Question

I have an addProductButton, click it and it brings up a DialogBox containing bookNameTextBox, bookCategoryTextBox and addBookButton. Click addBookButton, it inserts the bookNameTextBox and bookCategoryTextBox contents into a database. If successful, it should hide the DialogBox and updateList()

The following code works to accomplish that but I’m not sure if it’s proper or if there is a better way to achieve the same results.

Main class

addProductButton.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
    //display addBookDialogBox
    AddBookDialog abd = new AddBookDialog();
    abd.displayDialog(new Callback() {
        @Override
        public void onSuccess() {
            updateList();
        }
        public void onFailure() {               
        }
    });
}
});

public void updateList() {
}

AddBookDialog class

public class AddBookDialog extends DialogBox {

private Callback callback;

private static AddBookDialogUiBinder uiBinder = GWT
.create(AddBookDialogUiBinder.class);

interface AddBookDialogUiBinder extends UiBinder<Widget, AddBookDialog> {
}

public AddBookDialog() {
    setWidget(uiBinder.createAndBindUi(this));
}

public void displayDialog(Callback callback2) {
    callback = callback2;
    this.center();
}

@UiHandler("addBookButton")
void onAddBookButtonClick(ClickEvent event) {
    //save book to database
    Database db = Database.openDatabase("Store", "1.0", "My Store", 5 * 1024 * 1024);
    db.transaction(new TransactionCallback() { 
        public void onTransactionStart(SQLTransaction tx) {
            tx.executeSql("INSERT INTO products (bookName, bookCategory) VALUES (?, ?)", new Object[] { bookNameTextBox.getText().toString(), bookCategoryTextBox.getText().toString() }); 
        }
         public void onTransactionFailure(SQLError error) {
         }
         public void onTransactionSuccess() {
             callback.onSuccess();
         } 
    });
    this.hide();


  }
}

Callback interface

public interface Callback {
  void onSuccess();

  void onFailure();
}

Answer 1

I don’t see the use of it here, why don’t you just put updateList(); inside the onTransactionStart() method ?

CallBacks are used for Asynchronism, and the TransactionCallback here already does that, so I don’t see why you would use another callback inside.

And by the way, if you did need a callback, why don’t you use the AsyncCallback provided by gwt?

EDIT :
Then the appropriate way is to make an interface with your updateList() method. Make your main class implement it, and change the parameter type of your displayDialog() method to your interface type instead of CallBack type.