I'm planning to develop and app that presents the users with several different screens (of different information).
Was wondering what would be the best way to implement this?
Is it better to have separate XML layouts and an activity to display and allow the user to interact with each screen of data?
OR would handling all of these in the same activity be more efficient (and dynamically load / unload each layout)?
I'd say you want to go with the former, in the most cases, but obviously it all comes down to what it is that should be changing.
If you end up having two activities with layouts that only slightly differ, and you have to pass a lot of data between them, then it probably should have been one activity.
But in the most cases, where you're dealing with presenting quite separate things, I'd definitely create one activity for each presentation, so that you don't have to manually handle things like the click of the back button.
An Android Activity is a single, focused thing that the user can do.
The easier way to explain it is: An Activity is a screen in your app.
You want to have two different screens, then you should have two different Activities.
Related
I have an android application working in mobile, this app has two types of activities ones that loads a list of items, and forms that open when you touch one item.
Now I have to port the app to tablet and the layouts need to be fully restructured to fit big screens, so much that the java code has to be heavily changed so i thought to merge both activities in one as shown below
Is that possible?
And if its what i need to use, fragments?
Can each activity still in its own class?(this is critical)
Can each activity have its own network operations and AsyncTasks?
Yes as you said you can use fragments for your situation (Infact their main purpose is to support different screens without code duplication). So you'll have only 1 Activity class and 2 layouts for different devices and you just need to do some run time checks and perform actions according to them.
Here you can find tutorial :- https://developer.android.com/training/basics/fragments/index.html
is not possible because only one activity working in single screen in android. i have one idea to put two fragment in single activity then use your own AsyncTasks network operation.
I'm pretty much new to Android, but over the last two or three weeks I've managed to figure out most of its innards and how things work.
However, one thing is still bothering me - what's the basic difference between Activities and simple forms? Well, I know Android doesn't have such thing as a 'form', but by that I mean a fullscreen layout of elements that has an underlying class and all its functionality is executed in it, rather than in a process-wide class (Activity, to be precise).
As long as I understand, Activity is a separate process that's instantiated by OS to perform some actions that are basicly independent of the whole application. That also means that we can run only one of the application's activities, and it will still perform all of its functions without needing the whole application to be loaded. For example, if we have a movie player that can also convert movies from one codec to another, we can implement that functionality as a separate Activity so that other applications, like file managers, will also be able to convert movies between codecs using only that Activity, and not the whole application.
And that seems perfectly straightforward. The question is - why is everybody using separate Activities for functionality that cannot be separated from the application? In other words, people generally use Activities where I think simple forms within the same process would be more appropriate. For instance, I've seen people using a separate Activity for things like application settings, which obviously wouldn't be be launched outside the app itself, or editing application-specific data, which wouldn't be done outside the app as well, since the data to be edited should be selected from a list only known to the application.
Another example right from my experience - a unit converter application. It has a main menu with a GridView of units' categories, in each category there is a list of units and by clicking any unit we have a 'calculator' form for entering value that we want to convert. If I'd been doing that like everyone suggests I'd have three Activities - one for the main menu, one for the list of units and one for entering the value. But why? Why would I want to launch any of those three Activities separate from the application? If I'd want to launch main menu Activity - well, why not launch the whole application then? If I want just a list of units - again, just launch the whole application, it's not like some Facebook client is going to convert values between pressure units (since the list of units covers only one category at a time). And launching an activity for the calculator simply would not work, since it should return to the list to perform conversions and you'd have no list activity launched.
And anyway, even if I'm wrong and people use it wisely there's still an issue that Android SDK doesn't really provide any support for forms as I'm used to. Yes, there are things like ViewAnimator, ViewSwitcher etc. But all they do is switch layouts in their place, and that is hardly switching between forms as such. So the only choice to get close to that functionality at least is to use Activities. And we're back to the square one.
So to put it simply - am I missing something from the Android philosophy? Because I'm pretty sure that using a separate Activity (and a separate process as a result) for every single form in the application is an overkill. And if it really is and everybody knows that - why doesn't Android have any substantial form switching mechanism?
Thanks in advance for any clarification on this issue.
An activity isn't spawned in a separate process (unless you explicitly tell it to). Everything in your APK will be spawned in your process. Even if another application is using your Activity for whatever reason.
You can make your Activity "effectively" private to your application by not assigning any intent-filter to it in your manifest.
For the examples given, a form is equal to an activity. That isn't a universal statement as you delve deeper into Android, but for a beginner that's a decent analogy to make. Another common analogy is that Activities are more like web pages than traditional forms based UI.
I am building my first Android application that will guide the user through a series if listViews containing categories until the user reaches the final activity where a large block of text will be displayed.
My question is:
Can and should I build the listViews dynamically in one activity or should I build them all in eclipse manually?
There will be a lot of activities. I dont mind building them, i just dont want to bog down the application. From what I understand Android does a pretty good job of destroying old activities, but I am not sure the impact of having hundreds of activities would be.
Thanks in advance for your advice.
Sounds like one activity containing a ViewFlipper to hold the list(s). Presumably the list isn't the only thing you'll be wanting to display. You'll probably want to show a heading of some kind, and the user's location in the hierarchy.
What if the user hits back button? Will the app navigate to the previous activity?? Or will it be disabled?
I would suggest you make different activities since its the easiest way to do
I am creating an android application that has a lot of different screens where the user can navigate to those screens using the buttons or list provided in those screens. What would be the best way to design the entire app's navigation flow? Should I map each screen to be View or an Activity? Can an design an entire android app with just one activity and many views, where each view represents one screen with many other UI elements (buttons, lists, images etc)
I suggest you use for every "screen" that is significantly different from another screen (in both look and data that it is related to) a new activity. This gives you easier control and you don't have to mess up your code with plenty of variables to define different states. Using different activites you usually shouldn't have to worry about running in a undesirable or even undefined state.
