JavaMe MIDlet和Canvas

Question

我正试着制作一个使用中间菜单的程序。当从菜单访问某些命令时，它将访问画布(就像弹出按钮中的填充矩形和填充弧的选择)。如果选择填充矩形，它将访问绘制填充矩形的画布。

问题是，当我访问填充弧时，不会发生任何事情，但是在填充矩形上会发生任何情况。

另一个问题是，我不知道如何将菜单中的X和Y坐标应用于填充矩形，以便用户控制所选对象的位置。‘

这是我的代码：

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

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

/**
 * @author Nico
 */
public class emp extends MIDlet implements CommandListener {
    Display display;
    Form frm = new Form ("Main");
    ChoiceGroup Cg1;
    ChoiceGroup Cg2;
    TextField tfX = new TextField ("X Axis"," ",40,TextField.ANY);
    TextField tfY = new TextField ("Y Axis"," ",40,TextField.ANY);
    Command OK;

    public emp () {
        OK = new Command ("OK",Command.OK,1);
        Cg2 = new ChoiceGroup("Color", Choice.POPUP);
        Cg1 = new ChoiceGroup("Type", Choice.POPUP);
        Cg1.append("Rectangle", null);
        Cg1.append("Arc", null);
        Cg1.append("Line", null);
        Cg2.append("Red", null);
        Cg2.append("Blue", null);
        Cg2.append("Green", null);

        frm.append(Cg1);
        frm.append(tfX);
        frm.append(tfY);
        frm.append(Cg2);
        frm.addCommand(OK);

        frm.setCommandListener(this);
    }



      public void startApp () {
            display = Display.getDisplay(this);
            display.setCurrent(frm);
  }

  public void pauseApp () {}

  public void destroyApp (boolean forced) {}




class DrawingRect extends Canvas implements CommandListener {
    Command Bk;


    public DrawingRect (){
        this.addCommand(Bk= new Command("Back", Command.BACK, 0 ) );
        this.setCommandListener(this);
    }
  public void paint (Graphics g) {
    int x1=100,y1=100;

    g.setColor (0, 0, 0);
    g.fillRect(0, 0, getWidth(), getHeight());
    g.setColor (0, 0, 255);
    g.fillRect(x1,y1, 50, 50);
    g.drawString("aaaaaa", getWidth()/2, getHeight()/2, Graphics.TOP|Graphics.HCENTER);



  }

        public void commandAction(Command c, Displayable d) {
            if (c==Bk){
                display.setCurrent(frm);
            }
        }
    }

public class DrawingArc extends Canvas implements CommandListener {
    Command Bk;



    public DrawingArc (){
        this.addCommand(Bk= new Command("Back", Command.BACK, 0 ) );
        this.setCommandListener(this);
    }
  public void paint (Graphics g) {


    g.setColor (0, 0, 0);
    g.fillRect(0, 0, getWidth(), getHeight());
        g.setGrayScale(13*16);
        g.fillArc(0,0,getWidth(),getHeight(),90,360);



  }

        public void commandAction(Command c, Displayable d) {
            if (c==Bk){
                display.setCurrent(frm);
            }
        }
    }
    public void commandAction(Command c, Displayable d) {

        if (c==OK) {
        int select = Cg1.getSelectedIndex();
            if (select==0){
            display.setCurrent (new DrawingRect ());
            }
        }
        else if (c==OK){
        int select = Cg1.getSelectedIndex();
            if (select==1){
            display.setCurrent (new DrawingArc ());
        }
        }
        else {

        }
}
}

Answer 1

看看这段代码..。(本人的评论及注记)

public void commandAction(Command c, Displayable d) {
  if (c==OK) {
    int select = Cg1.getSelectedIndex();
    if (select==0){
      display.setCurrent (new DrawingRect ());
    }
  }else if (c==OK){
    // It will never ever ever reach this block
    int select = Cg1.getSelectedIndex();
    if (select==1){
      display.setCurrent (new DrawingArc ());
    }
  }else {
    // WTF?
  }
}

我不想无礼，但这个代码不太稳定.您应该澄清您的java概念或试图澄清您的代码..。我相信，如果您更改了下面的代码，您可以解决第一个问题：

public void commandAction(Command c, Displayable d) {
  if (c==OK) {
    int select = Cg1.getSelectedIndex();
    if (select==0){
      display.setCurrent (new DrawingRect ());
    }else if (select==1){
      display.setCurrent (new DrawingArc ());
    }
  }
}

对于第二个问题，我可能会在表单中添加某种Move to...按钮。如果你按下它，你可以用给定的X和Y创建画布，或者.以下是一些提示：

class DrawingRect extends Canvas implements CommandListener {
  Command Bk;
  int x1, y1;

  public DrawingRect (int newX, int newY){
    this.addCommand(Bk= new Command("Back", Command.BACK, 0 ) );
    this.setCommandListener(this);
    x1 = newX;
    y1 = newY;
  }


  public void paint (Graphics g) {
    g.setColor (0, 0, 0);
    g.fillRect(0, 0, getWidth(), getHeight());
    g.setColor (0, 0, 255);
    g.fillRect(x1,y1, 50, 50);
    g.drawString("aaaaaa", getWidth()/2, getHeight()/2, Graphics.TOP|Graphics.HCENTER);
  }

  public void commandAction(Command c, Displayable d) {
    if (c==Bk){
      display.setCurrent(frm);
    }
  }
}

很明显，这样称呼它：

display.setCurrent (new DrawingRect(tfX.getString(),tfY.getString()));

但是，所有这些都是非常基本的Java概念，我认为您应该在进一步研究之前对它们进行改进.只是个建议。