i think this not a specific problem to me; everybody might have encountered this issue before.
To properly illustrate it, here's a simple UI:
As you can see, those two spinners are controlling a single variable -- "A". The only difference is that they control it using different views.
Since these two spinners' displaying values are synchronized, cyclic event shows up.
If i change the top spinner, "A" will be changed and the bottom spinner's value will also be updated accordingly. However, updating the bottom spinner's call (such as setValue) will also trigger another event instructing the top spinner to update based on the bottom spinner's value. Thus creates a bad cycle which can eventually cause a StackOverFlow exception.
My previously solution is kinda cumbersome: i placed a guarding boolean to indicate whether the 2nd updating call should be performed.
Now i'd like to ask "how can i handle such situation elegantly? ( in general, not specific to spinners )"
thx
Update:
Since i've got 2 answers suggesting me to utilize the observer structure, i have to say something about it.
Like what i've said, it's great but far from being perfect. Not only because of its inherent complexity, but also Its inability to solve the problem.
Why? To see the reason, you must realize the tight coupling of the View and Model-Controller in Java Swing. Lets take my spinner UI for an example. Suppose the variable A is actually an Observer object. Then, after firing the first state change event from the top spinner, the Observer "A" will update its value and fire a PropertyChange event to notify the bottom spinner. Then comes the 2nd updating which updates the bottom spinner's View. However, changing bottom spinner's view inevitably triggers a redundant event that will try to set "A"'s value again. Afterwards, the deadly loop is fully constructed and the stack overflow will be thrown.
In theory, the Observer model tries to solve the direct cycle by introducing 2 independent feedback paths. The chained updating odds(in event-response codes) implicitly form a bridge connecting both paths, making a cycle again.
Going back to Model-View-Controller, think about what your Model is, and what your View is.
In your current implementation, you have two models (one for each Spinner control), and they're being synced through the View layer.
What you should be doing though is share the same backing model. For the spinner with a subtracted value, create a proxy to the original model. ie:
class ProxySpinnerModel implements SpinnerModel {
getValue() { return originalSpinner.getValue() - 10 }
setValue(v) { originalSpinner.setValue(v+10) }
}
spinnerA = new JSpinner()
spinnerB = new JSpinner( new ProxySpinnerModel( spinnerA.getModel() ) )
Now, you don't need to add listeners, since they're both working off the same model and the default implementation (the originalModel) already has change listeners which it fires to the view.
Problem Solved
I've got many different suggestions. Particularly,
i want to thank Marc W & Reverend Gonzo. I'm here to make a summary for these ideas; this can save your time navigating thru big chunk of texts.
This problem can be easily bypassed if you carefully decouple the View and Model-Controller.
The dead cycle is caused by dependent writes: write_1 -> write_2 -> write_1 ->.... Intuitively, breaking the dependency can solve the problem elegantly.
If we look into the problem in depth, we can find updating the corresponding views doesn't necessarily involves an external write call. Actually, a view only depends on the data it's representing. Known this, we can then re-write the logic as follow: write_1 -> read_2 & write_2 -> read_1.
To illustrate this idea, lets compare the 3 methods mentioned by different posters:
alt text http://www.freeimagehosting.net/uploads/2707f1b483.png
As you can see, only the proxied view can solve all the dependency thus it's the generic solution for this knid of problem.
In practice, it can be implemented as something like this (in your event-response codes):
setValue(newValue);
anotherSyncUI.parse(); // not anotherSyncUI.setValue() any more
anotherSyncUI.repaint();
No more loops. Solved.
It's a bit complicated, but you could make A actually be an object that's observable. Both spinners (or whatever needs to update itself based on A's value) would then observe A. Whenever A changes, the spinners (or again, whatever object) update themselves to reflect the new value of A. This decouples the spinners' logic from one another. In your example here, the spinners should not be coupled to one another because they really have nothing to do with each other. Instead, they should both simply be bound to A and take care of their own view updating individually.
Whenever the value in the first spinner is changed, you would simply update A's value to match it. Whenever the value in the second spinner is changed, you would of course add 10 to its value before assigning it to A.
Update
In response to the update to your original question, my answer is that the spinners do not listen to one another's change events. Have a separate event handling method for each spinner. A user clicking the up or down arrows in the spinner generates a different event than calling setValue on the spinner programmatically, correct? If the spinners are completely independent of one another, there will be no infinite loop.
E.g. for the second spinner, calculate A-10 and then compare it to the current value of the spinner. If it's the same, do nothing, ending the infinite loop. Similarly for the first spinner.
I think there are also ways to update the spinner's model in a way that doesn't fire an event, but I don't know them off the top of my head.
