choice.append(Title.detail, null);
this.append(nameField);
this.append(mobileField);
this.append(choice);
this.addCommand(saveCommand);
this.addCommand(backCommand);
this.setCommandListener(this);
this.setItemStateListener(this);
}
Canvas类代表了MIDP的低级用户界面，它是一个抽象类。你需要继承Canvas并实现它的抽象方法paint(Graphics g)来构建你自己的Canvas实例。Paint()方法中的参数g非常重要。因为通过它提供的方法你才能在屏幕上绘画你的界面。如果有时间您应该多多研究一下Canvas类和Graphics类。在个人通信录中我们提供了一个WaitCanvas类并通过它构建了Dialog组件。从下面的代码中您能学会如何使用Canvas类。
package com.north.phonebook.ui;
import java.util.*;
import javax.microedition.lcdui.*;
public class WaitCanvas extends Canvas
{
private int mCount, mMaximum;
private int mInterval;
private int mWidth, mHeight, mX, mY, mRadius;
private String mMessage;
private boolean run = false;
public WaitCanvas(String message, boolean run)
{
this.mMessage = message;
mCount = 0;
mMaximum = 36;
mInterval = 100;
mWidth = getWidth();
mHeight = getHeight();
// Calculate the radius.
int halfWidth = (mWidth - mRadius) / 2;
int halfHeight = (mHeight - mRadius) / 2;
mRadius = Math.min(halfWidth, halfHeight);
// Calculate the location.
mX = halfWidth - mRadius / 2;
mY = halfHeight - mRadius / 2;
// Create a Timer to update the display.
if (run)
{
TimerTask task = new TimerTask()
{
public void run()
{
mCount = (mCount + 1) % mMaximum;
repaint();
}
};
Timer timer = new Timer();
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