1、創建CompassUI類文件。
2、引入必要的類。
package com.nokia.example.location.tourist.ui;
import Java.io.IOException;
import Javax.microedition.lcdui.Canvas;
import Javax.microedition.lcdui.Command;
import Javax.microedition.lcdui.CommandListener;
import Javax.microedition.lcdui.Displayable;
import Javax.microedition.lcdui.Graphics;
import Javax.microedition.lcdui.Image;
import Javax.microedition.location.OrIEntation;
import com.nokia.example.location.tourist.TouristMIDlet;
import com.nokia.example.location.tourist.model.ConfigurationProvider;
3、創建CompassＵI類，並設置擴展Canvas。運行CommandListener和Runnable。定義這個類需要使用的常量和命令。
/**
* VIEwer class representing a compass.
*/
public class CompassUI extends Canvas implements CommandListener, Runnable
{
/** Constant value for X coordinate. Used in arrays. */
private final int X = 0;
/** Constant value for Y coordinate. Used in arrays. */
private final int Y = 1;
/** Compass center X point */
private int centerX;
/** Compass center Y point */
private int centerY;
/** Constant value representing one degree. */
private final float degree = (float) (2 * Math.PI / 360.0);
/** Current compass azimuth. */
private float azimuth =
/**
* Is orientation relative to the magnetic fIEld of the Earth or true north
* and gravity.
*/
private boolean isMagnetic;
/** Flag telling is the compass update thread active */
private boolean threadActive = false;
/** Sleep 1000ms during each compass update */
private final long SLEEPTIME = 1000;
/** A reference to Route UI */
private Displayable route = null;
/** A reference to Pitch and Roll UI */
private Displayable pitchrollUI = null;
/** Command that swithes current displayable to Route UI */
private Command routeCmd = new Command("Route", Command.BACK, 1);
/** Command that swithes current displayable to Pitch and Roll UI */
private Command prCmd = new Command("Pitch and Roll", Command.OK, 1);
/** Compss background image. */
private Image compassImage = null;
4、為類創建結構。
/**
* Construct instance of this displayable.
*
* @param route
* is a reference to Route UI.
*/
public CompassUI(Displayable route)
{
this.route = route;
pitchrollUI = new PitchRollUI(this);
loadCompassImage();
centerX = getWidth() / 2;
centerY = getHeight() / 2;
addCommand(routeCmd);
addCommand(prCmd);
setCommandListener(this);
}
5、為Compass創建方法，加載背景圖像。
/**
* Load compass backgound image from JAR file.
*/
private void loadCompassImage()
{
String imageName = "/compass_small.gif";
if (getWidth() > 160)
{
imageName = "/compass_large.gif";
}
try
{
compassImage = Image.createImage(getClass().getResourceAsStream(
imageName));
}
catch (IOException e)
{
e.printStackTrace();
}
}
6、創建以下兩個方法，根據Canvas的可見性，VM選擇調用。
/**
* VM calls this method immediately prior to this Canvas being made visible
* on the display.
*/
protected void showNotify()
{
// Actives compass update thread.
threadActive = true;
new Thread(this).start();
}
/**
* VM calls this method shortly after the Canvas has been removed from the
* display.
*/
protected void hideNotify()
{
// Stops the thread.
threadActive = false;
}
7、創建方法，引導canvas。
/**
* Renders the canvas.
*
* @param g -
* the Graphics object to be used for rendering the Canvas
*/
protected void paint(Graphics g)
{
// clean up canvas
g.setColor(255, 255, 255);
g.fillRect(0, 0, getWidth(), getHeight());
int spikeLen = 5;
int len = (compassImage.getWidth() / 2) - spikeLen;
// draw compass background
g.drawImage(compassImage, (getWidth() - compassImage.getWidth()) / 2,
centerY, Graphics.LEFT | Graphics.VCENTER);
// draw compass arrow
g.setColor(0, 0, 255);
drawArrow(g, degree * azimuth, len, spikeLen);
// draw orIEntation type
g.setColor(0, 0, 255);
String otext = "True North";
if (!isMagnetic)
{
otext = "Magnetic fIEld";
}
g.drawString("OrIEntation: " + otext, 0, getHeight(), Graphics.BOTTOM
| Graphics.LEFT);
}
8、創建方法，描述compass arrow。
/**
* Draw a compass arrow rotated to a certain angle.
