定位 API 開發指南：MessageUI 提示與 PitchRollUI 姿態儀實作 (第 8 部分)

4.4.10 MessageUI 類別：統一訊息提示

MessageUI 封裝常用的 Alert 顯示邏輯，提供靜態方法供全程式呼叫：

package com.nokia.example.location.tourist.ui;

import javax.microedition.lcdui.*;
import com.nokia.example.location.tourist.TouristMIDlet;

public class MessageUI {
    /** 裝置不支援 Location API */
    public static void showApiNotSupported() {
        Alert alert = new Alert("Information",
            "Device do not support Location API", null, AlertType.INFO);
        TouristMIDlet.getDisplay().setCurrent(alert);
    }

    /** 定位資料尚未可用 */
    public static void showLocationDataNotAvailable() {
        Alert alert = new Alert("Information",
            "Location data is not yet available.", null, AlertType.INFO);
        TouristMIDlet.getDisplay().setCurrent(alert);
    }

    /** 正在尋找定位資料（含進度指示器） */
    public static void showLocationProviderState() {
        Gauge indicator = new Gauge(null, false, 50, 1);
        indicator.setValue(Gauge.CONTINUOUS_RUNNING);
        Alert alert = new Alert("Information",
            "Please wait, looking for location data....", null, AlertType.INFO);
        alert.setIndicator(indicator);
        TouristMIDlet.getDisplay().setCurrent(alert);
    }
}

4.4.11 PitchRollUI 類別：俯仰/滾轉角度儀表

PitchRollUI 同樣繼承 Canvas 並實作 Runnable，專門將 Orientation 的 pitch（俯仰角 ±90°）與 roll（滾轉角 ±180°）以類儀表板方式視覺化。

類別結構

public class PitchRollUI extends Canvas implements CommandListener, Runnable {
    private CompassUI compass;
    private float pitch = Float.NaN, roll = Float.NaN;
    private boolean threadActive = false;
    private final long SLEEPTIME = 1000;
    private Command compassCmd = new Command("Compass", Command.BACK, 1);

    public PitchRollUI(CompassUI compass) {
        this.compass = compass;
        addCommand(compassCmd);
        setCommandListener(this);
    }
    // ...

執行緒控制

protected void showNotify() {
    threadActive = true;
    new Thread(this).start();
}
protected void hideNotify() {
    threadActive = false;
}

背景執行緒讀取感測器

public void run() {
    while (threadActive) {
        Orientation orientation = ConfigurationProvider.getInstance().getOrientation();
        if (orientation != null) {
            pitch = orientation.getPitch();
            roll = orientation.getRoll();
        }
        repaint();
        try { Thread.sleep(SLEEPTIME); }
        catch (InterruptedException e) {}
    }
}

繪製畫面

protected void paint(Graphics g) {
    g.setColor(255, 255, 255);
    g.fillRect(0, 0, getWidth(), getHeight());
    paintPitch(g);
    paintRoll(g);
}

通用刻度尺繪製方法

drawMeter 依參數繪製基線、小刻度、大刻度：

protected void drawMeter(Graphics g, int min, int max, int smallStep,
                         int largeStep, int baseline, int margin) {
    double scale = 100.0;
    g.setColor(0x0000ff);
    g.drawLine(margin, baseline, getWidth(), baseline);
    for (int i = min; i <= max; i += smallStep) {
        double pos = (((i + max) * scale * (getWidth() - margin)) / (2 * max)) / scale;
        int x = margin + (int) pos;
        g.drawLine(x, baseline - 3, x, baseline + 3);
    }
    for (int i = min; i <= max; i += largeStep) {
        double pos = (((i + max) * scale * (getWidth() - margin)) / (2 * max)) / scale;
        int x = margin + (int) pos;
        g.drawLine(x, baseline - 5, x, baseline + 5);
    }
}

繪製俯仰角儀表

protected void paintPitch(Graphics g) {
    int baseline = 10, textAreaWidth = 50;
    g.setColor(0x000000);
    g.drawString("Pitch", 0, baseline - 5, Graphics.TOP | Graphics.LEFT);
    g.drawString("-90", textAreaWidth + 1, baseline, Graphics.TOP | Graphics.LEFT);
    g.drawString("0", textAreaWidth + (getWidth() - textAreaWidth) / 2, baseline, Graphics.TOP | Graphics.HCENTER);
    g.drawString("+90", getWidth(), baseline, Graphics.TOP | Graphics.RIGHT);
    drawMeter(g, -90, 90, 10, 30, baseline, textAreaWidth);

    if (pitch != Float.NaN) {
        double pos = (((pitch + 90.0) * 100 * (getWidth() - textAreaWidth)) / (2 * 90)) / 100;
        g.setColor(0x000000);
        g.fillRect(textAreaWidth + (int) pos - 3, baseline - 2, 5, 5);
    }
}

繪製滾轉角儀表

protected void paintRoll(Graphics g) {
    int baseline = 40, textAreaWidth = 50;
    g.setColor(0x000000);
    g.drawString("Roll", 0, baseline - 5, Graphics.TOP | Graphics.LEFT);
    g.drawString("-180", textAreaWidth + 1, baseline, Graphics.TOP | Graphics.LEFT);
    g.drawString("0", textAreaWidth + (getWidth() - textAreaWidth) / 2, baseline, Graphics.TOP | Graphics.HCENTER);
    g.drawString("+180", getWidth(), baseline, Graphics.TOP | Graphics.RIGHT);
    drawMeter(g, -180, 180, 15, 60, baseline, textAreaWidth);

    if (roll != Float.NaN) {
        double pos = (((roll + 180.0) * 100 * (getWidth() - textAreaWidth)) / (2 * 180)) / 100;
        g.setColor(0x000000);
        g.fillRect(textAreaWidth + (int) pos - 3, baseline - 2, 5, 5);
    }
}

指令事件：返回羅盤

public void commandAction(Command command, Displayable d) {
    if (command == compassCmd) {
        TouristMIDlet.getDisplay().setCurrent(compass);
    }
}
}

總結： 本系列完整展示了 J2ME Location API (JSR-179) 在行動裝置上的實戰應用，涵蓋地標管理、定位監聽、鄰近偵測、電子羅盤與姿態感測器視覺化，為 LBS 應用開發提供了寶貴的參考架構。