Use a single SpinnerModel for both JSpinners. See the following code:
Note that the call to setValue() is only made once each time a new value is defined by one of the JSpinners.
import java.awt.BorderLayout;
import javax.swing.*;
public class Test {
public static void main(String[] args) {
JFrame jf = new JFrame();
SpinnerModel spinModel = new MySpinnerModel();
JSpinner jspin1 = new JSpinner(spinModel);
JSpinner jspin2 = new JSpinner(spinModel);
jf.setLayout(new BorderLayout());
jf.add(jspin1, BorderLayout.NORTH);
jf.add(jspin2, BorderLayout.SOUTH);
jf.pack();
jf.setVisible(true);
jf.setDefaultCloseOperation(3);
}
}
class MySpinnerModel extends AbstractSpinnerModel {
private int _value = 0;
private int _min = 0;
private int _max = 10;
#Override
public Object getNextValue() {
if (_value == _max) {
return null;
}
return _value + 1;
}
#Override
public Object getPreviousValue() {
if (_value == _min) {
return null;
}
return _value - 1;
}
#Override
public Object getValue() {
return _value;
}
#Override
public void setValue(Object value) {
System.out.println("setValue(" + value + ")");
if (value instanceof Integer) {
_value = (Integer) value;
fireStateChanged();
}
}
}
It seems you're really observing the wrong thing. From the example given I presume what you want to detect is the user's actions on the controls, not the changes in the values themselves. As you've outlined, changes in your model are reflected in the values of the spinners, and it is this which forms the infinite loop of events.
However, diving further into the UI implementation may not be the answer you want. In that case I'd say the best you can do is either your current guard solution, or to better extract the logic into your model (similar to what Marc and William have said). How that can be done will depend on the 'real world' model behind a particular implementation of the provided puzzle.
As a rule, your model should not be defined by your GUI. Ie, the SpinnerModel that backs each JSpinner should not be your value A. (That would be a horribly inelegant tightly coupled dependency on a particular view.)
Instead, your value A should either be a POJO or a property of an object. In which case, you can add PropertyChangeSupport to it. (And presumably have already done so in any case, as you want your spinners to update automatically if A is changed by other parts of your program).
I realise this is similar to Marc W's answer, and you were concerned that it's "complicated", but PropertyChangeSupport does almost all of it for you.
In fact, for trivially simple cases, you can just use a single class that wires a "setProperty" method through to a "firePropertyChange" call (as well as storing the value in a HashMap for any "getProperty" calls).
I don't really want to solve your problem but I find it interesting. I have already been confront to it and solved it each time a different way. But when I think about the 'why ?' and not about the 'how ?' am staying perplexed.
This problem only exists because I am using an automatism (MVC) which had to help me, and exactly in that way. The art how the components are used make this automatism a barrier to a beautiful code.
Why do set #setEvent() has to produce the same event as a GUI action?
Though, my opinion is also pretty close to Observer pattern but it is a bit lighter than that!!!
Have A as a variable with a setter
private Integer A;
setA(int A)
{
this.A = A;
refreshSpinners();
}
refreshSpinners()
{
setSpinnerA();
setSpinnerAMinus10();
}
setSpinnerA()
{
// show value of A
}
setSpinnerAMinus10()
{
// show value of A-10
}
Related
I have an application with a GUI with sliders and comboboxes mainly. I use the sliders and combos to change values and parameters in various classes in the project. I'm trying to implement the possibility to save and load this parameters and I have done so using the preferences API.
I can save and load parameters, but when I load them I can see the changes in values, so that works, but the GUI does not update to reflect those new values. is there a way to tell the GUI to do so?
For instance I have a frequency slider that changes the frequency value in an oscillator. If I change the value with the slider, save it, change the value of the slider again and then load the saved value, I can hear it has changed but the slider didn't move.(makes sense as I haven't told it too). Can I bind the position of the slider with that frequency value somehow?
gui
//OSC1 slider
JSlider Osc1FreqSlider = new JSlider(SwingConstants.HORIZONTAL, MIN_OSC_FREQ, MAX_OSC_FREQ, NOTE_A_FREQ);
Osc1FreqSlider.setOpaque(false);
Osc1FreqSlider.setMajorTickSpacing(50000);
Osc1FreqSlider.setMinorTickSpacing(50);
Osc1FreqSlider.addChangeListener(new ChangeListener() {
public void stateChanged(ChangeEvent e) {
JSlider source = (JSlider) e.getSource();
settings.setOsc1Freq((float)source.getValue()/100);
}
});
settings class
public void setOsc1Freq(float freq) {
m_Osc1Freq = freq;
}
After setOsc1Freq( freq ) you have to do jSlider.setValue( freq ).
