questions about DI, ViewModel etc

Question

I have the following code:

class ExampleView :View("My Example view") {
  val model:ExampleModel by inject()

  override val root= vbox {
    textfield(model.data)
    button("Commit") {
      setOnAction {
        model.commit()
        closeModal()
      }
    }
    button("Rollback") {
      setOnAction {
        model.rollback()
        closeModal()
      }
    }
    button("Just quit") {
      setOnAction {
        closeModal()
      }
    }
  }

}

class Example() {
  var data by property<String>()
  fun dataProperty() = getProperty(Example::data)
}

class ExampleModel(example: Example) : ItemViewModel<Example>() {
  init {
    item = example
  }
  val data = bind { item?.dataProperty() }
}

class MainView : View() {
  val example:Example
  override val root = BorderPane() 

  init {
    example = Example()
    example.data = "Data for example"
    val exampleModel = ExampleModel(example)
    with(root){
      top {
        menubar {
          menu("Test") {
            menuitem("Example - 1") {
              val scope = Scope()
              setInScope(exampleModel, scope)
              find<ExampleView>(scope).openWindow()
            }
            menuitem("Example - 2") {
              val scope = Scope()
              setInScope(exampleModel, scope)
              find<ExampleView>(scope).openWindow()
            }
          }
        }
      }
    }
  }
}

I have two questions for this example:

1) If i change the value and close the window without a commit (User can do this with help [X] button) then only ViewModel will store changes (and it will be displayed in GUI even after the re-opening ), but model POJO object will keep the old data.

if I used instance of Example class (without DI) then this instance received all the changes at once.

For example i don't want commit/rollback functionality but i want DI and immediate updating. What i should do? (ofcource i can call "commit" for "textfield change value event")

2) ViewModel has constructor with parameter and if i try open ExampleView like this

find<ExampleView>(Scope()).openWindow()

then I got an an obvious RuntimeException. Can I avoid this for example, by a compiler warnings (or by something else)?

Answer 1

1) This is the correct default behavior of the ViewModel. If you bind a property of the view model to an input, the changes are immediately reflected in that bound property, but will only be flushed into the underlying model object once you commit it.

If you want to autocommit changes in the view model properties back into the underlying model object, you can create the binding with the autocommit property set to true:

val data = bind(true) { item?.dataProperty() }

You can also write bind(autocommit = true) if that looks clearer to you. This will cause any changes to be automatically flushed back into the underlying object.

I also want to make you aware that by requiring an item in the constructor of your view model, you're effectively preventing it from being used with injection unless you prime it like you do using setInScope. This might be fine for your use case, but worth noting.

2) The upcoming TornadoFX 1.5.10 will give you a better runtime error message if you forget to pass a parameter. It also introduces default values for parameters. See https://github.com/edvin/tornadofx/pull/227 for more info.