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I know that Activities are designed to represent a single screen of my application, while Fragments are designed to be reusable UI layouts with logic embedded inside of them.
Until not long ago, I developed an application as it said that they should be developed.
I created an Activity to represent a screen of my application and used Fragments for ViewPager or Google Maps. I rarely created a ListFragment or other UI that can be reused several times.
Recently I stumbled on a project that contains only 2 Activities one is a SettingsActivity and other one is the MainActivity. The layout of the MainActivity is populated with many hidden full screen UI fragments and only one is shown. In the Activity logic there are many FragmentTransitions between the different screens of the application.
What I like about this approach is that because the application uses an ActionBar, it stays intact and does not move with the screen switching animation, which is what happens with Activity switching. This give a more fluent feel to those screen transitions.
So I guess what I'm asking is to share your current development manner regarding this topic, I know it might look like an opinion based question at first look but I look at it as an Android design and architecture question... Not really an opinion based one.
UPDATE (01.05.2014): Following this presentation by Eric Burke from Square, (which I have to say is a great presentation with a lot of useful tools for android developers. And I am not related in any way to Square)
http://www.infoq.com/presentations/Android-Design/
From my personal experience over the past few months, I found that the best way to construct my applications is to create groups of fragments that come to represent a flow in the application and present all those fragments in one Activity. So basically you will have the same number of Activities in your application as the number of flows.
That way the action bar stays intact on all the flow's screens, but is being recreated on changing a flow which makes a lot of sense. As Eric Burke states and as I have come to realize as well, the philosophy of using as few Activities as possible is not applicable for all situations because it creates a mess in what he calls the "God" activity.
Experts will tell you: "When I see the UI, I will know whether to use an Activity or a Fragment". In the beginning this will not have any sense, but in time, you will actually be able to tell if you need Fragment or not.
There is a good practice I found very helpful for me. It occurred to me while I was trying to explain something to my daughter.
Namely, imagine a box which represents a screen. Can you load another screen in this box? If you use a new box, will you have to copy multiple items from the 1st box? If the answer is Yes, then you should use Fragments, because the root Activity can hold all duplicated elements to save you time in creating them, and you can simply replace parts of the box.
But don't forget that you always need a box container (Activity) or your parts will be dispersed. So one box with parts inside.
Take care not to misuse the box. Android UX experts advise (you can find them on YouTube) when we should explicitly load another Activity, instead to use a Fragment (like when we deal with the Navigation Drawer which has categories). Once you feel comfortable with Fragments, you can watch all their videos. Even more they are mandatory material.
Can you right now look at your UI and figure out if you need an Activity or a Fragment? Did you get a new perspective? I think you did.
My philosophy is this:
Create an activity only if it's absolutely absolutely required. With the back stack made available for committing bunch of fragment transactions, I try to create as few activities in my app as possible. Also, communicating between various fragments is much easier than sending data back and forth between activities.
Activity transitions are expensive, right? At least I believe so - since the old activity has to be destroyed/paused/stopped, pushed onto the stack, and then the new activity has to be created/started/resumed.
It's just my philosophy since fragments were introduced.
Well, according to Google's lectures (maybe here, I don't remember) , you should consider using Fragments whenever it's possible, as it makes your code easier to maintain and control.
However, I think that on some cases it can get too complex, as the activity that hosts the fragments need to navigate/communicate between them.
I think you should decide by yourself what's best for you. It's usually not that hard to convert an activity to a fragment and vice versa.
I've created a post about this dillema here, if you wish to read some further.
Since Jetpack, Single-Activity app is the preferred architecture. Usefull especially with the Navigation Architecture Component.
source
Why I prefer Fragment over Activity in ALL CASES.
Activity is expensive. In Fragment, views and property states are separated - whenever a fragment is in backstack, its views will be destroyed. So you can stack much more Fragments than Activity.
Backstack manipulation. With FragmentManager, it's easy to clear all the Fragments, insert more than on Fragments and etcs. But for Activity, it will be a nightmare to manipulate those stuff.
A much predictable lifecycle. As long as the host Activity is not recycled. the Fragments in the backstack will not be recycled. So it's possible to use FragmentManager::getFragments() to find specific Fragment (not encouraged).
In my opinion it's not really relevant. The key factor to consider is
how often are you gonna reuse parts of the UI (menus for example),
is the app also for tablets?
The main use of fragments is to build multipane activities, which makes it perfect for Tablet/Phone responsive apps.
