Tuesday, May 8, 2018

Android Studio and Cannot Resolve Symbol 'R'

It is one of the error message that appears as Android Studio is used more frequently is,

Cannot resolve symbol 'R'

In the source code, it will show all usage of R as red in colour.

From what I know, here are two situations that cause this error to appear.
  1. Copy of a source file into the project. This include copying of Modules from another existing project.
  2. During one of the build, there was a problem


 This is how I did it on Android Studio 3.1.2.

Step 1: Rebuild the project.

Open the Java files that was just copied or the problematic files. Remove any reference of import to the 'R'. In the manifest/AndroidManifest.xml, correct the package name if it is not the same as the current project.

On the Menu bar click Build ->Clean Project.

Step 2: Sync files in the project.

On the Menu bar click Files ->Sync Project with Gradle Files. Close and restart Android Studio.

This will solve the error on most cases. However, if there are still any errors, gradle will not be able to update with the rectified pointer to R references. Read the list of errors as it will indicate the problem areas that you can easily rectify. Once you have fixed the error, or in my case most of the time I just delete them, just repeat Step 1.

Works all the time.

Wednesday, April 18, 2018

Create a Fragment App with Android Studio 3.1

This is a follow up from my previous Android Fragments in an Activity.

This example, demonstrates how Fragments are created and loaded by an Activity class. Android Studio 3.1.1 is the IDE with Java 1.8.0 and an emulator is created with API 23. All this is running on Centos 7.

Step 1: Create an Empty project with vertical orientation

Open Android Studio and create a new project.
Application name: My Fragment
Click Next

Click Checked for Phone and Tablet
Minimum SDK: choose API 23:Android 6.0 (Marshmallow)
Click Next

Choose "Basic Activity"
Click Next

Activity Name: MainActivity
Layout Name: activity_main
Title: MainActivity

Click checked Use a Fragment

Click "Finish"

This will provide a template to quickly create the rest of Fragments to be used with this Activity.

A total of 23 files are created in the app/src/main folder. By the time all steps are completed, there should be 29 files created in app/src/main folder.
=== Listing of 25 files at start of the project===
Project Structure of application - Newly create project

A default project contains the following layouts
  • CoordinatorLayout
    • AppBarLayout
    • Toolbar
    • an include layout tag
    • FloatingActionButton
  • ConstraintLayout 
  • TextView.
Edit the layout/activity_main.xml
In the CoordinatorLayout tag, insert following line before tools:context


Step 2: Add the buttons

Edit the file values/strings.xml and add within the <resources> tag

<string name="digital">Digital</string>
<string name="analog">Analog</string>

<string name="textclock">Text Clock</string>

Edit content_main.xml and remove the whole TextView tag. Replace with 2 buttons where you can just drag and drop the buttons from the widget list. Add a FrameLayout where we will position our Fragment layouts. Edit the button code as follows




Let build and run the project.

Click the Run App button (green play button) or press Shift+F10. I am using an API 23 emulator for my test applications. Create the Android emulator if it is not done yet.

Step 3: Create Analog Fragment

Click File ->New ->Fragment ->Fragment (Blank). Fill following values
Fragment Name: AnalogFragment
Fragment Layout Name: fragment_analog

Leave all other options checked.
Click Finish

In AnalogFragment.java, replace import android.support.v4.app.Fragment with

import android.app.Fragment;

I plan to provide support only to Android API 23 and above.

Lets explore the Design editor.
Edit layout/fragment_analog.xml and click the tab Design. Notice that the default is FrameLayout.

On the left is the Palette, in the middle is the screen design + blueprint, on the right is the Attributes list. In the Design area, click the menu to choose API 23. Right click any where on the design and choose Convert FrameLayout to ConstraintLayout. Click "Ok".

Delete the default TextView in the design.

From the Palette, notice there is no AnalogClock which means it will have to be manually added. Click the Text tab and insert the following



Step 4: Connect MainActivity with Analog Fragment

I have broken down the steps further in this step. Edit MainActivity class.

1. Add following member variables

Button analogButton;

2. Edit protected void onCreate(Bundle savedInstanceState), add after the line setSupportActionBar(toolbar)

analogButton = (Button) findViewById(R.id.button_analog);

There should be a wriggly red line at the text "this", click once then press Alt+Enter. Choose "Make MainActivityFragment implement android,view.View.OnClickListener". Choose "onClick(v:View):void" and press "OK".

3. Add onClick(View v) method
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
        f = new AnalogFragment();
transaction.replace(R.id.fragment_container, f);


4. Edit the class declaration with the AnalogFragment

public class MainActivity extends AppCompatActivity implements View.OnClickListener,
        AnalogFragment.OnFragmentInteractionListener  {

Implement AnalogFragment's OnFragmentInteractionListener, add the method near the end of the class.

public void onFragmentInteraction(Uri uri) {

Compile and run.

Step 5: Create Digital Fragment

Repeat steps 3 and 4 above but change the Analog to Digital. Below is the code to display a digital clock



Step 6: Create TextClock Fragment

Repeat steps 3 and 4 above but change the Analog to TextClock. Below is the code to display a digital clock

    android:format12Hour="HH:MM:ss EEEE"
    android:format24Hour="EE H:mm:ss"


Here is the complete source code for MainActvity.java

1:  package com.example.nicholas.myfragment;  
2:  import android.app.Fragment;  
3:  import android.app.FragmentManager;  
4:  import android.app.FragmentTransaction;  
5:  import android.net.Uri;  
6:  import android.os.Bundle;  
7:  import android.support.design.widget.FloatingActionButton;  
8:  import android.support.design.widget.Snackbar;  
9:  import android.support.v7.app.AppCompatActivity;  
10:  import android.support.v7.widget.Toolbar;  
11:  import android.view.View;  
12:  import android.view.Menu;  
13:  import android.view.MenuItem;  
14:  import android.widget.Button;  
15:  public class MainActivity extends AppCompatActivity implements View.OnClickListener,  
16:      AnalogFragment.OnFragmentInteractionListener, DigitalFragment.OnFragmentInteractionListener,  
17:      TextClockFragment.OnFragmentInteractionListener {  
18:    Button analogButton, digitalButton, textClockButton;  
19:    Fragment f;  
20:    @Override  
21:    protected void onCreate(Bundle savedInstanceState) {  
22:      super.onCreate(savedInstanceState);  
23:      setContentView(R.layout.activity_main);  
24:      Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);  
25:      setSupportActionBar(toolbar);  
26:      analogButton = (Button) findViewById(R.id.button_analog);  
27:      analogButton.setOnClickListener(this);  
28:      digitalButton = (Button) findViewById(R.id.button_digital);  
29:      digitalButton.setOnClickListener(this);  
30:      textClockButton = (Button) findViewById(R.id.button_textclock);  
31:      textClockButton.setOnClickListener(this);  
32:      FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);  
33:      fab.setOnClickListener(new View.OnClickListener() {  
34:        @Override  
35:        public void onClick(View view) {  
36:          Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)  
37:              .setAction("Action", null).show();  
38:        }  
39:      });  
40:    }  
41:    @Override  
42:    public boolean onCreateOptionsMenu(Menu menu) {  
43:      // Inflate the menu; this adds items to the action bar if it is present.  
44:      getMenuInflater().inflate(R.menu.menu_main, menu);  
45:      return true;  
46:    }  
47:    @Override  
48:    public boolean onOptionsItemSelected(MenuItem item) {  
49:      // Handle action bar item clicks here. The action bar will  
50:      // automatically handle clicks on the Home/Up button, so long  
51:      // as you specify a parent activity in AndroidManifest.xml.  
52:      int id = item.getItemId();  
53:      //noinspection SimplifiableIfStatement  
54:      if (id == R.id.action_settings) {  
55:        return true;  
56:      }  
57:      return super.onOptionsItemSelected(item);  
58:    }  
59:    @Override  
60:    public void onClick(View v) {  
61:      FragmentManager manager = getFragmentManager();  
62:      FragmentTransaction transaction = manager.beginTransaction();  
63:      if(v==analogButton){  
64:        f = new AnalogFragment();  
65:      } else if (v==digitalButton){  
66:        f = new DigitalFragment();  
67:      } else if (v==textClockButton) {  
68:        f = new TextClockFragment();  
69:      }  
70:      transaction.replace(R.id.fragment_container, f);  
71:      transaction.commit();  
72:    }  
73:    @Override  
74:    public void onFragmentInteraction(Uri uri) {  
75:      //  
76:    }  
77:  }  


