Java observablelist добавить элемент

JavaFX Observable Lists

Observable lists are used by control classes that display list items, such as ComboBox and List.

Both of those classes also have a getItems method that returns an ObservableList.

Observable lists are also used by layout panes, such as HBox and VBox.

The getChildren method that’s common to all layout classes returns an ObservableList.

Here’s an example of the add method from earlier:

And here’s an example which uses the addAll method to add buttons to a layout pane:

pane.getChildren().addAll(btnOK, btnCancel);

The ObservableList interface has many other methods besides add and addAll.

The following table shows the methods you’re most likely to use.

boolean remove(Object elem)

The ObservableList class extends the java.util.List class, which is implemented by classes, such as ArrayList and Vector.

As a result, any method that can be used with an ArrayList can also be used with an ObservableList.

For example, you can clear the contents of a choice box in the same way you’d clear the contents of an array list:

To know how many items are in a choice box, call the size method:

int count = cbox.getItems().size();

To remove a specific item from the list, use the remove method:

This method returns a boolean that indicates whether the string was removed from the list; if remove returns false, it simply means that «Grumpy» was not in the list.

You can easily insert items from an existing Java collection, such as an array list, into a choice box by specifying the collection in the addAll method.

For example, suppose you already have an array list named list that contains the items you want to display in the choice box.

You can add the items like this:

Note

The method addListener provides this capability by allowing you to add a listener that’s called whenever the contents of the list changes.

But the controls that use observable lists do call this method create event listeners that automatically update the control whenever the contents of the list changes.

Note: You do not use the addListener method to respond when the user selects an item in a choice box or other type of list control.

Related

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Cannot add element to ObservableList (UnsupportedOperationException) in JavaFX [duplicate]

Initial Starting Point I have an existing List of 1000 Person objects which I would like to insert an Extractor to listen for property changes within any Person objects (this ObservableList will be later attached to a TableView ). So my code would be like:

ObservableList observablePersons = FXCollections.observableList(personlist, personextractor); 

Error Message But when I try to add a new person objects to this ObservableList observablePersons, I run into this error:

run: Exception in thread "main" java.lang.UnsupportedOperationException at java.util.AbstractList.add(AbstractList.java:148) at com.sun.javafx.collections.ObservableListWrapper.doAdd(ObservableListWrapper.java:101) at javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:151) at java.util.AbstractList.add(AbstractList.java:108) at test.listchangelistener.listChangeDemo.main(listChangeDemo.java:72) Java Result: 1 

Could you please tell me why would I come across this error message? My java version is jdk1.8.0_91 (32-Bit) Person Class

package test.listchangelistener; import javafx.beans.property.IntegerProperty; import javafx.beans.property.SimpleIntegerProperty; import javafx.beans.property.SimpleStringProperty; import javafx.beans.property.StringProperty; class Person < private final IntegerProperty age = new SimpleIntegerProperty(); private final StringProperty name = new SimpleStringProperty(); public Person(String name, Integer age) < setName(name); setAge(age); >public int getAge() < return age.get(); >public final void setAge(int value) < age.set(value); >public IntegerProperty ageProperty() < return age; >public String getName() < return name.get(); >public final void setName(String value) < name.set(value); >public StringProperty nameProperty() < return name; >@Override public String toString() < return "Personpersons = Arrays.asList(p1, p2); // extractor to observe change of person properties Callback extractor = (Person p) -> < return new Observable[]< p.ageProperty(), p.nameProperty() >; >; // make list observable and attach extractor ObservableList observablePersons = FXCollections.observableList(persons, extractor); // create listchangeListener for observableList ListChangeListener listener = (ListChangeListener) (ListChangeListener.Change c) -> < while (c.next()) < if (c.wasAdded()) < System.out.println("these were added: "); List addedSubList = c.getAddedSubList(); addedSubList.forEach((Object t) ->< System.out.println("added Person: " + t); >); > else if (c.wasRemoved()) < System.out.println("these were removed"); List removedSubList = c.getRemoved(); removedSubList.forEach((Object t) ->< System.out.println("removed Person: " + t); >); > else if (c.wasUpdated()) < System.out.println("these were updated"); System.out.println("Updated elements are: " + c.getList().subList(c.getFrom(), c.getTo())); >> >; // attach listchangeListener to observableList observablePersons.addListener(listener); // testing changes observablePersons.add(new Person("Siegfried", 10)); > > 

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JavaFX ObservableList Tutorial

JavaFX ObservableList is JavaFX SDK’s special implementation of List interface. It is basically an observable list that provides option to attach listeners for list content change. ObservableList has an integral role in the JavaFX development because it is used for major components like TableView, ComboBox, etc.

In this tutorial, we will explore the JavaFX ObservableList and see how we can utilize its special functionalities.