Don't forget that an activity is application's block/component which can be shared and started through Intent! So each activity in your application should solve only one kind of task. If you have only one task in your application then I think you need only one activity and many fragments if needed. Of course you can reuse fragments in future activities which solve another tasks. This approach will be clear and logical separation of tasks. And you no need to maintain one activity with different intent filter parameters for different sets of fragments. You define tasks at the design stage of the development process based on requirements.
There's more to this than you realize, you have to remember than an activity that is launched does not implicitly destroy the calling activity. Sure, you can set it up such that your user clicks a button to go to a page, you start that page's activity and destroy the current one. This causes a lot of overhead. The best guide I can give you is:
** Start a new activity only if it makes sense to have the main activity and this one open at the same time (think of multiple windows).
A great example of when it makes sense to have multiple activities is Google Drive. The main activity provides a file explorer. When a file is opened, a new activity is launched to view that file. You can press the recent apps button which will allow you to go back to the browser without closing the opened document, then perhaps even open another document in parallel to the first.
Thing I did: Using less fragment when possible. Unfortunately, it's possible in almost case. So, I end up with a lot of fragments and a little of activities.
Some drawbacks I've realized:
ActionBar & Menu: When 2 fragment has different title, menu, that
will hard to handle. Ex: when adding new fragment, you can change action bar title, but when pop it from backstack there is no way to restore the old title. You may need an Toolbar in every fragment for this case, but let believe me, that will spend you more time.
When we need startForResult, activity has but fragment hasn't.
Don't have transition animation by default
My solution for this is using an Activity to wrap a fragment inside. So we have separate action bar, menu, startActivityForResult, animation,...
The one big advantage of a fragment over activity is that , the code which is used for fragment can be used for different activities. So, it provides re-usability of code in application development.
use one activity per application to provide base for fragment
use fragment for screen ,
fragments are lite weight as compared to activites
fragments are reusable
fragments are better suited for app which support both phone & tablet
You are free to use one of those.
Basically, you have to evaluate which is the best one to your app. Think about how you will manage the business flow and how to store/manage data preferences.
Think about, how Fragments store garbage data. When you implement the fragment, you have a activity root to fill with fragment(s). So, if your trying to implement a lot of activities with too much fragments, you have to consider performance on your app, coz you're manipulating (coarsely speaks) two context lifecycle, remember the complexity.
Remember: should I use fragments? Why shouldn't I?
regards.
I use Fragments for better user experience. For example if you have a Button and you want to run let's say a webservice when you click it, I attach a Fragment to the parent Activity.
if (id == R.id.forecast) {
ForecastFragment forecastFragment = new ForecastFragment();
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.main_content, forecastFragment);
ft.addToBackStack("backstack");
forecastFragment.setArguments(b);
ft.commit();
}
In that way the user won't have to move in another activity.
And secondly I prefer Fragments because you can handle them easily during rotation.
It depends what you want to build really. For example the navigation drawer uses fragments. Tabs use fragments as well. Another good implementation,is where you have a listview. When you rotate the phone and click a row the activity is shown in the remaining half of the screen. Personally,I use fragments and fragment dialogs,as it is more professional. Plus they are handled easier in rotation.
Almost always use fragments. If you know that the app you are building will remain very small, the extra effort of using fragments may not be worth it, so they can be left out. For larger apps, the complexity introduced is offset by the flexibility fragments provide, making it easier to justify having them in the project.
Some people are very opposed to the additional complexity involved with fragments and their lifecycles, so they never use them in their projects. An issue with this approach is that there are several APIs in Android that rely on fragments, such as ViewPager and the Jetpack Navigation library. If you need to use these options in your app, then you must use fragments to get their benefits.
Excerpt From: Kristin Marsicano. “Android Programming: The Big Nerd Ranch Guide, 4th Edition.” Apple Books.
Some wrong ideas:
Always put an activity in your app and handle different screens with fragments.
Write the UI code directly in the activity.
Handle navigating between screens (I don't mean tabs, I mean for example full-screen views) by fragments.
Activities can be replaced by fragments.
Here is the thing!
Fragments are designed to implement reusable parts of UI and use them in any part of the app that is needed. They are not designed for substituting activities.
When we must use each of them?
When we have an independent screen in which there are some different UI parts (tabs, expandable screens, partial screens, etc...) we should use an activity with some fragments to implement and handle different UI parts separately in the same screen.
