GPS在Android的使用經驗

GPS的開發、使用，有兩個關鍵點：

1. 選擇並激活合適的Provider；

2. 建立合理刷新機制。

 

下面是通用的方法，以“選擇並激活合適的Provider”：

 

protected void getAndTraceLocation(){
		//geocoder = new Geocoder(this, Locale.getDefault());;
		geocoder = new Geocoder(this, Locale.ENGLISH);;
		// Acquire a reference to the system Location Manager
		locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

		Criteria criteria = new Criteria();
		criteria.setAccuracy(Criteria.ACCURACY_FINE);
		criteria.setAltitudeRequired(false);
		criteria.setBearingRequired(false);
		criteria.setCostAllowed(true);
		criteria.setPowerRequirement(Criteria.POWER_LOW);

		String provider = locationManager.getBestProvider(criteria, true);
		if(provider!=null){
			Log.i(TAG, "GPS provider is enabled:" + provider.toString());
			// Get the location
			latestLocation = locationManager.getLastKnownLocation(provider);
			updateWithNewLocation(latestLocation);
	
			// Register the listener with the Location Manager to receive location
			locationManager.requestLocationUpdates(provider, 1000, 5, locationListener);
		}else{
			Log.i(TAG, "No GPS provider found!");
			updateWithNewLocation(null);
		}
	}

	protected final LocationListener locationListener = new LocationListener() {
		public void onLocationChanged(Location location) {
			Log.i(TAG, "location changed to: " + location);
			updateWithNewLocation(location);
		}
		public void onProviderDisabled(String provider) {}
		public void onProviderEnabled(String provider) {}
		public void onStatusChanged(String provider, int status, Bundle extras) {}
	};

 

需要注意的是：

這裏的locationManager.getBestProvider(criteria, true) 之後，必須進行是否爲null的判斷，否則在終端禁用GPS和網絡以後會出現NPE異常。

 

注意這裏回調了一個通用的updateWithNewLocation(latestLocation)方法，用戶只要實現這個方法，即可實現第二個關鍵點，即“建立合理刷新機制”。

 

下面是最簡單的例子：

 

@Override
protected void updateWithNewLocation(Location location) {
    	super.updateWithNewLocation(location);
    	
		String location_msg = context.getString(R.string.msg_no_gps);
		if (location != null) {
			location_msg = location.getLatitude() + "," + location.getLongitude();			
			Log.i(TAG, location_msg);
		} else {
			Log.i(TAG, location_msg);
		}
		
		location_msg = String.format(_location_msg, location_msg);
		_location.setText(location_msg);
	}

 

完畢！