I have seen applications with add-on modules on market - these modules add-up some new functionality.
What would be the best way to do that ?
I cannot think of a descent and neat way to do that.
There are many ways. The most common is to just install another application and access it via Intents. It's definitely worth looking at Open Intents. If you are really adventurous, you can even load custom plugins with DexClassLoader.
IMHO the only way to cleanly implement this is to use Android's build-in extensibility, namely by using Intents and/or BroadcastReceivers. This is the way Android apps are supposed to communicate with each other, but it may work perfectly also for your own app by creating a main version which is extensible through Intents by your "plug-ins" which can be downloaded separately from the market.
The things you need to learn about and look for on the web to implement such functionality are
Intents: Learn how you can use intents to pass data from one app to another or to invoke certain functionality on other apps.
BroadcastReceiver: For listening to certain events broadcasted by your app in your "plug-ins"
ContentProvider: The content provider is used to provide an abstraction over your data and allows your "plug-ins" to access your app data easily and nicely decoupled through Content URIs.
Intent Filters: These are used to tell the system which kind of actions/Intents my specific Activity is able to accept. You will need them as a way for invoking your plug-ins (by broadcasting an Intent with the given action/category) as well as for providing a space in your menus where "compatible" Intents may hook in automatically.
I hope I was able to provide you some of the topics you need to know about. I'm sure that once you get a deeper understanding on these, you will get a much clearer picture on how to realize such a modular app.
Related
I've been coding for my Android phone lately, and i've been wondering... is this Intent class supposed to outline a new programming style?
I've been suspecting the API design discourages MVC: Intents are the main way to interact with all user-related objects (Activities, Services, Other apps...).
Is my train of thought right? Should is stick to "contaminating" Activities with business logic?
I have been reading the android developers site and no particular coding style is encouraged though.
Your question isn't entirely clear, because you seem to be confusing coding style with program architecture.
In my mind, Android really changes nothing in terms of coding style. Your coding style from Java will still work fine, and most Android apps look very similar to other apps. In the abstract, there are some things that you might want to do in Android you don't do as much in other languages, see the Android guide for details. The basic idea is: memory is limited, don't use it if you don't have to.
As far as whole program architecture goes, yes, the Android style is highly based around the message passing (through Intent objects) style. The way you react to GUI events within an Activity is still largely the same: you use event handlers to react to events like button presses, etc... But the platform is strongly centered around designing apps using different components (Activities, Services, BroadcastReceivers, etc...) and Intents to communicate between them. While Intents provide a flexible way of exchanging data between components, you still shouldn't be passing massive amounts of data within Intents, instead you should put those kinds of things in a ContentProvider or something similar.
I took a lot of the following ideas I took from this OReilly book. This is just whats worked best for me.
As far as architecture goes, its helped me to think of Android's UI as a Page Controller pattern - I found it to be similar to .Net Web Forms actually. So yes, it does fit with MVC (at least the Page Controller flavor of it). An Activity is your controller, you typically store your view in XML, and you can build out your Model however you like.
You see a lot of web-ish ideas in Android. Intents are a lot like HTTP, or more generally REST. Intents have a 'noun' that says what they are concerned with (can be explicit class declaration ie: go to a specific Activity, or can be more implicit using Intent Filters), the Action is a lot like an HTTP verb (Get, Post, etc), a Bundle is a lot like a list of query string parameters or payload...etc.
And similar to a web page, you want an Activity to be able to take care of itself. What I mean is, you don't want to pass around some big serialized object from activity to activity, its a lot cleaner/resilient/reliable to just pass the id of the a given record to the next Activity and let that activity grab the record with that id from the db (ContentProvider, some other persistent source...). Activities are also meant to be loosely coupled, and you're supposed to be able to navigate to one from various paths, it also makes them more re-usable. Thus, allowing the callers of an Activity to simply provide a recordId is a lot easier then the Activity expecting its consumer to have provided a large serialized object.
Bottom line - no, you don't need to contaminate Activities with Business Logic, tuck that stuff away in an application layer, or a gateway or something like that. As for persistence, the ContentProvider interface is pretty well designed - I like it alot. It also continues the Android RESTful theme, accessing content via URLs and verbs (query, delete, update, insert).
Sending and receiving intends is much like sending and registering (similar to a publish-subscribe channel) for command messages (e.g. in a distributed enterprise application, and this is about architecture, not style). This pattern helps designing a loosely coupled system of interacting applications.
I cannot remember having seen a similar architecture before used for the interaction of components and applications on a single computer but it helps to design application using other applications to easily build an ecosystem of features/components.
I want to develop an application that supports plugins and that provides data to these plugins. It seems to me that the correct way to implement this plugin-archtitecture on Android would be one apk for the main app and one apk per plugin.
But as the main app and every plugin are in different apks I can't easily pass (data) objects from the one to the other, the applications run in different processes and even if they run in one process (which can be achieved) they have different classloaders and this doesn't work. Currently I see two promising approaches for getting data from my main app to my plugins:
Declaring the main app as a ContentProvider. This seems to me to be the intended approach because it does exactly what I want to achieve: providing content/data to another process.
Making my data objects Parcelable and pushing them around with AIDL or - if I do not need multithreading - with the Messenger-approach. In my opinion, this approach seems to be easier because I can use an ORM-library which cares about the Database in the background. I never used ContentProviders before but at a first look at it I thought that using a ContentProvider is a bit like building SQL-Queries by hand (please tell me if I'm wrong), and I would like to avoid that work!
Now I would like to know if I missed any pros or cons and if there are notable performance differences between these two approaches. And which solution would you prefer and why would you do so?
Thanks in advance! Any replies are appreciated!