Each independent part of the application is actually a component that is conceptually different from other parts and it needs to have an independent activity. For example, the login part may contain some different scenarios like using username-password or using fingerprint. Each scenario can be implemented by a fragment and all login-related fragments should be handled by LoginActivity. But for example, the part of the orders in the application doesn't have a conceptual relationship with login, so it must have a different activity and of course, it may contain some fragments like OrdersFragment, SubmitNewOrderFragment, and etc that all of them must be managed by OrdersActivity.
Do not implement a UI directly in an activity. Always implement UI in fragments and add those fragments in the activity even if there is only one fragment in that activity. It helps you to have more reusable code and change UIs easier.
Never use fragments to navigate infinitely in the application even if you force the user to have a limited number of fragments in the back stack. The fact is that when you add a new fragment into the back stack and remove it, it will not be removed from the memory unless the parent activity gets destroyed and it is only not visible. So when you are using fragment manager back stack, by navigating multiple times between fragments in the same activity (especially in the case of you create a new fragment on each navigation and put them into the back stack) you will get an OutOfMemoryException in the application.
I hope it to be helpful.
This question needs to be reevaluated since Jetpack Compose has reached stable.
Jetpack Compose is Android’s recommended modern toolkit for building
native UI.
from https://developer.android.com/jetpack/compose
The typical jetpack-compose architecture is:
Single Activity, multiple composables, and glued together by jetpack navigation.
Note there's no (need for) Fragments anymore.
See Now in Android for a sample.
I've recently been looking into the navigation system that Android uses with as intention to port my iOS app that uses an UITabBarController containing multiple UINavigationControllers. To replace the tab bar (which is not available on Android) I settled on using the built in DrawerLayout.
From what I've read, navigation in Android is generally done by creating an Intent, providing it with extras and then just replacing the current activity. This automatically makes sure the back button works, and optionally the back button in the top left if enabled.
However, I am not sure how to implement this way of navigation with the navigation drawer. The tutorial tells me to create a DrawerLayout containing a FrameLayout and a ListLayout where the FrameLayout will contain the actual application and the ListLayout will contain the navigation. This would mean that when I use the method described above to "navigate", it would replace the activity and thus removing the drawer.
What would be the best way to implement what I want (basic navigation with back button support while maintaining a global drawer navigation menu)? The possible options I can come up with is always keeping the same activity and dynamically replacing the FrameLayout, but that would mean a lot of boilerplate to render and possibly a hack to support the back button (and there would be no animations :(). The other option would be to just render the drawer on every activity (via subclassing or something), but that would mean that if the user navigates a lot the back button "stack" would become quite large.
I have tried to explain what I need in as much detail as possible, but it is quite hard to explain the concept. Basically, I want something similar to the UINavigationControllers in the UITabBarController.
You can either have one Activity with one NavigationDrawer and present the user with different views by switching Fragments back and forth within that one Activity. You would use the FragmentManager to switch between different Fragments.
Or you can use multiple Activities that all have a NavigationDrawer.
Second option might sound more difficult but it really isn't. You create a base Activity that all your Activities inherit from and all let them have their own NavigationDrawer, no problem.
Sure there's something in between or something completely different, but that's the most straightforward approaches I can think of.
The tutorial you've probably used (the one with the planets) is imho a bit misleading because it assumes a very basic app structure. If you have only little different 'screens' that might work, for a very complex application it's not suitable (again, in my opinion).
I've always opted for the second option because handling the navigation / backstack is just easier with Activities / Intents.
There's loads of different flags that you can set to your Intent to influence their navigation behaviour.
Also see this and that documentation. These documents might have been written when the NavigationDrawer pattern was not all that common but they are still useful.
I know that Activities are designed to represent a single screen of my application, while Fragments are designed to be reusable UI layouts with logic embedded inside of them.
Until not long ago, I developed an application as it said that they should be developed.
I created an Activity to represent a screen of my application and used Fragments for ViewPager or Google Maps. I rarely created a ListFragment or other UI that can be reused several times.
Recently I stumbled on a project that contains only 2 Activities one is a SettingsActivity and other one is the MainActivity. The layout of the MainActivity is populated with many hidden full screen UI fragments and only one is shown. In the Activity logic there are many FragmentTransitions between the different screens of the application.
What I like about this approach is that because the application uses an ActionBar, it stays intact and does not move with the screen switching animation, which is what happens with Activity switching. This give a more fluent feel to those screen transitions.
