FRAGMENT_TAG");
t.commit();
}
you can use ViewSwitcher. ViewSwitcher is a ViewAnimator that switches between two views, and has a factory from which these views are created. You can either use the factory to create the views, or add them yourself. A ViewSwitcher can only have two child views, of which only one is shown at a time.Or you can use fragments.
If you refer to if it is possible to have different layouts in the same activity, the answer is yes.
Activities are independent of layouts, you don't assign the layout for an activity in the manifest, you define what layout to use in the activity calling setContentView() method from Activity class to set a layout.
So if you want to have some layouts (screens) the only thing you have to do is define various layouts and use them when you want calling setContentView(R.layout.the layout), after this call, the layout chosen will be displayed.
If you can't create the layout statically by xml, you can create it dinamically by code as needed by demand each time you want.
In addition you can have a stack of layouts, each time you need a new screen, build it, push it to the stack and call setContentView() method, when you don't need it more, pop off the stack and call setContentView() with the new layout in the top of the stack.
Hope it help you