android: Simplified handling of error dialog that is displayed if VpnService API is not supported

src/frontends/android/src/org/strongswan/android/ui/MainActivity.java

@@ -46,10 +46,8 @@ import android.widget.EditText;
 public class MainActivity extends Activity implements OnVpnProfileSelectedListener
 {
 	public static final String CONTACT_EMAIL = "[email protected]";
-	private static final String SHOW_ERROR_DIALOG = "errordialog";
 	private static final int PREPARE_VPN_SERVICE = 0;
 
-	private AlertDialog mErrorDialog;
 	private Bundle mProfileInfo;
 
 	@Override
@@ -62,32 +60,10 @@ public class MainActivity extends Activity implements OnVpnProfileSelectedListen
 		ActionBar bar = getActionBar();
 		bar.setDisplayShowTitleEnabled(false);
 
-		if (savedInstanceState != null && savedInstanceState.getBoolean(SHOW_ERROR_DIALOG))
-		{
-			showVpnNotSupportedError();
-		}
-
 		/* load CA certificates in a background task */
 		new CertificateLoadTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, false);
 	}
 
-	@Override
-	protected void onSaveInstanceState(Bundle outState)
-	{
-		super.onSaveInstanceState(outState);
-		outState.putBoolean(SHOW_ERROR_DIALOG, mErrorDialog != null);
-	}
-
-	@Override
-	protected void onDestroy()
-	{
-		super.onDestroy();
-		if (mErrorDialog != null)
-		{	/* avoid any errors about leaked windows */
-			mErrorDialog.dismiss();
-		}
-	}
-
 	@Override
 	public boolean onCreateOptionsMenu(Menu menu)
 	{
@@ -134,7 +110,7 @@ public class MainActivity extends Activity implements OnVpnProfileSelectedListen
 				 * don't have the VPN components built into the system image.
 				 * com.android.vpndialogs/com.android.vpndialogs.ConfirmDialog
 				 * will not be found then */
-				showVpnNotSupportedError();
+				new VpnNotSupportedError().show(getFragmentManager(), "ErrorDialog");
 			}
 		}
 		else
@@ -180,25 +156,6 @@ public class MainActivity extends Activity implements OnVpnProfileSelectedListen
 		}
 	}
 
-	/**
-	 * Show an error dialog if case the device lacks VPN support.
-	 */
-	private void showVpnNotSupportedError()
-	{
-		mErrorDialog = new AlertDialog.Builder(this)
-			.setTitle(R.string.vpn_not_supported_title)
-			.setMessage(getString(R.string.vpn_not_supported))
-			.setCancelable(false)
-			.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
-				@Override
-				public void onClick(DialogInterface dialog, int id)
-				{
-					mErrorDialog = null;
-					dialog.dismiss();
-				}
-			}).show();
-	}
-
 	/**
 	 * Class that loads or reloads the cached CA certificates.
 	 */
@@ -263,4 +220,27 @@ public class MainActivity extends Activity implements OnVpnProfileSelectedListen
 			return adb.create();
 		}
 	}
+
+	/**
+	 * Class representing an error message which is displayed if VpnService is
+	 * not supported on the current device.
+	 */
+	public static class VpnNotSupportedError extends DialogFragment
+	{
+		@Override
+		public Dialog onCreateDialog(Bundle savedInstanceState)
+		{
+			return new AlertDialog.Builder(getActivity())
+				.setTitle(R.string.vpn_not_supported_title)
+				.setMessage(getString(R.string.vpn_not_supported))
+				.setCancelable(false)
+				.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
+					@Override
+					public void onClick(DialogInterface dialog, int id)
+					{
+						dialog.dismiss();
+					}
+				}).create();
+		}
+	}
 }