When using Fragments in Android I can call fragment elements as following one.
HashMap<String, ArrayList<MyProduct>> orderAdap = InvocieProductFragment.mapOrderd;
In this case does it creates a new instance. Or else is it passing a copy or is it using the same resource. When I update a value on such an item does it updates in all places. I'm somewhat excited on this matter and can someone help me on this.
You're working on regular object instances. There's no magic involved. So you have to propagate changes yourself.
Related
Imagine the following object
data class CourseState(
val key:Int=0,
val name:String="",
val courses:Courses=Courses())
Implementing the following pattern
private val _courseState = mutableStateOf(CourseState())
val courseState: State<CourseState> = _courseState
I can trigger recomposition of my UI by calling:
_courseState.value = CourseState()
but not by calling:
_courseState.value.courses.addCourse(Course("some course))
this is a bit frustrating because even though the object has clearly changed I am forced to create a whole new instance of the parent object in order to elicit a small change in it.
Now, I know than behind the scenes Compose is using the .equals() method in order to acertain if it should recompose the layout so I ve had a few ideas on how to achieve the desired behaviour.
overwrite the equals method: it would imply a bit of boilerplate code and it would have to be done for the entire set of nested classes that make up my object. this might work but seems dangerous and cumbersome.
use a clone method or a constructor that accepts an instance of its own class as a parameter to create an identical copy of my object that would nevertheless represent a new instance that I can modify and then pass as the mutable state value. sounds easier than the previous optoin but elegance is something different
dive deep into the State and MutableState classes and find out if there is a way to make them behave as I want. I am relying on some of you to have done this before so I dont have to XD
Let me know what you think or if there is some other ovbious solution that has just eluded me so far
There are two options I would consider:
As you mention, create new instances of your objects for every change. With data classes and copy, it's quite easy, it will add some overhead though.
Make all the data that you need to change observable. If you only want to observe them from compose, make it State, otherwise you can use Flow or LiveData. I suppose that your Courses class contains some List to which
you are adding items. Make it a
mutableStateListOf(),
whenever you add something there, composables that use it should
recompose automatically.
I have two adapters:
private StreamingNowAdapter mStreamingNowAdapter;
private UserStreamingNowAdapter mUserStreamingNowAdapter;
When I load them with Arrays
mStreamingNowAdapter = new StreamingNowAdapter(mEventId, mEventName,
mEventPreview, mNumberViewers, mContext);
mUserStreamingNowAdapter = new UserStreamingNowAdapter(mUserId,
mUsername, mProfilePic, mStreamingUserNumberViewers, mContext);
and call notifyDataSetChanged(); how come when I call this method on one adapter, both adapters become notified and displayed?
I only called the method on the first adapter
mStreamingNowAdapter.notifyDataSetChanged();
and it loads my data into my second recycler mUsersStreamingNowAdapter without me calling notifyDataSetChanged on the second adapter.
Is this a bug or is it supposed to be like this?
Edit1: Two separate recyclerviews, both adapters attached to their own recyclers.
RecyclerView mRecyclerViewStreaming =
view.findViewById(R.id.fraghome_recycler_streaming_now);
RecyclerView mRecyclerViewFollowing =
view.findViewById(R.id.fraghome_recycler_followed_users);
mRecyclerViewStreaming.setLayoutManager(new
LinearLayoutManager(getContext()));
mRecyclerViewFollowing.setLayoutManager(new
LinearLayoutManager(mContext, LinearLayoutManager.HORIZONTAL, false));
mRecyclerViewStreaming.setAdapter(mStreamingNowAdapter);
mRecyclerViewFollowing.setAdapter(mUserStreamingNowAdapter);
I've checked the layout multiple times to make sure both the recyclerview's id's are not identical. Still can't figure out why this is happening.
A correctly managed RecyclerView and its required artifact (an Adapter, its data, etc.) should not interfere with another correctly managed RecyclerView or any other component for what is worth.
Unfortunately, the shared code you provided is not sufficient to determine what could be happening in your project.
To the best of my knowledge, RecyclerView adapters don't talk to each other in any way so a notifyDataSetChanged() on an adapter, should have no impact whatsoever on another adapter, regardless of where said adapters are declared (assuming they are different instances, of course).
All this being said, I'll offer you my personal comments about the code you posted. Please don't take it personally, for I'm reviewing the code, not the author, from a pure technical point of view based upon my experience with Android.
Fragment
It immediately caught my attention to see that a Fragment, a component known for being completely wild when it comes to lifecycle management and state, has so many responsibilities.
