I am new to android and one thing I am very confused about is Fragment vs Activity. Everywhere now it is suggested that you should use Fragment instead of Activity.
So does it mean that I should make a single Activity and every UI element as Fragment and handle user actions through fragment transactions.
SO my doubt is do every application have single Activity nowdays? If no, why there is need for extra Activities.
Hope I am clear and sorry if it is already answered in some other way.
Thanks
this question has already been asked. However, Fragment is a portion of UI. A fragment relies on an activity, which can handle as many fragments as needed.
I don't think that you absolutely have to limit yourself to having a single activity only. Though, that pattern (1 activity + N fragments) proved useful to me. In my app, a simple quiz game, each of the fragments capture user actions and trigger async activity calls by the means of callbacks.
Example:
// Implements the main view of the app (home page)
public class HomeFragment extends Fragment {
/**
* A pointer to the current callbacks instance (an Activity).
*/
private HomeMenuCallbacks callbacks;
/**
* Callbacks interface (implemented by the Activity)
*/
public static interface HomeMenuCallbacks {
/**
* Called when an item in the navigation drawer is selected.
*/
void onHomeMenuItemSelected(int position);
}
}
public class MainActivity extends Activity implements
HomeFragment.HomeMenuCallbacks {
#Override
public void onHomeMenuItemSelected(int position) {
// Do whatever action based on which
// item from the home page menu was selected
}
}
Check this thread for discussions and link to Android dev guide: Android - I need some clarifications of fragments vs activities and views
Related
I'm aware the View structure for Android is completely different (ie. Activities instead of View Controllers) but I need to create a Navigation Bar that persists between views.
Is the best way really to have just one single Activity and then a lot of Fragments?
If so, has this implementation already been done somewhere else that I can use? It seems like something that would come up a lot as I've seen numerous Android apps do this.
I made a Framework (github) to provide a hierarchical navigation pattern, with animations to provide sense of navigation, rather than launching new Activities every time.
Here's how to use it:
Add the framework to your project as a Module
Add a new Java class in your project ("File - New - Java Class").
Note: If you are editing the Activity.java file that provides you the template, delete all its implementations and leave it empty.
Make it extend NavigationActivity
Implement all the NavigationActivity abstract methods
(in Android Studio if you click Alt + insert and select implement - methods all the function definitions are automatically generated).
public class NavigationTest extends NavigationActivity{
#Override
public Fragment firstFragment() {
//return the first fragment that will be shown
}
#Override
public Boolean showBackButtonInFirstFragment() {
//show back button already in the first Fragment
//set to True if this activity is called by another Activity
//the back button will then pop back to the previous Activity
}
#Override
public Boolean showMasterDetailLayoutInTablets() {
//set to false if you don't want a master-detail layout in tablets
}
}
Presenting a new Fragment
You can present a new fragment (with a nice animation) by calling the pushFragment method from NavigationActivity.
public void pushFragment(Fragment newFragment, animationType animation, boolean showAsDetailFragmentIfPossible)
newFragment (Fragment): New Fragment that will be presented
animation (animationType): Animation type enum: RIGHT_TO_LEFT, BOTTOM_TO_TOP, FLIP
showAsDetailFragmentIfPossible (boolean): If set as True, the user is in a Tablet, and you are using a master-detail layout, the Fragment will be shown in the detail Fragment (the panel in the right)!
Since you can access the activity from any Fragment with the getActivity() method, you can show a new Fragment from the currently displaying Fragment.
For example you can put this code within a button click listener:
NextFragment f = new NextFragment();
NavigationActivity nav =((NavigationActivity)getActivity());
nav.pushFragment(f,NavigationActivity.animationType.RIGHT_TO_LEFT,false);
You don't have to worry about implementing the back button behaviour. This is handled automatically by the NavigationActivity class.
I have a two problems and struggle for a few days. I am not sure what the right way is.
I want to combine a tab layout with a view pager containing three fragments (the tab layout and the view pager are the home screen) and a navigation drawer.
And I think that everything you can navigate to from the drawer should be a fragment accept settings or something similar.
So should I let the tab layout in the layout of the main activities layout or should I put the this layout also in a fragment (so view pager with fragments inside a so calling home fragment)?
When starting the app I check if the user is logged in and if he is download data from Firebase. I do this in another fragment (data fragment) there I setretaininstance to true.
So currently one of the tab fragments needs the data from Firebase but soon all of them will need it.
How do I pass the data (Lists) from the data fragment to the tab fragments or the so called home fragment and then to the tabs.
I already tried interfaces but I don't know how to handle confirmation changes.