Tuesday, April 17, 2018

Upgrade Android Studio to 3.1

New in Android Studio v3.1.1 on Stable channel are
  • For those who use C++, there is a CPU performance profiler that troubleshoot codes with the  simpleperf tool. 
  • Better lint support to check quality of codes for Kotlin (an alternative JAVA language). From the command line, lint can be accessed with the tool gradlew lint.
  • Improved  SQLite's and Room's table query and creation.
  • The default compiler uses D8 dexer which have the capability to make codes much smaller and more accurate step debugging.
  • Improved build output window to trace errors in a tree view.
  • Upgrade to the IntelliJ Idea 3.3 platform. This is the base platform of which Android Studio IDE is built.
  • Improved network profiler to trace network request on multi-threaded traffic.
The new version patch size is 456MB. Can hardly spot any difference from previous versions but its running much more smoother.

Android Studio 3.1.1 Workspace

Here is the current PC setup
  • Android Studio version: 3.0.1 (build 171.4443003) 
  • Centos 7.4 (64 bits) Linux 3.10.0 x86_64 amd64
  • OpenJDK 64-bit v1.8.0_161
  • Gradle 4.3.1
  • Apache Ant 1.9.6

This is how I upgraded to Android Studio 3.1.1

Check for updates

Canary or Stable channels can be check with the following steps.
Open Android Studio menu and click File ->Settings ->Preferences. On left panel choose Appearance & Behavoir ->System Setting ->Updates. Choose the Stable Channel from Automatically check updates for.

Click Check Now. This should retrieve latest update on the Stable Channel.

Step 1: Update Android Studio

Choose to update from the popup window when Android Studio is open.

Do the steps above if you have not retrieved the updates information. Click Update and Restart.

Alternatively, at the bottom of the Android Studio start page, click "Check" if you do not find the update option.

Once update starts, this will begin with download of the required files.

Step 2: Configuration

After it has installed the update, choose to import my settings from a previous version (keep existing configuration) from the window Import Studio Settings from: choose the option below and click "Ok"

Previous version (~/.AndroidStudio3.0/config)

Step 3: Update Plugin and other components

Close all emulators then open an existing project. This will have the usual build checks, once the gradle has started processing, the following window will appear.

Click Update to update Android Gradle Plugin to version 3.1.1 and Gradle to version 4.4. Wait until the Gradle project sync in progress... is completed.

At the window IDE and Plugin Updates, click "update". To update currently installed SDK and it tools, click "Update now".

Once completed download, click Finish. In my case it took 1.5GB of downloads.

Next up: Will write on creating a Fragment type application with Android Studio 3.1.

Friday, April 13, 2018

Howto Install Evernote on Linux Mint

One of the tools to capture my notes on a PC and Android mobile device is Evernote. Searching online today, it is clear that Evernote is not available on Linux (Mint), however it has been implied that their API is sufficient for anyone to develop a version of Evernote (Evernote on Linux). This means no Evernote application on Linux. Good news for the Linux community as the API documentations are available at https://dev.evernote.com/

Nixnote by baumgarr provides you access to Evernote on Linux Mint along with a user manual in PDF. Download the version suitable for you at https://sourceforge.net/projects/nevernote/files

Nixnote2 on Linux Mint

My set up (inxi -S)
Kernel: 4.10.0-38-generic x86_64 (64 bit)
Distro: Linux Mint 18.3 Sylvia
Desktop: Cinnamon 3.6.7

Step 1: Download nixnote

Locate the file online from Sourceforge and download. The file I downloaded to my Download folder is


Step 2: Install from command prompt

$ cd ~/Download
$ sudo apt install ./nixnote2-2.0.2_amd64.deb
$ apt install libcurl3 libcurl3-nss

This installed the dependency packages libcurl3, libpoppler-qt5-1 and tidy.

Troubleshoot: Error

QSqlDatabase: QSQLITE driver not loaded
QSqlDatabase: available drivers:
ERROR 2018-04-13 00:50:37.788 ( sql/databaseconnection.cpp @ 44 ) Error opening database:  QSqlError(-1, "Driver not loaded", "Driver not loaded")

Solution: At CLI type

$ apt install lua5.2-sql-sqlite3
$ apt install libqt4-sql-sqlite

Step 3: Run Nixnote

At the Desktop Menu ->Internet ->Nixnote2

Troubleshoot: Nothing appears after click Nixnote2.

At CLI the error shows:

nixnote2: error while loading shared libraries: libpoppler-qt4.so.4: cannot open shared object file: No such file or directory

Solution: Open CLI and type

$ apt install libpoppler-qt4-4
$ nixnote2


Once its started, Click in the menu File ->Add another user. Key in your new user name.
Click File ->User Account Maintenance. Choose the new user.
Click Tools ->Synchronised

Wait for it to download from Evernote.

Friday, March 16, 2018

VNC Troubleshoot Cannot access vdagent virtio channel /dev/virtio-ports/

On Centos 7, the vncserver started for each service is able to launch and users can login remotely. Within 1 minute, this service crashes and the usual command (see below) to start the vncserver fails.

$ sudo systemctl start vncserver@:1

The reason for this failure is capture in the command;

$ sudo systemctl status vncserver@:1

There were 2 items to take note,
  1. Users were launching the vncviewer almost immediately upon the server boot up.
  2. The following error appears "Cannot access vdagent virtio channel /dev/virtio-ports/" upon checking the status.

Whats on the Linux?

Centos Linux version 7.4.1708 (Core)
Tigervnc version 1.8.0

Spice [reference Fedora]

Spice aims to provide a complete open source solution for interaction with virtualized desktop.  The Simple Protocol for Independent Computing Environments (SPICE) is used for client-server communication. Spice adds a QXL display device to QEMU and provides drivers for this device for both X and Windows. It also provides a Spice server and VDAgent to handle connections and transmit the information via the SPICE protocol to clients. The Spice project provides a Linux, Windows, and HTML5 client. There are experimental Mac OS X and Android clients as well.

This /dev/virtio-ports is created in this feature that modifies the current single-port virtio-console device to guests running on top of qemu and kvm. It exposes multiple ports to the guest in the form of simple char devices for simple IO between the guest and host userspaces. It also allows for multiple such devices to be exposed, lifting the current single device restriction.

Somehow, these were installed on the server.

$ rpm -qa \*spice\*

The RPM documentation on spice-vdagent states
"* Client mouse mode (no need to grab mouse by client, no mouse lag)
this is handled by the daemon by feeding mouse events into the kernel via uinput. This will only work if the active X-session is running a spice-vdagent process so that its resolution can be determined.
* Automatic adjustment of the X-session resolution to the client resolution
* Support of copy and paste (text and images) between the active X-session and the client"

I make an assumption that if no virtualisations are needed on the server, its a matter of deleting these packages. However, I have an Android Emulator that have dependency on the virtio-ports. Its still a question mark if VNC depends on spice-vdagent.


Step 1. Start SPICE agent.

At the command line on the host server, start the spice agent.
$ sudo systemctl start spice-vdagentd.service

Check and ensure that this service runs at boot up.
$ sudo systemctl show spice-vdagentd |grep enable

Step 2. Give host server time

Allow the Linux server to fully boot up all processed before attempting to start a VNC client session.


