To Lecture Notes

IT 372 -- May 20, 2026

Review Exercises

1. Check that the last parameter of the JPC Button element is named content, which accepts a lambda function. Verify that this parameter can be written in trailing lambda notation.
   Answer: Here is a Button element calling its onClick and content parameters:
   

   Button(onClick = { /*Button action.*/ },
       content = { Text(text = "Button Text") })
   

   Here is the same Button element written using trailing lambda notation:
   

   Button(onClick = { /*Button action.*/ }) {
       Text(text = "Button Text") 
   }
   

2. Run the JPCEx ClickCounter2 Example. Click the button several times, then rotate the emulator. Notice that the click count is reset to 0. In a JPC app, how can we save the count in a Bundle and restore it when the app is recreated and restarted?
   Answer: when defining a state variable, replace remember with s like this:
   

   var newCaption = rememberSaveable { mutableStateOf("Click Me") }
   

3. For the TheRaven Example, we used the Scanner class, which comes from Java. Test these alternative Kotlin versions for reading from a file in the raw folder:
   

   // Read the entire file into a string:
   val s = inputStream.bufferedReader().use { 
       it.readText( ) 
   }
   
   // Read the file line by line:
   var s = ""
   inputStream.bufferedReader( ).useLines { 
       lines -> lines.forEach { 
           line -> s += line + "\n"
       } 
   }
   // Or
   var s = ""
   inputStream.bufferedReader( ).useLines { 
       it.forEach { 
           s += it + "\n"
       } 
   }
   

   Look at the WriteToFile JPC Example to see the last construct used.
4. Create a practice JPC app with a CustomButton composable with two parameters:
   

   caption : String,
   clickListener : ( ) -> Unit
   

   Use CustomButton to add three buttons to the app. Also add a Text element. The first button should have the caption "Button A" and its click listener should show the message "Button A clicked" in the Text element. Same for buttons B and C.
   Answer: here is the MainActivity.kt file.

JetPack Compose Examples

• Look at JPCEx 22, 23, 25, 26, 28
• Examples 25 through 30 apply to Project 5. For these examples, use the following drawing functions to draw lines, circles, and rectangles on a Canvas element:
  

  drawLine  drawCircle  drawRect
  

  Here are these functions with their required and optional parameters. Required parameters and some optional parameters are shown with sample values.  Look up other optional parameters as needed.
  

  drawLine(
      color = Color.Blue,           // Required
      start = Offset(x=5f, y=5f),   // Required
      end = Offset(x=120f, y=150f), // Required
      strokeWidth = 1f              // Optional
  )       
  
  drawCircle(
      color = Color.Red,            // Required
      radius = 50f,                 // Optional
      center = Offset(x=100f,y=75f),// Optional
      style = Stroke(width=10f)     // Optional
  )
  
  drawRect(
      color = Color(0xFF000080),    // Required
      topLeft = Offset(x=50f,y=50f),// Optional
      size = Size(x=95f,y=95),      // Optional
      style = Fill                  // Optional
  )