So I guess what I'm asking is to share your current development manner regarding this topic, I know it might look like an opinion based question at first look but I look at it as an Android design and architecture question... Not really an opinion based one.
UPDATE (01.05.2014): Following this presentation by Eric Burke from Square, (which I have to say is a great presentation with a lot of useful tools for android developers. And I am not related in any way to Square)
http://www.infoq.com/presentations/Android-Design/
From my personal experience over the past few months, I found that the best way to construct my applications is to create groups of fragments that come to represent a flow in the application and present all those fragments in one Activity. So basically you will have the same number of Activities in your application as the number of flows.
That way the action bar stays intact on all the flow's screens, but is being recreated on changing a flow which makes a lot of sense. As Eric Burke states and as I have come to realize as well, the philosophy of using as few Activities as possible is not applicable for all situations because it creates a mess in what he calls the "God" activity.
Experts will tell you: "When I see the UI, I will know whether to use an Activity or a Fragment". In the beginning this will not have any sense, but in time, you will actually be able to tell if you need Fragment or not.
There is a good practice I found very helpful for me. It occurred to me while I was trying to explain something to my daughter.
Namely, imagine a box which represents a screen. Can you load another screen in this box? If you use a new box, will you have to copy multiple items from the 1st box? If the answer is Yes, then you should use Fragments, because the root Activity can hold all duplicated elements to save you time in creating them, and you can simply replace parts of the box.
But don't forget that you always need a box container (Activity) or your parts will be dispersed. So one box with parts inside.
Take care not to misuse the box. Android UX experts advise (you can find them on YouTube) when we should explicitly load another Activity, instead to use a Fragment (like when we deal with the Navigation Drawer which has categories). Once you feel comfortable with Fragments, you can watch all their videos. Even more they are mandatory material.
Can you right now look at your UI and figure out if you need an Activity or a Fragment? Did you get a new perspective? I think you did.
My philosophy is this:
Create an activity only if it's absolutely absolutely required. With the back stack made available for committing bunch of fragment transactions, I try to create as few activities in my app as possible. Also, communicating between various fragments is much easier than sending data back and forth between activities.
Activity transitions are expensive, right? At least I believe so - since the old activity has to be destroyed/paused/stopped, pushed onto the stack, and then the new activity has to be created/started/resumed.
It's just my philosophy since fragments were introduced.
Well, according to Google's lectures (maybe here, I don't remember) , you should consider using Fragments whenever it's possible, as it makes your code easier to maintain and control.
However, I think that on some cases it can get too complex, as the activity that hosts the fragments need to navigate/communicate between them.
I think you should decide by yourself what's best for you. It's usually not that hard to convert an activity to a fragment and vice versa.
I've created a post about this dillema here, if you wish to read some further.
Since Jetpack, Single-Activity app is the preferred architecture. Usefull especially with the Navigation Architecture Component.
source
Why I prefer Fragment over Activity in ALL CASES.
Activity is expensive. In Fragment, views and property states are separated - whenever a fragment is in backstack, its views will be destroyed. So you can stack much more Fragments than Activity.
Backstack manipulation. With FragmentManager, it's easy to clear all the Fragments, insert more than on Fragments and etcs. But for Activity, it will be a nightmare to manipulate those stuff.
A much predictable lifecycle. As long as the host Activity is not recycled. the Fragments in the backstack will not be recycled. So it's possible to use FragmentManager::getFragments() to find specific Fragment (not encouraged).
In my opinion it's not really relevant. The key factor to consider is
how often are you gonna reuse parts of the UI (menus for example),
is the app also for tablets?
The main use of fragments is to build multipane activities, which makes it perfect for Tablet/Phone responsive apps.
Don't forget that an activity is application's block/component which can be shared and started through Intent! So each activity in your application should solve only one kind of task. If you have only one task in your application then I think you need only one activity and many fragments if needed. Of course you can reuse fragments in future activities which solve another tasks. This approach will be clear and logical separation of tasks. And you no need to maintain one activity with different intent filter parameters for different sets of fragments. You define tasks at the design stage of the development process based on requirements.
There's more to this than you realize, you have to remember than an activity that is launched does not implicitly destroy the calling activity. Sure, you can set it up such that your user clicks a button to go to a page, you start that page's activity and destroy the current one. This causes a lot of overhead. The best guide I can give you is:
** Start a new activity only if it makes sense to have the main activity and this one open at the same time (think of multiple windows).
