Added optional tasks

app/src/main/java/eu/faircode/email/SimpleTask.java

@@ -49,6 +49,7 @@ import java.util.concurrent.Future;
 public abstract class SimpleTask<T> implements LifecycleObserver {
     private boolean log = true;
     private boolean count = true;
+    private boolean optional = false;
 
     private String name;
     private long started;
@@ -78,6 +79,11 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
         return this;
     }
 
+    public SimpleTask<T> setOptional(boolean optional) {
+        this.optional = optional;
+        return this;
+    }
+
     public SimpleTask<T> setExecutor(ExecutorService executor) {
         this.localExecutor = executor;
         return this;
@@ -144,6 +150,15 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
             }
         }
 
+        LifecycleObserver watcher = new LifecycleObserver() {
+            @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
+            public void onDestroy() {
+                EntityLog.log(context, EntityLog.Type.Debug, "Cancelling task=" + name);
+                cancel(context);
+                owner.getLifecycle().removeObserver(this);
+            }
+        };
+
         future = getExecutor(context).submit(new Runnable() {
             private Object data;
             private long elapsed;
@@ -181,7 +196,11 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
                         if (state.equals(Lifecycle.State.DESTROYED)) {
                             // No delivery
                             cleanup(context);
-                        } else if (state.isAtLeast(Lifecycle.State.RESUMED)) {
+                        } else {
+                            if (optional)
+                                owner.getLifecycle().removeObserver(watcher);
+
+                            if (state.isAtLeast(Lifecycle.State.RESUMED)) {
                                 // Inline delivery
                                 Log.i("Deliver task " + name + " state=" + state + " elapse=" + elapsed + " ms");
                                 deliver();
@@ -207,6 +226,7 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
                                 });
                             }
                         }
+                    }
 
                     private void deliver() {
                         try {
@@ -249,6 +269,9 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
             }
         });
 
+        if (optional)
+            owner.getLifecycle().addObserver(watcher);
+
         updateTaskCount(context);
     }
 

app/src/main/java/eu/faircode/email/ViewModelMessages.java

@@ -431,7 +431,7 @@ public class ViewModelMessages extends ViewModel {
                         Log.i("Observe previous/next fallback=" + result);
                         return result;
                     }
-                }.execute(context, owner, args, "model:fallback");
+                }.setOptional(true).execute(context, owner, args, "model:fallback");
             }
         });
     }