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

@@ -144,6 +144,14 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
             }
         }
 
+        LifecycleObserver watcher = new LifecycleObserver() {
+            @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
+            public void onDestroy() {
+                cancel(context);
+                owner.getLifecycle().removeObserver(this);
+            }
+        };
+
         future = getExecutor(context).submit(new Runnable() {
             private Object data;
             private long elapsed;
@@ -181,7 +189,10 @@ 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 {
+                            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 +218,7 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
                                 });
                             }
                         }
+                    }
 
                     private void deliver() {
                         try {
@@ -249,6 +261,8 @@ public abstract class SimpleTask<T> implements LifecycleObserver {
             }
         });
 
+        owner.getLifecycle().addObserver(watcher);
+
         updateTaskCount(context);
     }