It starts by having no less than eight array lists, and managing two recyclerviews, and its respective adapters, and even the LayoutManagers used by the lists.
Not happy with having to manage all this, this Fragment also needs to handle a networking layer, error handling (not yet implemented), and data storage (in memory for now).
Because you may have put this together really fast simply to illustrate a case, I will let the fragment in peace for now.
Data
You're putting a lot of stress on your fragment and adapters by splitting the data in a very inefficient way. 4 array lists, one per field? What?
for(HomeFragmentPojo.StreamingNow streamingNow : streamingNowArrayList){
mEventId.add(streamingNow.getEvent_id());
mEventName.add(streamingNow.getEvent_name());
mEventPreview.add(streamingNow.getEvent_preview());
mNumberViewers.add(streamingNow.getNumber_viewers());
}
Why are you doing this?
If you have a StreamingNow object that has all 4 fields.
Why don't you have a ListAdapter<StreamingNow, ViewHolder>() that simply takes a list of StreamingNow objects?
You can simply do adapter.submitList(...) to pass the list once you get it and the adapter (when properly created) will do the right thing.
If you ever update the list, you simply submit it again, and the adapter will calculate the difference and only update the rows that need to be updated.
The BIND method, is also simple, because it would look like: (pseudo code)
viewHolder.eventName = getItem(position).name
viewHolder.viewerCount = getItem(position).viewerCount
//For the image...
Glide.with(mContext)
.load(getItem(position).preview)
.apply(RequestOptions.centerCropTransform())
.into(viewHolder.preview);
...
You get the idea.
Based upon the properties I see, your StreamingNow "pojo" kinda looks like that
class StreamingNow {
String id;
String name;
String preview; //maybe an URL? You use Glide so in the bind method, use it.
String viewerCount;
}
When I look at your other adapter, I see that it has the same data...
Id, Name, Pic, Count of Viewers.
There is no need to use a different adapter, you can reuse the same adapter assuming they have to behave the same way; if the Users adapter has to do something different on click, for example, you could pass the min information needed for the adapter to decide what to do when an item is clicked. Or better yet, you could simply pass a generic Listener so the adapter simply calls "this item "X" was clicked". Because these adapters aren't here to make decisions and call framework things, they have a lot of work in their plates, and this is not and should not be their responsibility.
Whoever manages, creates, and maintains these adapters (so far, your Fragment) should be the one in charge of doing this. Or even better yet, a ViewModel or Presenter should receive this and make an informed decision.
In any case, the click event inside the adapter is not the biggest problem here, and it will work anyway.
What I am trying to leave written here, is that your problem is a lack of separation of concerns between components.
The smaller and more concrete your classes are, the easier it is to replace them, test them, debug them, enhance them, etc.
You're throwing all your code in a big place. If you separate it, it's a lot easier to keep it under control.
So, what's the deal?
I suggest you take a step back, enhance your RecyclerView to use a ListAdapter
I wouldn't perform the network request in onCreate, instead do it in onViewCreated or similar, because during onCreate in a Fragment, there's no guarantee that the view will be created. (Remember when I told you Fragments were a pain?).
I wouldn't have that network code in the Fragment to be honest; it's quite simple to add a ViewModel and have the data there. Then you can have the ViewModel request the data during onCreate, but you'll only get the LiveData from it when your lifecycle allows it... which is the whole point of LiveData and observing it.
If this sounds like a lot of work, it may as well be, especially if you are new to Android. But it will pay off.
Good luck!
Good day developers, I'm having trouble figuring out how and what should I do correctly so that I won't violate the MVP principle so I have the following situation.
A view that shows List of object, when a particular object is clicked my ViewHolder tells the Presenter about the click event.
What I want is ,when the object is clicked I want to start a new Activity that will display that particular object that was clicked.
Option 1.
Pass the id of the clicked object to Interactor(How should I do it I have no idea) of newly started activity, where a new api call will be called and will return a result based on given id.
Option 2.
On the other hand if I don't want to make a new api call and would like to simply pass the Object to the Iterator of new activity.
(What is better for performance to make a new api call or pass the object around?)
If any of my options seems somehow okay, then how should I implement them correctly?
If they are not then what is a alternative way of doing it?
Your best option is to use the new Blueprints which include Viewmodels in the form of LiveData, and there are specific mechanisms in the viewmodel for sharing the model between views. Basically the model is held with the key being a view id, but if you have a view and then a number of fragments, they can all access it.
