我正在構建一個Xamarin.Android應用程序。我有一個正在運行的服務，我正在嘗試將數據從該服務獲取到我擁有的活動。我知道人們對發布過多的代碼感到不滿，但是我不確定我的問題在哪里。我要發布我認為必要的內容：服務[Service]public class DataService : Service{ public List<MyObjects> MyObjectList { get; private set; } public IBinder Binder { get; private set; } public override IBinder OnBind(Intent intent) { this.Binder = new DataServiceBinder(this); return this.Binder; } public override void OnCreate() { base.OnCreate(); pendingIntent = PendingIntent.GetActivity(this, 0, new Intent(this, typeof(MainActivity)), 0); StartForeground(NotificationID, GetNotification("Started Sync")); //Do some work here to instantiate and populate the List }}服務活頁夾public class DataServiceBinder : Binder{ public DataServiceBinder(DataService service) { Service = service; } public DataService Service { get; private set; }}服務連接public class DataServiceConnection : Object, IServiceConnection { public DataService Service { get; private set; } public DataServiceBinder dataServiceBinder; public bool IsConnected { get; private set; } public void OnServiceConnected(ComponentName name, IBinder service) { dataServiceBinder = service as DataServiceBinder; IsConnected = this.dataServiceBinder != null; Service = dataServiceBinder.Service; ServiceConnectionChanged?.Invoke(this, true); } public void OnServiceDisconnected(ComponentName name) { ServiceConnectionChanged?.Invoke(this, false); Service = null; } public event EventHandler<bool> ServiceConnectionChanged; }在我的活動中，當我嘗試通過服務傳遞適配器列表時，“服務”為null，因此我得到了null引用異常。為什么我的服務為空？我是否無法正確綁定我的服務？為了記錄，它們服務在“應用程序”上下文中啟動。
1 回答
白衣非少年
TA貢獻1155條經驗 獲得超0個贊
好的，我找到了解決方案。由于連接到服務是異步的，所以我不能期望適配器能夠像這樣同步獲取數據：
var adapter = new MyDataAdapter(DataServiceConnection.Service.MyObjectList);
相反，我將自己的活動修改為如下所示：
public class MyDataActivity : AppCompatActivity
{
private DataServiceConnection DataServiceConnection;
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
if (DataServiceConnection == null)
{
this.DataServiceConnection = new DataServiceConnection();
}
Intent serviceToStart = new Intent(this, typeof(DataService));
BindService(serviceToStart, this.DataServiceConnection, Bind.AutoCreate);
DataServiceConnection.ServiceConnectionChanged += ServiceConnectionChanged;
SetContentView(Resource.Layout.MyDataLayout);
}
private void ServiceConnectionChanged(object sender, bool isConnected)
{
if(DataServiceConnection.Service == null)
{
return;
}
if(isConnected)
{
var adapter = new MyDataAdapter(DataServiceConnection.Service.MyObjectList);
}
}
protected override void OnResume()
{
var intent = new Intent(this, typeof(DataService));
BindService(intent, DataServiceConnection, Bind.AutoCreate);
base.OnResume();
}
protected override void OnPause()
{
UnbindService(DataServiceConnection);
base.OnPause();
}
我還對服務連接進行了如下修改：
public class DataServiceConnection : Object, IServiceConnection
{
public DataService Service { get; private set; }
public MyDataActivity DataActivity;
public event EventHandler<bool> ServiceConnectionChanged;
public DataServiceConnection(MyDataActivity myDataActivity)
{
DataActivity = myDataActivity;
}
public void OnServiceConnected(ComponentName name, IBinder service)
{
dataServiceBinder = service as DataServiceBinder;
Service = dataServiceBinder.Service;
ServiceConnectionChanged?.Invoke(this, true);
}
public void OnServiceDisconnected(ComponentName name)
{
ServiceConnectionChanged?.Invoke(this, false);
Service = null;
}
}
現在，我的解決方案僅在連接服務時嘗試將數據發送到適配器。該解決方案對我有用，希望對其他任何人有幫助。
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