To exchange data between activities you can use putExtra() to add "simple" data to an INTENT or for more complex data you can extend Application and use that instance as a singleton, which you then can access via (MyApplication)getApplication();
You really want to stay away from the single activity idea. That's actually an anti-pattern from the java model 1 web application days called "The magic servlet". I guess here it would be called "The magic activity". Each logical "screen" that the user interacts with should be an instance of the Activity class.
Modifying individual user interface elements based on user interaction is fine as long as it's just one or two elements, or just a portion of the screen, but for the most part you should be looking for reasons to split things out into their own activities, not looking for reasons to keep things together. In the long run it will make your code easier to maintain and understand.
I have developed some apps for Android, and this questions stays always:
How should I structure my UI? Should I launch activity after activity and leave the phone to make the "back" button, or should I choose more optimized, but more complex to implement, way with switching manually Views and then manually doing the "Back" button functionality?
What do you think (or know) is the better practice?
I would say that multiple Activities almost always makes more sense. I just don't think Android is designed for constantly switching its own views - you miss out on so much. You have to implement Back yourself, you don't get any inter-Activity transitions, you have to implement a lot of internal logic to resume an application in the correct state. If you don't partition your app into Activities, it makes it a lot more difficult later on to change the flow of your application. It also results in one mega-Activity that can be a lot harder to handle than a lot of smaller pieces of code.
I have trouble imagining that speed is really an issue; if it is then there's something wrong with the way you're initializing each Activity. For example, I used try to pass Serializable objects between Activities, and that proved to be incredibly slow; when I switched to a faster method of passing objects, the speed of launching Activities increased immensely.
Also, I think it's telling that the Android guidelines for Activity and Task Design don't mention switching Views at all; it's centered around an Activity-as-View design.
I'd like to point out some instances when a single activity might be better design for an Android application that has more than one full screen View:
If the application screens are tightly coupled and share a common Object that they are all operating on. In this case passing around the Object may require a Bundle and can be error prone since there will be copies of it. A good example might be a wizard. Yes you could use static's to access the common Object but static can be dangerous in Android (think configuration changes!)
If you want some really cool animations in between screens. Maybe you want a bird to take off in one screen and land in another screen. Try doing that when each screen is an activity!
On the other hand if one of your screens is designed to be shown by any number of other applications then that screen should be its own Activity.
UPDATE March 2014:
At this point the question should now include the choice of Fragments. I think that Views are probably the least likely choice of the 3: Activity, Fragment, View. If you want to implement screens that make use of the back button then it should be either Activties or Fragments because both handle the back button natively. Fragments will need to be added to the FragmentManager back stack for the back button to work. Managing fragments, dialogs and the back stack can be a bit of an annoyance though!
UPDATE Sept 2018:
Some devs at Google are recommending single activity apps using the new navigation architecture component.
Also keep in mind that implementing your app with multiple Activities will give the user a more coherent experience with the platform as a whole. Part of the experience will be shaped by using the built-in Google apps, so users will probably have an easier time using your application if it behaves similarly to the ones that are already installed on the phone.
Different from others I use a mixture of both, for example,
1. There is a main menu when the application starts
2. You click on search, takes you to search activity
3. Then there's a filter button, which just switches view and shows you filter options
4. There are two buttons at the end of the filter view, You hit "Search" or "Cancel" and you are back to the Search View again (without switching activity)
5. Now if the user hits the phone back button he's taken back to the main menu instead of the search filter options. Which I guess is the correct behavior.
Use it the way user will feel natural. And keeping everything in one activity will make it complex.
It all depends on application, what are you trying to achieve better performance, smoother UI. IMHO I prefer the second approach of controlling the Activities manually even that it is more complex as you have stated. This is a approach I have used in my android tabs project, also you might want to take a look at a class called ActivityGroup (not sure the package) it allows you to have multiple activities that you can switch between, good thing about this class is that your activities are not unloaded when you switch but a bad thing is it takes longer to load your main app.
Just my opinion.
The problem with switching views, that I stumbled upon, is also caused by garbage collector. Seems that GC is triggered when you leave activity and not the view. So, changing tabs with a fairly complex children views, for instance, will almost inevitably lead to stack overflow exception..
I've experienced so many problems with multiple activity layout that I strongly discourage it, unless there's good reason to pick it.
Disadvantage of multiple activities
Using multiple activities it is much hard to refactor code to return data from activity.
If you call a 'sub'-activity then the main activity may be killed. But you never experience that while debugging on a decent device, hence you need to handle always saving state and correctly recovering state. That is a pain. Imagine calling a method on a library (ie. another activity), and you would have to be ensure that when that method returns your app must be able to recreate its state completely with all fields on all objects in the VM (ie. activity.restoreIntance). Its insane.
Also the other way round, when you open a subactivity the VM might have been killed since the subactivity was first spawned, such as when app is minimized while subactivity is displayed.
Its so much cleaner to just have one place to store the relevant app-state, and in my case, most often if VM is killed, I want to return user to main-screen, and let them do their stuff again, because I don't spend 30-50 hours coding save/resume functionality that 0.1% of users will ever experience.
Alternative
Fragments or just manage you activity views yourself. Managing views manually, requires coding some view-switching alternative to activities/fragments with transitions if desired.
And no it does not mean one mega-activity, as suggested in the accepted answer, in any other way than its one mega-app. It just requires a bit more design of the codebase into fitting pieces, because there's slightly more work managing views, though much less work managing activity-state and other weirdness.
Possibly relevant: Reddit: It's official : Google officially recommends single activity app architecture