The way I do this in my own projects is that I never use free-standing primitive values like float freq; instead, I have an observable class with a getter and a setter, which issues an event when the value changes, and then I wrap every single one of my controls in another class which knows how to interact with such an observable. So, every time the value of the control changes, the value in the observable changes too, but also, every time my program changes the value of the observable, the control also takes notice and updates itself too.
I would think that it is practically impossible to write any kind of gui without this functionality, but apparently I seem to be contradicted by the existence of a myriad of gui frameworks out there that do not support this and force you to re-invent.
(Posted on behalf of the OP).
I solved my problem by splitting components declaration, moving them to another singleton class, creating accessor methods and then in the gui class I assigned the variables to the getters.
I have something like this.
Grid<Stock> mygrid = new Grid<Stock>(store, cm)
{
#Override
protected void onAfterFirstAttach()
{
super.onAfterFirstAttach();
//here do the binding for the cell elements that have myclass
}
};
And for the view of mygrid I have this
view.setViewConfig(new GridViewConfig<Stock>()
{
#Override
public String getRowStyle(Stock model, int rowIndex)
{
return "";
}
#Override
public String getColStyle(Stock model, ValueProvider<? super Stock, ?> valueProvider, int rowIndex, int colIndex)
{
String style = "";
if(SOME_CASE)
{
style = "myclass";
}
return style;
}
});
What I want to do is onAfterFirstAttach I want to add some listener/handler that during hover will do something, let's say for the sake of simplicity, give an alert.
Is what I'm trying to do possible? Can I accomplish what I want without using JSNI or a library like gwtquery? Is it sure that onAfterFirstAttach all the cells that should have the class myclass will be available and accessible? If yes how can I attach the listener/handler that I want?
The questions seem a lot, but I believe they are all interconnected.
I'm using GWT 2.6 with GXT 3.1 on top of it.
Update
I forgot to mention that a feasible solution would be to add a listener for the mouse move on the whole grid, and then get each cell and check if it has the required class, but this seems such an overkill. There must be a simpler way.
A browser fires native events (click, focus, blur, etc.) regardless of whether you need them. These events "bubble up" the DOM tree giving you a chance to "listen" to them at the right level.
In your example you can create 30 listeners at the cell level, waiting for something to happen in "their" cell. This is a heavy (30 objects) and slow (it takes time to build and bind all of them) solution. Alternatively, you can create a single listener at the grid level, which listens to all events that bubble up from the cells and decides if something needs to be done or an event should be ignored. A single listener is lighter and can be created faster. On the flip side, it needs to examine events, although it's usually a fast and efficient operation (e.g. checking of an event source has a particular class name). Note also that this operation takes time when a browser typically does not have much to do anyway, so examining events only to ignore them does not impact user experience.
In my experience a single listener is almost always a better solution, although modern browsers and computers are so fast that the difference is rarely noticeable.
I am having trouble understanding the undo/redo functions using UndoManager, and integrating it with the MVC model.
I am not sure where to put the various methods(in model, view or control)
and I am still not sure how to use the undo manager.
My control class implements UndoableEditListener
It creates:
private UndoManager manager = new UndoManager();
and in:
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("Undo")) {
try {
manager.undo();
} catch (CannotUndoException ex) {
ex.printStackTrace();
}
}
}
I understand up to here, but the rest I am not sure what to do. I know I will have to add more in the model and view class, but not sure where.
DO I have to have the following classes?
public class UndoAction extends AbstractAction {}
public void undoableEditHappened(UndoableEditEvent e) {
I am simply placing an integer number in a textfield, and then I want to be able to undo this.I set the number in the textfield in the view class.I want to acheive this the simplest way possible, no fancy coding! This is a minor part of my assg but I just cant get it working!!
==========================================================
Here is a more detailed description of my code, maybe it will help:
I have a model, view and control package.
Contol has:
ButtonGUIControl.java, which implements both
ActionListener and
UndoableEditListener.
final UndoManager manager = new UndoManager();
In the actionPerformed method, it calls
if (e.getActionCommand().equals("Undo")){
try {
manager.undo();
}
and in:
public void undoableEditHappened(UndoableEditEvent evt) {
manager.addEdit(evt.getEdit());
}
In the View:
Grid.java , which extends JTextField will add the following, wherever it needs to display a number on the GUI:(model is simply an instance of my Model class)
getDocument().addUndoableEditListener(new ButtonGUIControl(model));
Could it be because the UndoManager is being created in a different package? I really have no idea how to debug this anymore!!
I could post my entire code if that helps. I guess Im not sure how to integrate this with my mvc model structure.
Take a step back for a second. The whole idea here is that a user will use your app and will make a series of changes to something. A text editor is a good example. You can insert characters and lines, delete them again, replace text with other text, scroll the text, etc. In order to support this with MVC you have a model that holds state and a View that displays it.
