Java：setCellValuefactory; Lambda与PropertyValueFactory;优点缺点

问题描述

今天我在尝试更多地了解JavaFX和Java时遇到了另一件我并不理解的事情。

today i encountered another thing i don't really understand while trying to learn more about JavaFX and Java in general.

参考是以下教程（我试图将原则应用于组织者）：

Reference is the following tutorial (im trying to apply the principle to an organizer):

我将简要介绍一下我有问题的特定部分：

I will give a short outline of the particular part on which i've got a question:

我的主窗口包含一个显示一些约会数据的tableview。
所以我得到了一些这种风格的线条（与教程相同）：

My main window contains a tableview which shows some appointment-data.So i got some lines of this style(same as in the tutorial):

aColumn.setCellValueFactory(cellData ->cellData.getValue().getAColumnsProperty());

可以通过额外的EditDialog操作数据。
这很好用。如果我编辑的东西立即显示更改，但我做了一些额外的研究，以更好地了解Lambda（不太成功）。现在......在在线java文档中它说：
Callback-Interface的便捷实现，[...]

The data can be manipulated via an additional EditDialog.That works just fine. If i edit things the changes are displayed immediately but i did some additional research to better understand the Lambda (not too successful). Now...in the online java documentation Java Doc PropertyValueFactory it says:"A convenience implementation of the Callback-Interface,[...]"

所以我将我的代码重构为这种风格：

So i refactored my code into this style:

aColumn.setCellValueFactory(new PropertyValueFactory<Appointment,LocalDate>("date"));

我发现它比Lambda更具可读性。
但我注意到，当我进行更改时，我需要在显示更改之前对TableView进行一些排序。

Which i find much more readable than the Lambda.But i noticed that when i make changes i need to do some sorting on the TableView before the changes are displayed.

是否可以立即显示第二种方法的变化？

Is it possible to achieve an immediate display of change in the second approach?

如果是：是否存在阻碍这种修改的主要障碍？即Lambda是这种情况下的最佳做法吗？

If yes: are there major disavantages which would discourage such a modification? I.e. would the Lambda be the best practice in this situation?

我感谢任何帮助。

推荐答案

PropertyValueFactory 需要正确命名的属性getter。 getAColumnsProperty 可能不是一个。

PropertyValueFactory expects correctly named property getters. getAColumnsProperty is probably not one.

如果新的PropertyValueFactory< Appointment，LocalDate> （date） 约会类需要包含 dateProperty（）方法;返回值需要扩展 ReadOnlyProperty 才能使其工作，任何编辑只会导致模型自动更新，如果返回的对象也 WritableValue 。

In case of new PropertyValueFactory<Appointment, LocalDate>("date") the Appointment class needs to contain a dateProperty() method; the returned values need to extend ReadOnlyProperty for this to work and any edits will only lead to an update in the model automatically, if the returned object also WritableValue.

示例约会应该与一起使用的类PropertyValueFactory< ;>（date）：

public class Appointment {
    private final ObjectProperty<LocalDate> date = new SimpleObjectProperty<>();

    public final LocalDate getDate() {
        return this.date.get();
    }

    public final void setDate(LocalDate value) {
        this.date.set(value);
    }

    public final ObjectProperty<LocalDate> dateProperty() {
        return this.date;
    }
}

如果不存在此类方法， PropertyValueFactory 将使用getter来检索值，即 getDate（），但是此模型中的更新将不会在UI中显示直到它更新 Cell ，因为 PropertyValueFactory 不知道添加监听器的位置。

If no such method exists, PropertyValueFactory will use a getter to retrieve the value, i.e. getDate(), but this case updates in the model will not be visible in the UI until it updates the Cell, since the PropertyValueFactory "does not know" where to add a listener.

• 可以只能在公共类中找到 public 方法


• PropertyValueFactory 使用反射


• 非类型安全。在 new PropertyValueFactory< Appointment，LocalDate>（date）中，如果有合适的方法，编译器不检查该方法是否返回合适的类或者例如属性getter返回 String 而不是 ReadOnlyProperty< LocalDate> ，这可能导致 ClassCastException s。


• 无编译时检查。在lambda表达式中，编译器可以检查方法是否存在并返回适当的类型; PropertyValueFactory 这是不行的。

• Can only find public methods in a public class
• PropertyValueFactory uses reflection
• Not typesafe. In new PropertyValueFactory<Appointment, LocalDate>("date") the compiler does not check, if there is a appropriate method, if that method even returns a suitable class or if e.g. the property getter returns a String instead of a ReadOnlyProperty<LocalDate> which can lead to ClassCastExceptions.
• No compile time checking. In the lambda expression the compiler can do some checking if the method exists and returns a appropriate type; with PropertyValueFactory this is not done.

如果你确定要实现正确的项类中的适当方法，使用 PropertyValueFactory 没有任何问题，但如上所述它有它的缺点。此外，实现 Callback 更加灵活。你可以，例如做一些额外的修改：

If you are sure to implement the appropriate methods in the item class correctly, there is nothing wrong with using PropertyValueFactory, but as mentioned above it has it's disadvantages. Moreover implementing the Callback is much more flexible. You could e.g. do some additional modifications:

TableColumn<Appointment, String> column = ...

column.setCellValueFactory(new Callback<TableColumn.CellDataFeatures<Appointment, String>, ObservableValue<String>> {
    @Override
    public ObservableValue<String> call(TableColumn.CellDataFeatures<Appointment, String> cd) {
        Appointment a  = cd.getValue();

        return Bindings.createStringBinding(() -> "the year: " + a.getDate().getYear(), a.dateProperty());
    }

});

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