Last updated: Saturday 22nd September 2018, 7:30 PT, AD
Contents Android Developer Fundamentals - Videos Installing Android Studio
Running Android Studio
Android Developer Guide
My Android Blog
Android Studio 3.1.x — How to fix it
What is an Android app?
Check out an existing Android app from Version Control (GitHub)
How to copy an existing Android project to a new project (ALWAYS: File -> Sync Project with Gradle Files before running app!)
Intents and Intent Filters
What happens when you click on an app's launch icon?
Android Activity Lifecycle
What is a View?
How to show the bounds of layouts in an app
Using different branches of app code stored on GitHub (Git)
Images for different resolutions and devices
Convert text to mp3 to make audio resource file
Save data using SQLite
MySQL for reference
Run a command script in sqlite3
Create an SQLite database and table and populate with data from text file (in csv format)
Create an SQLite database from a text file
Create an SQLite database using DB Browser for SQLite
Writing the result of an SQLite query to a text file
SQLite Primary key and other Constraints
Android Content Provider
More learning resources...
What is an Android app? Android Developer Fundamentals - Videos An Android app is a software application running on the Android platform. In other words, an Android app is a small program that runs on your Android phone or tablet. You may have an app for online banking, an app for emailing. You can download many free apps from the Google Play Store. Watch the video below to see a running app... Because the Android platform is built for mobile devices, a typical Android app is designed for a smartphone or a tablet PC running on the Android OS. Android apps can be written using Kotlin, Java, and C++ languages. The Android SDK tools compile your code along with any data and resource files into an APK, an Android package. The Android package is an archive file with an .apk suffix. One APK file contains all the contents of an Android app and is the file that Android-powered devices use to install the app. Each Android app lives in its own security sandbox, protected by the following Android security features: The Android operating system is a multi-user Linux system in which each app is a different user. By default, the system assigns each app a unique Linux user ID (the ID is used only by the system and is unknown to the app). The system sets permissions for all the files in an app so that only the user ID assigned to that app can access them. Each process has its own virtual machine (VM), so an app's code runs in isolation from other apps. By default, every app runs in its own Linux process. The Android system starts the process when any of the app's components need to be executed, and then shuts down the process when it's no longer needed or when the system must recover memory for other apps. The Android system implements the principle of least privilege. That is, each app, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an app cannot access parts of the system for which it is not given permission. However, there are ways for an app to share data with other apps and for an app to access system services... Reference Another Developer Guide Android Tutorial 1 Android Tutorial 2
Check out an existing Android app
from Version Control (GitHub) Go to the GitHub project you want to clone, click on the "Clone or Download" button, copy the URL shown in the GitHub textbox... then open Android Studio and from the first screen click on "Check out an existing Android app from Version Control" and select "GitHub" from the list of version controls... Paste in the URL copied from GitHub. The Parent Directory and Directory Name boxes should be automatically filled in for you. Then click on the Clone button at the bottom of the screen... Click on "Yes" on the following screen... Click on "OK" on the following screen... IMPORTANT: If you are presented with the "Edit configuration" window shown below, click on the "Update Project" link, then "Run". Using the method above, clone and open the GitHub project: ud839_CustomAdapter_Example and study the files while reading the following...