Your first instinct might be to have the view directly access the model, and then refresh the view every time the user makes a change, but it's very hard to undo those changes with that implementation. Instead, you encode every kind of change the user can make in classes that are able to perform that change and can later undo that change.
For example, an action that inserts text would be implemented by a class that knows the character offset of the insertion point and the string of characters that is to be inserted. The perform action would insert the string at the offset and the undo action would remove the right number of characters after that insertion point. You'd have a different class that would handle deletion, another to handle scrolling etc.
Every time the user takes some action, the view would construct one of these UndoableEdit classes and would tell the instance to run itself (redo()). Once executed, you put that UndoableEdit at the end of a list of UndoableEdit instances that represent all of the actions the user has taken so far. This list makes it very easy to support any sequence of undo requests, redo requests and actual edit actions (resulting in more UndoableEdit's being put on the list).
So back to your question. If your app needs to support undo and redo, then you'll need to implement an UndoManager which simply manages the list of UndoableEdit's and performs undo and redo as necessary. You also have to implement a whole bunch of UndoableEdits, one for each kind of thing your user will do against the UI. As for a listener, I can't see that you really need to do that one.
If you need only simple undo/redo, you can use UndoManager as it is, you don't need to subclass or customize it in any way.
JTextField (more specifically its model, the Document) has some built-in support for undo, which means you don't need to write UndoableEdit implementations either, the UndoableEdit objects will be automagically created for you (actually AbstractDocument.DefaultDocumentEvent implements UndoableEdit).
Full simple working example is here
I have a custom component based on the JSlider. It's essentially the same thing only it has 2 thumbs, which I named a DualSlider.
I need to change the maximum value of the slider once in a while, so every time I do, I call updateUI to reflect this.
public void updateUI() {
this.setUI(new DualSliderUI(this));
this.updateLabelUIs();
}
However, the maximum value of the DualSlider when I try to use it is still set at the original value no matter how many times I try to change it while using my program. I can confirm with a few println statements that a new DualSliderUI is being made with the slider that has the new max value, but for whatever reason the original DualSliderUI I initialized the slider with is the one that is in use.
What other things do I have to make sure I do when I update a property so I can avoid this?
1) I can't see reason for usage updateUI() this should be done once time, only when you built this JSlider, never do that repeately
2) you have look at BoundedRangeModel, maybe
I try to realize a link (in fact many links) that update a table in an website using an AjaxLink of Wicket. But I fail, the table is never updated (I have "setOutputMarkupId(true)" and call "setDefaultModelObject" and "addComponent", but there must be something other thats wrong).
How can I realize a panel with a number of links and a table that displays dynamic data, dependent on the link clicked? Can someone give an example (Maybe two links, when the first one is clicked the table displays two random numbers from 1-10, when the second is clicked the table displays random numbers from 1-100)? Without reloading the entire page, but only the html for the table?
One possible reason might be that you are not using a 'refreshable' model, but rather fetching the list items and passing them directly to the component, thus the list get's serialized in the session and doesn't get updated.
If this is the case, pass a LoadableDetachableModel (that retrieves the list in it's load method) to the component. I can't be more specific without seeing your code.
I don't think you've defined what you are doing very clearly.
Are these 2 tables different implementations? If so, then your code is correct - you have to replace the old component with the new one, then add the new one to the ajax response.
Realistically though, I'd imagine that you have 1 table component implementation.
What you therefore need to do, is something like this:
public class RandomNumberListModel extends LoadableDetachableModel {
private int upperBound;
public RandomNumberListModel(int upperBound) {...}
public void setUpperBound(int upperBound) {...}
protected Object load() {
// generate random number list using upper bound
// return list
}
}
...
final MyTableComponent table = new MyTableComponent(new RandomNumberListModel(30));
add(table);
AjaxLink link = new AjaxLink("myButton") {
public void onClick(final AjaxRequestTarget target) {
table.getModel().setUpperBound(100);
target.addComponent(table);
}
};
add(link);
(Edit) I've added a dynamic, reusable model to illustrate how the model would work. There are different ways of implementing this, depending on what you want to be reusable. The key point is that the model generates the list dynamically, i.e. per request, and the upperBound of the number range can be manipulated in the onClick callback.
Like jboyd was asking do you have code that knows to send the table contents back in the Ajax response?:
final Component tableComponent = ....;
AjaxLink link = new AjaxLink("myButton"){
public void onClick(final AjaxRequestTarget target) {
target.addComponent(tableComponent);
}
};
add(link);
The addComponent piece is the part jboyd is referring to.
There is one such example among the wicketstuff.org examples, the tree/tree table one. The three links at the top change the table.