don't let users try to send texts if we don't have a node id

app/src/main/java/com/geeksville/mesh/model/NodeDB.kt

@@ -44,7 +44,7 @@ class NodeDB(private val ui: UIViewModel) {
     private val seedWithTestNodes = isEmulator
 
     /// The unique ID of our node
-    val myId = object : MutableLiveData<String>(if (isEmulator) "+16508765309" else "invalid") {}
+    val myId = object : MutableLiveData<String?>(if (isEmulator) "+16508765309" else null) {}
 
     /// A map from nodeid to to nodeinfo
     val nodes =
@@ -53,5 +53,5 @@ class NodeDB(private val ui: UIViewModel) {
                 .toTypedArray())) {}
 
     /// Could be null if we haven't received our node DB yet
-    val ourNodeInfo get() = nodes.value!![myId.value]
+    val ourNodeInfo get() = nodes.value?.get(myId.value)
 }

app/src/main/java/com/geeksville/mesh/ui/MessagesFragment.kt

@@ -14,6 +14,7 @@ import com.geeksville.android.Logging
 import com.geeksville.mesh.R
 import com.geeksville.mesh.model.TextMessage
 import com.geeksville.mesh.model.UIViewModel
+import com.geeksville.mesh.service.MeshService
 import kotlinx.android.synthetic.main.adapter_message_layout.view.*
 import kotlinx.android.synthetic.main.messages_fragment.*
 import java.text.SimpleDateFormat
@@ -167,6 +168,12 @@ class MessagesFragment : ScreenFragment("Messages"), Logging {
         model.messagesState.messages.observe(viewLifecycleOwner, Observer { it ->
             messagesAdapter.onMessagesChanged(it)
         })
+
+        model.isConnected.observe(viewLifecycleOwner, Observer { connected ->
+            // If we don't know our node ID and we are offline don't let user try to send
+            textInputLayout.isEnabled =
+                connected != MeshService.ConnectionState.DISCONNECTED || model.nodeDB.myId.value != null
+        })
     }
 
     private val dateFormat = SimpleDateFormat("h:mm a")