如果調用requestLocationUpdates來獲取用戶的新位置，應用程序崩潰

我正在開發使用MonoDroid Platform的android應用程序。該應用程序中有兩個模塊，一個是驅動模塊，另一個是乘客模塊。每當乘客預訂出租車時，他/她將能夠在地圖上查看出租車的位置。如果調用requestLocationUpdates來獲取用戶的新位置，應用程序崩潰

在驅動程序模塊中，我實現了兩個類，一個是GPSTracker類，另一個是NorthStarBackgroundService類（代碼如下）。

NorthStarBackgroundService上名爲UpdatePosition的方法負責更新乘客模塊獲取座標的數據庫中的駕駛員位置，並在地圖中顯示駕駛員位置。方法UpdatePosition從實現ILocationListener的GPSTracker類中獲取驅動程序的座標。如您在代碼中看到的，我已將RequestLocationUpdates註釋掉了。每當我運行應用程序而不註釋掉那行代碼時，我的應用程序崩潰。但是當我用註釋運行它時，它不會崩潰。我不知道這個問題。駕駛員移動時該位置也不會更新。

有人可能熟悉單聲道環境，請幫我解決這個問題。它已經5天，我正在努力解決這個問題，但我無法做到這一點。

我只使用網絡提供商來獲得粗略位置。如果這件作品完美無缺，我將擴展到Gps提供商。因爲計時器已被設置爲

代碼GPSTracker

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 

using Android.App; 
using Android.Content; 
using Android.OS; 
using Android.Runtime; 
using Android.Views; 
using Android.Widget; 
using Android.Locations; 
using Java.IO; 

namespace NorthStar.Driver 
{ 
    public class GPSTracker : Service, ILocationListener 

    { 

     public readonly Context mContext; 

     // flag for network status 
     Boolean isNetworkEnabled = false; 

     Location location; // location 
     public double latitude; // latitude 
     public double longitude; // longitude 

     public LocationManager locationManager; 



     public GPSTracker(Context context) 
     { 
      this.mContext = context; 
      getLocation(); 

     } 


     public Location getLocation() 
     { 
      locationManager = (LocationManager)mContext.GetSystemService(Context.LocationService); 

      // getting network status 
      isNetworkEnabled = locationManager.IsProviderEnabled(LocationManager.NetworkProvider); 

      if (isNetworkEnabled) 
      { 
       // locationManager.RequestLocationUpdates(LocationManager.NetworkProvider, 1000, 10, this); 

       if (locationManager != null) 
       { 
        location = locationManager.GetLastKnownLocation(LocationManager.NetworkProvider); 
        if (location != null) 
        { 
         latitude = location.Latitude; 
         longitude = location.Longitude; 
        } 
       } 
      } 

      return location; 
     } 


     /** 
     * Function to get latitude 
     * */ 
     public double getLatitude() 
     { 

      latitude = location.Latitude; 
      // return latitude 

      return latitude; 
     } 


     /** 
     * Function to get longitude 
     * */ 
     public double getLongitude() 
     { 
      latitude = location.Longitude; 
      // return latitude 

      return longitude;   
     } 

     public void OnLocationChanged(Location location) 
     { 
     } 


     public void OnProviderDisabled(String provider) 
     { 
     } 


     public void OnProviderEnabled(String provider) 
     { 
     } 


     public void OnStatusChanged(string provider, Availability status, Bundle extras) 
     { 
     } 


     public override IBinder OnBind(Intent arg0) 
     { 
      return null; 
     } 


    } 
}

代碼NorthStarBrackgroundService

UpdatePosition被稱爲每20秒。我已經創建了一個GPSTracker類的對象，並設置發送到數據庫的緯度和經度的值。

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Threading; 
using Android.App; 
using Android.Content; 
using Android.OS; 
using Android.Preferences; 
using Android.Runtime; 
using Android.Views; 
using Android.Widget; 
using NorthStar.Driver.Application; 
using TheNorthStar.Api.Requests; 
using TheNorthStar.Api.Results; 

namespace NorthStar.Driver 
{ 
    [Service] 
    public class NorthStarBackgroundService : Service 
    { 
     private string driverId; 
     private System.Timers.Timer timer; 

     public override IBinder OnBind(Intent intent) 
     { 
      return null; 
     } 

     public override void OnCreate() 
     { 
      base.OnCreate(); 
      timer = new System.Timers.Timer(20000); 
      timer.Elapsed += TimerElapsed;    
     } 

     void TimerElapsed(object sender, System.Timers.ElapsedEventArgs e) 
     { 
      ThreadPool.QueueUserWorkItem(UpdatePosition); 
     } 

     public override void OnStart(Intent intent, int startId) 
     { 
      base.OnStart(intent, startId); 

      driverId = intent.GetStringExtra("driverId"); 

      timer.Start(); 
     } 

     public override void OnDestroy() 
     { 
      base.OnDestroy(); 
      timer.Stop(); 
     } 

     private void UpdatePosition(object data) 
     { 

      ConnectToSever api = new ConnectToSever(Helper.GetServer(ApplicationContext)); 

