Question

我在我的网络应用中Binding Data to Forms, Checking a return value使用了代码的binder.addStatusChangeListener( ... )部分。从中得出的MCVE是：

Person Bean

public class Person implements Serializable {

    private String name;

    public Person() {}

    public Person( final String name ) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName( final String name ) {
        this.name = name;
    }
}

人物视图

public class PersonView extends VerticalLayout {

    private final Person person = new Person( "Gerold Broser" );
    private final TextField name = new TextField( "Name:" );
    private final BeanValidationBinder<Person> binder =
            new BeanValidationBinder<>( Person.class );
    private final Button button = new Button( "Button" );

    public PersonView() {
        super();

        binder.bindInstanceFields( this );
        binder.setBean( person );

        addComponent( name );
        addComponent( button );

        binder.addStatusChangeListener( event -> {
            final boolean hasChanges, isValid;
            out.println( "hasChanges=" + (hasChanges = event.getBinder().hasChanges()) );
            out.println( "isValid=" + (isValid = event.getBinder().isValid()) );
            button.setEnabled( hasChanges && isValid );
        } );
    }
}

只要我在浏览器中更改了TextField的内容，我就会得到以下输出：

hasChanges=false
isValid=true

这是一个错误还是我错过了什么？

Answer 1

来自javadoc：

public boolean hasChanges()

检查是否有任何绑定字段＆＃39;自上次显式调用readBean(Object)，removeBean()，writeBean(Object)或之后，我们发生了未提交的更改    writeBeanIfValid(Object)。不成功的写入操作不会影响此值。

请注意，如果您使用setBean(Object)方法，Binder会在所有验证程序通过后立即尝试提交更改。因此，在使用时   这种方法很少有意义，几乎总是回归   假

每种情况的返回值都编译成如下   表：

╔════════════╦════════════╦═════════╦═════════╦══════════════════╦════════════════════╗ ║ ║ After ║ After ║ After ║ After successful ║ After unsuccessful ║ ║ ║ readBean, ║ valid ║ invalid ║ writeBean or ║ writeBean or ║ ║ ║ setBean or ║ user ║ user ║ writeBeanIfValid ║ writeBeanIfValid ║ ║ ║ removeBean ║ changes ║ changes ║ ║ ║ ╠════════════╬════════════╬═════════╬═════════╬══════════════════╬════════════════════╣ ║ A bean is ║ ║ ║ ║ ║ ║ ║ currently ║ false ║ false ║ true ║ false ║ no change ║ ║ bound ║ ║ ║ ║ ║ ║ ╟────────────╫────────────╫─────────╫─────────╫──────────────────╫────────────────────╢ ║ No bean is ║ ║ ║ ║ ║ ║ ║ currently ║ false ║ true ║ true ║ false ║ no change ║ ║ bound ║ ║ ║ ║ ║ ║ ╚════════════╩════════════╩═════════╩═════════╩══════════════════╩════════════════════╝

Returns: 自上次调用setBean，readBean，writeBean或writeBeanIfValid以来是否有任何绑定字段的值发生了变化

总之，使用setBean(myBean)将触发自动提交。因此，如果您想manually commit changes，请使用binder.readBean(myBean)＆amp; binder.writeBean(myBean)。

Vaadin的Binder＃hasChanges（）错误地返回＆＃39; false＆＃39;

Person Bean

人物视图

1 个答案: