To Lecture Notes

IT 372 -- Apr 23, 2025

Review Questions

1. Look again at the ClickCounter Example.
2. Look at the StopWatch Example.
3. Look at the SendMessage Example. This example shows how to add a second activity to an app.

Practice with ConstraintLayout

• Create an Android Studio Project named CLPractice (ConstraintLayoutPractice).
• Go to the Design Window
• Delete the TextView widget with the "Hello, World!" text.
• Drag a Button onto the layout from the Palette.
• Resize the button with the blue square resizing handles located on the corners of the button:
  
• Setting widgets to fixed size is not always recommended. It is often better to set the layout width and height to match_parent, wrap_content, or 0dp (match contstraint), depending on the layout.
• Set the layout_width and layout_height attributes of the button to wrap_content.
• An easy way to set constraints to position a widget is to use the Constraint Widget in the Layout Window. This widget contains these buttons: Create Left Constraint, Create Top Constraint, Create Right Constraint, Create BottomConstraint, and WrapContent buttons:
  
  
• Add vertical constraints to the left and top of the button widget to give the button left and top margins of 24dp each.  This creates these contraints in the XML file for the button.  Select the Code Window to view them.
  

  android:layout_marginStart="24dp"
  android:layout_marginTop="24dp"
  app:layout_constraintStart_toStartOf="parent"
  app:layout_constraintTop_toTopOf="parent"

• The terms Start and End mean Left and Right in an English Language user interface. However, Start and End allow the flexibility of using a right-to-left language interface, such as Arabic or Hebrew. For right-to-left anguage, Start means right and End means left.
• The Constraint Widget in the Layout Window now looks like this:
  
  
  
• Set the id of the first button to @+id/btn_first.
• Add a second button to the layout. Set constraints of size 24dp to the left edge of the layout and to the bottom of the first button. The contraints for the second button in the Code Window are:
  

  android:layout_marginStart="24dp" 
  android:layout_marginTop="24dp" 
  app:layout_constraintStart_toStartOf="parent" 
  app:layout_constraintTop_toBottomOf="@+id/btn_first" 
  

StudentEntryForm Example

• Build the StudentEntryForm Example.
• Look at the Project 3a Description.

Practice Problem

1. Set up a ConstraintLayout form to input grocery item data with these fields: description (String), code (int), and price (double). When the Submit Grocery Item button is clicked, contatenate the information to the String variable groceryItems that is displayed on a new activity. Ans:
        activity_main.xml  MainActivity.java
        activity_display_items.xml  DisplayItemsActivity.java
   When the virtual device is rotated, save the groceryItems variable in a Bundle object so that this variable can be restored when the activity is recreated after the activity is destroyed due to device rotation.
   Ans: Main activity after adding onSaveInstanceState method and statements in onCreate to restore bundle.
        MainActivity.java

The weight Attribute

• The android:layout_weight attribute controls the relative amount of space that a widget takes up in a linearlayout.
• Create a linear layout with three buttons with captions "BUTTON1", "BUTTON2", "BUTTON3" and layout_weight values 1, 2, and 3.
• Practice Problem: Match the emulator screen shots 1, 2, 3, 4, 5 with the linear layouts a, b, c, d, e.
  Ans: 1 c; 2 b; 3 a; 4 e; 5 d.