To Lecture Notes

IT 372 -- June 3, 2019

Practice Problems

1. Research and test the SeekBar widget.
   Ans: Here are the XML layout file and the Java activity file. The SeekBar class is a class derived from ProgressBar, which represents a value by its horizontal position on the bar. This position is the progress attribute. Here are the relevant properties of the SeekBar:
   
   

   Attribute	Description
   progress	Value represented by the seek bar.
   min	Minimum progress value of seek bar
   max	Minimum progress value of seek bar

2. Write an Android app that connects the dots to draw a five pointed star.
   Ans: See the DrawStar Example.
3. Write an Android app that connects the dots to draw the rivers for Project 4.
   Ans: See the DrawRivers Example.
4. Look at the TouristInfo Example.
5. Finish the HPCalculator Project. Here are the layout file and activity file with event handler stubs to get you started:
   activity_main.xml    ActivityMain.java    Here is also an emulator screen shot.

Introduction to Kotlin

• An Online Kotlin Tutorial:
      https://www.callicoder.com/categories/kotlin/
• Kotlin was released by the JetBrains company in 2011.
• It is named after Kotlin Island close to St. Petersburg, Russia.
• Kotlin was designed to be a "better" language than Java, but to run on the JVM and be interoperational with Java.
• It can also be compiled to Javascript or native binary code.
• Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference (lead sentence in Kotlin Language Wikipedia article).
• Kotlin has no primitive types. Every datatype is a class.
• The Kotlin primitive types:
  

  Boolean  Byte  Char  Double  
  
  Float  Int  Long  Short  String
  

• Here are two Kotlin Hello World main methods:
  

  // args parameter for command 
  // line arguments is optional.
  fun main( ) {
      print("Hello, World.")
  }
  
  // args parameter included.
  fun main(args : Array<String>) {
      println("Hello, " + args[0] + ".")
  }
  

• Translate these Java statements into Python:
  

  // a.
  int a = 3, b = 5;
  System.out.println(a + b);
  
  // Ans: Kotlin statements:
  var a = 3
  var b = 5
  println(a + b)
  
  // b.
  int a;
  double b;
  a = 3;
  b = 5.25;
  System.out.println(a + b);
  
  // Ans: Kotlin statements:
  var a : Int
  var b : Double
  a = 3
  b = 5.25
  println(a + b)
  
  // c. 
  String a, b;
  a = "dog"
  b = "cat"
  System.out.println(a + b.toUpperCase( ));
  
  // Ans: Kotlin statements:
  var a : String
  var b : String
  a = "dog"
  b = "cat"
  println(a + b.toUpperCase( ));
  
  // d.
  Scanner s = new Scanner(System.in);
  String name = s.readLine( );
  System.out.println("Hello, " + name);
  
  // Ans: Kotlin statements:
  // No Scanner object is necessary.
  var s = readLine( )
  println("Hello, " + name)
  
  // e.
  public static void main(String[ ] args) {
      System.out.println(greeting("Larry"));
  }
  
  public String greeting(String theName) {
      return "Hello, " + theName;
  }
  

• Write the Person class defined by this UML diagram.
  Ans: See the KotlinPerson Example.

Setting the App Icon

• To set the icon and label for an Android app, set the icon and label attributes in the application tag in the manifest:
  

  android:icon="@drawable/icon_name" 
  android:label="@string/app_name"
  

• Alternatively, an XML file that has drawing directions can be used for the icon. For example, here are the contents of the the default icon  file ic_launcher_background.xml:
  

  <?xml version="1.0" encoding="utf-8"?>
      <vector 
          xmlns:android=
              "http://schemas.android.com/apk/res/android"
          android:width="108dp"
          android:height="108dp"
          android:viewportWidth="108"
          android:viewportHeight="108">
  
      <path
          android:fillColor="#008577"
          android:pathData="M0,0h108v108h-108z" />
  
      <path
          android:fillColor="#00000000"
          android:pathData="M9,0L9,108"
          android:strokeWidth="0.8"
          android:strokeColor="#33FFFFFF" />
  
      <path
          android:fillColor="#00000000"
          android:pathData="M19,0L19,108"
          android:strokeWidth="0.8"
          android:strokeColor="#33FFFFFF" />
  
      <!-- 31 paths are omitted. -->
  
      <path
          android:fillColor="#00000000"
          android:pathData="M79,19L79,89"
          android:strokeWidth="0.8"
          android:strokeColor="#33FFFFFF" />
  
  </vector>
  

Themes

• To set the theme for an app, set the theme attribute in the application tag in the manifest:
  

  android:theme="@style/AppTheme"
  

• The beginning of the styles.xml file in app/src/main/res/values:
  

  <resources>
  <!-- Base application theme. -->
  <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
      <!-- Customize your theme here. -->
      <item name="colorPrimary">@color/colorPrimary</item>
      <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
      <item name="colorAccent">@color/colorAccent</item>
  </style>
  </resources>
  

  The meanings of these color titles:
  
  • name="colorPrimary"   The color used in the app bar, the main color that "brands" the app.
  • name="colorPrimaryDark"   A darker variant of the main color, used for the status bar.
  • name="colorAccent"   the color of UI controls, such as EditText or RadioButton widgets.
• The colors.xml file, also in app/src/main/res/values.
  

  <?xml version="1.0" encoding="UTF-8"?>
  <resources>
      <color name="colorPrimary">#00BCD4</color>
      <color name="colorPrimaryDark">#660F09</color>
      <color name="colorAccent">#D81B60</color>
  </resources>
  

  These colors can be customized as desired.
• Alternatives to the default theme
  

  Theme.AppCompat.Light.DarkActionBar
  

  are

  Theme.AppCompat
  Theme.AppCompat.Light
  Theme.AppCompat.Light.NoActionBar
  Theme.AppCompat.NoActionBar