Technically you have control over the key:
final UserModel viewModel = ViewModelProviders.of(this).get(UserModel.class);
What I like about this is it solves the scoping problem that has haunted MVC: either use Singletons or pass data around all over the place.
I am working on my second Android Application, first being, hello world. The application code is quite crazy looking because I love to test new libraries and ideas in it. I have been working on this application for well over 3 months and one of my activities is getting way to large and difficult to work with. I find myself getting lost in the code and it is taking longer to do simple things. There might be simple solutions to solving this issue. I really want to split my activity into two and reference each other if possible. Is there are any suggestions to simplifying and organizing code that would be greatly helpful. Even example will help me very much.
Part of my activity is adding a ton of data into a database and the other part is a long equation with multiple values. Another part is implementing the HoloGraphLibrary (Which I love). It is also implementing a listView with custom adapter. It also has a custom dialog............ I can go on and on. I hope you get my point.
EDIT
Going to work with this.
HoloGraphHelper holoGraph = new HoloGraphHelper();
holoGraph.initialize();
Try creating classes for each responsibility.
A Database Helper that has functions to insert data too:
DatabaseHelper database = new DatabaseHelper();
database .insertData(whatever);
A HoloGraphHelper that initializes the HoloGraph
HoloGraphHelper holoGraph = new HoloGraphHelper();
holoGraph.initialize();
And so on.
Break into multiple files. First classes defined in the Activity like the adapter. Change anonymous classes to classes defined in their own file. Look for ways to break out other related code into a class.
Right click on src folder of your Project and select new - class to create a new class. You can use a class for storing methods but you won't be able to display anything on screen.
To display contents to user, you can create a new Activity bu pressing Ctrl + N and selecting Android - Android Activity.
The best way is modularise your code.
I.e split your code into various related modules, for example a separate class for each part that your testing. So you could have a database entry class, a class for Gui testing, i.e. for your custom dialog. That class does all the work for that test, into various functions, I always try to keep functions as small as possible as they are easy to read.
As an example for your database entry, you could have a function which checks the database if the record already exists and then insert it. But a better way would be your insert function only performs the insert code and instead within this function it calls CheckIfDatAlreadyExists function which can return a bool so you know whether you should go ahead and insert the record. This would keep the code tidy and clean to manage.
Then from your main activity all would need to do is instantiate the relative class and call the relevant method.
I'm looking for guidance as to how to modularize my code. I have an activity and a listAdapter and they are getting pretty complex. I'm not sure what code should live where and how much knowledge each of these 2 classes should have of each other. How do you decide whether to put code in an activity or its adapter? And what patterns do you use to keep these classes as lean as possible?
Your description is too generic, so I cannot give you an exact answer (would be useful to explain why they are getting bigger and bigger, what is the extra code good for).
But generically speaking, just think about what each class supposed to do. The "Activity" (as I see it), is a main controller, it "knows everybody", and it connects the other components together (the ListView with the list adapter). The list adapter's purpose is simply to map data to views. If they are getting bigger, extract new (utility) classes.
For example assume a big part of the code in ListAdapter formats timestamps (eg. takes timestamp as long value, and based on current time creates a string like "2 hours ago"). Then it makes sense to create a new utility class called TimeFormat (with a constructor which takes a context, you'll need it later to fetch string resources). Then the ListAdapter will create an instance of this class.
Another example would be data saving. In that case you could create a class called "Model" or "Document" (again with a constructor taking a "Context" instance). It would be responsible (for example) to load the data by parsin XML files, and to save the data by generating XML files. In this case this class would be instantiated by the activity.
Also note that the ListAdapter should really do what it supposed to do: create/setup views based on data. It should never depend on other views (in other views it should work with any ListView in any layout file). So if you have "findViewById" call, which access a view outside of the ListView (or the ListView itself), then that code should be moved to the activity.
Also, when in doubt you can try to find an open source application, which is relatively mature, and does something similarn (and see how that is solving the problem).
Per the adapater documentation in android
An Adapter object acts as a bridge between an AdapterView and the underlying data for that view. The Adapter provides access to the data items. The Adapter is also responsible for making a View for each item in the data set.
So if your code has to do with getting the data to display or creating the views, then it goes in the adapter. Everything else goes in the Activity or else where. If you're spending a lot of code retrieving the information you want to display, consider using some sort of AsyncTaskLoader class. Note that loader classes can be accessed from API Levels less than 3.0 using the android compatibility package.