AbstractSelector.java

/*
 * Copyright (c) 2012 Data Harmonisation Panel
 * 
 * All rights reserved. This program and the accompanying materials are made
 * available under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the License,
 * or (at your option) any later version.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution. If not, see <http://www.gnu.org/licenses/>.
 * 
 * Contributors:
 *     HUMBOLDT EU Integrated Project #030962
 *     Data Harmonisation Panel <http://www.dhpanel.eu>
 */

package eu.esdihumboldt.hale.ui.util.selector;

import java.util.concurrent.CopyOnWriteArraySet;

import org.eclipse.jface.layout.TableColumnLayout;
import org.eclipse.jface.viewers.ColumnWeightData;
import org.eclipse.jface.viewers.ILabelProvider;
import org.eclipse.jface.viewers.ISelection;
import org.eclipse.jface.viewers.ISelectionChangedListener;
import org.eclipse.jface.viewers.ISelectionProvider;
import org.eclipse.jface.viewers.IStructuredSelection;
import org.eclipse.jface.viewers.SelectionChangedEvent;
import org.eclipse.jface.viewers.StructuredSelection;
import org.eclipse.jface.viewers.TableViewer;
import org.eclipse.jface.viewers.TableViewerColumn;
import org.eclipse.jface.viewers.ViewerFilter;
import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Control;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

import eu.esdihumboldt.hale.ui.util.viewer.ObjectContentProvider;

/**
 * Abstract selector control based on a {@link TableViewer}.
 * 
 * @param <T> the type of the object to be selected
 * @param <E> the type of object selected in the dialog
 * @author Simon Templer
 */
public abstract class AbstractSelector<T, E> implements ISelectionProvider {

	private static enum NoObject {
		NONE;

		@Override
		public String toString() {
			return "<Click to select>";
		}

	}

	private final CopyOnWriteArraySet<ISelectionChangedListener> listeners = new CopyOnWriteArraySet<ISelectionChangedListener>();

	private final TableViewer viewer;

	private final Composite main;

	private final ViewerFilter[] filters;

	/**
	 * Tracks the current input. Set by inputChanged of the content provider.
	 */
	private Object currentInput;

	/**
	 * Create a selector.
	 * 
	 * @param parent the parent composite
	 * @param labelProvider the label provider for the selector
	 * @param filters the filters for the selector, may be <code>null</code>
	 */
	public AbstractSelector(Composite parent, ILabelProvider labelProvider, ViewerFilter[] filters) {
		main = new Composite(parent, SWT.NONE);
		TableColumnLayout columnLayout = new TableColumnLayout();
		main.setLayout(columnLayout);

		// entity selection combo
		/*
		 * Use MULTI selection so having an empty selection is possible on
		 * Linux/GTK. Otherwise when the control gets the focus it will
		 * automatically select the entry and launch the selection dialog. This
		 * especially is a problem when a selector gets the focus automatically.
		 */
		viewer = new TableViewer(main, SWT.BORDER | SWT.MULTI | SWT.FULL_SELECTION | SWT.NO_SCROLL);

		TableViewerColumn column = new TableViewerColumn(viewer, SWT.NONE);
		columnLayout.setColumnData(column.getColumn(), new ColumnWeightData(1, false));

		viewer.setContentProvider(ObjectContentProvider.getInstance());
		viewer.setLabelProvider(labelProvider);

		this.filters = filters;

		// initial selection
		Object select = NoObject.NONE;
		currentInput = select;
		viewer.setInput(select);

		viewer.addSelectionChangedListener(new ISelectionChangedListener() {

			@Override
			public void selectionChanged(SelectionChangedEvent event) {
				if (event.getSelection().isEmpty()) {
					return;
				}