      GPSTracker gps = new GPSTracker(ApplicationContext); 

      var pos = new DriverPosition() { Latitude = gps.latitude, Longitude = gps.longitude, DriverId = driverId }; 
      try 
      { 
       api.UpdatePosition(pos); 
      } 
      catch 
      { 
       Android.Util.Log.Info("EXC_update1", "update driver failed"); 
      } 
     } 
    } 
}

我不知道哪一點我出錯，使應用程序崩潰。對此的任何提示都會很感激。

登錄貓輸出

I/EXC_logstart( 306): **************** starting driver module **************** 
I/ActivityManager( 60): Displayed activity MyDriver_Driver.MyDriver_Driver/northstar.driver.Activity1: 6632 ms (total 6632 ms) 
D/dalvikvm( 128): GC_EXPLICIT freed 201 objects/9848 bytes in 188ms 
D/dalvikvm( 120): GC_EXTERNAL_ALLOC freed 3163 objects/207880 bytes in 144ms 
D/dalvikvm( 120): GC_EXTERNAL_ALLOC freed 935 objects/60072 bytes in 172ms 
W/KeyCharacterMap( 306): No keyboard for id 0 
W/KeyCharacterMap( 306): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 
I/ARMAssembler( 60): generated scanline__00000077:03515104_00000000_00000000 [ 33 ipp] (47 ins) at [0x3bce60:0x3bcf1c] in 8041202 ns 
I/ActivityManager( 60): Starting activity: Intent { cmp=MyDriver_Driver.MyDriver_Driver/northstar.driver.MainActivity (has extras) } 
I/ActivityManager( 60): Displayed activity MyDriver_Driver.MyDriver_Driver/northstar.driver.MainActivity: 1216 ms (total 1216 ms) 
E/mono ( 306): 
E/mono ( 306): Unhandled Exception: Java.Lang.NullPointerException: Exception of type 'Java.Lang.NullPointerException' was thrown. 
E/mono ( 306): at Android.Runtime.JNIEnv.CallNonvirtualObjectMethod (IntPtr jobject, IntPtr jclass, IntPtr jmethod, Android.Runtime.JValue[] parms) [0x00000] in <filename unknown>:0 
E/mono ( 306): at Android.Content.ContextWrapper.GetSystemService (System.String name) [0x00000] in <filename unknown>:0 
E/mono ( 306): at NorthStar.Driver.GPSTracker.getLocation() [0x00000] in <filename unknown>:0 
E/mono ( 306): at NorthStar.Driver.GPSTracker..ctor (Android.Content.Context context) [0x00000] in <filename unknown>:0 
E/mono ( 306): at NorthStar.Driver.MainActivity.RequestWork() [0x00000] in <filename unknown>:0 
E/mono ( 306): at NorthStar.Driver.MainActivity.<OnCreate>b__2 (System.Object x) [0x00000] in <filename unknown>:0 
E/mono ( 306): --- End of managed exception stack trace --- 
E/mono ( 306): java.lang.NullPointerException 
E/mono ( 306): at android.content.ContextWrapper.getSystemService(ContextWrapper.java:363) 
E/mono ( 306): at dalvik.system.NativeStart.run(Native Method) 
E/mono ( 306): 
D/Zygote ( 33): Process 306 exited cleanly (255) 
I/ActivityManager( 60): Process MyDriver_Driver.MyDriver_Driver (pid 306) has died. 
I/WindowManager( 60): WIN DEATH: Window{45103638 MyDriver_Driver.MyDriver_Driver/northstar.driver.Activity1 paused=false} 
I/WindowManager( 60): WIN DEATH: Window{4511aac0 MyDriver_Driver.MyDriver_Driver/northstar.driver.MainActivity paused=false} 
W/ActivityManager( 60): Scheduling restart of crashed service MyDriver_Driver.MyDriver_Driver/northstar.driver.NorthStarBackgroundService in 5000ms 
I/ActivityManager( 60): Start proc MyDriver_Driver.MyDriver_Driver for activity MyDriver_Driver.MyDriver_Driver/northstar.driver.Activity1: pid=320 uid=10042 gids={3003, 1015} 
I/UsageStats( 60): Unexpected resume of MyDriver_Driver.MyDriver_Driver while already resumed in MyDriver_Driver.MyDriver_Driver 
I/ActivityThread( 320): Publishing provider MyDriver_Driver.MyDriver_Driver.__mono_init__: mono.MonoRuntimeProvider 
D/dalvikvm( 320): Trying to load lib /data/data/MyDriver_Driver.MyDriver_Driver/lib/libmonodroid.so 0x44edf660 
D/dalvikvm( 320): Added shared lib /data/data/MyDriver_Driver.MyDriver_Driver/lib/libmonodroid.so 0x44edf660 
E/mono ( 320): WARNING: The runtime version supported by this application is unavailable. 
E/mono ( 320): Using default runtime: v2.0.50727 
I/monodroid-gc( 320): environment supports jni NewWeakGlobalRef 
W/monodroid-gc( 320): GREF GC Threshold: 1800 
I/EXC_logstart( 320): **************** starting driver module **************** 
W/InputManagerService( 60): Got RemoteException sending setActive(false) notification to pid 306 uid 10042 
I/ActivityManager( 60): Displayed activity MyDriver_Driver.MyDriver_Driver/northstar.driver.Activity1: 4214 ms (total 4214 ms) 
I/MonoDroid( 320): UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object 
I/MonoDroid( 320): at NorthStar.Driver.NorthStarBackgroundService.OnStart (Android.Content.Intent,int) <0x00038> 
I/MonoDroid( 320): at Android.App.Service.n_OnStart_Landroid_content_Intent_I (intptr,intptr,intptr,int) <0x00067> 
I/MonoDroid( 320): at (wrapper dynamic-method) object.0333e05f-221e-4109-91bd-6a13aa2251bd (intptr,intptr,intptr,int) <0x0003b> 
E/mono ( 320): 
E/mono ( 320): Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object 
E/mono ( 320): at NorthStar.Driver.NorthStarBackgroundService.OnStart (Android.Content.Intent intent, Int32 startId) [0x00000] in <filename unknown>:0 
E/mono ( 320): at Android.App.Service.n_OnStart_Landroid_content_Intent_I (IntPtr jnienv, IntPtr native__this, IntPtr native_intent, Int32 startId) [0x00000] in <filename unknown>:0 
E/mono ( 320): at (wrapper dynamic-method) object:0333e05f-221e-4109-91bd-6a13aa2251bd (intptr,intptr,intptr,int) 
D/Zygote ( 33): Process 320 exited cleanly (1) 
I/ActivityManager( 60): Process MyDriver_Driver.MyDriver_Driver (pid 320) has died. 
W/ActivityManager( 60): Scheduling restart of crashed service MyDriver_Driver.MyDriver_Driver/northstar.driver.NorthStarBackgroundService in 20000ms 
I/WindowManager( 60): WIN DEATH: Window{45127238 MyDriver_Driver.MyDriver_Driver/northstar.driver.Activity1 paused=false} 
I/UsageStats( 60): Unexpected resume of com.android.launcher while already resumed in MyDriver_Driver.MyDriver_Driver 
W/InputManagerService( 60): Got RemoteException sending setActive(false) notification to pid 320 uid 10042 
I/ActivityManager( 60): Start proc MyDriver_Driver.MyDriver_Driver for service MyDriver_Driver.MyDriver_Driver/northstar.driver.NorthStarBackgroundService: pid=327 uid=10042 gids={3003, 1015} 
I/ActivityThread( 327): Publishing provider MyDriver_Driver.MyDriver_Driver.__mono_init__: mono.MonoRuntimeProvider 
D/dalvikvm( 327): Trying to load lib /data/data/MyDriver_Driver.MyDriver_Driver/lib/libmonodroid.so 0x44edf580 
D/dalvikvm( 327): Added shared lib /data/data/MyDriver_Driver.MyDriver_Driver/lib/libmonodroid.so 0x44edf580 
E/mono ( 327): WARNING: The runtime version supported by this application is unavailable. 
E/mono ( 327): Using default runtime: v2.0.50727 
I/monodroid-gc( 327): environment supports jni NewWeakGlobalRef 
W/monodroid-gc( 327): GREF GC Threshold: 1800

