ui_ex7.java

J2ME 无线通信技术应用开发源代码

// 程序名UI_Ex7.java
// 测试使用命令多屏幕浏览
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class UI_Ex7 extends MIDlet implements CommandListener {
  private Display display; // 引用MIDlet的Display 对象
  private TextBox scrHelp;
  private TextBox scrJump;
  private TextBox[] myScreen;

  private Command cmdBack;
  private Command cmdForw;
  private Command cmdJump;
  private Command cmdExit;
  private Command cmdHelp;

  private Command cmdCanc;
  private Command cmdConf;

  static int MaxHistory = 8;
  static int MaxScreen = 4;
  int[] history;
  int currentPos;
  int historyLen;

  // MIDlet构造程序
  public UI_Ex7() {
    display = Display.getDisplay(this);// 获取一个Display实例，它是唯一的
    
    cmdForw = new Command("前进",Command.SCREEN,1);
    cmdBack = new Command("后退",Command.BACK,1);
    cmdJump = new Command("跳转",Command.SCREEN,2);
    cmdHelp = new Command("帮助",Command.HELP,1);
    cmdExit = new Command("退出",Command.SCREEN,2);
    
    cmdConf = new Command("确定",Command.OK,1);
    cmdCanc = new Command("取消",Command.CANCEL,1);
    
    String helpStr = new String("\"前进\" 跳转到前一个浏览过的屏幕，"
                                +"\"后退\" 跳转到后一个浏览过的屏幕，"
                                +"\"跳转\" 指定你要到达的屏幕，"
                                +"\"退出\" 退出应用程序，");
    scrHelp = new TextBox("帮助",helpStr,100,0);
    scrHelp.addCommand(cmdCanc);
    scrHelp.setCommandListener(this);
    
    scrJump = new TextBox("跳转到","",2,2);
    scrJump.addCommand(cmdConf);
    scrJump.addCommand(cmdCanc);
    scrJump.setCommandListener(this);
    myScreen = new TextBox[MaxScreen];
    myScreen[0] = createScreen("屏幕一","床前明月光");
    myScreen[1] = createScreen("屏幕二","疑是地上霜");
    myScreen[2] = createScreen("屏幕三","举头望明月");
    myScreen[3] = createScreen("屏幕四","低头思故乡");

    history = new int[MaxHistory];
    currentPos = -1;
    historyLen = 0;
  }

  // 被应用程序管理器调用来启动MIDlet。
  public void startApp() {
    gotoScreen(0);// 把textBox设置为当前屏幕或当前Displayable对象
    addHistory(0);
  }

  // 一个必要的方法
  public void pauseApp() {
  }

  // 一个必要的方法
  public void destroyApp(boolean unconditional) {
  }

  private TextBox createScreen(String screenTitle,String screenContent) {
    TextBox tempScreen = new TextBox(screenTitle,screenContent,50,0);
    tempScreen.addCommand(cmdForw);
    tempScreen.addCommand(cmdBack);
    tempScreen.addCommand(cmdJump);
    tempScreen.addCommand(cmdHelp);
    tempScreen.addCommand(cmdExit);
    tempScreen.setCommandListener(this);
    return tempScreen;
  }
  private void addHistory(int num) {
    if (historyLen < MaxHistory) {
      historyLen++;
      history[historyLen] = num;
      currentPos++;
    } else {
      for (int i=0;i<MaxHistory;i++) {
        history[i] = history[i+1];
      }
      history[MaxHistory] = num;
      currentPos = historyLen-1;
    }
  }
  
  void gotoScreen(int num) {
    display.setCurrent(myScreen[num]);
  } 

  // 设置事件触发时的动作
  public void commandAction(Command c, Displayable d) {
    if (c == cmdBack) {
      if (currentPos > 0) {
        currentPos--;
        gotoScreen(history[currentPos]);
      }
      return;
    }

    if (c == cmdForw) {
      if (currentPos < historyLen) {
        currentPos++;
        gotoScreen(history[currentPos]);
      }
      return;
    }

    if (c == cmdJump) {
      display.setCurrent(scrJump);
      return;
    }

    if (c == cmdHelp) {
      display.setCurrent(scrHelp);
      return;
    }
      
    if (c == cmdCanc) {
      gotoScreen(history[currentPos]);
      return;
    }

    if (c == cmdConf) {
      int next = Integer.parseInt(scrJump.getString());
      if ((next > 0)&&(next <= MaxScreen)) {
        display.setCurrent(myScreen[next-1]);
        addHistory(next-1);
      }
      return;
    }
    
    if (c == cmdExit) {
      destroyApp(false);
      notifyDestroyed();
    }
  }
}