将Java swing MVC与Android设计模式进行比较

Question

I'm doing a small research on design patterns in various platforms and I have prior experience in programming with Java.

While reading these posts: MVC pattern on Android and MVC architecture in Android ,
I had an interesting question in mind: Why Java swing MVC can not be compared with Android development pattern? or Why we can't say that Android follows MVC? (in the context of overall "look and feel").

In one answer, someone clarified MVC as:

• Model: What to render

• View: How to render

• Controller: Events, user input

OK. well, now what I understand is:

Java Swing MVC:

• In Java swing MVC, component class is an abstract class for all attributes in visual environment. There is a distinct keyword called controls is used for some components such as buttons, lists etc. So, all controls and components are part of Model in MVC.

• Container inherits component . and there are several LayoutManagers that defines layouts and place of components in container . Also there are Listeners have to be registered with according EventSources . So, they all are the View in MVC.

• Class that implements Listener interface methods in which we put our main logic and there are some EventClasses for each event. They all are part of Controller in MVC.

putting all these examples together in an image; in swing MVC we have:

Android design pattern (visualizing as MVC):

• I think widgets are same as controls here. Also, there are some other EventSources .They all act as a Model .

• View package has viewgroups (that also contains several kinds of layouts .) and Listener interfaces . they all are the part of View in MVC.

• Same as swing MVC, we can say Listener interface methods and activities are the part of controller .

putting all together in an image; in Android we have:

As per above comparison, I consider following similarities :

• Container - same as View

• Layout managers - same as ViewGroup

• Listeners - overall same in both architecture

• controls - overall same as widgets

• Event delegation (registering appropriate listener with Event source and then implementing Listener's methods) - overall same in both architecture

So, can anyone explain which are the things that makes the Android design pattern different than Java swing MVC pattern?
or If you believe that both are different things (in the context of design patterns used for development), then explain why?

Answer 1

Each Swing JComponent has ComponentUI that is responsible for displaying a component. While JComponent has a paint method, only user derived classes use it directly - "standard" implementations very often just call the paint method of the attached UI instead. This allows to plug-in various look and feel implementations very easily - a different look and feel just provides different ComponentUI's. Very clearly component is the "model" and the UI is the "view". And Android does not inherit this decoupling in very obvious way. For instance, its TextView seems just painting drawables when a similar JLabel has UI .

This is however not the only place where MVC approach is used, and for some other specific cases Android and Swing MVC are very similar. For instance, Android ListView has a model ( ListAdapter ) very much like Swing JList has ListModel . In both cases the model provides data while the component itself provides possibilities to display. The possible difference is that Swing has more components with such decoupled data and presentation. JTable and JTree have similar models when Android does not provide such components out of box. There is no tree at all, and TableLayout is a that is called GridLayout in Swing, not similar to JTable .

The general approach for invalidating and repainting is not much different and in both frameworks only dedicated master thread can touch components. Also, event listeners (probably other group of "controllers") are very similar in Java and Android, all differences between them could probably be called "subtle" only.

Containers and layout manages are also quite similar between Swing and Android, the main differences being that Swing has much more possible implementations of its LayoutManager to choose from than Androids ViewGroup (classes like DatePicker , while derived from ViewGroup , are not general purpose layout managers). Also, part of Android layout is encoded in XML while Swing is typically plain Java only. If layout managers are also kind of "controllers" responding to events like resizing or reorientation, this part is very similarly done. However I am not sure if layout managers are really "controllers" as they update more the view than the model.

In general, Swing seems more optimized for the large, complex GUI that shows up on a large screen when Android is better suited for small screens with just a few visible components, large enough to be operated with fingers without stylus.

Answer 2

The key feature of MVC is the separation of concerns between the three components:

• The Model is responsible for maintaining an internal representation of the data.
• The View is responsible for displaying that data to the user and allowing them to interact with it.
• The Controller is responsible for updating the Model in response to user interactions with the View and to ensure that the View reflects the current state of the Model.

Depending on how strict a definition of MVC you're applying, you could also specify constraints around decoupling of the components; for example you could assert that the Model should have no knowledge of the View or the Controller. However, in most cases it would probably be considered sufficient to show that the three components are reflected separately in the software and conform to the general responsibilities above.

In terms of your mappings of MVC to Swing and Android, I think the main issue you're struggling with is that of identifying the Model. The Model does not have to be a distinct type of component in the UI framework, it can just be a simple class or set of classes that encapsulate the data in question. So, where you have the Model mapping to widgets and controls, I would argue that's incorrect: the Model is simply whatever data is being represented to the user. So, for Swing I would map the MVC components as follows:

• Model: Any domain classes that represent your data, for example com.example.Order .
• View: The controls, containers and layout managers.
• Controller: The event listener implementations that manipulate the Model and update the View.

You could come up with a stricter MVC implementation in Swing, but the above is probably a reasonable mapping.

The Android UI framework is more restrictive than Swing because applications on mobile devices are more constrained and Google would prefer that they behave in a fairly consistent manner, hence the need for classes like Activity to represent a particular thing that the user needs to do, and the relatively tight coupling with an Activity and given View / ViewGroup .

Even so, you could map the Android components as follows:

• Model: Any domain classes that represent your data, for example com.example.Order .
• View: The Views and ViewGroups
• Controller: The Activity , assuming that the event listener code for your View s are part of the Activity , which is often the case.

Now, you could also argue that the above is actually more of a Model-View-Presenter pattern with the Activity playing the part of the Presenter, but given that MVP can be thought of as a more specific variety of MVC, that doesn't necessarily invalidate the MVC mapping.