README.md

VMF Tutorial 2

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Using the Change Notification API

What you will learn

In this tutorial you will learn how to

• use the change notification API to listen to property changes

Defining the Model

For this tutorial we reuse the model from Tutorial 1

package eu.mihosoft.vmf.tutorial02.vmfmodel;

interface Parent {
    String getName();
}

Listening to Changes

First, we create a new instance of Parent. Now we can register a change listener. Notice, how all VMF related API can be accessed via the vmf() method. Here's the code:

package eu.mihosoft.vmf.tutorial02;

public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        // create a new parent instance
        Parent parent = Parent.newInstance();

        // register change listener
        parent.vmf().changes().addListener(
                (evt)-> {
                    System.out.println("evt: " + evt.propertyName());

                    if(evt.propertyChange().isPresent()) {
                        System.out.println("  -> oldValue: " + evt.propertyChange().get().oldValue());
                        System.out.println("  -> newValue: " + evt.propertyChange().get().newValue());
                    } else if (evt.listChange().isPresent()) {
                        System.out.println("  -> " + evt.listChange().get().toStringWithDetails());
                    }
                }
        );

        // cause a change by setting the name of parent
        parent.setName("Parent 1");

        // cause another  change
        parent.setName("Parent 2");
        
    }
}

After registering the listener, we can make some changes to the name property (see parent.setName(...) calls). The output will look like this:

> Task :run
evt: name
  -> oldValue: null
  -> newValue: Parent 1
evt: name
  -> oldValue: Parent 1
  -> newValue: Parent 2

This is exactly what we expected. The first change indicates that property name was previously null and is now set to "Parent 1". The second change indicates that the name property was previously set to "Parent 1" and is now set to "Parent 2".

Conclusion

Congrats, you have learned how to use the change notification API.

If you are lazy you can get the full project here. To run the code checkout the corresponding section in the introduction tutorial.

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