Content provider is just way to share data (that are stored in different ways [database, files and so on]) between applications. If you want just share data between application it is the best way to do this.
However, if you want services to perform some tasks with data (for instance, sum several values provided by you) it's better to have a remote service.
In general case, application - plugin interaction is more similar to a remote service. In this case the main application exposes a remote service (an API of this application) that can be used by plugins to perform some actions.
I'm a newbie of Android world. I'm so confused about some terms.
Especially, why do we call Activity, Service, Broadcast receiver and Content Provider as "Component"? Of course, I know the original meaning of Component. However, I think there are special reasons that Android developers use this terminology. Please somebody tell me exactly meaning or definition about Component.
Thanks!
Nope, as far as I know there is no special Android-specific meaning of "Component". Activities, Services, Broadcast Receivers and Content Providers are just core building blocks of a standard Android application so they are called application components. The docs use the term "component" in other places to refer to other things too, see this doc for an example.
I just got done writing an Android Activity that allows other Activities to call it for some result (it's not intended to be a stand-alone Activity). I'm now working on the equivalent iOS application and can't find any resources for how I would enable similar functionality on iOS.
The situation: The tool I'm producing is intended to be used by other applications, rather than as a standalone application. The thing is, the GUI that needs to be presented to the user is rather involved so I'd like to be able to provide the developer with a "all-in-one" package that they can simply launch and get results from. Doing this in Android was very straight forward. I simply wrote an Activity and instructed the developer to launch this Activity for result. I've looked around and can't find a similar functionality to allow an iOS developer to do the same. What would be the best way to go about doing this?
I think part of the problem I'm having in finding resources is that I'm not entirely sure what what I'm making is called. A library? extension? plug-in? I would think a library doesn't have a GUI and it seems extensions and plug-ins are made for an extensible application (that is, one in which the user can install the extension/plug-in).
Your API could be à single call that would pop up a modal view. A target and selector can be specified to receive an answer. Supplying it to other developers means packing it into a "framework". I'm not sure if you can include resources.
There isn't really any equivalent. The closest you can come is having the second application call UIApplication's openURL with a custom scheme that is listened to by your app, and then when your app is done it would do the same with a custom scheme that is listened to by the calling app.
In practice, the iOS app would usually include the entire activity-equivalent as some sort of library, which at the high level would take the form of a UIViewController subclass that is presented modally and then calls a delegate method or completion selector of some sort on completion.
iPhone development is a different design than Android development, so you may need to rethink what it is you are trying to do.
Most likely you will want to look at just including the code in each program, initially, just so you can get it testable, but that may not be the best solution.
But, without knowing more details about what you are trying to do it is hard to give some suggestions as to better solutions.
For example, you may find LocalNotifications as one solution (http://useyourloaf.com/blog/2010/7/31/adding-local-notifications-with-ios-4.html), but again, it depends on what your needs are.
I found that using local notifications to call a REST service, then to process it and decide if I need to inform the user was helpful, as a replacement for how I used Intents in the Android application.
it's been some time now, since I started reading about android.
I've already made a few basic applications, but I still miss something: How is actually sharing application component being done?
This is what the Android Dev Guide says:
A central feature of Android is that one application can make use of elements of other applications (provided those applications permit it). For example, if your application needs to display a scrolling list of images and another application has developed a suitable scroller and made it available to others, you can call upon that scroller to do the work, rather than develop your own. Your application doesn't incorporate the code of the other application or link to it. Rather, it simply starts up that piece of the other application when the need arises.
I think I came across some question like this, but I think I'm still confused.
Is the only way of getting such a 'private application' information to contact the developers of that application?
Is information about the data that the application operates with private, too?
If it is described in the AndroidManifest.xml file is it available for the other applications, or it is available only to Android?
When I started satisfying my interest in Android - one of the things that grabbed me was the impression of immense interoperability...
:)
Have I been wrong or I still haven't found the way?
Thanks!
How is actually sharing application component being done?
That depends entirely on what you consider an "application component" to be, and what you consider "sharing" to be.
This is what the Android Dev Guide says
That is a fairly bad piece of the documentation. Here is how I would write it:
A central feature of Android is that one application can make use of components (e.g., activities, services) of other applications (provided those applications permit it). For example, if your application needs to display a list of contacts and another application has developed an activity that does just that and made it available to others, you can call upon that activity to do the work, rather than develop your own. Your application doesn't incorporate the code of the other application. Rather, it simply starts up that piece of the other application when the need arises.
Is the only way of getting such a 'private application' information to contact the developers of that application?
Either developers are intending for you to integrate with them, or they are not. If they are, they should be documenting how to do that (e.g., Intent formats to be used with startActivity() to trigger their code). If they do not document such integration points, you can certainly ask the developers to add some. However, randomly shooting Intents at them in hopes of getting a response, even if it temporarily works, is little better than script kiddie tactics -- those developers are not obligated to ensure you code works when they upgrade their app.
Is information about the data that the application operates with private, too?
I do not know what "information about the data that the application operates with" means. Data managed by an application is private by default. Again, application developers can offer integration points for data (e.g., content provider, remote service API) -- some do, some do not.
one of the things that grabbed me was the impression of immense interoperability
Android offers greater interoperability potential than some other mobile platforms. However, using that potential requires consent among the interoper-ees. You cannot unilaterally decide to hack into another app's database, or invoke private activities, just because you feel like it.
Should more Android developers offer more integration points? In the abstract, sure. However, bear in mind that this adds support costs (e.g., answering integration questions) and limits coding flexibility (e.g., need to maintain a stable API for those doing the integrating). Developers cannot be blamed if they do not wish to incur all that.