我正在使用MonoDroid平台开发Android应用程序。该应用程序中有两个模块，一个是驱动程序模块，另一个是乘客模块。每当乘客预订出租车时，他/她将能够在地图上查看出租车的位置。
在驱动程序模块中，我实现了两个类，一个是GPSTracker类，另一个是NorthStarBackgroundService类。（CODE GIVEN BELOW FOR BOTH）。
NorthStarBackgroundService上名为UpdatePosition的方法负责更新乘客模块获取坐标的数据库中的驾驶员位置，并在地图中显示驾驶员位置。方法UpdatePosition从实现ILocationListener的GPSTracker类获取驱动程序的坐标。
正如您在代码中看到的，我已注释掉RequestLocationUpdates。每当我运行应用程序而不注释掉那行代码时，我的应用程序崩溃了。但是当我用注释运行它时它不会崩溃。我不知道这个问题。此外，当驾驶员移动时，该位置不会更新。
可能熟悉单声道环境的人，请帮我解决这个问题。我试图解决这个问题已经5天了，但我无法做到。
我只使用网络提供商来获取粗略的位置。如果这个工作完美，我将扩展到Gps提供商。
GPSTracker代码
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;
}
}
}
NorthStarBrackgroundService的代码
UpdatePosition每20秒调用一次，因为已为此设置了计时器。 我创建了一个GPSTracker类的对象，并设置了发送到数据库的纬度和经度值。
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");
}
}
}
}
我不知道哪个方面出错导致应用程序崩溃。 对此的任何暗示都将非常感激。
记录Cat输出
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
答案 0 :(得分：1)
我认为你以错误的方式解决这个问题。
发生了什么，您是否每次想要一个位置时实例化一个新的GPSTracker，然后尝试检索碰巧为空的位置的属性。
相反，我会直接在 NorthStarBackgroundService 中实现 ILocationListener 。
Greg Shackles＆＃39;这样一个听众here的例子就应该有你所需要的一切。具体来说，获取最后一个已知位置并请求更新，如示例所示：
_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);
然后执行：
public void OnLocationChanged(Location location)
{
// Update your instance variable for location
}
在此之后你可以让 UpdatePosition（）使用在 OnLocationChanged（）中写入的位置。
答案 1 :(得分：0)
从堆栈跟踪看起来OnStart（）中存在NullReferenceException。
我不熟悉服务 - 但可能是Intent为空 - 当然this reference说：
提供给startService（Intent）的Intent，如给定的那样。这可能是 如果服务在其进程消失后重新启动，则返回null 离开了，之前它还没有返回任何东西 START_STICKY_COMPATIBILITY。