Considering the two problems or the combination of both how would you solve this / which design approach is better only use fragments or let the home screen inside the main activity and change the view when the user navigates from the drawer to fragment?
PS. I will add some code as soon as possible.
Thanks.
TabLayout and the ViewPager should be in the Activity layout since it makes more sense, as the Activity manages the Fragments. Also, navigation drawer should navigates through Activities, and Activities between Fragments. Again, that's the logical thing for a decent code organization, and it prevents repetitions in layout (AKA more than one button to navigate to the same fragment).
For the Firebase issue, I suggest you start the call in the Activity, and then call a function in all fragments with the retrieved information. Something like this:
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(MyFragment f : mFragmentList)
f.addData(dataSnapshot);
}
}
If you really want the Fragment to make the call to Firebase, then you can create you own Event and Listener set.
public class SnapshotRetrievedEvent {
private static List<SnapshotRetrievedListener> listeners = new ArrayList<>();
public static void addListener(SnapshotRetrievedListener listener){
listeners.add(listener);
}
public static void notify(DataSnapshot snapshot) {
for(SnapshotRetrievedListener listener : listeners)
listener.onSnapshotRetrived( snapshot );
}
}
public interface SnapshotRetrievedListene {
void onSnapshotRetrieved(DataSnapshot snapshot);
}
Then in your Fragment waiting for the snapshot, you add the listener like this:
SnapshotRetrievedEvent.addListener(
new SnapshotRetrievedListener(){
#Override
public void onSnapshotRetrieved(DataSnapshot snapshot){
// Do stuff
}
}
);
onSnapshotRetrieved will be called when you call SnapshotRetrievedEvent.notify(snapshot) in your other Fragment.
Hope this helps
I am creating a tabbed application using a FragmentPagerAdapter and android.support.v4.view.ViewPager. In order to follow best practices and separation of concerns I have separated my app into several different fragments. Each of the fragments has an interaction listener that requires an Activity to subscribe to. Since I only have one activity in the entire app do I have to make the parent (tabbed navigation) activity implement all the listeners in the entire app? This seems like it would be bad practice and create one large monolithic Activity class that controls the flow of everything.
I have three fragments inside of another fragment that I use as a home page tab. The home page fragment implements the interfaces of the three sub fragments. The problem is that the home page fragment is not an Activity so the sub fragments throw an exception on onAttach.
What am I missing? How can I implement fragment listeners in a tabbed application without making one large and messy Activity class
After researching further with different keywords I found a good answer here: https://stackoverflow.com/a/23144683/2435006
They key was to make an onAttachFragment(Fragment f) method rather than using the onAttach(Activity a) and calling it in the onCreate method.
Here is the example from the answer above:
public void onAttachFragment(Fragment fragment)
{
try
{
mListener = (OnInteractionListener) fragment;
} catch (ClassCastException e)
{
throw new ClassCastException(fragment.toString() + " must implement OnInteractionListener");
}
}
#Override
public void onCreate(Bundle savedInstanceState)
{
Log.i(TAG, "onCreate");
super.onCreate(savedInstanceState);
this.mContext = getActivity().getApplicationContext();
onAttachFragment(getParentFragment());
....
}
I think you need a good sample related to Fragments. Here is a sample with detailed explanations # ViewPager with FragmentPagerAdapter. The listeners are at onCreateView method at the Fragment. You don't want to set a bunch of listeners in the Activity.
I'm wondering why are the Fragments communicating through the container Activity are called reusable.
From: http://developer.android.com/guide/components/fragments.html I know that:
You should design each fragment as a modular and reusable activity
component. That is, because each fragment defines its own layout and
its own behavior with its own lifecycle callbacks, you can include one
fragment in multiple activities, so you should design for reuse and
avoid directly manipulating one fragment from another fragment.
Let's take an example; I have a DateSetFragment which contains two buttons; first button fires TimePickerDialog (FragmentDialog) which allows user to pick an hour and the second one DatePickerDialog (FragmentDialog) which allows user to pick a day. At the end gathered data should be sent back to the DateSetFragment.
According the: http://developer.android.com/training/basics/fragments/communicating.html:
All Fragment-to-Fragment communication is done through the associated
Activity. Two Fragments should never communicate directly.
communication between fragments should be done via interfaces through the container activity. Given that I should send my collected data from both Fragment Dialogs to the container activity and then from the Activity back to the DateSetFragment. I don't see how this make my DateSetFragment reusable and modular in any way. Doing so I have to implement fragment interfaces and some crucial logic in my container Activity which makes it connected with it.
