Customer Validations and ControlDecoration

This chapter will demonstrate the usage of validators and decorators for the controls.

The result will look like the following.

Create a new Eclipse RCP project "de.vogella.databinding.validation" use "Hello RCP" as a template.

In your new project re-create the pojo example. Re-create the dependencies to the required plugins.

Create the following class "StringLongerThenTwo" which implements org.eclipse.core.databinding.validation.IValidator.

   
package de.vogella.databinding.validation.validators;

import org.eclipse.core.databinding.validation.IValidator;
import org.eclipse.core.databinding.validation.ValidationStatus;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.jface.fieldassist.ControlDecoration;

public class StringLongerThenTwo implements IValidator {

 private final String message;
 private final ControlDecoration controlDecoration;

 public StringLongerThenTwo(String message,
   ControlDecoration controlDecoration) {
  super();
  this.message = message;
  this.controlDecoration = controlDecoration;
 }

 @Override
 public IStatus validate(Object value) {
  if (value instanceof String) {
   String s = (String) value;
   // We check if the string is longer then 2 signs
   if (s.length() > 2) {
    controlDecoration.hide();
    return Status.OK_STATUS;
   } else {
    controlDecoration.show();
    return ValidationStatus.error(message);
   }
  } else {
   throw new RuntimeException(
     "Not supposed to be called for non-strings.");
  }
 }
}

  

To use the validator you have to use your own UpdateValueStrategy. We are also adding a label to the UI which displays the status in case something is wrong in this field. We are also registering a change listener to the field "lastName" and changing the background color of the field if the input is not correct. So you see both how to use a decorator and how to change a field based on the values.

The following shows the coding for the view with the ID "de.vogella.databinding.validation.personview".

   
package de.vogella.databinding.validation;

import org.eclipse.core.databinding.AggregateValidationStatus;
import org.eclipse.core.databinding.DataBindingContext;
import org.eclipse.core.databinding.UpdateValueStrategy;
import org.eclipse.core.databinding.beans.PojoObservables;
import org.eclipse.core.databinding.observable.ChangeEvent;
import org.eclipse.core.databinding.observable.IChangeListener;
import org.eclipse.core.databinding.observable.value.IObservableValue;
import org.eclipse.jface.databinding.swt.SWTObservables;
import org.eclipse.jface.fieldassist.ControlDecoration;
import org.eclipse.jface.fieldassist.FieldDecoration;
import org.eclipse.jface.fieldassist.FieldDecorationRegistry;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Layout;
import org.eclipse.swt.widgets.Text;
import org.eclipse.ui.part.ViewPart;

import de.vogella.databinding.validation.model.PersonPojo;
import de.vogella.databinding.validation.validators.StringLongerThenTwo;

public class PersonViewValidation extends ViewPart {
 private static final String MESSAGE = "Name must be longer two letters";
 public static final String ID = "de.vogella.databinding.validation.personview";
 private PersonPojo person;
 private Text firstName;

 private Label errorLabel;
 private IObservableValue uiElement;
 private ControlDecoration firstNameDecorator;
 private ControlDecoration lastNameDecorator;
 private Text lastName;

 public PersonViewValidation() {
 }

 @Override
 public void createPartControl(Composite parent) {
  person = new PersonPojo();
  person.setFirstName("Lars");
  person.setLastName("Vogel");
  person.setGender("m");
  person.setAge(12);
  // Lets put thing to order
  Layout layout = new GridLayout(2, false);
  parent.setLayout(layout);

  // Firstname
  Label nameLabel = new Label(parent, SWT.None);
  nameLabel.setText("Firstname: ");
  firstName = new Text(parent, SWT.BORDER);
  // Create the decorator which make the error message look really nice
  firstNameDecorator = createDecorator(firstName, MESSAGE);

  GridData gridData = new GridData();
  gridData.horizontalAlignment = SWT.FILL;
  gridData.grabExcessHorizontalSpace = true;
  firstName.setLayoutData(gridData);

  // Lastname
  nameLabel = new Label(parent, SWT.None);
  nameLabel.setText("Lastname: ");
  lastName = new Text(parent, SWT.BORDER);
  // Create the decorator which make the error message look really nice
  lastNameDecorator = createDecorator(lastName, MESSAGE);
  lastName.setLayoutData(gridData);

  Button button1 = new Button(parent, SWT.PUSH);
  button1.setText("Write model");
  button1.addSelectionListener(new SelectionAdapter() {

   @Override
   public void widgetSelected(SelectionEvent e) {
    System.out.println(person.getFirstName());
    System.out.println(person.getLastName());
   }
  });
  // Button should take 2 rows
  gridData = new GridData();
  gridData.horizontalSpan = 2;
  button1.setLayoutData(gridData);

  // This label will display all errors of all bindings
  Label descAllLabel = new Label(parent, SWT.NONE);
  descAllLabel.setText("All Validation Problems:");
  errorLabel = new Label(parent, SWT.NONE);
  gridData = new GridData();
  gridData.horizontalAlignment = SWT.FILL;
  gridData.grabExcessHorizontalSpace = true;
  gridData.horizontalAlignment = GridData.FILL;
  gridData.horizontalSpan = 1;
  errorLabel.setLayoutData(gridData);

  bindValues();

 }

 @Override
 public void setFocus() {
 }

 private ControlDecoration createDecorator(Text text, String message) {
  ControlDecoration controlDecoration = new ControlDecoration(text,
    SWT.LEFT | SWT.TOP);
  controlDecoration.setDescriptionText(message);
  FieldDecoration fieldDecoration = FieldDecorationRegistry.getDefault()
    .getFieldDecoration(FieldDecorationRegistry.DEC_ERROR);
  controlDecoration.setImage(fieldDecoration.getImage());
  return controlDecoration;
 }

 private void bindValues() {
  // The DataBindingContext object will manage the databindings
  DataBindingContext bindingContext = new DataBindingContext();
  // First we bind the text field to the model
  // Here we define the UpdateValueStrategy
  UpdateValueStrategy update = new UpdateValueStrategy();
  update.setAfterConvertValidator(new StringLongerThenTwo(MESSAGE,
    firstNameDecorator));
  // Bind fistName
  bindingContext.bindValue(SWTObservables.observeText(firstName,
    SWT.Modify), PojoObservables.observeValue(person, "firstName"),
    update, null);

  // Bind lastName
  bindingContext.bindValue(SWTObservables.observeText(lastName,
    SWT.Modify), PojoObservables.observeValue(person, "lastName"),
    new UpdateValueStrategy()
      .setAfterConvertValidator(new StringLongerThenTwo(
        MESSAGE, lastNameDecorator)), null);

  // We listen to all errors via this binding
  uiElement = SWTObservables.observeText(errorLabel);
  // This one listenes to all changes
  bindingContext.bindValue(uiElement, new AggregateValidationStatus(
    bindingContext.getBindings(),
    AggregateValidationStatus.MAX_SEVERITY), null, null);

  // Lets change the color of the field lastName
  uiElement.addChangeListener(new IChangeListener() {
   @Override
   public void handleChange(ChangeEvent event) {
    if (uiElement.getValue().equals("OK")) {
     lastName.setBackground(Display.getCurrent().getSystemColor(
       SWT.COLOR_WHITE));

    } else {
     lastName.setBackground(Display.getCurrent().getSystemColor(
       SWT.COLOR_RED));
    }
   }
  });
 }
}