A great example of when it makes sense to have multiple activities is Google Drive. The main activity provides a file explorer. When a file is opened, a new activity is launched to view that file. You can press the recent apps button which will allow you to go back to the browser without closing the opened document, then perhaps even open another document in parallel to the first.
Thing I did: Using less fragment when possible. Unfortunately, it's possible in almost case. So, I end up with a lot of fragments and a little of activities.
Some drawbacks I've realized:
ActionBar & Menu: When 2 fragment has different title, menu, that
will hard to handle. Ex: when adding new fragment, you can change action bar title, but when pop it from backstack there is no way to restore the old title. You may need an Toolbar in every fragment for this case, but let believe me, that will spend you more time.
When we need startForResult, activity has but fragment hasn't.
Don't have transition animation by default
My solution for this is using an Activity to wrap a fragment inside. So we have separate action bar, menu, startActivityForResult, animation,...
The one big advantage of a fragment over activity is that , the code which is used for fragment can be used for different activities. So, it provides re-usability of code in application development.
use one activity per application to provide base for fragment
use fragment for screen ,
fragments are lite weight as compared to activites
fragments are reusable
fragments are better suited for app which support both phone & tablet
You are free to use one of those.
Basically, you have to evaluate which is the best one to your app. Think about how you will manage the business flow and how to store/manage data preferences.
Think about, how Fragments store garbage data. When you implement the fragment, you have a activity root to fill with fragment(s). So, if your trying to implement a lot of activities with too much fragments, you have to consider performance on your app, coz you're manipulating (coarsely speaks) two context lifecycle, remember the complexity.
Remember: should I use fragments? Why shouldn't I?
regards.
I use Fragments for better user experience. For example if you have a Button and you want to run let's say a webservice when you click it, I attach a Fragment to the parent Activity.
if (id == R.id.forecast) {
ForecastFragment forecastFragment = new ForecastFragment();
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.main_content, forecastFragment);
ft.addToBackStack("backstack");
forecastFragment.setArguments(b);
ft.commit();
}
In that way the user won't have to move in another activity.
And secondly I prefer Fragments because you can handle them easily during rotation.
It depends what you want to build really. For example the navigation drawer uses fragments. Tabs use fragments as well. Another good implementation,is where you have a listview. When you rotate the phone and click a row the activity is shown in the remaining half of the screen. Personally,I use fragments and fragment dialogs,as it is more professional. Plus they are handled easier in rotation.
Almost always use fragments. If you know that the app you are building will remain very small, the extra effort of using fragments may not be worth it, so they can be left out. For larger apps, the complexity introduced is offset by the flexibility fragments provide, making it easier to justify having them in the project.
Some people are very opposed to the additional complexity involved with fragments and their lifecycles, so they never use them in their projects. An issue with this approach is that there are several APIs in Android that rely on fragments, such as ViewPager and the Jetpack Navigation library. If you need to use these options in your app, then you must use fragments to get their benefits.
Excerpt From: Kristin Marsicano. “Android Programming: The Big Nerd Ranch Guide, 4th Edition.” Apple Books.
Some wrong ideas:
Always put an activity in your app and handle different screens with fragments.
Write the UI code directly in the activity.
Handle navigating between screens (I don't mean tabs, I mean for example full-screen views) by fragments.
Activities can be replaced by fragments.
Here is the thing!
Fragments are designed to implement reusable parts of UI and use them in any part of the app that is needed. They are not designed for substituting activities.
When we must use each of them?
When we have an independent screen in which there are some different UI parts (tabs, expandable screens, partial screens, etc...) we should use an activity with some fragments to implement and handle different UI parts separately in the same screen.
Each independent part of the application is actually a component that is conceptually different from other parts and it needs to have an independent activity. For example, the login part may contain some different scenarios like using username-password or using fingerprint. Each scenario can be implemented by a fragment and all login-related fragments should be handled by LoginActivity. But for example, the part of the orders in the application doesn't have a conceptual relationship with login, so it must have a different activity and of course, it may contain some fragments like OrdersFragment, SubmitNewOrderFragment, and etc that all of them must be managed by OrdersActivity.
Do not implement a UI directly in an activity. Always implement UI in fragments and add those fragments in the activity even if there is only one fragment in that activity. It helps you to have more reusable code and change UIs easier.