*
* @param g
* is a reference to Graphics object.
* @param angle
* in degrees [0.0,360.0)
* @param len
* is arrows length.
* @param spikeLen
* is length of arrows spike.
*/
private void drawArrow(Graphics g, float angle, int len, int spikeLen)
{
int a[] = rotate(angle, 0, -(len - spikeLen));
int b[] = rotate(angle, -spikeLen, -(len - spikeLen));
int c[] = rotate(angle, 0, -len);
int d[] = rotate(angle, spikeLen, -(len - spikeLen));
int e[] = rotate(angle + (degree * 180.0), 0, -len);
// use red foreground color
g.setColor(255, 0, 0);
g.drawLine(centerX, centerY, centerX + a[X], centerY + a[Y]);
g.drawLine(centerX + b[X], centerY + b[Y], centerX + d[X], centerY
+ d[Y]);
g.drawLine(centerX + b[X], centerY + b[Y], centerX + c[X], centerY
+ c[Y]);
g.drawLine(centerX + c[X], centerY + c[Y], centerX + d[X], centerY
+ d[Y]);
// use black foreground color
g.setColor(0, 0, 0);
g.drawLine(centerX, centerY, centerX + e[X], centerY + e[Y]);
}
9、創建方法，旋轉箭頭方向。
/**
* Rotate point (x,y) by degrees that angle parameter defines. The new
* coordinate calculation is performed with a 2x2 rotate matrix.
*
* @param angle
* to be rotated
* @param x
* coordinate
* @param y
* coordinate
* @return new coordinate pair in int array format [x,y]
*/
private int[] rotate(double angle, int x, int y)
{
int rotated[] = new int[2];
rotated[X] = (int) (Math.cos(angle) * x + Math.sin(angle) * y);
rotated[Y] = (int) (-Math.sin(angle) * x + Math.cos(angle) * y);
return rotated;
}
10、通過Runnable創建一個運行的方法。目的是更新角度、高度和長度，覆蓋canvas。isOrIEntationMagnetic方法將返回一個布爾值，用來說明OrIEntation方法是否與地球的地磁連接或者使用的是真實的北極點。
/**
* run method from Runnable interface. Updates azimuth, pitch and roll
* values and repaints the canvas.
*
* If OrIEntation is supported on the terminal, compass sensor is either 2D
* or 3D. If the terminals compass sensor providers only compass azimuth,
* pitch and roll values are Float.NaN.
*
* @see HideNotify() method.
*/
public void run()
{
// Keep the thread running until another displayable is set visible.
// See also hideNotify() method.
while (threadActive)
{
Orientation orIEntation = ConfigurationProvider.getInstance()
.getOrIEntation();
if (orIEntation != null)
{
isMagnetic = orientation.isOrIEntationMagnetic();
azimuth = orIEntation.getCompassAzimuth();
}
repaint();
try
{
// Pause this thread for a secord before next update.
Thread.sleep(SLEEPTIME);
}
catch (InterruptedException e)
{
}
}
}
11、創建方法，檢測命令按鍵的輸入。
/**
* Event indicating when a command button is pressed.
*
* @see Javax.microedition.lcdui.CommandListener#commandAction
(Javax.microedition.lcdui.Command,
* Javax.microedition.lcdui.Displayable)
*/
public void commandAction(Command command, Displayable d)
{
if (command == routeCmd)
{
TouristMIDlet.getDisplay().setCurrent(route);
}
else if (command == prCmd)
{
TouristMIDlet.getDisplay().setCurrent(pitchrollUI);
}
}
