在XamarinForms应用程序中使用Android定位服务
本文关键字:Android 定位 服务 XamarinForms 应用程序 | 更新日期: 2023-09-27 18:27:16
我有一个Xamarin Forms应用程序。相当基本的设置与包含一些XAML页面的PCL。
我正试图在我的Xaml页面上点击一个按钮,运行一个非常简单的"显示我的gps坐标"样本。
我在PCL中创建了一个ILocationService接口,并在android应用程序中创建了特定于android的实现,标记有[assembly:Dependency]
属性,这样我就可以使用XamForms DI服务获取它。
这是Android实现的代码。
[assembly: Dependency(typeof(AndroidLocationService))]
namespace LoginDemo.Droid
{
public class AndroidLocationService : ILocationService, ILocationListener
{
Location _currentLocation;
LocationManager _locationManager;
String _locationProvider;
public AndroidLocationService()
{
this.InitializeLocationManager();
}
//When the DI Container fetches a new instance of the AndroidLocationService
//Wire up the _locationManager/Provider stuff and tell it to start fetching updates every 2 ses
void InitializeLocationManager()
{
_locationManager = (LocationManager)Forms.Context.GetSystemService(Context.LocationService);
Criteria criteriaForLocationService = new Criteria { Accuracy = Accuracy.Fine };
try
{
_locationProvider = _locationManager.GetBestProvider(criteriaForLocationService, true);
if (_locationManager.IsProviderEnabled(_locationProvider))
{
_locationManager.RequestLocationUpdates(_locationProvider, 2000, 1, this);
}
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex);
}
}
//MyInterface Method
public LocationResult GetLocation()
{
if (_currentLocation == null)
{
return new LocationResult() { Data = "Can't determine the current address." };
}
return new LocationResult { Data = string.Format("{0} - {1}", _currentLocation.Latitude, _currentLocation.Longitude)};
}
public void Dispose()
{
}
public IntPtr Handle { get; private set; }
public void OnLocationChanged(Location location)
{
_currentLocation = location;
}
public void OnProviderDisabled(string provider)
{
//Not Implemented
}
public void OnProviderEnabled(string provider)
{
//Not Implemented
}
public void OnStatusChanged(string provider, Availability status, Bundle extras)
{
//Not Implemented
}
}
}
_locationProvider
通过GetBestProvider
方法设置为值gps
,并且它通过了isEnabled
检查,但一旦它尝试请求更新。。。我得到以下(相当于事无补)异常。我已经仔细检查了应用程序清单,以确保课程&精细定位请求。有什么想法吗?
{Java.Lang.IllegalArgumentException: Exception of type 'Java.Lang.IllegalArgumentException' was thrown.
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x00000] in <filename unknown>:0
at Android.Runtime.JNIEnv.CallVoidMethod (IntPtr jobject, IntPtr jmethod, Android.Runtime.JValue[] parms) [0x00063] in /Users/builder/data/lanes/1131/2a7b6821/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:508
at Android.Locations.LocationManager.RequestLocationUpdates (System.String provider, Int64 minTime, Single minDistance, ILocationListener listener) [0x0004a] in /Users/builder/data/lanes/1131/2a7b6821/source/monodroid/src/Mono.Android/platforms/android-15/src/generated/Android.Locations.LocationManager.cs:814
at LoginDemo.Droid.AndroidLocationService.InitializeLocationManager () [0x00058] in c:'Work'Code'Sandbox'LoginDemo'LoginDemo'LoginDemo.Android'LocationService.cs:46
--- End of managed exception stack trace ---
java.lang.IllegalArgumentException: invalid listener: null
at android.location.LocationManager.checkListener(LocationManager.java:1606)
at android.location.LocationManager.requestLocationUpdates(LocationManager.java:426)
at xamarin.forms.platform.android.ButtonRenderer_ButtonClickListener.n_onClick(Native Method)
at xamarin.forms.platform.android.ButtonRenderer_ButtonClickListener.onClick(ButtonRenderer_ButtonClickListener.java:29)
at android.view.View.performClick(View.java:4247)
at android.view.View$PerformClick.run(View.java:17728)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5289)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
at dalvik.system.NativeStart.main(Native Method)
}
在"正常"Android示例中,在OnResume中调用RequestLocationUpdates。在我看来,通过在构造函数中调用这个方法(通过init方法),您试图过早地获取这些信息。您可以尝试将对RequestLocationUpdates的调用移动到Start()方法,然后可以在页面的OnAppearing方法中调用该方法。我正在尝试让一个样本工作,但我的mac需要一些约塞米蒂更新后的工作;-)
更新:
好吧,我想我想通了。虽然我之前的评论可能仍然成立,但我发现,您不是在ILocationListener实现中实现Handle和Dispose,而是从Java.Lang.Object派生它http://forums.xamarin.com/discussion/19559/xamarin-gps-location-code-fails-exception-in-mono-works-in-native-android-bug-or-mistake.
因此,在您的代码中,删除Dispose()和Handle代码,并将类定义更改为:
public class AndroidLocationService : Java.Lang.Object, ILocationService, ILocationListener
我在我的小测试应用程序中做了这些更改,它如预期的那样工作。请注意,我确实在OnAppearing()(在PCL中)中启动了该过程,并且我使用消息传递(MessagingCenter)来更新标签。在一个完整的应用程序中,我会使用MVVM并将标签绑定到ViewModel,但即使这样,ILocationService可能仍然会通过MessagingCenter发送更新(你也可以使用事件,但根据我的经验,消息传递更可靠)。
如果您使用Xamarin Forms Labs,会变得更容易
var geolocator = DependencyService.Get<IGeolocator> ();