In JavaFX, I have an ObservableList of objects, and want another ObservableList that will mirror the first list but contain a String representation of each object. Is there anything simpler than writing a custom ListChangeListener to do the conversion ? I have a StringConverter which can provide the mirrored value.
Similarly, given an ObservableList<String>, how do I create a second ObservableList<String> that has a constant entry at index 0, and mirrors the first list beginning at index 1?
For the first question, the easiest way to do this is to use the EasyBind framework. Then it is as simple as
ObservableList<String> stringList = EasyBind.map(myBaseList, myConverter::toString);
Here is an SSCCE using EasyBind:
import org.fxmisc.easybind.EasyBind;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ListChangeListener.Change;
import javafx.collections.ObservableList;
import javafx.util.StringConverter;
public class MappedAndTransformedListExample {
public static void main(String[] ags) {
ObservableList<Person> baseList = FXCollections.observableArrayList(
new Person("Jacob", "Smith", "jacob.smith@example.com"),
new Person("Isabella", "Johnson", "isabella.johnson@example.com"),
new Person("Ethan", "Williams", "ethan.williams@example.com"),
new Person("Emma", "Jones", "emma.jones@example.com")
);
StringConverter<Person> converter = new StringConverter<Person>() {
@Override
public String toString(Person person) {
return person.getFirstName() + " " + person.getLastName();
}
@Override
public Person fromString(String string) {
int indexOfDelimiter = string.indexOf(' ');
return new Person(string.substring(0, indexOfDelimiter),
string.substring(indexOfDelimiter+1),
"");
}
};
ObservableList<String> namesList = EasyBind.map(baseList, converter::toString);
namesList.forEach(System.out::println);
namesList.addListener((Change<? extends String> c) -> {
while (c.next()) {
if (c.wasAdded()) {
System.out.println("Added "+c.getAddedSubList());
}
}
});
System.out.println("\nAdding Michael to base list...\n");
baseList.add(new Person("Michael", "Brown", "michael.brown@example.com"));
namesList.forEach(System.out::println);
}
public static class Person {
private final StringProperty firstName = new SimpleStringProperty(this, "firstName");
private final StringProperty lastName = new SimpleStringProperty(this, "lastName");
private final StringProperty email = new SimpleStringProperty(this, "email");
public Person(String firstName, String lastName, String email) {
this.firstName.set(firstName);
this.lastName.set(lastName);
this.email.set(email);
}
public final StringProperty firstNameProperty() {
return this.firstName;
}
public final String getFirstName() {
return this.firstNameProperty().get();
}
public final void setFirstName(final String firstName) {
this.firstNameProperty().set(firstName);
}
public final StringProperty lastNameProperty() {
return this.lastName;
}
public final java.lang.String getLastName() {
return this.lastNameProperty().get();
}
public final void setLastName(final java.lang.String lastName) {
this.lastNameProperty().set(lastName);
}
public final StringProperty emailProperty() {
return this.email;
}
public final java.lang.String getEmail() {
return this.emailProperty().get();
}
public final void setEmail(final java.lang.String email) {
this.emailProperty().set(email);
}
}
}
If you prefer not to use a third-party framework for some reason, you can use a TransformationList (which is what EasyBind does under the hood: I copied the code below from the source code there and modified it).
In the above, you would replace
ObservableList<String> namesList = EasyBind.map(baseList, converter::toString);
with
ObservableList<String> namesList = new TransformationList<String, Person>(baseList) {
@Override
public int getSourceIndex(int index) {
return index ;
}
@Override
public String get(int index) {
return converter.toString(getSource().get(index));
}
@Override
public int size() {
return getSource().size();
}
@Override
protected void sourceChanged(Change<? extends Person> c) {
fireChange(new Change<String>(this) {
@Override
public boolean wasAdded() {
return c.wasAdded();
}
@Override
public boolean wasRemoved() {
return c.wasRemoved();
}
@Override
public boolean wasReplaced() {
return c.wasReplaced();
}
@Override
public boolean wasUpdated() {
return c.wasUpdated();
}
@Override
public boolean wasPermutated() {
return c.wasPermutated();
}
@Override
public int getPermutation(int i) {
return c.getPermutation(i);
}
@Override
protected int[] getPermutation() {
// This method is only called by the superclass methods
// wasPermutated() and getPermutation(int), which are
// both overriden by this class. There is no other way
// this method can be called.
throw new AssertionError("Unreachable code");
}
@Override
public List<String> getRemoved() {
ArrayList<String> res = new ArrayList<>(c.getRemovedSize());
for(Person removedPerson: c.getRemoved()) {
res.add(converter.toString(removedPerson));
}
return res;
}
@Override
public int getFrom() {
return c.getFrom();
}
@Override
public int getTo() {
return c.getTo();
}
@Override
public boolean next() {
return c.next();
}
@Override
public void reset() {
c.reset();
}
});
}
};
For the second question, you must use a transformation list. Here's an updated main(...) method that shows how to do this. (It works just as well with the second version of part 1.)
public static void main(String[] ags) {
ObservableList<Person> baseList = FXCollections.observableArrayList(
new Person("Jacob", "Smith", "jacob.smith@example.com"),
new Person("Isabella", "Johnson", "isabella.johnson@example.com"),
new Person("Ethan", "Williams", "ethan.williams@example.com"),
new Person("Emma", "Jones", "emma.jones@example.com")
);
StringConverter<Person> converter = new StringConverter<Person>() {
@Override
public String toString(Person person) {
return person.getFirstName() + " " + person.getLastName();
}
@Override
public Person fromString(String string) {
int indexOfDelimiter = string.indexOf(' ');
return new Person(string.substring(0, indexOfDelimiter),
string.substring(indexOfDelimiter+1),
"");
}
};
ObservableList<String> namesList = EasyBind.map(baseList, converter::toString);
ObservableList<String> namesListWithHeader = new TransformationList<String, String>(namesList) {
@Override
public int getSourceIndex(int index) {
return index - 1 ;
}
@Override
public String get(int index) {
if (index == 0) {
return "Contacts";
} else {
return getSource().get(index - 1);
}
}
@Override
public int size() {
return getSource().size() + 1 ;
}
@Override
protected void sourceChanged(Change<? extends String> c) {
fireChange(new Change<String>(this) {
@Override
public boolean wasAdded() {
return c.wasAdded();
}
@Override
public boolean wasRemoved() {
return c.wasRemoved();
}
@Override
public boolean wasReplaced() {
return c.wasReplaced();
}
@Override
public boolean wasUpdated() {
return c.wasUpdated();
}
@Override
public boolean wasPermutated() {
return c.wasPermutated();
}
@Override
public int getPermutation(int i) {
return c.getPermutation(i - 1) + 1;
}
@Override
protected int[] getPermutation() {
// This method is only called by the superclass methods
// wasPermutated() and getPermutation(int), which are
// both overriden by this class. There is no other way
// this method can be called.
throw new AssertionError("Unreachable code");
}
@Override
public List<String> getRemoved() {
ArrayList<String> res = new ArrayList<>(c.getRemovedSize());
for(String removed: c.getRemoved()) {
res.add(removed);
}
return res;
}
@Override
public int getFrom() {
return c.getFrom() + 1;
}
@Override
public int getTo() {
return c.getTo() + 1;
}
@Override
public boolean next() {
return c.next();
}
@Override
public void reset() {
c.reset();
}
});
}
};
namesListWithHeader.forEach(System.out::println);
namesListWithHeader.addListener((Change<? extends String> c) -> {
while (c.next()) {
if (c.wasAdded()) {
System.out.println("Added "+c.getAddedSubList());
System.out.println("From: "+c.getFrom()+", To: "+c.getTo());
}
}
});
System.out.println("\nAdding Michael to base list...\n");
baseList.add(new Person("Michael", "Brown", "michael.brown@example.com"));
namesListWithHeader.forEach(System.out::println);
}