Add support for offline use

app/src/main/java/net/underdesk/circolapp/fragments/CircularLetterFragment.kt

@@ -22,10 +22,12 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import androidx.constraintlayout.widget.ConstraintLayout
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.Observer
 import androidx.lifecycle.ViewModelProviders
 import androidx.recyclerview.widget.LinearLayoutManager
+import com.google.android.material.snackbar.Snackbar
 import kotlinx.android.synthetic.main.fragment_circular_letters.view.*
 import net.underdesk.circolapp.R
 import net.underdesk.circolapp.adapters.CircularLetterAdapter
@@ -49,6 +51,17 @@ class CircularLetterFragment : Fragment() {
         circularLetterViewModel.circulars.observe(this, Observer {
             root.circulars_list.adapter = CircularLetterAdapter(it)
         })
+        circularLetterViewModel.showMessage.observe(this, Observer {
+            if (it) activity?.findViewById<ConstraintLayout>(R.id.container)?.let { view ->
+                Snackbar.make(
+                    view,
+                    getString(R.string.snackbar_connection_not_available),
+                    Snackbar.LENGTH_LONG
+                ).show()
+
+                circularLetterViewModel.showMessage.postValue(false)
+            }
+        })
         return root
     }
 }

app/src/main/java/net/underdesk/circolapp/viewmodels/CircularLetterViewModel.kt

@@ -25,6 +25,7 @@ import androidx.lifecycle.MutableLiveData
 import net.underdesk.circolapp.data.AppDatabase
 import net.underdesk.circolapp.data.Circular
 import net.underdesk.circolapp.server.DataFetcher
+import java.io.IOException
 
 class CircularLetterViewModel(application: Application) : AndroidViewModel(application) {
 
@@ -35,6 +36,7 @@ class CircularLetterViewModel(application: Application) : AndroidViewModel(appli
     }
 
     val circulars: LiveData<List<Circular>> = _circulars
+    val showMessage = MutableLiveData<Boolean>().apply { value = false }
 
     private fun loadCirculars() {
         object : Thread() {
@@ -48,11 +50,15 @@ class CircularLetterViewModel(application: Application) : AndroidViewModel(appli
     private fun updateCirculars() {
         val fetcher = DataFetcher()
 
-        val newCirculars = fetcher.getCircularsFromServer()
-        if (newCirculars.size != _circulars.value?.size ?: true) {
-            _circulars.postValue(newCirculars)
-            AppDatabase.getInstance(getApplication()).circularDao().deleteAll()
-            AppDatabase.getInstance(getApplication()).circularDao().insertAll(newCirculars)
+        try {
+            val newCirculars = fetcher.getCircularsFromServer()
+            if (newCirculars.size != _circulars.value?.size ?: true) {
+                _circulars.postValue(newCirculars)
+                AppDatabase.getInstance(getApplication()).circularDao().deleteAll()
+                AppDatabase.getInstance(getApplication()).circularDao().insertAll(newCirculars)
+            }
+        } catch (exception: IOException) {
+            showMessage.postValue(true)
         }
     }
 }

app/src/main/java/net/underdesk/circolapp/works/PollWork.kt

@@ -32,6 +32,7 @@ import net.underdesk.circolapp.R
 import net.underdesk.circolapp.data.AppDatabase
 import net.underdesk.circolapp.data.Circular
 import net.underdesk.circolapp.server.DataFetcher
+import java.io.IOException
 import java.util.concurrent.TimeUnit
 
 
@@ -72,7 +73,11 @@ class PollWork(appContext: Context, workerParams: WorkerParameters) :
         val fetcher = DataFetcher()
 
         val oldCirculars = AppDatabase.getInstance(applicationContext).circularDao().getCirculars()
-        val newCirculars = fetcher.getCircularsFromServer()
+        val newCirculars = try {
+            fetcher.getCircularsFromServer()
+        } catch (exception: IOException) {
+            return Result.retry()
+        }
 
         if (newCirculars.size != oldCirculars.size) {
             createNotificationChannel()

app/src/main/res/values/strings.xml

@@ -11,4 +11,6 @@
 
     <string name="channel_name">Circular letters</string>
     <string name="channel_description">Notify when your school issue a new circular letter</string>
+
+    <string name="snackbar_connection_not_available">Network not available. Results may be outdated</string>
 </resources>