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IT 372 -- Apr 7, 2025

Review Questions

  1. How do you use Android Studio to create a zipfile of your app for submitting on D2L?
  2. In this layout file, why does line 13 end with /> but line 7 only ends with >? 
      1 <LinearLayout
 2     xmlns:android="http://schemas.android.com/apk/res/android"
 3     xmlns:tools="http://schemas.android.com/tools"
 4     android:layout_width="match_parent"
 5     android:layout_height="match_parent"
 6     android:gravity="center"
 7     tools:context=".MainActivity">
 8
 9     <TextView
11         android:layout_width="wrap_content"
12         android:layout_height="wrap_content"
13         android:text="@string/greeting" />
14 </LinearLayout>
  3. What is Hungarian notation?
  4. Create an Android app with a Button widget in a linear layout. Set the text of the button to "Click me.". When the button is clicked, the text should change to "I\'ve been clicked".
    Ans: activity_main.xml  MainActivity.xml  strings.xml
  5. Change the TempDesc class so that it has the instance variable temperature, the getter getTemperature, the setter setTemperature, and the method getDescriptor, Also include a parameterized constructor that initializes the instance variable. Use this UML diagram:
    +--------------------------------+
|            TempDesc            |
+--------------------------------+
| - temperature : double         |
+--------------------------------+
| + TempDesc(temp: double)       |
| + getTemperature( ) : double   |
| + setTemperature(temp : double)|
| + getDescriptor( )             |
+--------------------------------+
    Test your TempDesc class like this:
    double[ ] temps = {-13.0, 27.0, 52.0, 68.0, 87.0, 103.0};
TempDesc tempObj = new TempDesc(0);
String output = "";
for(double temp : temps) {
    tempObj.setTemperature(temp);
    output += tempObj.getDescriptor( ) + "\n";
}
// Display the output variable contents
// in a TextView widget:
tv.setText(String.valueOf(output));
    Then display the output in a TextView widget in an Android app.
    Answer: activity_main.xml   MainActivity.java   TempDescriptor.java
  6. Use an object from the Random class to output a random integer between 0 and n - 1?
  7. What is the package of the TextView class? What is its base class? Look this up in the documentation on the Android Developer site: developer.android.com
  8. Why should literal strings not be displayed directly on an app layout? How do you move the literal string definitions to the resource file strings.xml?
    Answer: (a) If a string is used more than once on a form, if it is changed, it need only changed once in the resource file.
    (b) For globalization: if an app is available in more than once language, switching languages, requires only switching to the resource file for that language.
  9. How is a string defined in the strings.xml resource file? Answer:
    <string name="greeting">Hello, World!</string>
  10. How is a string accessed from a resource file? Answer:
    In a layout file:
    android:text="@string/greeting"
    In a Java activity file:
    String s = getString(R.string.greeting);
  11. In an event handler, how can you access and change the text that is displayed in a TextView control?. Answer:
    // Access the text:
String s = txtValue.getText( ).toString( );

// Change the text:
txtValue.setText(s);
  12. In the statement
    int count = Integer.parseInt(tv.getText( ).toString( ));
    why do we need the the method call toString( )?
    Answer: tv.getText( ) returns an object of type CharSequence, which is an interface that is implemented by these classes: CharBuffer, Editable, Spannable, Segment, String, StringBuffer, StringBuilder. This allows for more flexibility than simply returning a String object.
  13. For what is the measurement unit dp used?
  14. For what is the measurement unit sp used?
  15. Create an app named TriColor that consists of a linear layout with blue background and no wigits. Set up an event handler, so that each time the linear layout is clicked, the background color changes blue to red, red to lime, or lime to blue.  Use an int instance variable in the MainActivity class to keep track of the background color. Use the codes Blue=0, Red=1, and Lime=2.
    Ans: activity_main.xml  MainActivity.java  colors.xml

Margin and Padding Attributes

Project 1b

Magic8Ball Example