I'm designing a similar interface to MathStep pictured below but my main activity already extends
public class MainActivity extends Activity implements TextWatcher
and Java doesn't have multiple inheritance.
In this program, you can ViewPager between Basic, functions and extra tabs. My program is not using tabs but I am swiping between fragments of buttons in a RelativeView.
How do I have part of my screen as a ViewPager, if I'm already extending Activity? Do I need to have a separate java file? How do I link the fragments that will contain the button sets back to the original activity?
I have been working on this with a friend for, I'm not kidding, 8 hours before we resorted to asking a question here. I have looked at this and this post and they were very helpful in understanding how ViewPager and Fragments work, but in all the examples they reference full paged ViewPagers, every time we attempted to create this scenario, something either wouldn't compile, or we weren't linking our XML correctly and code wasn't running... I've searched extensively for this answer and I hope I'm not the only one who has struggled with this so others can learn.
I'll admit, part of the confusion has been the learning curve but that's why I'm doing this, to learn.
How do I have part of my screen as a ViewPager, if I'm already extending Activity? Do I need to have a separate java file? How do I link the fragments that will contain the button sets back to the original activity?
All Fragments have a reference to the Activity via the getActivity() method, but you should only use it if you really need a handle to the context.
Inheritance is not required in any way whatsoever (technicality: other than for your activity, fragment, and FragmentPagerAdapter which must inherit from their respective parent classes...). The ViewPager itself can be included in the view heirarchy by referencing it from XML. The different fragments are displayed in the ViewPager by a FragmentPagerAdapter that you will have to implement yourself, this should be a separate class. If you want, it can be an inner static class, but, do not use an inner class. Keeping the scope organized by forcing dependencies to be passed through constructors will keep your code clean.
You should start by reading the ViewPager/Fragment related documentation on d.android.com. There is example code for these things and once you understand them individually everything will come together.
Related
I used to have 3 activities with 3 layouts.
1. HomeActivity.java (activity_home.xml)
2. HelpActivity.java (activity_help.xml)
3. SettingsActivity.java (activity_settings.xml)
Whenever i had to open other activities, i used animated slide-in-out intents using overridePendingIntent. In this way, all the variables of HomeActivity stayed in itself and HelpActivity's variables/methods were in itself and same for SettingsActivity. I used onCreate() in these to perform some activity specific code. and, android:onClick="fetchSarcasm" from activity_home.xml was calling specified method in HomeActivity.java. So, there were no conflicts. All the normal things, that happen in an AndroidProject with 3 activities and used intents to switch to one another, were happening as i wanted.
But now, I wanted to migrate to ViewPager instead of slide-in-out intent transitions. In this way, there will be only one Activity with an XML of ViewPager. This ViewPager and its FragmentPagerAdapter gets the Pages from 3 classes extending Fragment with relative XML layouts.
I want to ask: Where do i write my Page Specific Code for onCreate(), layoutView's onClick="" and for onChangeListeners. Because, 3 classes extending Fragment do not have any Context or findViewById() and they do not respond to android:onClick="method" in different layouts.
Do i need to mix all that code of three activities into one containing ViewPager? If so, this makes ViewPager activity pretty heavy. and, writing if(page=2){ dothis(); } seems absurd for all pages at every code point. Any checkbox(view) that is in page 3, becomes null in other pages.
I know this might be a stupid question. I have spent almost 4 days trying to achieve something but i can't. Also, this is just my 2nd month in android, so i am new. I do not use Action Bars, Tabbed Bars or Navigation Drawers.
I am available on SO Chat too if you want to ask something more.
I just want to know how do i merge all the work i did when I was not using ViewPager.
If you're only reading the Preferences once for each Fragment, you can move your previous Activity.onCreate() logic to each Fragments onViewCreated() or onCreateView(). Read your shared Preferences there and set your Checkboxes accordingly.
Fragments inside a ViewPager aren't necessarily recreated on each page change. You can change how many Fragments are instantiated at a time with ViewPager.setOffscreenPageLimit(int).
Fragment Lifecycles explained
I'm beginner to android and currently I'm working on a small project.
In my project I have a fragment with text and imageview, and in my Main activity I have a button and imageview.
When I press the button in my activity class it opens up the fragment, but I want to animate(Move) the the imageview in main activity to the position of the imageview present in the fragment.
Is there any simple way of getting the position of the views present in the fragments to activity class?
I'm stuck in this situation from few hours. Please help me.
What you are attempting is difficult because that is not how you are supposed to do it. Fragments are supposed to be self contained units, completely modular and interchangeable. On the other hand Activities are just supposed to be empty containers for Fragments. All the logic and UI has to be contained in the Fragments them selves and the Activities are supposed to be used to arrange and display those Fragments. Nothing from outside a Fragment should have anything to do with something inside the Fragment. So if you restructure your app with that in mind you will find that everything will be MUCH simpler.
