java - 我如何将两个子字符串绑定(bind)到一个？

Question

我有两个字符串

private StringProperties firstName;
private StringProperties lastName;
private StringProperties nickName;

名字和姓氏由用户选择，昵称是名字和姓氏的前3个字符的串联

我该怎么做？

实际上我是这样初始化它的(这是整个类)。

public class Person {
private StringProperty firstName;
private StringProperty lastName;
private StringProperty nickName;
private ObservableList<Evento> eventi = FXCollections.observableArrayList();

public Person(String firstName, String lastName) {
    this.firstName = new SimpleStringProperty(firstName);
    this.lastName = new SimpleStringProperty(lastName);
    if (firstName.length() > 2 && lastName.length() > 2)
        this.nickName = new SimpleStringProperty(firstName.trim().substring(0,3).concat(lastName.trim().substring(0,3)));
    else
        this.nickName = new SimpleStringProperty("");
}

public ObservableList<Evento> getEventi() {
    return eventi;
}

public String getFirstName() {
    if(firstName == null) firstName = new SimpleStringProperty(this,"firstName");
    return firstName.get();
}

public StringProperty firstNameProperty() {
    return firstName;
}

public void setFirstName(String firstName) {
    this.firstName.set(firstName);
}

public String getLastName() {
    if(lastName == null) lastName = new SimpleStringProperty(this, "lastName");
    return lastName.get();
}

public StringProperty lastNameProperty() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName.set(lastName);
}

public String getNickName() {
    if(nickName == null) nickName = new SimpleStringProperty(this,"nickName");
    return nickName.get();
}

public StringProperty nickNameProperty() {
    return nickName;
}

@Override
public String toString() {
    return getNickName() + "(" + getLastName() + " " + getFirstName() + ")";
}

但是当我让用户更改名字或姓氏时，昵称不会更新。

Answer 1

您应该使用 ReadOnlyStringProperty 作为昵称:

private ReadOnlyStringWrapper nickName= new ReadOnlyStringWrapper();
...
public final String getNickName() {
    return nickName.get();
}

public final ReadOnlyStringProperty nickNameProperty() {
    return nickName.getReadOnlyProperty();
}

至于绑定(bind)，您可以使用 Bindings 类中的实用方法或为任何其他复杂情况实现您自己的绑定(bind)。此示例使用 createStringBinding() 方法。它采用 Callable 功能接口(interface)，将用于计算新值，以及可观察属性列表，将观察哪些值的变化:

public Person(String firstName, String lastName) {
    this.firstName = new SimpleStringProperty(firstName);
    this.lastName = new SimpleStringProperty(lastName);

    this.nickName.bind(Bindings.createStringBinding(()->{
        if(this.firstName.get().length() > 2 && this.lastName.get().length() > 2) {
            return this.firstName.get().substring(0,3).concat(this.lastName.get().trim().substring(0,3));
        } else {
            return "";
        }
    }, this.firstName, this.lastName));

}