Revised operation handling

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

@@ -0,0 +1,92 @@
+package eu.faircode.email;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.util.Log;
+
+import androidx.appcompat.app.AppCompatActivity;
+import androidx.fragment.app.Fragment;
+import androidx.loader.app.LoaderManager;
+import androidx.loader.content.AsyncTaskLoader;
+import androidx.loader.content.Loader;
+
+public abstract class SimpleLoader {
+    private Context context;
+    private LoaderManager manager;
+
+    public void load(AppCompatActivity activity, int id, Bundle args) {
+        this.context = activity;
+        this.manager = LoaderManager.getInstance(activity);
+        manager.restartLoader(id, args, callbacks).forceLoad();
+    }
+
+    public void load(Fragment fragment, int id, Bundle args) {
+        this.context = fragment.getContext();
+        this.manager = LoaderManager.getInstance(fragment);
+        manager.restartLoader(id, args, callbacks).forceLoad();
+    }
+
+    public Object onLoad(Bundle args) {
+        return null;
+    }
+
+    public void onLoaded(Bundle args, Result result) {
+    }
+
+    private static class CommonLoader extends AsyncTaskLoader<Result> {
+        Bundle args;
+        SimpleLoader loader;
+
+        CommonLoader(Context context) {
+            super(context);
+        }
+
+        void setArgs(Bundle args, SimpleLoader x) {
+            this.args = args;
+            this.loader = x;
+        }
+
+        @Override
+        public Result loadInBackground() {
+            Result result = new Result();
+            try {
+                result.data = loader.onLoad(args);
+            } catch (Throwable ex) {
+                Log.e(Helper.TAG, ex + "\n" + Log.getStackTraceString(ex));
+                result.ex = ex;
+            }
+            return result;
+        }
+    }
+
+    private LoaderManager.LoaderCallbacks callbacks = new LoaderManager.LoaderCallbacks<Result>() {
+        @Override
+        public Loader<Result> onCreateLoader(int id, Bundle args) {
+            CommonLoader loader = new CommonLoader(context);
+            loader.setArgs(args, SimpleLoader.this);
+            return loader;
+        }
+
+        @Override
+        public void onLoadFinished(Loader<Result> loader, Result data) {
+            manager.destroyLoader(loader.getId());
+
+            CommonLoader common = (CommonLoader) loader;
+            onLoaded(common.args, data);
+
+            common.args = null;
+            common.loader = null;
+
+            manager = null;
+        }
+
+        @Override
+        public void onLoaderReset(Loader<Result> loader) {
+        }
+    };
+
+    public static class Result {
+        Throwable ex;
+        Object data;
+    }
+}