src/java.desktop/share/classes/javax/imageio/IIOParamController.java

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package javax.imageio;

/**
 * An interface to be implemented by objects that can determine the
 * settings of an {@code IIOParam} object, either by putting up a
 * GUI to obtain values from a user, or by other means.  This
 * interface merely specifies a generic {@code activate} method
 * that invokes the controller, without regard for how the controller
 * obtains values (<i>i.e.</i>, whether the controller puts up a GUI
 * or merely computes a set of values is irrelevant to this
 * interface).
 *
 * <p> Within the {@code activate} method, a controller obtains
 * initial values by querying the {@code IIOParam} object's
 * {@code get} methods, modifies values by whatever means, then
 * invokes the {@code IIOParam} object's {@code set} methods
 * to modify the appropriate settings.  Normally, these
 * {@code set} methods will be invoked all at once at a final
 * commit in order that a cancel operation not disturb existing
 * values.  In general, applications may expect that when the
 * {@code activate} method returns {@code true}, the
 * {@code IIOParam} object is ready for use in a read or write
 * operation.
 *
 * <p> Vendors may choose to provide GUIs for the
 * {@code IIOParam} subclasses they define for a particular
 * plug-in.  These can be set up as default controllers in the
 * corresponding {@code IIOParam} subclasses.
 *
 * <p> Applications may override any default GUIs and provide their
 * own controllers embedded in their own framework.  All that is
 * required is that the {@code activate} method behave modally
 * (not returning until either cancelled or committed), though it need
 * not put up an explicitly modal dialog.  Such a non-modal GUI
 * component would be coded roughly as follows:
 *
 * <br>
 * <pre>
 * class MyGUI extends SomeComponent implements IIOParamController {
 *
 *    public MyGUI() {
 *        // ...
 *        setEnabled(false);
 *    }
 *
 *    public boolean activate(IIOParam param) {
 *        // disable other components if desired
 *        setEnabled(true);
 *        // go to sleep until either cancelled or committed
 *        boolean ret = false;
 *        if (!cancelled) {
 *            // set values on param
 *            ret = true;
 *        }
 *        setEnabled(false);
 *        // enable any components disabled above
 *        return ret;
 *    }
 * </pre>
 *
 * <p> Alternatively, an algorithmic process such as a database lookup
 * or the parsing of a command line could be used as a controller, in
 * which case the {@code activate} method would simply look up or
 * compute the settings, call the {@code IIOParam.setXXX}
 * methods, and return {@code true}.
 *
 * @see IIOParam#setController
 * @see IIOParam#getController
 * @see IIOParam#getDefaultController
 * @see IIOParam#hasController
 * @see IIOParam#activateController
 *
 */
public interface IIOParamController {

    /**
     * Activates the controller.  If {@code true} is returned,
     * all settings in the {@code IIOParam} object should be
     * ready for use in a read or write operation.  If
     * {@code false} is returned, no settings in the
     * {@code IIOParam} object will be disturbed (<i>i.e.</i>,
     * the user canceled the operation).
     *
     * @param param the {@code IIOParam} object to be modified.
     *
     * @return {@code true} if the {@code IIOParam} has been
     * modified, {@code false} otherwise.
     *
     * @throws IllegalArgumentException if {@code param} is
     * {@code null} or is not an instance of the correct class.
     */
    boolean activate(IIOParam param);
}