AndroidManifest.xml Every app project must have an AndroidManifest.xml file (with precisely that name) at the root of the project source set. If you're using Android Studio to build your app, the manifest file is created for you, and most of the essential manifest elements are added as you build your app (especially when using code templates). The manifest file describes essential information about your app to the Android build tools (Gradle), the Android operating system, and Google Play. Examples of types of information stored are values for app: icon, label, theme and main activity. For each app component that you create in your app, you must declare a corresponding XML element in AndroidManifest.xml: e.g. Activity, Service, BroadcastReceiver or ContentProvider... Merge multiple manifest files Your APK file can contain just one AndroidManifest.xml file, but your Android Studio project may contain several—provided by the main source set, build variants, and imported libraries. So when building your app, the Gradle build merges all manifest files into a single manifest file that's packaged into your APK. The manifest merger tool combines all XML elements from each file by following some merge heuristics and by obeying merge preferences that you have defined with special XML attributes. Reference
Intents and Intent Filters An intent starts an activity, a service or a broadcast. 1. Starting an activity An activity represents a single screen in an app. You can start a new activity by passing an intent to startActivity(), e.g. startActivity(numbersIntent); The intent describes the activity to start and carries any necessary data. If you want to receive a result from the activity when it finishes, call startActivityForResult(). Your activity receives the result as a separate Intent object in your activity's onActivityResult() callback. For more information, see the Activities guide. 2. Starting a service A Service is a component that performs operations in the background without a user interface. 3. Starting a broadcast A broadcast is a message that any app can receive. The system delivers various broadcasts for system events, such as when the system boots up or the device starts charging. You can deliver a broadcast to other apps by passing an Intent to sendBroadcast() or sendOrderedBroadcast(). Figure 1. How an implicit intent is delivered through the system to start another activity:  Activity A creates an Intent with an action description and passes it to startActivity().  The Android System searches all apps for an intent filter that matches the intent. When a match is found,  the system starts the matching activity (Activity B) by invoking its onCreate() method and passing it the Intent. Sometimes the intention is to start an activity such as displaying a web page at a certain URL. Such an activity will require a URI, a URL or a URN. How an explicit intent is delivered through the system to start another activity:
// Executed in an Activity, so 'this' is the Context (i.e. scope of the activity) // The fileUrl is a string URL, such as "http://www.example.com/image.png" Intent downloadIntent = new Intent(this, DownloadService.class); downloadIntent.setData(Uri.parse(fileUrl)); startService(downloadIntent);Reference
What happens when you click on an app's launch icon? In Android, the launcher is your phone's home screen - the screen where you launch your apps... the icon launcher (ic_launcher.png) is the icon you click on to launch the app... Launcher app calls startActivity() with an intent (as defined in the AndroidManifest.xml file). [action = Intent.ACTION_MAIN, category = Intent.CATEGORY_LAUNCHER flag = Intent.FLAG_ACTIVITY_NEW_TASK]. Regarding Intent.FLAG_ACTIVITY_NEW_TASK from docs: When using this flag, if a task is already running for the activity you are now starting, then a new activity will not be started; instead, the current task will simply be brought to the front of the screen with the state it was last in. Reference What happens at launch time? What happens when you start an app?
Android Activity Lifecycle Activity Lifecycle Google created the following figure showing the Android activity lifecycle the methods related to every transition. In most cases you would need to take care only about things that happen at the beginning in onCreate(). The Android system takes care about the rest. An application might consist of just one activity - or it may contain several. Typically, one of the activities is marked as the first one that should be presented to the user when the application is launched. This information is contained in the manifest file. Moving from one activity to another is accomplished by having the current activity start the next one.
