org.eclipse.jface.examples.databinding.snippets.Snippet008ComputedValue.java Source code

Introduction

Here is the source code for org.eclipse.jface.examples.databinding.snippets.Snippet008ComputedValue.java

Source

/*******************************************************************************
 * Copyright (c) 2006, 2018 Brad Reynolds and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     Brad Reynolds - initial API and implementation
 *     Matthew Hall - bug 260329
 *     Patrik Suzzi - 479848
 ******************************************************************************/

package org.eclipse.jface.examples.databinding.snippets;

import org.eclipse.core.databinding.DataBindingContext;
import org.eclipse.core.databinding.UpdateValueStrategy;
import org.eclipse.core.databinding.observable.ObservableTracker;
import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.core.databinding.observable.value.ComputedValue;
import org.eclipse.core.databinding.observable.value.IObservableValue;
import org.eclipse.core.databinding.observable.value.WritableValue;
import org.eclipse.jface.databinding.swt.DisplayRealm;
import org.eclipse.jface.databinding.swt.typed.WidgetProperties;
import org.eclipse.jface.layout.GridDataFactory;
import org.eclipse.jface.layout.GridLayoutFactory;
import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;

/**
 * Snippet that demostrates a simple use case using ComputedValue to format a
 * name as the user enters first and last name.
 *
 * @since 3.2
 */
public class Snippet008ComputedValue {
    /**
     * @param args
     */
    public static void main(String[] args) {
        final Display display = new Display();
        Realm.runWithDefault(DisplayRealm.getRealm(display), () -> {
            Shell shell = new Shell(display);
            shell.setLayout(new FillLayout());

            final UI ui = new UI(shell);
            final Data data = new Data();

            // Bind the UI to the Data.
            DataBindingContext dbc = new DataBindingContext();
            dbc.bindValue((IObservableValue<String>) WidgetProperties.text(SWT.Modify).observe(ui.firstName),
                    data.firstName);
            dbc.bindValue((IObservableValue<String>) WidgetProperties.text(SWT.Modify).observe(ui.lastName),
                    data.lastName);

            // Construct the formatted name observable.
            FormattedName formattedName = new FormattedName(data.firstName, data.lastName);

            // Bind the formatted name Text to the formatted name
            // observable.
            dbc.bindValue((IObservableValue<String>) WidgetProperties.text(SWT.None).observe(ui.formattedName),
                    formattedName, new UpdateValueStrategy<String, String>(false, UpdateValueStrategy.POLICY_NEVER),
                    null);

            shell.pack();
            shell.open();
            while (!shell.isDisposed()) {
                if (!display.readAndDispatch())
                    display.sleep();
            }
        });
        display.dispose();
    }

    /**
     * Creates the formatted name on change of the first or last name
     * observables.
     * <p>
     * The key to understanding ComputedValue is understanding that it knows of
     * the observables that are queried without being told. This is done with
     * {@link ObservableTracker} voodoo. When calculate() is invoked
     * <code>ObservableTracker</code> records the observables that are
     * queried. It then exposes those observables and <code>ComputedValue</code>
     * can listen to changes in those objects and react accordingly.
     * </p>
     *
     * @since 3.2
     */
    static class FormattedName extends ComputedValue<String> {
        private IObservableValue<String> firstName;

        private IObservableValue<String> lastName;

        FormattedName(IObservableValue<String> firstName, IObservableValue<String> lastName) {
            this.firstName = firstName;
            this.lastName = lastName;
        }

        @Override
        protected String calculate() {
            String lastName = this.lastName.getValue();
            String firstName = this.firstName.getValue();
            lastName = (lastName != null && lastName.length() > 0) ? lastName : "[Last Name]";
            firstName = (firstName != null && firstName.length() > 0) ? firstName : "[First Name]";

            StringBuilder buffer = new StringBuilder();
            buffer.append(lastName).append(", ").append(firstName);

            return buffer.toString();
        }
    }

    static class Data {
        final WritableValue<String> firstName;

        final WritableValue<String> lastName;

        Data() {
            firstName = new WritableValue<>("", String.class);
            lastName = new WritableValue<>("", String.class);
        }
    }

    /**
     * Composite that creates the UI.
     *
     * @since 3.2
     */
    static class UI extends Composite {
        final Text firstName;

        final Text lastName;

        final Text formattedName;

        UI(Composite parent) {
            super(parent, SWT.NONE);

            GridLayoutFactory.swtDefaults().numColumns(2).applyTo(this);

            new Label(this, SWT.NONE).setText("First Name:");
            new Label(this, SWT.NONE).setText("Last Name");

            GridDataFactory gdf = GridDataFactory.swtDefaults().align(SWT.FILL, SWT.FILL).grab(true, false);
            firstName = new Text(this, SWT.BORDER);
            gdf.applyTo(firstName);

            lastName = new Text(this, SWT.BORDER);
            gdf.applyTo(lastName);

            gdf = GridDataFactory.swtDefaults().span(2, 1).grab(true, false).align(SWT.FILL, SWT.BEGINNING);
            Label label = new Label(this, SWT.NONE);
            label.setText("Formatted Name:");
            gdf.applyTo(label);

            formattedName = new Text(this, SWT.BORDER);
            formattedName.setEditable(false);
            gdf.applyTo(formattedName);
        }
    }
}