Creating and using ObservableList

You cannot instantiate an ObservableList class directly using a new call. Instead, FXCollections should be used to create an ObservableList. Let’s see how we can create an ObservableList of String type. The most common way to create it is using observableArrayList() function.

ObservableList listInstance = FXCollections.observableArrayList(); //Add a single entry listInstance.add("Java"); System.out.println(listInstance); //Add multiple entries listInstance.addAll("Cpp", "C#", "Python"); System.out.println(listInstance); //Remove entry listInstance.remove("Cpp"); System.out.println(listInstance);

As you have already noted, the basic operations are similar to normal lists, except the addAll() function availability. You can add multiple entries to the ObservableList using comma separated values. The output of the above code is as follows.

[Java] [Java, Cpp, C#, Python] [Java, C#, Python]

Now, let’s see some special advanced features of the ObservableList.

Listening for changes in the ObservableList

ObservableList allows us to add listeners into the list so that we can execute some logic when the contents of the list is changed. In the previous code snippet, we have added system.out.println after each change we made into the list to print the list. Instead, we can actually attach a listener to the ObservableList and it will help us to print the list as soon as it is changed. To achieve this, we will make use of javafx.collections.ListChangeListener. The onChanged() function will be called as soon as any change is made to the contents of the list.

ObservableList listInstance = FXCollections.observableArrayList(); //Add a ListChangeListener that will execute as soon as the contents of the list is changed. listInstance.addListener(new ListChangeListener() < @Override public void onChanged(Changec) < System.out.println(listInstance); >>); //Manipulate contents of the list listInstance.add("Java"); listInstance.addAll("Cpp", "C#", "Python"); listInstance.remove("Cpp");

The output of the code snippet is given below. The “System.out.println(listInstance);” was executed three times, once after each list change.

[Java] [Java, Cpp, C#, Python] [Java, C#, Python]

ObservableList also provides a second type of listener called InvalidationListener. Unlike ListChangeListener that provides the actual change as a parameter to the onChanged function, it doesn’t provide the change. You can read more about it in the dedicated observable tutorial.

Getting values from the ObserableList is similar to getting value from normal lists in Java. To get an item at specific index, you can call “observableList.get(index)”. You can also get iterator through observableList.iterator() function.

Video Tutorial for JavaFX ObservableList

If you are interested in learning more about the ObservableList, please have a look into this ObservableList video tutorial. The video shows how to make use of the ObservableList for JavaFX ListView with realworld example.

ObservableList size change listener

Thanks to JavaFX Binding class, we can add listeners to some observable properties of the list, like the size of the list. This way, similar to how we tracked the list-content-change using a listener, we can also easily track the list size. Let’s adjust the above list content listener code to list size listener code and learn how to create a binding value to an ObservableList’s size and add a listener to it.

ObservableList listInstance = FXCollections.observableArrayList(); //Listen for changes in list size IntegerBinding listSizeProperty = Bindings.size(listInstance); listSizeProperty.addListener(new ChangeListener() < @Override public void changed(ObservableValueobservable, Number oldValue, Number newValue) < System.out.println("Updated list size: " + newValue); >>); listInstance.add("something"); listInstance.addAll("something1", "random_data", "something2"); listInstance.remove("somethin3");

Output of the above code snippet is given below. As you can see, the size of the list is tracked and printed for each 3 changes we have made.

Updated list size: 1 Updated list size: 4 Updated list size: 3

Conclusion

In this tutorial, we have learned how to create and use ObservableList in JavaFX. It provides all the functionalities of normal Java lists along with cool observable support. You might also be interested in the other articles on JavaFX like JavaFX Scene Switch Animation and JavaFX Animation Tutorial.

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Java observablelist добавить элемент

Interface ObservableList

• Type Parameters: E — the list element type All Superinterfaces: Collection, Iterable, List, Observable All Known Subinterfaces: ObservableListValue, WritableListValueAll Known Implementing Classes: FilteredList , ListBinding , ListExpression , ListProperty , ListPropertyBase , ModifiableObservableListBase , ObservableListBase , ReadOnlyListProperty , ReadOnlyListPropertyBase , ReadOnlyListWrapper , SimpleListProperty , SortedList , TransformationList

Method Summary

Methods inherited from interface java.util.Collection

Methods inherited from interface java.lang.Iterable

Methods inherited from interface java.util.List

Methods inherited from interface javafx.beans.Observable

Method Detail

addListener

removeListener

Tries to remove a listener from this observable list. If the listener is not attached to this list, nothing happens.

addAll

setAll

setAll

removeAll

retainAll

remove

void remove​(int from, int to)

A simplified way of calling sublist(from, to).clear() . As this is a common operation, ObservableList has this method for convenient usage.

filtered

default FilteredListE> filtered​(PredicateE> predicate)

sorted

default SortedListE> sorted​(ComparatorE> comparator)

sorted

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