Never use fragments to navigate infinitely in the application even if you force the user to have a limited number of fragments in the back stack. The fact is that when you add a new fragment into the back stack and remove it, it will not be removed from the memory unless the parent activity gets destroyed and it is only not visible. So when you are using fragment manager back stack, by navigating multiple times between fragments in the same activity (especially in the case of you create a new fragment on each navigation and put them into the back stack) you will get an OutOfMemoryException in the application.
I hope it to be helpful.
This question needs to be reevaluated since Jetpack Compose has reached stable.
Jetpack Compose is Android’s recommended modern toolkit for building
native UI.
from https://developer.android.com/jetpack/compose
The typical jetpack-compose architecture is:
Single Activity, multiple composables, and glued together by jetpack navigation.
Note there's no (need for) Fragments anymore.
See Now in Android for a sample.
This is a bit of a desperation call for some good advice.
I began doing a project which involves Navigation drawer as the main menu for the application. After looking at the Android tutorial I followed the example and start developing on top of that. That example is a single activity that replaces the fragments depending on the selected option in the drawer. In part, I followed this design because if I launched Activities the drawer was lost and the Activity would appear with the launching transition and didn't look nice at all.
Now, my project is not a small one. During development I faced several issues like:
onResume not being called on the Fragments (due to not being attached to several activities but one instead.
All the data between Fragments should pass through the single Activity
Managing the Options Menus in the ActionBar became a real pain.
And many others I don't recall now
Now I am facing a new issue. In one of the fragments I need to have a Spinner that will switch fragments inside this one. And of course, the fragment will need to change the navigation mode in the action bar. This was a major headache to develop, but now I am facing a bigger problem with some fragments inside losing the activity context (like if they were detached).
After so many problems I just decided to switch back the whole app to Activities (this is a custom app that will run in just 1 tablet model, so no worries about fragmentation). So, in short I am looking for advice on the less painful way to do this.
I am on a extremely tight deadline that lead me to start implementing without designing (like a complete noob). Now I am being hit with so many issues that, if I didn't need the money, I would cancel this project at once.
Please help!
I can give a little advice, but sadly your situation can't really be solved by any one answer here.
First off, switching from a Fragment design to an Activity design is a lot easier than switching the opposite way. You can actually use all of the fragments you had before, and just have each activity loading only 1 of the fragments (or multiple if you prefer).
Also, when handling Intents (starting new activity), after the startActivity() call you can call overridePendingTransition() to make the launching transition whatever you want (or remove it completely).
Which you think is the best way of doing a wizard like application (user can navigate between screens with a next and back button, and each screen has to save some state data) in Android platform.
I mainly can think in two approaches:
Having one activity+view for each screen and then i make the screen switch by calling each activity. What make this nice is that i can use the system back button as my back handler and i don't have to take care of that myself, aslo each activity will save it's own state.
Having one activity and many views, and what i switch views in each screen change, this helps me re-use more code, but makes saving states a mess.
What do you think? Which is the best way of doing this on Android?
This library is no longer being developed.
Use Android Navigation Component with combination of ViewModels to build a wizard flow.
I've developed a lightweight Android library, which is built on top of Android's ViewPager that can be used for creating wizard like activities. Check it out: WizarDroid.
I suggest going with 2 as it fits the goal of activities and views. Saving state in this case is easy - if you use the MVC pattern, you can simply have a model object that is passed along to the views. Each view will have portions of the model that it can read/write. No matter where you are, the model should always have the current state. If you get disposed, just save the model. Restore works automatically since you already read from the model when you show each page.
I've gone with the first approach as it seems more natural. Another app uses ViewFlipper for switching views but that's far from anything like wizard.
9 years ago this was obviously a very different kettle of fish - but I think the best way to do this now is with Fragments.
Have a Fragment for each 'page' in the wizard, letting it handle its own lifecycle and state.
Change page from within each Fragment with Fragment.getFragmentManager() - this returns the FragmentManager from the parent Activity, allowing the Fragment to replace itself.
I think 2 is better. Put each "page" in a view and then just alternate between showing and hiding them. Makes it trivial to do nice transitions. What state are you thinking of maintaining? The only one that doesn't work automatically would be focus and I think you probably want to reset that every time you switch pages. It is also trivial to catch back if you think that is the right behavior for your app.
With 1 you can reuse almost all of your code (just define your own WizardBase class) but I think activities are much slower to launch (and require more memory) than switching between views.