Changed activity creation logic

- for home activity it will reuse existing activity from back stack and
  also clears all current activities
- for nearby, about and settings, it will use the existing activity from
  back stack

app/src/main/java/fr/free/nrw/commons/AboutActivity.java

@@ -27,9 +27,4 @@ public class AboutActivity extends NavigationBaseActivity {
         versionText.setText(BuildConfig.VERSION_NAME);
         initDrawer();
     }
-
-    public static void startYourself(Context context) {
-        Intent settingsIntent = new Intent(context, AboutActivity.class);
-        context.startActivity(settingsIntent);
-    }
 }

app/src/main/java/fr/free/nrw/commons/auth/LoginActivity.java

@@ -30,6 +30,7 @@ import fr.free.nrw.commons.R;
 import fr.free.nrw.commons.Utils;
 import fr.free.nrw.commons.WelcomeActivity;
 import fr.free.nrw.commons.contributions.ContributionsActivity;
+import fr.free.nrw.commons.theme.NavigationBaseActivity;
 import timber.log.Timber;
 
 import static android.view.KeyEvent.KEYCODE_ENTER;
@@ -176,7 +177,7 @@ public class LoginActivity extends AccountAuthenticatorActivity {
     }
 
     public void startMainActivity() {
-        ContributionsActivity.startYourself(this);
+        NavigationBaseActivity.startActivityWithFlags(this, ContributionsActivity.class, Intent.FLAG_ACTIVITY_CLEAR_TOP);
         finish();
     }
 

app/src/main/java/fr/free/nrw/commons/contributions/ContributionsActivity.java

@@ -343,9 +343,4 @@ public class ContributionsActivity extends AuthenticatedActivity
     public void refreshSource() {
         getSupportLoaderManager().restartLoader(0, null, this);
     }
-
-    public static void startYourself(Context context) {
-        context.startActivity(new Intent(context, ContributionsActivity.class));
-    }
-
 }

app/src/main/java/fr/free/nrw/commons/nearby/NearbyActivity.java

@@ -350,9 +350,4 @@ public class NearbyActivity extends NavigationBaseActivity {
         fragmentTransaction.replace(R.id.container, fragment);
         fragmentTransaction.commitAllowingStateLoss();
     }
-
-    public static void startYourself(Context context) {
-        Intent settingsIntent = new Intent(context, NearbyActivity.class);
-        context.startActivity(settingsIntent);
-    }
 }

app/src/main/java/fr/free/nrw/commons/settings/SettingsActivity.java

@@ -54,9 +54,4 @@ public class SettingsActivity extends NavigationBaseActivity {
                 return super.onOptionsItemSelected(item);
         }
     }
-
-    public static void startYourself(Context context) {
-        Intent settingsIntent = new Intent(context, SettingsActivity.class);
-        context.startActivity(settingsIntent);
-    }
 }

app/src/main/java/fr/free/nrw/commons/theme/NavigationBaseActivity.java

@@ -3,6 +3,7 @@ package fr.free.nrw.commons.theme;
 import android.accounts.Account;
 import android.accounts.AccountManager;
 import android.content.ActivityNotFoundException;
+import android.content.Context;
 import android.content.Intent;
 import android.support.annotation.NonNull;
 import android.support.design.widget.NavigationView;
@@ -95,31 +96,21 @@ public abstract class NavigationBaseActivity extends BaseActivity
         switch (itemId) {
             case R.id.action_home:
                 drawerLayout.closeDrawer(navigationView);
-                if (!(this instanceof ContributionsActivity)) {
+                startActivityWithFlags(
-                    ContributionsActivity.startYourself(this);
+                        this, ContributionsActivity.class, Intent.FLAG_ACTIVITY_CLEAR_TOP,
-                    this.finish();
+                        Intent.FLAG_ACTIVITY_SINGLE_TOP);
-                }
                 return true;
             case R.id.action_nearby:
                 drawerLayout.closeDrawer(navigationView);
-                if (!(this instanceof NearbyActivity)) {
+                startActivityWithFlags(this, NearbyActivity.class, Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
-                    NearbyActivity.startYourself(this);
-                    this.finish();
-                }
                 return true;
             case R.id.action_about:
                 drawerLayout.closeDrawer(navigationView);
-                if (!(this instanceof AboutActivity)) {
+                startActivityWithFlags(this, AboutActivity.class, Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
-                    AboutActivity.startYourself(this);
-                    this.finish();
-                }
                 return true;
             case R.id.action_settings:
                 drawerLayout.closeDrawer(navigationView);
-                if (!(this instanceof SettingsActivity)) {
+                startActivityWithFlags(this, SettingsActivity.class, Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
-                    SettingsActivity.startYourself(this);
-                    this.finish();
-                }
                 return true;
             case R.id.action_introduction:
                 drawerLayout.closeDrawer(navigationView);
@@ -170,4 +161,12 @@ public abstract class NavigationBaseActivity extends BaseActivity
             finish();
         }
     }
+
+    public static <T> void startActivityWithFlags(Context context, Class<T> cls, int... flags) {
+        Intent intent = new Intent(context, cls);
+        for (int flag: flags) {
+            intent.addFlags(flag);
+        }
+        context.startActivity(intent);
+    }
 }