SelectOneListBox.java

package com.turbomanage.gwt.client.ui.widget;

import com.google.gwt.event.dom.client.ChangeEvent;
import com.google.gwt.event.dom.client.ChangeHandler;
import com.google.gwt.event.logical.shared.ValueChangeEvent;
import com.google.gwt.event.logical.shared.ValueChangeHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.ui.ListBox;

import java.util.ArrayList;
import java.util.Collection;

/**
 * A ListBox that can be populated with any Collection
 * 
 * Published under Apache License v2
 * 
 * @author David Chandler
 * @param <T>
 */
public class SelectOneListBox<T> extends ListBox implements HasSelectedValue<T>
{

	public interface OptionFormatter<T>
	{
		abstract String getLabel(T option);
		abstract String getValue(T option);
	}
	
	private boolean valueChangeHandlerInitialized;
	private T[] options;
	private OptionFormatter<T> formatter;

	public SelectOneListBox(Collection<T> selections, OptionFormatter<T> formatter)
	{
		setSelections(selections);
		setFormatter(formatter);
	}

	public SelectOneListBox(OptionFormatter<T> formatter)
	{
		this(new ArrayList<T>(), formatter);
	}

	public void setFormatter(OptionFormatter<T> formatter)
	{
		this.formatter = formatter; 
	}

	@SuppressWarnings("unchecked")
	@Override
	public void setSelections(Collection<T> selections)
	{
		// Remember selected value
		T selectedValue = getSelectedValue();
		// Remove prior options
		if (options != null)
		{
			int numItems = this.getItemCount();
			int firstOption = numItems - options.length;
			for (int i=firstOption; i<numItems; i++)
				this.removeItem(firstOption);
		}
		options = (T[]) selections.toArray();
		for (T option : options)
		{
			String optionLabel = formatter.getLabel(option);
			String optionValue = formatter.getValue(option);
			this.addItem(optionLabel, optionValue);
		}
		// Replace selected value
		setSelectedValue(selectedValue);
	}

	@Override
	public T getSelectedValue()
	{
		if (getSelectedIndex() >= 0)
		{
			String name = getValue(getSelectedIndex());

			for (T option : options)
			{
				if (formatter.getValue(option).equals(name))
					return option;
			}
		}

		return null;
	}

	private void setSelectedValue(T value)
	{
		if (value == null)
			return;
		
		for (int i=0; i < this.getItemCount(); i++)
		{
			String thisLabel = this.getItemText(i);
			if (formatter.getLabel(value).equals(thisLabel))
			{
				this.setSelectedIndex(i);
				return;
			}
		}
		throw new IllegalArgumentException("No index found for value " + value.toString());
	}

	/*
	 * Methods to implement HasValue 
	 */
	
	@Override
	public T getValue()
	{
		return this.getSelectedValue();
	}

	@Override
	public void setValue(T value)
	{
		this.setValue(value, false);
	}

	@Override
	public void setValue(T value, boolean fireEvents)
	{
		T oldValue = getValue();
		this.setSelectedValue(value);
		if (fireEvents)
		{
			ValueChangeEvent.fireIfNotEqual(this, oldValue, value);
		}
	}

    @Override
    public void clearSelectedValue() {
        this.setSelectedIndex(0);
    }

    @Override
	public HandlerRegistration addValueChangeHandler(ValueChangeHandler<T> handler)
	{
		// Initialization code
		if (!valueChangeHandlerInitialized)
		{
			valueChangeHandlerInitialized = true;
			super.addChangeHandler(new ChangeHandler()
			{
				public void onChange(ChangeEvent event)
				{
					ValueChangeEvent.fire(SelectOneListBox.this, getValue());
				}
			});
		}
		return addHandler(handler, ValueChangeEvent.getType());
	}

}