Monday, March 12, 2018

Laravel 5 and Error key was too long

The server was running PHP applications without any fuss, everyone is happy on this 12th March 2018. Laravel 5 came in that one day and a simple application was launched to show the default Laravel welcome screen. The next step was to create a CRUD application with storage to the local database.

A Model is created of a simple Task object. The room fell silence after the command, php artisan migrate

SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes (SQL: alter table users add unique users_email_uniq(email))

What was wrong? Never mind that, lets see whats on the server!

  • Centos version 7.4.1708
  • Apache httpd  version Apache/2.4.6 (CentOS)
  • Mariadb (MySQL fork) version 5.5.56-MariaDB
  • PHP version 7.2.2 (cli) with Zend Engine v3.2.0
  • Laravel 5.6.7
  • Composer versioon 1.6.3
  • npm version 3.10.10

All of above are tested and working on its own. Going back to analyse the error, its database related. The respective tables of migrate, users were generated in the database, but the new model "task" isn't.The related code is in the file <laravel5>/database/migrations/2014_10_12_000000_create_users_table.php

On the database side, changed Collation to utf8mb4_unicode_ci but the error is still there. This is a 4-byte UTF-8 Unicode Encoding and as described in MySQL 5.5, it is
  1. In UTF8 it uses 3 bytes per character, containing only BMP characters. Utf8mb4 supports maximum 4 bytes per character and includes supplementary characters. 
  2. Utf8mb4 is a superset of Utf8.
  3. To save space, utf8mb4 is to use VARCHAR instead of CHAR type for BMP characters. 
 Changing a table from utf8 to utf8mb4 can be done with
ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

ALTER TABLE `users` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;


Make the whole Laravel application and the database server utf8mb4 aware.

Step 1. Edit file  <laravel5>/config/database.php

'charset' => 'utf8mb4',
'collation' => 'utf8mb4_unicode_ci',
'engine' => 'InnoDB ROW_FORMAT=DYNAMIC',
DYNAMIC allows to store of long key indexes.

Step 2.  Edit file /etc/my.cnf

# default character set and collation
collation-server = utf8mb4_unicode_ci
character-set-server = utf8mb4

# utf8mb4 long key index
innodb_large_prefix = 1
innodb_file_format = barracuda
innodb_file_format_max = barracuda
innodb_file_per_table = 1

 Step 3. Edit file /etc/my.cnf.d/client.cnf


Step 4. Restart database server

Stop then start the database server with

$ sudo systemctl stop mysqld
$ sudo systemctl start mysqld


Points to note

The error states maximum key length is 767 bytes for the email field. In Laravel 5 the migration file for "Users" declared a string that gets created in the Mariadb database. Problem in question is adding the "unique" string that get generated in the database "Users" for field "email" with type VARCHAR(255) and collation utf8mb4. MySQL has to actually index the whole value to complete the operation. This calculates to give maximum size of

255 characters x 4 bytes = 1,020 bytes (MAXIMUM BYTES)

This looks like sufficient space, but why the error?
When Laravel writes/reads data to MySQL, it utilises a call to the local MySQL client/server that takes this as default of uf8 which is having maximum 3 bytes per character (due to the mysql default client/server settings). A little bit of calculation gives

255 characters x 3 bytes = 765 bytes (MAXIMUM BYTES)

In the above solution, there is access to modify the database configurations. What if you do not have such an access? The solution is to reduce the default string length sent by Laravel. Taking 191 as maximum characters, we get

191 characters x 4 bytes = 764 bytes

Edit file <laravel5>/app/Providers/AppServiceProvider.php

Add after the "use .... \ServiceProvider;"
use Illuminate\Support\Facades\Schema;

Add in the "public function boot( )"

Save and from the project's main folder, run migration
$ php artisan migrate

Alternatively, changed the field "email" that was declared unique to collation "utf8". It worked for me, but some people have mentioned it didn't work for them.


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