Fixed drawer's updateComputerList not being called when there were changes

Plus removed some unnecessary calls in other places.

src/org/kde/kdeconnect/BackgroundService.java

@@ -61,12 +61,13 @@ public class BackgroundService extends Service {
 
     private final HashSet<Object> discoveryModeAcquisitions = new HashSet<>();
 
-    public void acquireDiscoveryMode(Object key) {
+    public boolean acquireDiscoveryMode(Object key) {
         boolean wasEmpty = discoveryModeAcquisitions.isEmpty();
         discoveryModeAcquisitions.add(key);
         if (wasEmpty) {
             onNetworkChange();
         }
+        return wasEmpty;
     }
 
     public void releaseDiscoveryMode(Object key) {
@@ -76,11 +77,18 @@ public class BackgroundService extends Service {
         }
     }
 
-    public static void addGuiInUseCounter(final Activity activity) {
+    public static void addGuiInUseCounter(Activity activity) {
+        addGuiInUseCounter(activity, false);
+    }
+
+    public static void addGuiInUseCounter(final Activity activity, final boolean forceNetworkRefresh) {
         BackgroundService.RunCommand(activity, new BackgroundService.InstanceCallback() {
             @Override
             public void onServiceStart(BackgroundService service) {
-                service.acquireDiscoveryMode(activity);
+                boolean refreshed = service.acquireDiscoveryMode(activity);
+                if (!refreshed && forceNetworkRefresh) {
+                    service.onNetworkChange();
+                }
             }
         });
     }

src/org/kde/kdeconnect/UserInterface/MaterialActivity.java

@@ -159,21 +159,33 @@ public class MaterialActivity extends AppCompatActivity {
     @Override
     protected void onStart() {
         super.onStart();
-        BackgroundService.addGuiInUseCounter(this);
+        BackgroundService.addGuiInUseCounter(this, true);
+        BackgroundService.RunCommand(this, new BackgroundService.InstanceCallback() {
+            @Override
+            public void onServiceStart(BackgroundService service) {
+                service.addDeviceListChangedCallback("MaterialActivity", new BackgroundService.DeviceListChangedCallback() {
+                    @Override
+                    public void onDeviceListChanged() {
+                        updateComputerList();
+                    }
+                });
+            }
+        });
+        updateComputerList();
     }
 
     @Override
     protected void onStop() {
         BackgroundService.removeGuiInUseCounter(this);
+        BackgroundService.RunCommand(this, new BackgroundService.InstanceCallback() {
+            @Override
+            public void onServiceStart(BackgroundService service) {
+                service.removeDeviceListChangedCallback("MaterialActivity");
+            }
+        });
         super.onStop();
     }
 
-    @Override
-    protected void onResume() {
-        super.onResume();
-        updateComputerList();
-    }
-
     //TODO: Make it accept two parameters, a constant with the type of screen and the device id in
     //case the screen is for a device, or even three parameters and the third one be the plugin id?
     //This way we can keep adding more options with null plugin id (eg: about)

src/org/kde/kdeconnect/UserInterface/PairingFragment.java

@@ -98,9 +98,10 @@ public class PairingFragment extends Fragment implements PairingDeviceItem.Callb
                     public void run() {
 
                         if (listRefreshCalledThisFrame) {
-                            return; // This makes sure we don't try to call list.getFirstVisiblePosition()
+                            // This makes sure we don't try to call list.getFirstVisiblePosition()
-                                    // twice per frame, because the second time the list hasn't been drawn
+                            // twice per frame, because the second time the list hasn't been drawn
-                                    // yet and it would always return 0.
+                            // yet and it would always return 0.
+                            return;
                         }
                         listRefreshCalledThisFrame = true;
 
@@ -183,9 +184,9 @@ public class PairingFragment extends Fragment implements PairingDeviceItem.Callb
                         updateComputerList();
                     }
                 });
-                service.onNetworkChange();
             }
         });
+        updateComputerList();
     }
 
     @Override
@@ -199,12 +200,6 @@ public class PairingFragment extends Fragment implements PairingDeviceItem.Callb
         });
     }
 
-    @Override
-    public void onResume() {
-        super.onResume();
-        updateComputerList();
-    }
-
     @Override
     public void pairingClicked(Device device) {
         mActivity.onDeviceSelected(device.getDeviceId(), !device.isPaired() || !device.isReachable());