Value Transformers

ValueTransformer<M, V> defines how to convert and validate values from view to model and viceversa (because Arena has a two-way binding).

• M viewToModel(V valueFromView): converts a value from the UI component to the model format
• V modelToView(M valueFromModel): converts a value from the model to the UI format
• Class<M> getModelType(): returns type of model
• Class<V> getViewType(): returns type of view

Date Transformer

• Implements ValueTransformer<Date, String>
• Converts a string in a dd/MM/yyy format to Date and viceversa
• Allows null values

// Xtend
new TextBox(mainPanel) => [
      width = 80
      value <=> "dateOfBirth".transformer = new DateTransformer
]

// Java
new TextBox(mainPanel)
      .setWidth(80)
      .bindValueToProperty("dateOfBirth").setTransformer(new DateTransformer());

NotEmptyTransformer

• implements ValueTransformer<String, Boolean>
• maps a String object with a boolean value true (string is empty or null) / false (string is not empty or null)

NotNullTransformer

• implements ValueTransformer<Object, Boolean>
• maps any object with a boolean value true (object is not null) / false (object is null)

What do you need to define a new Value Transformer

• Find concrete classes for M and V
• Implement a Value Transformer for this concrete classes M and V
• Define getModelType() and getViewType() methods. They should return concrete classes.
• In viewToModel() method you define how to convert a view value to its model
• In modelToView() method you define how to convert a value model to its view

class BigDecimalTransformer implements ValueTransformer<BigDecimal, String> {
      override getModelType() {
            BigDecimal
      }
 
      override getViewType() {
            String
      }
 
      override modelToView(BigDecimal valueFromModel) {
            valueFromModel.toString
      }
 
      override viewToModel(String valueFromView) {
            if (valueFromView == null || valueFromView.equals(""))
                  null
            else
                  try
                        new BigDecimal(valueFromView)
                  catch (NumberFormatException e)
                        throw new UserException("Value must be a number", e)
 
      }
}

Links

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