A few pointers:
Move all of the UI to the Fragment
It is completely fine to perform FragmentTransactions from inside a Fragment. You don't have to take a detour through the Activity.
Try to understand the difference between Fragments and Activities and don't let yourself be mislead by tutorials which don't adhere to this separation. Most Android tutorials on the internet are outdated and wrong. Refer to the official tutorials here.
I am planning an app and trying to explore all the possible development options/methods I have available. One thing I'm struggling to get my head around is Fragments. I see a lot of people praising them as you can "resuse" fragments throughout the app but I can't think of an example situation.
From some example apps I have looked at (all been tabular layouts) the code for each fragment has one layout, so why not have a seperate activity instead?
I am hoping to implement a tabular layout in my app. If anyone can give me an example of a fragment being reused within an app I hope it will give me a better understanding of the benefits.
"Reuse" is overrated. Of course - you can put this same fragment (with this same features) in different places of your application - let's say that you can use a fragment in different, horizontal and vertical layouts (as you probably saw in Google's tutorial).
But at the end using fragments simplifies your project - for example - you can switch fragments inside one activity and get benefits of much easier navigation and in app communication.
Using fragments gives you one more thing - flexibility. It's much easier to move some view from one place to another, or just remove from application. All that because fragment encapsulates logic and usually a view, still offering power of externally managed lifecycle.
(Thanks for comment from Richard Le Mesurier)
Fragment is not a View neither a ViewGroup. It is not a visual element at all. Fragment inherits directly from Object.
One should think of a Fragment as a unity of a reusable code, reusable in various Activities (the Activities consist of visible elements).
Thus if you can think of any code you can reuse through several Activities (even the same Activity with different layout) and that code somehow depends on Activity lifecycle, then you probably should make this code a Fragment.
Let's say I have an Activity with a certain content. Now I need to create a new screen with tabs, so that the content of this activity will become the content of one of those tabs. I know I can do tabs with ViewPagerIndicator, for example. But, in order to do that, I need the screens to be implemented as Fragments. The problem is that the current implementation relies heavily on the Activity hierarchy (lots of calls to methods on the superclass, etc). So, I cannot simply make the current class extend Fragment. What other options do I have in this case?
Now I need to create a new screen with tabs, so that the content of this activity will become the content of one of those tabs
Having activities be the contents of tabs has been deprecated as a technique for nearly three years.
The problem is that the current implementation relies heavily on the Activity hierarchy (lots of calls to methods on the superclass, etc). So, I cannot simply make the current class extend Fragment.
Replace most of those "calls to methods on the superclass" to use getActivity(). as a prefix, where relevant.
What other options do I have in this case?
You could remove the activities entirely and rewrite your UI as custom views. This would be more work than converting them to fragments.
Or, you can just not do tabs.
So, I cannot simply make the current class extend Fragment.
That sounds like you have a huge Software architecture problem. In this case you may consider a complete rewrite (or more a copy & paste rewrite)
Normally it should be really straight forward to "convert" a Activity to a Fragment.
Fragment has nearly the same lifecycle callbacks:
Activity.onCreate() ---> Fragment.onCreateView() etc.
You can also access the parent Activity of the Fragment by calling Fragment.getActivity().
I don't know your code, but it should be definitely possible to "convert" Activities to Fragments.
You may split your activities code in own classes and inject them to the Fragment.
There is not really a alternative I could recommend you!
If you want tabs, use a ViewPager with Fragments. DO NOT USE OLD DEPRECATED STUFF like TabActivity
I am trying to make a sudoku application. It's a fragment based design, in which a fragment hosts a custom view which is a board. I am trying to learn how to build an effective communication within FragmentActivity, Fragment and View
Although a view is created using the FragmentActivity context and I can catch a reference to that context within the current view and then call methods inside FragmentActivity I don't want to tie views so directly to a fragment activity. Instead I want to tie the view to use methods inside a fragment. How can i do that, I can I capture a reference to a fragment and call methods inside that fragment from a view?
First of all, I strongly recommend that you read through the documentation on Fragments, as you clearly don't understand the whole concept/purpose of using Fragments in the first place (which is OK, because they are confusing the first time you learn them :P).
A lot of your question doesn't make very much sense to me, because I'm not sure what the View you are speaking of refers to. What I can tell you is that Fragments have their own UI/layout, along with their own separate lifecycle. So it sounds like you don't want your FragmentActivity to interact with the Fragments layouts/methods at all... instead, you should implement the UI's behavior and layout inside of the Fragment itself. That is, the Fragment will be in charge of updating the UI, receiving click/touch events, displaying information on the screen etc. The FragmentActivity will simply hold a reference to the current Fragment(s), and will be in charge of displaying/swapping in and out new Fragments as necessary (via the activity's FragmentManager).
Hope that answers the question somewhat... read through the documentation a couple times, it sounds like you are just misunderstanding the theory/purpose behind Fragments.