Design issue in swing application
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From: Lew on 17 Feb 2010 12:41 Fencer wrote: > On 2010-02-17 17:41, Lew wrote: >> Fencer wrote: >>> MVC, hmm. Ok, so imagine WelcomePanel is a view and instead of knowing >>> about the CenteredGroup class directly it knows about an interface for >>> a Controller. >> >> Normally you'd do it the other way around - the controller knows about >> the view, but the view doesn't know about the controller. >> >>> When the user presses the button "Open BioModel" the view informs the >>> controller about this. What should happen now is that a file >> >> This is where the controller knows the view. The central view method >> returns a value, and takes arguments, that the controller understands. >> The view types know nothing about how the arguments are created or the >> return values are used. > > Thanks for your reply. > > I will read some more and try to make a concept implementation. Just one > question, if the view (a JPanel in my case) doesn't know about the > controller but the controller knows about the view, how should I > implement my button listener? Right now it's an anonymous inner class to > the JPanel-extended class, I don't get how to handle that and not have > the view know the controller? The listener does exist in the view because it's part of the view. If you actually read the links to which I pointed, you will see that ultimately the job of the view is to return state to the controller; you can do that from the listener or from some other part of the view triggered by the listener. Read the links, explore their transitive links, think about what you've read, play with it for a while, then ask questions, in that order. If you haven't even assimilated the information already provided, then you're going to ask redundant questions. Read, study, experiment, then ask. -- Lew
From: Lew on 17 Feb 2010 12:48 Fencer wrote: > package gui; > > import java.awt.Dimension; > import java.awt.GridBagConstraints; > import java.awt.GridBagLayout; > import java.awt.event.ActionEvent; > import java.awt.event.ActionListener; > > import javax.swing.JButton; > import javax.swing.JPanel; > import javax.swing.border.TitledBorder; > > public class WelcomePanel extends JPanel { > > private static final long serialVersionUID = 1596841645688614873L; > > public WelcomePanel(final CenteredGroup inst) { > this.inst = inst; > > setPreferredSize(new Dimension(480, 100)); > setBorder(new TitledBorder("Start a new session by opening a > BioModel or load a previously saved session")); > setLayout(new GridBagLayout()); > > initButtons(); > } > > private void initButtons() { > final CenteredGroup inst2 = this.inst; ^ You don't need this line. > b1 = new JButton("Open BioModel"); > > b1.addActionListener(new ActionListener() { > @Override public void actionPerformed(ActionEvent e) { > inst2.eventOpenBioModel(); > }}); > > b2 = new JButton("Load Saved Session"); > > b2.addActionListener(new ActionListener() { > @Override public void actionPerformed(ActionEvent e) { > inst2.eventLoadSavedSession(); > }}); > > addButtonsToGroupPanel(b1, b2); > } > > private void addButtonsToGroupPanel(JButton b1, JButton b2) { > GridBagConstraints gbc = new GridBagConstraints(); > > gbc.gridx = 0; > gbc.gridy = 0; > gbc.gridwidth = 1; > gbc.gridheight = 1; > gbc.weightx = 0.5; > gbc.weighty = 0; > gbc.anchor = GridBagConstraints.CENTER; > gbc.fill = GridBagConstraints.NONE; > > add(b1, gbc); > > gbc.gridx = 1; > > add(b2, gbc); > } > > private CenteredGroup inst = null; > > private JButton b1 = null; > private JButton b2 = null; > } Why do you initialize these instance members to 'null' when a) the language already does that anyway, and b) you initialize them to non-'null' values in your constructor anyway? Just curious. It's a matter of style, but personally I find placement of member variable declarations at the top to be clearer than at the bottom. For example, in this code it would make it more obvious that you are assign values to those instance variables three times apiece. For this particular class, where the 'CenteredGroup' and the two 'JButton's each need exactly one value, you should declare those variables 'final' and assign their 'new' values in the constructor rather than a separate method. -- Lew
