我的J2ME编程练习(7)——Canvas2

王朝java/jsp·作者佚名  2006-01-09
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/*

* Canvas2let.java

*

* Created on 2005年4月19日, 下午5:27

*/

import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

/**

*

* @author Administrator

* @version

*/

public class Canvas2let extends MIDlet implements CommandListener {

private ChoiceGroup faceChoice;

private ChoiceGroup styleChoice;

private ChoiceGroup sizeChoice;

private Command okCommand;

private Command exitCommand;

private Command backCommand;

private TextBox faceTextBox;

private TextBox styleTextBox;

private TextBox sizeTextBox;

private Form choiceForm;

private Display aDisplay;

private MyCanvas canvas;

int face;

int size;

int style;

public Canvas2let(){

choiceForm=new Form("Select Font");

faceChoice=new ChoiceGroup("外观",Choice.EXCLUSIVE);

faceChoice.append("PROPORTIONAL",null);

faceChoice.append("MONOSPACE",null);

faceChoice.append("SYSTEM",null);

styleChoice=new ChoiceGroup("风格",Choice.MULTIPLE);

styleChoice.append("PLAIN",null);

styleChoice.append("BOLD",null);

styleChoice.append("ITALIC",null);

styleChoice.append("UNDERLINED",null);

sizeChoice=new ChoiceGroup("大小",Choice.EXCLUSIVE);

sizeChoice.append("SMALL",null);

sizeChoice.append("MEDIUM",null);

sizeChoice.append("LARGE",null);

exitCommand=new Command("退出",Command.EXIT,1);

okCommand=new Command("确定",Command.OK,1);

backCommand=new Command("后退",Command.BACK,2);

choiceForm.append(faceChoice);

choiceForm.append(styleChoice);

choiceForm.append(sizeChoice);

choiceForm.addCommand(exitCommand);

choiceForm.addCommand(okCommand);

choiceForm.setCommandListener(this);

canvas=new MyCanvas();

}

public void startApp() {

aDisplay=Display.getDisplay(this);

aDisplay.setCurrent(choiceForm);

}

public void pauseApp() {

}

public void destroyApp(boolean unconditional) {

}

public void commandAction(Command c ,Displayable d){

if (c==exitCommand){

destroyApp(false);

notifyDestroyed();

}

else {

//select the face and size

face=faceChoice.getSelectedIndex();

switch(face){

case 0: face=Font.FACE_PROPORTIONAL;break;

case 1: face=Font.FACE_MONOSPACE;break;

case 2: face=Font.FACE_SYSTEM;break;

}

size=sizeChoice.getSelectedIndex();

switch(size){

case 0:size=Font.SIZE_SMALL;break;

case 1:size=Font.SIZE_MEDIUM;break;

case 2:size=Font.SIZE_LARGE;break;

}

//select the style

boolean[] styleSelect =new boolean[4];

for(int i=0;i<4;i++){

if (styleChoice.isSelected(i)&&i==0){

style |= Font.STYLE_PLAIN;

}

else if (styleChoice.isSelected(i)&&i==1){

style |=Font.STYLE_BOLD;

}

else if (styleChoice.isSelected(i)&&i==2){

style |=Font.STYLE_ITALIC;

}

else if (styleChoice.isSelected(i)&&i==3){

style |=Font.STYLE_UNDERLINED;

}

}

//canvas=new MyCanvas();

aDisplay.setCurrent(canvas);

}

}

class MyCanvas extends Canvas implements CommandListener{

public MyCanvas(){

addCommand(backCommand);

setCommandListener(this);

}

public void paint(Graphics g){

g.setColor(0xFFFFFF);

g.fillRect(0,0,getWidth(),getHeight());

g.setColor(0);

String s="Hello World";

Font f=Font.getFont(face,style,size);

g.setFont(f);

g.drawString(s,150,250,Graphics.RIGHT|Graphics.BOTTOM);

}

public void commandAction(Command c ,Displayable d){

if (c==backCommand){

aDisplay.setCurrent(choiceForm);

}

}

}

}

这个程序主要是加深对Canvas的Font的认识。

1.MIDlet类的构造函数应该是public Canvas2let()而不应该是public void Cancas2let()。因为加了void就不会返回该类的对象,导致程序运行后没有反映。这是一个教训。

2.在Canvas中,需要使用代码

g.setColor(0xFFFFFF);

g.fillRect(0,0,getWidth(),getHeight());

来清除上一个界面。然后再使用 g.setColor(0);来设置绘画颜色。

3.关于这一点,应该这样理解:

既然使用了低级界面,那么就意味着屏幕上的一切都归你管,你有最大的权利。但你也有相应的义务,清除屏幕的工作自然也要你来做

 
 
 
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