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IT 372 -- Apr 29, 2024

Review Questions

1. Where is this message displayed?
   

   Log.i("001", "This is a test message?");
   

2. How do you add a second activity to an app?
3. Look at the details of the SendMessage Example.
4. Create an Android app named Greeter with three activities named MainActivity, Greeter2Activity, and Greeter3Activity. MainActivity displays the greeting
   

   Hello, how are you?
   Click for next activity.
   

   Greeter2Activity displays the message
   

   I'm fine, thank you, and you?
   Click for next activity.
   

   Greeter3Activity displays the message
   

   I'm fine too, thanks.
   Click for main activity.
   

   Implement the onClick event handlers with lambda functions.
   Ans: Here are the source code files:
   activity_main.xml   MainActivity.java
   activity_greeter2.xml  Greeter2Activity.java
   activity_greeter3.xml  Greeter3Activity.java

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:
  
• In general, setting widgets to fixed size is not always recommended. Often, it is better to set the layout width and height to match_parent or wrap_content, depending on the layout.
• Set the layout_width and layout_height attributes of the button to wrap_content.
• You can also use the Create a connection button in the Attributes Window. Click View fewer attributes above the Attributes Window so that you see these buttons:
  
  
  
• 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" 
  

• Practice Problem: Use a ConstraintLayout to implement an entry form that inputs three pieces of information about a pet: name, age, and is_vaccinated. Use EditText widgets to enter the name and the age; use a checkbox to enter whether the pet is vaccinated. Include textviews to label the entry widgets and a submit button to display the entered information, something like this:
  

  Name: Luna
  Age: 3
  Is Vaccinated: Yes
  

  Put the ConstraintLayout in a ScollView to facilitate data entry with the on-screen keyboard.

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 Android Studio IDE

• Locate these Android Studio windows:
      Project   Code   Layout Design   Layout Text   Attributes
      Palette   Component Tree   Terminal   Logcat
• Practice Problem. Write an onClick event handler that writes a message to the Logcat window using the Log object:
  
  

  Method	Signature	Meaning
  Log.d	(String, String)	Debug
  Log.e	(String, String)	Error
  Log.i	(String, String)	Information
  Log.v	(String, String)	Verbose
  Log.w	(String, String)	Warning

  
  The arguments to each method are the message id, and the message itself.
• Locate these buttons in the Main Menu (upper left) by hovering over them with the mouse and reading the tooltips.
      Build Project   |   Run 'app'   |   Debug  |   Stop 'app'  |  Sync Project with Gradle Files   | 
      Device Manager  |  SDK Manager  |  Project Settings  | 
• Locate these buttons above the Layout Design Window:
      Select Design Surface   |    Orientation for Preview   |   Device for Preview
      Theme for Preview   |   Locale for Preview  |   Zoom Out   |   Zoom In
      Zoom to Fit Screen

Practice Problem

1. Create an app named ShowSuit. Add a radiobutton group with four radio buttons and an ImageView widget to the ConstraintLayout. Set the text for the radio buttons to Club, Diamond, Heart, and Spade. Set up an onCheckedChangListener event handler that changes the image of the imageview to club.png, diamond.png, heart.png, or spade.png, depending on the radiobutton that is clicked. Here is a zipfile of the suit images.  Use an anonymous inner class to set up the event handler.
   Ans: Copy the suit images files into the res/drawable folder. Here are the layout and activity files. Also, see the ShowSuit Example for a different implementation of this problem.

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.

Android Platform

• Some Details about the Android Platform.
• To view files on the virtual device, use the Device Explorer.