From: markspace on 17 Feb 2010 12:52 Fencer wrote: > Thanks for your reply. > MVC, hmm. Ok, so imagine WelcomePanel is a view and instead of knowing > about the CenteredGroup class directly it knows about an interface for a > Controller. When the user presses the button "Open BioModel" the view > informs the controller about this. What should happen now is that a file > selection dialog should appear where the user can select a biomodel file > which is then processed. But who should display this file selection dialog? > Maybe WelcomePanel should do that and then inform the controller that > this event has occurred and this biomodel file was choosen and the > controller would then proceed from there? > Lew gave some good links and advice. Here's the same stuff in a slightly different format. Normally, the Controller has references to the View and the Model, not the other way around. public class Controller { View view; Model model; public Controller ( View view, Model model ) { this.view = view; this.model = model; ... } .... } View would be some interface that this controller knows how to deal with. Your View would be named "WelcomeScreen" or something like that; this controller might be called a "WelcomeController". The implementation of the view would be a JPanel or JFrame but your controller wouldn't care about that. The thing that receives the user interaction is the controller too. The view only knows about the controller via a call back, so that needs to be set. public Controller ( View view, Model model ) { this.view = view; this.model = model; this.view.addLoadFileActionListener( new ActionListener() { @Override public actionPerformed( final ActionEvent e ) { loadFile( e ); } } ... } loadFile( ActionEvent e ) { ... show JFileDialog here... } Something like that. (Note this controller now likely needs to be synchronized and created on the EDT.) The result is that your Controller is very procedural. It's a "driver object". It mostly contains methods that drive the operation of your program, it doesn't contain a lot of "state." This makes testing easier. Try to keep controllers specific to one task or idea. If needed, you should only have one action listener per controller. (More are OK, if the concept is tightly scoped.) You may need lots of controllers to implement a single window if that window has lots of buttons or controls. Views should be "dumb" and just fire events. Don't keep any state in a view, other than the state it already has (like the text string in a JTextField). Model objects span the gamut. Some are "dumb," just data, like value objects. Some are more active, and will do things like persists (save) data, write to databases, or download from URLs or whatnot. It's up to your design and your requirements how you do the model. Your model would probably be a "BioModel". In classic MVC, the model updates the view via a call back, and the view has a reference to the model. However, Java uses a "split model" design where views (JComponents) have their own model. So I think it's kind of a toss up how your model updates the view when needed. I'd be inclined to have it go through the Controller too, meaning no direct linkage. In Java it's also possible to dispense with the Controller entirely and just use the ActionLisenter. However, it's still a useful concept sometimes, and you should at least keep it in mind for when it's useful. That's my two minute lesson on MVC. Hopefully some of it is is even correct. ;) > As you can see I have trouble deciding what goes where, heh. :-) That's normal in software development. ;)
From: Fencer on 17 Feb 2010 13:04 On 2010-02-17 18:52, markspace wrote: > Fencer wrote: > >> Thanks for your reply. >> MVC, hmm. Ok, so imagine WelcomePanel is a view and instead of knowing >> about the CenteredGroup class directly it knows about an interface for >> a Controller. When the user presses the button "Open BioModel" the >> view informs the controller about this. What should happen now is that >> a file selection dialog should appear where the user can select a >> biomodel file which is then processed. But who should display this >> file selection dialog? >> Maybe WelcomePanel should do that and then inform the controller that >> this event has occurred and this biomodel file was choosen and the >> controller would then proceed from there? >> > > > Lew gave some good links and advice. Here's the same stuff in a slightly > different format. > > Normally, the Controller has references to the View and the Model, not > the other way around. > > public class Controller { > > View view; > Model model; > > public Controller ( View view, Model model ) { > this.view = view; > this.model = model; > ... > } > ... > } > > View would be some interface that this controller knows how to deal > with. Your View would be named "WelcomeScreen" or something like that; > this controller might be called a "WelcomeController". The > implementation of the view would be a JPanel or JFrame but your > controller wouldn't care about that. > > The thing that receives the user interaction is the controller too. The > view only knows about the controller via a call back, so that needs to > be set. > > public Controller ( View view, Model model ) { > this.view = view; > this.model = model; > > this.view.addLoadFileActionListener( new ActionListener() { > @Override > public actionPerformed( final ActionEvent e ) { > loadFile( e ); > } > } > ... > } > > loadFile( ActionEvent e ) { > ... show JFileDialog here... > } > > Something like that. (Note this controller now likely needs to be > synchronized and created on the EDT.) > > The result is that your Controller is very procedural. It's a "driver > object". It mostly contains methods that drive the operation of your > program, it doesn't contain a lot of "state." This makes testing easier. > Try to keep controllers specific to one task or idea. If needed, you > should only have one action listener per controller. (More are OK, if > the concept is tightly scoped.) You may need lots of controllers to > implement a single window if that window has lots of buttons or controls. > > Views should be "dumb" and just fire events. Don't keep any state in a > view, other than the state it already has (like the text string in a > JTextField). > > Model objects span the gamut. Some are "dumb," just data, like value > objects. Some are more active, and will do things like persists (save) > data, write to databases, or download from URLs or whatnot. It's up to > your design and your requirements how you do the model. Your model would > probably be a "BioModel". > > In classic MVC, the model updates the view via a call back, and the view > has a reference to the model. However, Java uses a "split model" design > where views (JComponents) have their own model. So I think it's kind of > a toss up how your model updates the view when needed. I'd be inclined > to have it go through the Controller too, meaning no direct linkage. > > In Java it's also possible to dispense with the Controller entirely and > just use the ActionLisenter. However, it's still a useful concept > sometimes, and you should at least keep it in mind for when it's useful. > > That's my two minute lesson on MVC. Hopefully some of it is is even > correct. ;) > > >> As you can see I have trouble deciding what goes where, heh. :-) > > That's normal in software development. ;) Thank you for posting that!
From: Fencer on 17 Feb 2010 13:09
On 2010-02-17 18:48, Lew wrote: > Fencer wrote: >> package gui; >> >> import java.awt.Dimension; >> import java.awt.GridBagConstraints; >> import java.awt.GridBagLayout; >> import java.awt.event.ActionEvent; >> import java.awt.event.ActionListener; >> >> import javax.swing.JButton; >> import javax.swing.JPanel; >> import javax.swing.border.TitledBorder; >> >> public class WelcomePanel extends JPanel { >> >> private static final long serialVersionUID = 1596841645688614873L; >> >> public WelcomePanel(final CenteredGroup inst) { >> this.inst = inst; >> >> setPreferredSize(new Dimension(480, 100)); >> setBorder(new TitledBorder("Start a new session by opening a BioModel >> or load a previously saved session")); >> setLayout(new GridBagLayout()); >> >> initButtons(); >> } >> >> private void initButtons() { >> final CenteredGroup inst2 = this.inst; > ^ > You don't need this line. > >> b1 = new JButton("Open BioModel"); >> >> b1.addActionListener(new ActionListener() { >> @Override public void actionPerformed(ActionEvent e) { >> inst2.eventOpenBioModel(); >> }}); >> >> b2 = new JButton("Load Saved Session"); >> >> b2.addActionListener(new ActionListener() { >> @Override public void actionPerformed(ActionEvent e) { >> inst2.eventLoadSavedSession(); >> }}); >> >> addButtonsToGroupPanel(b1, b2); >> } >> >> private void addButtonsToGroupPanel(JButton b1, JButton b2) { >> GridBagConstraints gbc = new GridBagConstraints(); >> >> gbc.gridx = 0; >> gbc.gridy = 0; >> gbc.gridwidth = 1; >> gbc.gridheight = 1; >> gbc.weightx = 0.5; >> gbc.weighty = 0; >> gbc.anchor = GridBagConstraints.CENTER; >> gbc.fill = GridBagConstraints.NONE; >> >> add(b1, gbc); >> >> gbc.gridx = 1; >> >> add(b2, gbc); >> } >> >> private CenteredGroup inst = null; >> >> private JButton b1 = null; >> private JButton b2 = null; >> } > > Why do you initialize these instance members to 'null' when a) the > language already does that anyway, and b) you initialize them to > non-'null' values in your constructor anyway? > > Just curious. > > It's a matter of style, but personally I find placement of member > variable declarations at the top to be clearer than at the bottom. For > example, in this code it would make it more obvious that you are assign > values to those instance variables three times apiece. Ah, I learned something useful there! I usually initialize to null even though that is done automatically but now you taught me that if I dont initalize to null I can use final! Thank you. > > For this particular class, where the 'CenteredGroup' and the two > 'JButton's each need exactly one value, you should declare those > variables 'final' and assign their 'new' values in the constructor > rather than a separate method. > |