The question is; Is it wrong in this situation if Fragment Dialogs will communicate directly with the DateSetFragment ?
It is "modular" because those interfaces are well defined and explicitly implemented by the hosting activity.
Anywhere you drop that fragment in, if the activity implements the callback interface defined by the fragment events the activity can choose what to do depending on what environment the fragment is attached in.
Example,
DatePickerFragment extends Fragment {
public interface DatePickerFragmentEventListener {
public void onDateSelected(DateTime dt);
}
}
Activity1 extends Activity implements DatePickerFragmentEventListener {
DatePickerFragment mDatePickerFragment;
OtherFragment mFragment2;
#Override
public void onDateSelected(DateTime dt) {
mFragment2.setSomeViewsText(dt.toString());
}
}
Activity2 extends Activity implements DatePickerFragmentEventListener {
DatePickerFragment mDatePickerFragment;
#Override
public void onDateSelected(DateTime dt) {
SharedPrefClient c = SharedPrefClient.getInstance();
c.setExpirationDateTime(dt);
}
}
I have a dateTimePickerFragment (or whatever), in one activity I have 2 fragments, when you change the date on the picker I want to update the other fragment's text view to display that date. In another activity I might use that exact same callback to write the chosen date to SharedPreferences.
The point is that the Fragment is a contained piece of UI interaction, and certain events it will notify the enclosing Activity of what just happened to it, so that the activity dictates that the result of an action on the fragment does to either other fragment or the application itself. There is no reason to implement a custom fragment for each and every situation.
On the iPhone I use a Navigation Controller to push and pop Views from. Very handy.
Is there an equivalent in Android?
This is an old question, but I believe the answer has changed. It is now possible to imitate the Nav stack in iOS in android using Fragments.
http://developer.android.com/reference/android/app/Fragment.html
Basically instead of jumping from Activity to Activity you instead stay in one Activity that controls the display, organization, and animation of Fragments which each contain their own behavior much like the NavController / UIViewController model in iOS.
It is also backwards compatible as a static library so you can implement it on pre-Honeycomb devices.
Strategies for Honeycomb & backward compatibility
Typically in android, each view is displayed in its own Activity. You can read about activities in the application fundamentals documentation. To move to a new Activity, or view, you use an intent.
If you haven't done so yet, I'd highly recommend reading through those introductary android docs. They aren't too long, and do a good job of explaning the basic program structure.
I made a Framework (github) to provide a hierarchical navigation pattern, with animations to provide sense of navigation, rather than launching new Activities every time.
Here's how to use it:
Add the framework to your project as a Module
Add a new Java class in your project ("File - New - Java Class").
Note: If you are editing the Activity.java file that provides you the template, delete all its implementations and leave it empty.
Make it extend NavigationActivity
Implement all the NavigationActivity abstract methods
(in Android Studio if you click Alt + insert and select implement - methods all the function definitions are automatically generated).
public class NavigationTest extends NavigationActivity{
#Override
public Fragment firstFragment() {
//return the first fragment that will be shown
}
#Override
public Boolean showBackButtonInFirstFragment() {
//show back button already in the first Fragment
//set to True if this activity is called by another Activity
//the back button will then pop back to the previous Activity
}
#Override
public Boolean showMasterDetailLayoutInTablets() {
//set to false if you don't want a master-detail layout in tablets
}
}
Presenting a new Fragment
You can present a new fragment (with a nice animation) by calling the pushFragment method from NavigationActivity.
public void pushFragment(Fragment newFragment, animationType animation, boolean showAsDetailFragmentIfPossible)
newFragment (Fragment): New Fragment that will be presented
animation (animationType): Animation type enum: RIGHT_TO_LEFT, BOTTOM_TO_TOP, FLIP
showAsDetailFragmentIfPossible (boolean): If set as True, the user is in a Tablet, and you are using a master-detail layout, the Fragment will be shown in the detail Fragment (the panel in the right)!
Since you can access the activity from any Fragment with the getActivity() method, you can show a new Fragment from the currently displaying Fragment.
For example you can put this code within a button click listener:
NextFragment f = new NextFragment();
NavigationActivity nav =((NavigationActivity)getActivity());
nav.pushFragment(f,NavigationActivity.animationType.RIGHT_TO_LEFT,false);
You don't have to worry about implementing the back button behaviour. This is handled automatically by the NavigationActivity class.
There are thee basic types in Android to show UI in Android:
View
Fragment
Activity
Google IO 2018 introduced Navigation component which should make life easier. It is a wrapper under a standard mechanisms.
Here you can find NavGraph which looks like storyboard and NavController which help to navigate to destination