uidemo.java

java编程百例

package ch09.section01;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

//UIDemo是主类。此实例中的每个控件类都继承了BaseDemo框架类或BaseListDemo框架类
public class UIDemo
    extends MIDlet
    implements CommandListener {
  private static UIDemo instance = null;
  private Displayable currentDemo = null;

  //存储控件实现类列表的数组
  private Class[] demos = {
      getClassObject("ch09.section01.LabelDemo"),
      getClassObject("ch09.section01.DateFieldDemo"),
      getClassObject("ch09.section01.AlertDemo"),
      getClassObject("ch09.section01.ChoiceGroupDemo"),
      getClassObject("ch09.section01.GaugeDemo"),
      getClassObject("ch09.section01.ListDemo"),
      getClassObject("ch09.section01.TextBoxDemo"),
      getClassObject("ch09.section01.TextFieldDemo"),
      getClassObject("ch09.section01.TickerDemo")
  };

  //存储控件名称的数组
  private static final String[] demoNames = {
      "标签控件",
      "日期域控件",
      "提示框控件",
      "选择组控件",
      "进度条控件",
      "列表控件",
      "文本框控件",
      "文本域控件",
      "文本滚动条控件"
  };

  //改列表控件用于用户选择各个控件
  private List selectionList = new List("用户界面控件实例", List.IMPLICIT, demoNames, null);

  //此方法用于动态装入类
  private static Class getClassObject(String className) {
    try {
      return (Class.forName(className));
    }
    catch (Throwable err) {
      System.out.println(err.getClass().getName() + ": " + err.getMessage());
      err.printStackTrace();
    }
    return (null);
  }

  //此方法用于获取一个MIDlet实例
  static UIDemo getInstance() {
    return (instance);
  }

  //默认构造器
  public UIDemo() {
    instance = this;
  }

  //此方法用于使MIDlet应用程序终止，进入销毁状态。
  protected void destroyApp(boolean unconditional) {
    demos = null;
    selectionList = null;
    currentDemo = null;
  }

  //该方法使MIDlet应用程序停止，进入挂起状态。
  protected void pauseApp() {
  }

  //该方法使MIDlet应用程序进入活动状态。
  protected void startApp() {
    Display.getDisplay(this).setCurrent(selectionList);
    selectionList.setCommandListener(this);
  }

  //该方法用于退出当前midlet
  public static void quit() {
    instance.destroyApp(true);
    instance.notifyDestroyed();
    instance = null;
  }

  //该方法用于返回初始界面
  public static void goBack() {
    instance.currentDemo = null;
    instance.startApp();
  }

  //该方法用于获取当前运行的Demo
  Displayable getCurrentDemo() {
    return (currentDemo);
  }

  //响应事件
  public void commandAction(Command c, Displayable d) {
    int pos = selectionList.getSelectedIndex();
    try {
      currentDemo = (Displayable) demos[pos].newInstance();
      Display.getDisplay(this).setCurrent(currentDemo);
    }
    catch (Exception err) {
      Alert a = new Alert("Error");
      a.setString("Failed in handling the command at position: " + pos);
      a.setTimeout(Alert.FOREVER);
      Display.getDisplay(this).setCurrent(a);
    }
  }

  //创建按钮
  static Command[] getDemoCommands() {
    Command[] commands = {
        new Command("返回", Command.BACK, 1),
        new Command("退出", Command.STOP, 2)
    };
    return (commands);
  }

  //响应事件
  static Runnable[] getDemoActions() {
    class BackCallback
        implements Runnable {
      //响应返回事件
      public void run() {
        UIDemo.goBack();
      }
    }

    //响应退出事件
    class QuitCallback
        implements Runnable {
      public void run() {
        UIDemo.quit();
      }
    }

    //响应菜单返回
    class MenuCallback
        implements Runnable {
      public void run() {
      }
    }

    Runnable[] callbacks = {
        new BackCallback(), new QuitCallback()
    };
    return (callbacks);
  }
}