Java ME 处理多个屏幕

Question

我正在创建一个应用程序，当应用程序启动时，用户可以选择将文件添加到驻留在存储卡上的应用程序。有一个名为 add new 的按钮；当用户单击添加新时，将出现一个表单，用户将在其中输入文件名并可以添加文件，但添加新文件的命令不起作用，任何人都可以告诉我出了什么问题吗？那里？

我的代码片段是

import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
import javax.microedition.io.file.*;
import javax.microedition.io.Connector;
import java.io.IOException;
import java.util.*;

public class HelloMIDlet
    extends MIDlet 
    implements CommandListener {
  private List list;
  private Alert alert;
  private Display display;
  private Form form;
  private TextField fname,fpath;
  private Command select,remove,add,fadd,back,exit;

  public HelloMIDlet() {
    form=new Form("add new:");
    fname=new TextField("enter File Name","",40,TextField.ANY);
    fpath=new TextField("enter File path","file:///SDCard/",50,TextField.ANY);
    list = new List("Welcome", List.IMPLICIT); 
    remove=new Command("Remove Selected",Command.SCREEN,2);
    exit=new Command("Exit",Command.EXIT,0);
    select=new Command("Select",Command.SCREEN,1);
    add=new Command("Add New",Command.SCREEN,2);
    list.addCommand(exit);
    list.addCommand(select);
    list.addCommand(add);
    list.addCommand(remove);
    form.append(fname);
    form.append(fpath);
    list.setCommandListener(this);
  }
  public void startApp() {

    display=Display.getDisplay(this);
    display.setCurrent(list);
  }

  public void pauseApp() {}

  public void destroyApp(boolean unconditional) {}

  public void commandAction(Command c, Displayable s) {
   if(c==exit)
   {
    notifyDestroyed();
    }
    else if(c==add)
    {
    // display.setCurrent(form);
     addfile();

    }
    else if(c==remove)
    {

    }
    else if(c==back)
    {
        display.setCurrent(list);
    }
    else if(c==fadd)
    {
        alert=new Alert("Open the file:","Would you like to open the current file??",null,null);
        alert.setTimeout(Alert.FOREVER);

    }
    else if(c==list.SELECT_COMMAND)
    {

    }
  }
  public void addfile()
  {fadd=new Command("add File",Command.SCREEN,0);
   back=new Command("Back",Command.BACK,1);
   form.addCommand(fadd);
   form.addCommand(back);

   form.setCommandListener(this);
   display.setCurrent(form); 
  }
}

Answer 1

当您选择“添加文件”时，该命令将由 commandAction 触发并处理，具体来说，这段代码：

else if(c==fadd)
{
  alert=new Alert("Open the file:","Would you like to open the current file??",null,null);
  alert.setTimeout(Alert.FOREVER);
  // You were creating a Alert instance, but not showing it, this line below is one you 
  // were missing
  display.setCurrent(alert, list);
}

您可以使用 setCurrent(Alert alert, Displayable nextDisplayable) 或 setCurrent(Displayable nextDisplayable)，具体取决于您的需要。