				AbstractViewerSelectionDialog<E, ?> dialog = createSelectionDialog(Display
						.getCurrent().getActiveShell());
				dialog.setFilters(AbstractSelector.this.filters);
				if (dialog.open() == AbstractViewerSelectionDialog.OK) {
					T selected = convertFrom(dialog.getObject());
					if ((selected == null && currentInput == null)
							|| (selected != null && selected.equals(currentInput)))
						return;
					if (selected != null) {
						currentInput = selected;
					}
					else {
						currentInput = NoObject.NONE;
					}
					viewer.setInput(currentInput);
					/*
					 * XXX Bug on Mac? - Viewer is not refreshed correctly until
					 * user clicks on the wizard. Manually refreshing, layouting
					 * the parent composite or calling
					 * forceActive/forceFocus/setActive on the Shell doesn't
					 * help. XXX is this fixed with TableColumnLayout?
					 */
				}
				viewer.setSelection(new StructuredSelection());

				// inform about the input change
				fireSelectionChange();
			}

		});
	}

	/**
	 * Convert from an object selected in the dialog to a selector object.
	 * 
	 * @param object the dialog selected object, may be <code>null</code>
	 * @return the converted object
	 */
	protected abstract T convertFrom(E object);

	/**
	 * Determines if the given object matches the selector's filters.
	 * 
	 * @param candidate the object to test
	 * @return if the object is accepted by all filters
	 */
	public boolean accepts(Object candidate) {
		return AbstractViewerSelectionDialog.acceptObject(viewer, filters, candidate);
	}

	/**
	 * @see ISelectionProvider#addSelectionChangedListener(ISelectionChangedListener)
	 */
	@Override
	public void addSelectionChangedListener(ISelectionChangedListener listener) {
		listeners.add(listener);
	}

	/**
	 * @see ISelectionProvider#getSelection()
	 */
	@Override
	public ISelection getSelection() {
		Object input = currentInput;
		if (input == null || input == NoObject.NONE) {
			return new StructuredSelection();
		}
		return new StructuredSelection(input);
	}

	/**
	 * @see ISelectionProvider#removeSelectionChangedListener(ISelectionChangedListener)
	 */
	@Override
	public void removeSelectionChangedListener(ISelectionChangedListener listener) {
		listeners.remove(listener);
	}

	/**
	 * @see ISelectionProvider#setSelection(ISelection)
	 */
	@Override
	public void setSelection(ISelection selection) {
		if (!selection.isEmpty() && selection instanceof IStructuredSelection) {
			Object selected = ((IStructuredSelection) selection).getFirstElement();
			if (selected != null) {
				// run against filters
				if (AbstractViewerSelectionDialog.acceptObject(viewer, filters, selected)) {
					// valid selection
					currentInput = selected;
					viewer.setInput(selected);

					fireSelectionChange();

					return;
				}
				else {
					// TODO user error message?
				}
			}
		}

		currentInput = NoObject.NONE;
		viewer.setInput(NoObject.NONE);
		viewer.setSelection(StructuredSelection.EMPTY);

		fireSelectionChange();
	}

	/**
	 * Resets the current selection, but shows the given text instead of the
	 * default.
	 * 
	 * @param text the text to show
	 */
	public void showText(String text) {
		currentInput = NoObject.NONE;
		viewer.setInput(text);
		viewer.setSelection(StructuredSelection.EMPTY);

		fireSelectionChange();
	}

	/**
	 * Fires a selection change and sets the last selection to the given
	 * selection.
	 */
	protected void fireSelectionChange() {
		SelectionChangedEvent event = new SelectionChangedEvent(this, getSelection());

		for (ISelectionChangedListener listener : listeners) {
			listener.selectionChanged(event);
		}
	}

	/**
	 * Create the dialog for selecting an entity.
	 * 
	 * @param parentShell the parent shell for the dialog
	 * @return the entity dialog
	 */
	protected abstract AbstractViewerSelectionDialog<E, ?> createSelectionDialog(Shell parentShell);

	/**
	 * Get the main selector control
	 * 
	 * @return the main control
	 */
	public Control getControl() {
		return main;
	}

	/**
	 * Get the selected entity definition
	 * 
	 * @return the selected entity definition or <code>null</code>
	 */
	@SuppressWarnings("unchecked")
	public T getSelectedObject() {
		ISelection selection = getSelection();
		if (selection.isEmpty() || !(selection instanceof IStructuredSelection)) {
			return null;
		}

		Object element = ((IStructuredSelection) selection).getFirstElement();
		if (element != null && element != NoObject.NONE) {
			return (T) element;
		}

		return null;
	}

}