screen.java

symbian的蓝牙名片交换源代码

// Copyright 2006 Nokia Corporation.
//
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// and may be changed substantially prior to final release. Nokia Corporation
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package bcexchanger.ui;

import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;

import bcexchanger.*;

/**
 * 
 * This class is an abstract base class for all the UI screen in this
 * application. This class implements CommandListner interface.
 * 
 * @version 1.0 29.09.2005
 * @see example.BCExchanger.ui.Screen Design patterns: State
 * 
 */
public abstract class Screen implements CommandListener {

  protected BCExchangerMIDlet midlet;
  protected Displayable displayable;

  /**
   * Constructor
   * 
   * @param _midlet -
   *          the parent class which keeps the current UI state
   */
  public Screen(BCExchangerMIDlet _midlet) {
    midlet = _midlet;
  }

  /**
   * Makes current screen active
   * <p>
   * Each class inherited from Screen has a displayable associated.
   * When this method is called the displayble is made visiable and
   * active
   * 
   */
  public void makeActive() {
    try {
      Display d = Display.getDisplay(midlet);

      if (d.getCurrent() != displayable) { // this prevents from
                                            // bringing application to
                                            // foreground in case is
                                            // application is in
                                            // background and the
                                            // current displayable is
                                            // the same as the one
                                            // made active
        d.setCurrent(displayable);
      }

    } catch (NullPointerException e) {
      throw new RuntimeException(
          "Internal error #2: Screen.midlet == null");
    }
  }

}