What is a View? Views, Layouts and Resources Common Android Views - Cheat Sheet pdf View objects are the basic building blocks of User Interface(UI) elements in Android. A view is a screen on your phone. View is a simple rectangle box which responds to the user's actions. Examples are TextView, EditText, ImageView, Button, CheckBox etc.. View refers to the android.view.View class, which is the base class of all UI classes. View class represents the basic building block for user interface components. A View occupies a rectangular area on the screen and is responsible for drawing and event handling. View is the base class for widgets, which are used to create interactive UI components such as buttons, text fields, etc. View (TextView) A user interface element that displays text to the user. To provide user-editable text, see EditText. View (ImageView) Displays image resources, for example Bitmap or Drawable resources. ImageView is also commonly used to apply tints to an image and handle image scaling. View (EditText) A user interface element that allows user-editable text. View (Button) View (CheckBox) A checkbox is a specific type of two-states button that can be either checked or unchecked. View (ViewGroup) is an invisible container. It holds Views and ViewGroups. For example, LinearLayout is the ViewGroup that contains other views such as Button views, TextViews and other Layouts. LinearLayout is a layout that arranges other views either horizontally in a single column or vertically in a single row. ViewGroup is the base class for Layouts. A ViewGroup is a special view that can contain other views (called children.) The view group is the base class for layouts and views containers. This class also defines the ViewGroup.LayoutParams class which serves as the base class for layouts parameters. View (ListView) displays a vertically-scrollable collection of views, where each view is positioned immediately below the previous view in the list. For a more modern, flexible, and performant approach to displaying lists, use RecyclerView. A ListView object is an adapter view that does not know the details, such as type and contents, of the views it contains. Instead a ListView object requests views on demand from a ListAdapter as needed, such as to display new views as the user scrolls up or down. Android Layouts are made from Views Android's res/layout/activity_main.xml is the layout for the main activity of the app. You can view the text of the layout files and see the Preview at the same time by clicking the Preview tab on the right hand side of the Android Studio screen when a layout file is currently in view... The LinearLayout class The ConstraintLayout class The ConstraintLayout view container is the preferred ViewGroup for performance reasons. Mastering the ConstraintLayout
How to show the bounds of layouts in an app On your phone or tablet, go to Settings -> Developer Options -> Show Layout Bounds
Using different branches of app code stored on GitHub (Git) This is assuming that Git is installed and an account on GitHub is current. To import a project branch from GitHub into Android Studio, this is one method that works for me: at the very bottom line of any Android Studio screen, on the right hand side shows a link to all git branches available at the GitHub repository for the current app... On the very bottom line on screen above you will see the word "Git:"... Click on the word Git: at the bottom right of the screen Simply select the branch you want to import into Android Studio. IMPORTANT NOTE WHEN IMPORTING A GITHUB BRANCH The code will run on your device, however you may notice that the AppCompatActivity class is highlighted in red in MainActivity.java with the error: 'Cannot resolve symbol AppCompatActivity'. There may be other symbols that are highlighted in red. This means that the current project is out of sync with the Gradle files. To correct this, from Android Studio, simply click on the main File menu then select: "Sync Project with Gradle Files".
Images for different resolutions and devices
SQLite SQL is query language. Sqlite is embeddable relational database management system. Unlike other databases (like SQL Server and MySQL) SQLite does not support stored procedures. SQLite is file-based, unlike other databases, like SQL Server and MySQL which are server-based. Save data using SQLite
SQLite comes with the Android SDK and is located in /tools folder of your install. You can add this folder to your PATH variable and thus open a database file from every command prompt. Remember that there are some older Android ROMs which don't come with an SQLite Editor installed. You would have to install SQLite manually in that case. Working with databases from within your app should work seemlessly as it's a basic feature of the Android OS. The following is a very useful tutorial on how to make an app to create a database and store to the database data entered on screen: All code is there so I suggest try it: Android Studio example app using SQLite. Use
sqlite3to inspect Android Studio databases from the command line. anne@Inspiron-15R:~$ sqlite3 SQLite tutorial
Run a command script in sqlite3 Execute SQL statements from a file Suppose we have a file named commands.txt in the c:/sqlite/ folder with the following content: SELECT albumid, title FROM albums ORDER BY title LIMIT 10; To execute the SQL statements in the commands.txt file, you use the .read FILENAME command as follows: sqlite> .mode column sqlite> .read c:/sqlite/commands.txt 156 ...And Justice For All 257 20th Century Masters - 296 A Copland Celebration, 94 A Matter of Life and D 95 A Real Dead One 96 A Real Live One 285 A Soprano Inspired NOTE: The above is taken from: sqlitetutorial.net/sqlite-commands
Create an SQLite database and table and populate with data from text file (in csv format) If you want to delete any previous questions.db database, simply navigate to the file on your file system, and delete the file. To open the database questions.db (or create a new one if it doesn't aleady exist)...
anne@Inspiron-15R:~$ sqlite3 questions.dbIf you put the following code in a text file (e.g. commands.txt), then you can execute the textfile commands through sqlite3 by following the instructions shown below the code.
