Bug 121709 [Commands] parameters: Add types
I'm going to attach a patch that adds support for typed command parameters. This addresses several issues: - parameter values are strings, but handlers may want to work on objects - multiple handlers of a command should have a consistent way of converting string parameter values to objects - tooling to construct parameterized commands that starts with object parameter values needs a way of producing string parameter values that will work when the command is executed - there should be a way to classify commands by their object parameter types so, given an object, a set of commands that may work with it can be suggested To address these issues, the patch allows parameter types to be declared in the extension-point XML. The example below defines a command for negating integers and a parameter type that works with it. <extension point="org.eclipse.ui.commands"> <command id="org.example.commands.negateInteger" defaultHandler="org.example.commands.NegateIntegerHandler" name="Negate an Integer"> <commandParameter id="param" name="the param" optional="false" typeId="org.example.commands.Integer"/> </command> <commandParameterType id="org.example.commands.Integer" converter="org.example.commands.IntegerConverter" type="java.lang.Integer"/> </extension> In addition to extending the schema for org.eclipse.ui.commands, code has been added to a number of plugins (primarily org.eclipse.core.commands) to support the notion of typed parameters.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
"Cannot remove a null execution listener"); 
		}
		if (executionListeners != null) {
			executionListeners.remove(executionListener);
			if (executionListeners.isEmpty()) {
				executionListeners = null;
			}
		}
	}
	/**
	 * <p>
	 * Removes a state from this command. This will remove the state from the
	 * active handler, if the active handler is an instance of
	 * {@link IObjectWithState}.
	 * </p>
	 * 
	 * @param stateId
	 *            The identifier of the state to remove; must not be
	 *            <code>null</code>.
	 */
	public void removeState(final String stateId) {
		if (handler instanceof IObjectWithState) {
			((IObjectWithState) handler).removeState(stateId);
		}
		super.removeState(stateId);
	}
	/**
	 * Changes the handler for this command. This will remove all the state from
	 * the currently active handler (if any), and add it to <code>handler</code>.
	 * If debugging is turned on, then this will also print information about