📄 j2me中使用缓存将屏幕内容存储为image-软件-j2me-天极yesky.htm
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<H1>J2ME中使用缓存将屏幕内容存储为Image</H1></DIV>
<DIV id=conauthor><SPAN>2006-06-07 08:57 </SPAN><SPAN>作者: MINIJAVA
</SPAN><SPAN>出处: J2ME开发网 </SPAN><SPAN>责任编辑:<A title=向本编辑提问
href="http://comments.yesky.com/t/·½ÖÛ/6,324/2433021.shtml" target=_blank>方舟</A>
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<DIV class=guanggao><SPAN
id=contentAdv></SPAN></DIV> 本文介绍如何将手机屏幕的内容存储为Image对象,这里认为手机屏幕上显示的是一个Canvas。完成这一个功能的思想就是使用缓冲机制。我们不能直接获得Canvas上的像素,因此不能直接从Canvas上的内容获得Image对象。转换一下思路,如果把要绘制的Canvas上的内容首先绘制到一个Image上,而这个Image并不显示到屏幕上,只是在绘画完成后一次性的显示到屏幕上。有经验的朋友一定联想到了双缓冲机制,不过这里并不是要使用双缓冲解决闪屏的问题,而是要得到当前Canvas的内容。
<BR><BR> 下面我们编写一个简单的Canvas类来测试一下这个想法,SimpleCanvas是Canvas的子类,为了保存Canvas的内容,我们创建一个Image,大小与Canvas的尺寸相当。<BR><BR>
<TABLE borderColor=#cccccc width="90%" align=center bgColor=#e3e3e3 border=1>
<TBODY>
<TR>
<TD>class SimpleCanvas extends Canvas{<BR><BR> int w;<BR> int
h;<BR> private Image offImage = null;<BR> private boolean buffered =
true;<BR> public SimpleCanvas(boolean _buffered){<BR> buffered =
_buffered;<BR> w = getWidth();<BR> h =
getHeight();<BR> if(buffered)<BR> offImage =
Image.createImage(w,h);<BR> }<BR> protected void paint(Graphics g)
{<BR><BR> int color =
g.getColor();<BR> g.setColor(0xFFFFFF);<BR> g.fillRect(0,0,w,h);<BR> g.setColor(color);<BR><BR> Graphics
save = g;<BR> if(offImage != null)<BR> g =
offImage.getGraphics();<BR> //draw the
offimage<BR> g.setColor(128,128,0);<BR> g.fillRoundRect((w-100)/2,(h-60)/2,100,60,5,3);<BR> //draw
the offimage to the
canvas<BR> save.drawImage(offImage,0,0,Graphics.TOP|Graphics.LEFT);<BR> }<BR><BR> public
Image printMe(){<BR> return
offImage;<BR> }<BR></TD></TR></TBODY></TABLE><BR> 可以看到paint()方法,并不是直接对Canvas操作,而是先把要画的内容绘制到一个Image上,然后再绘制到Canvas上。这样到你想抓取屏幕内容的时候就可以调用printMe()方法了,返回offImage。编写一个MIDlet测试一下这个效果。<BR><BR>
<TABLE borderColor=#cccccc width="90%" align=center bgColor=#e3e3e3 border=1>
<TBODY>
<TR>
<TD>package com.j2medev;<BR><BR>import
javax.microedition.midlet.*;<BR>import
javax.microedition.lcdui.*;<BR><BR>/**<BR>*<BR>* @author mingjava<BR>*
@version<BR>*/<BR>public class PrintScreen extends MIDlet implements
CommandListener{<BR><BR> private Display display = null;<BR> private
SimpleCanvas canvas = new SimpleCanvas(true);<BR> private Command
printCommand = new Command("Print",Command.OK,1);<BR><BR> public void
startApp() {<BR> if(display == null)<BR> display =
Display.getDisplay(this);<BR> canvas.addCommand(printCommand);<BR> canvas.setCommandListener(this);<BR> display.setCurrent(canvas);<BR> }<BR><BR> public
void pauseApp() {}<BR><BR> public void destroyApp(boolean unconditional)
{}<BR><BR> public void commandAction(Command command, Displayable
displayable) {<BR> if(command == printCommand){<BR> Form form = new
Form("screen");<BR> form.append(canvas.printMe());<BR> display.setCurrent(form);<BR> }<BR> }<BR>}</TD></TR></TBODY></TABLE><BR> 运行PrintScreen,选择Print,即可把当前的屏幕显示到一个Form中。如下图所示:<BR><BR>
<TABLE width="90%" align=center border=0>
<TBODY>
<TR>
<TD>
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