CREATE TABLE questions_mc ( question_id integer, question_text text , answer_1 text NOT NULL, answer_2 text NOT NULL, answer_3 text NOT NULL, answer_4 text NOT NULL, correct_answer text NOT NULL, category text NOT NULL, difficulty text NOT NULL );Note that questions.csv is a simple text file saved with the extension .csv and has comma separated values. This is the contents of questions.csv
1,What is the data type of the following value: 3.142,string,boolean,float,int,float,data types,easy 2,What is the data type of the following value: 3,string,boolean,float,int,float,data types,easysqlite> .read commands.txt sqlite> .mode csv sqlite> .import questions.csv questions_mc sqlite> select * from questions_mc; Read this about .mode: .mode MODE ?TABLE? Set output mode where MODE is one of: ascii Columns/rows delimited by 0x1F and 0x1E csv Comma-separated values column Left-aligned columns. (See .width) html HTML <table> code insert SQL insert statements for TABLE line One value per line list Values delimited by "|" quote Escape answers as for SQL tabs Tab-separated values tcl TCL list elements the above from: https://www.sqlite.org/cli.html
Tutorial on creating a table in SQLite
Create an SQLite database from a text file Say you have a file text.txt of CSV format: name1,content1 name2,content2 Try the commands below to import the data in test.txt into a new database called test.db D:\test>sqlite3 test.db SQLite version 3.6.23 Enter ".help" for instructions Enter SQL statements terminated with a ";" sqlite> create table myTable(nameOfText TEXT, contents TEXT); sqlite> .separator "," sqlite> .import test.txt myTable sqlite> select * from myTable; name1,content1 name2,content2 sqlite>
Create an SQLite database using DB Browser for SQLite Ubuntu -> Software -> DB Browser for SQLite Usage: https://www.youtube.com/watch?v=2pbL7gTHMRw
Writing the result of an SQLite query to a text file 6. Writing results to a file By default, sqlite3 sends query results to standard output. You can change this using the ".output" and ".once" commands. Just put the name of an output file as an argument to .output and all subsequent query results will be written to that file. Or use the .once command instead of .output and output will only be redirected for the single next command before reverting to the console. Use .output with no arguments to begin writing to standard output again. For example: sqlite> .mode list sqlite> .separator | sqlite> .output test_file_1.txt sqlite> select * from tbl1; sqlite> .exit $ cat test_file_1.txt hello|10 goodbye|20 $ If the first character of the ".output" or ".once" filename is a pipe symbol ("|") then the remaining characters are treated as a command and the output is sent to that command. This makes it easy to pipe the results of a query into some other process. For example, the "open -f" command on a Mac opens a text editor to display the content that it reads from standard input. So to see the results of a query in a text editor, one could type: sqlite3> .once '|open -f' sqlite3> SELECT * FROM bigTable; If the ".output" or ".once" commands have an argument of "-e" then output is collected into a temporary file and the system text editor is invoked on that text file. Thus, the command ".once -e" achieves the same result as ".once '|open -f'" but with the benefit of being portable across all systems. If the ".output" or ".once" commands have a "-x" argument, that causes them to accumulate output as Comma-Separated-Values (CSV) in a temporary file, then invoke the default system utility for viewing CSV files (usually a spreadsheet program) on the result. This is a quick way of sending the result of a query to a spreadsheet for easy viewing: sqlite3> .once -x sqlite3> SELECT * FROM bigTable; The ".excel" command is an alias for ".once -x". It does exactly the same thing. NOTE: The above is taken from: sqlite.org
Indexing Indexing is a way of sorting a number of records on multiple fields. Creating an index on a field in a table creates another data structure which holds the field value, and a pointer to the record it relates to. This index structure is then sorted, allowing Binary Searches to be performed on it. NOTE: The above is taken from: sqlite.org
SQLite Primary key, ROWID and Constraints Whenever you create a table without the WITHOUT ROWID constraint, you get an implicit auto increment column called rowid. Such a table is known as a rowid table. The true primary key for a rowid table is the rowid. rowid is a pseudocolumn that uniquely defines a single row in a database table. The term pseudocolumn is used because you can refer to ROWID in the WHERE clauses of a query as you would refer to a column stored in your database; the difference is you cannot insert, update, or delete ROWID values. You won't see it if you do this:
SELECT * FROM tablename;You have to specifically ask for it:
SELECT rowid,otherfield FROM tablename;rowid https://www.sqlite.org/rowidtable.html https://www.sqlite.org/lang_createtable.html#rowid
Android Content Providers A content provider is only required if you need to share data between multiple applications. If you don't need to share data amongst multiple applications you can use a database directly via SQLiteDatabase. If you want to harness the power of a content provider (e.g. query and send results to file), you would create a contact provider and link it to your pre-made database originally imported from a csv file. A content provider component supplies data from one application to other applications on request. Such requests are handled by the methods of the ContentResolver class.
An android app
that displays Android Operating System flavors
from data accessed
via content provider and SQLite. https://www.tutorialspoint.com/android/android_content_providers.htm How to create a content provider... More learning resources... Udacity Android Studio Android Developer Guides Android App Development on Ubuntu Linux Android Developer Fundamentals Course – Practicals Android Developer Fundamentals Course – Concepts Android Developer Fundamentals - Videos