來源

2012-10-06 Amrit Sharma

請提供崩潰的日誌輸出：http://docs.xamarin.com/android/advanced_topics/android_debug_log –

我附加了日誌cat輸出。 –

我認爲你會以錯誤的方式去做。

這是怎麼回事，你是在每次想要某個位置時都實例化一個新的GPSTracker，然後嘗試檢索碰巧爲null的位置的屬性。

相反，我會實施ILocationListener直接在您的NorthStarBackgroundService。

Greg Shackles對這樣一位聽衆here的例子應該是你所需要的。

具體來說，得到最後已知位置，並要求更新作爲例子：

_locationManager = (LocationManager)GetSystemService(LocationService); 
Location lastKnownLocation = _locationManager.GetLastKnownLocation(bestProvider); 

if (lastKnownLocation != null) ... // Set your instance variable for location. 

// You can set the thresholds that suit you here. 
_locationManager.RequestLocationUpdates(bestProvider, 5000, 2, this);

然後實現：

public void OnLocationChanged(Location location) 
{ 
    // Update your instance variable for location 
}

在這之後你可以有UpdatePosition（）使用正在寫入的位置OnLocationChanged（）。

來源

2012-10-07 09:56:46 manadart

謝謝SpriritMachine，你解決了我的問題。 –

不客氣:) – manadart

從堆棧跟蹤它看起來像存在的OnStart（）一個NullReferenceException。

我不熟悉的服務 - 但會不會是意圖是空 - 當然this reference說：

提供給startService（意向），給出的意圖。這可能是如果服務在其進程已經離開之後重新啓動並且之前已返回除 START_STICKY_COMPATIBILITY之外的任何內容，則返回null。

來源

2012-10-07 00:21:28 Stuart

但是，如果我沒有請求位置更新運行此應用程序它運行沒有崩潰。有人可以提供解決方案嗎？ –

如果調用requestLocationUpdates來獲取用戶的新位置，應用程序崩潰

回答

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