screenmanager.java

j2me下的1套UI框架.包含j2me开发中会应用的各种低级组件

package com.jmobilecore.ui.core;

import javax.microedition.lcdui.*;
import javax.microedition.midlet.MIDlet;
import java.util.Stack;

/**
 * This class provides access to the MIDlet's environment
 * and supports navigation among the screens.
 *
 * @author Greg Gridin
 */
public class ScreenManager {

    /**
     * A stack of the path to the currently-displayed screen.
     */
    protected static Stack screens = new Stack();

    /**
     * Current midlet
     * @see #setMIDlet
     */
    protected static MIDlet application = null;

    /**
     *  Reference to Display object that is unique to this MIDlet
     *  @see #setMIDlet
     */
    protected static Display display = null;

    /**
     * Sets the current MIDlet.  If a MIDlet calls this method then environmental
     * information which can only be accessed via the MIDlet object, such as the
     * {@link javax.microedition.lcdui.Display javax.microedition.lcdui.Display},
     * will be accessible to other objects via this class.
     *
     * @param midlet The midlet
     */
    public static void setMIDlet(MIDlet midlet) {
      application = midlet;
      display = Display.getDisplay(midlet);
    }

    /**
     * Returns the current MIDlet.
     *
     * @return The current MIDlet if {@link #setMIDlet} was previously
     * called, else <code>null</code>.
     */
    public static MIDlet getMIDlet() {
      return application;
    }

    /**
     * Gets the Display object associated with the midlet.  This may allow another
     * object, such as an {@link Component Component}, to use
     * environment information which is accessible only via a MIDlet object.  For
     * example, the following code in
     {@link #beep beep} causes the handset to emit a beep.
     * <pre><code>
     * if ( ScreenManager.getDisplay() != null )
     *	AlertType.WARNING.playSound( ScreenManager.getDisplay() );
     * </code></pre>
     *
     * @return The Display object for the MIDlet, or null if the MIDlet has not
     * previously called {@link #setMIDlet setMIDlet}
     */
    public static Display getDisplay() {
      return display;
    }

    /**
     * Causes the handset to emit a beep if {@link #setMIDlet setMIDlet} has
     * been previously called.
     */
    public static void beep(AlertType alert) {
      if (display != null)
        alert.playSound(display);
    }

    /**
     * Display a new screen, and the new screen supports going back to the
     * previous screen.
     *
     * @param newScreen The new screen to display
     */
    public static void goForward(Displayable newScreen) {
        screens.push(newScreen);
        getDisplay().setCurrent(newScreen);
    }

    /**
     * Replaces the currently displayed screen to the new displayed screen.
     *
     * @param newScreen The new replacement screen to display
     */
    public static void replaceScreen(Displayable newScreen) {
        if (!screens.empty()) screens.pop();
        screens.push(newScreen);
        getDisplay().setCurrent(newScreen);
    }

    /**
     * Makes the previously displayed screen the currently displayed screen.
     */
    public static void goBack() {
        if (!screens.empty()) {
            screens.pop();
            if (!screens.empty()) {
                getDisplay().setCurrent((Displayable) screens.peek());
            }
        }
    }

    /**
     * Gets the current screen (the screen at the top of the stack).
     *
     * @return the current screen as <code>Displayable</code> object
     */
    public static Displayable getCurrentScreen() {
        Displayable current = null;
        if (!screens.empty()) {
            current = (Displayable) screens.peek();
        }
        return current;
    }

    /**
     * Goes back to the first (home) screen.
     */
    public static void goHome() {
        Displayable home = null;
        while (!screens.empty()) {
            home = (Displayable) screens.pop();
        }
        getDisplay().setCurrent(home);
        screens.push(home);
    }

    /**
     * Shows alert message and backs to current scrren
     *
     * @param title The title for alert screen
     * @param text The alert message
     * @param delay How long the alert will be displayed, If delay is <code>Alert.FOREVER</code> then
     * alert will be visible until user dismisses it
     * @param type The alert type
     * @see javax.microedition.lcdui.Alert
     */
    public static void showAlert(String title, String text, int delay, AlertType type) {
        showAlert(title, text, delay, type, getCurrentScreen());
    }

    /**
     * Shows alert message and moves to specified scrren
     *
     * @param title The title for alert screen
     * @param text The alert message
     * @param delay How long the alert will be displayed, If delay is <code>Alert.FOREVER</code> then
     * alert will be visible until user dismisses it
     * @param type The alert type
     * @param next The next screen
     * @see javax.microedition.lcdui.Alert
     */
    public static void showAlert(String title, String text, int delay, AlertType type, Displayable next) {
        Alert currentAlert = new Alert(title);
        currentAlert.setTimeout(delay);
        currentAlert.setString(text);
        currentAlert.setType(type);

        display.setCurrent(currentAlert, next);
    }

    /**
     * Resets screen stack
     */
    public static void resetScreens() {
        screens.removeAllElements();
    }

    /**
     * Default destructor. Helps VM to perform garbage collection
     */
    public static void destructor() {
        screens.removeAllElements();
        screens = null;
        display = null;
        application = null;
    }

} // class ScreenManager