May 7, 2025 -- Notes

IT 372 -- May 7, 2025

Review Questions

What are the steps to adding a widget dynamically to a linear layout?
Ans: (a) Create a new widget by calling the constructor like this:
```
Button button = new Button(this);  // this is the context.
```
(b) Configure the widget, for example:
```
button.setText("Push Me");
```
(c) Add the widget to the layout:
```
layout.addView(button);
```
Look up methods from the Canvas class in the Android Developer class docmentation, found at
developer.android.com.
Select More >> Develop >> Android Platform (in Libraries)
The package name is android.graphics. The Canvas class contains methods for drawing shapes. Here are some of its methods to check out:
```
drawCircle  drawOval   drawLine  drawPath
drawPoint  drawPoints  drawRect   
```
Try out the TouchEvent1 Example.
Write an Android app that draws a circle in a MyView widget when a touch up event occurs. Hint: combine the Drawing0 and TouchEvent1 examples.

Repeatedly draw circles with touch up events. Keep track of the locations of the circles in Point objects stored in an arraylist. Here is the UML diagram for the Point class:

+---------------------------+
|          Point            |
+---------------------------+
| - x: int                  |
| - y: int                  |
+---------------------------+
| + Point(x : int, y : int) |
| + getX( ) : int           |
| + getY( ) : int           |
| + toString( ) : String    |
+---------------------------+

To the app in Exercise 5, add a reset button to erase all circles and start over.
Ans: activity_main.xml Point.java MyView.java ActivityMain.java
In Exercise 6, instead of drawing circles, draw a polyline (connected line segments).
Research and test this widget: SeekBar.
Ans: Here are the layout and activity files:
activity_main.xml MainActivity.java
Look at the DrawStar Example.

Project 4

Look at the Project 4 Description.

Read from File

The easiest way to make a text file, for example myfile.txt available to an Android app is to place the file in this folder:
```
app/src/main/res/raw
```

The file can then be opened for reading like this:

InputStream is = getResources( ).openRawResource(R.raw.myfile);
Scanner scanner = new Scanner(is);

Look at the ReadFromFile Example.
Replace the input file in the ReadFromFile Example with this input file: theraven.txt
Also, put the constraint layout in a ScrollView so that the entire poem can be read.
Ans: The layout and Java activity files.

Draw Rivers Example

Use the DrawRivers Example to plot the rivers from the rivers.txt input file.

ZooMap App

Create an Android app named ZooMap
Create a layout that contains a linear layout, which is 400x400 pixels
Place the input file zoomap.txt in this Android folder:
```
app/src/main/res/raw
```
This map shows the locations of the zoo cages and the animals that live in them.
Create a MyView class derived from View with an onDraw method that reads the input file zoomap.txt and plots the points according to the x and y coordinates. Multiply the x and y values by 2 before plotting them.
Instantiate a MyView object and add it to the linear layout.
Add an onTouch event handler to the MyView object.
When the object is touched, if the touch location is close to one of the animal cages, look up the id in the input file, and display the id in a toast. Use a HashMap to store the id, x, and y values so that you don't need to read the input file every time that a touch occurs.
After testing that the toast displays the correct values, instead of showing the toast, pass the id to a new activity.
The new activity should look up the id in the input file and show the animal and gender in TextView widgets.
Source code files for the ZooMap app:
activity_main.xml activity_details.xml
MainActivity.java DetailsActivity.java
MyView.java Point.java zoomap.txt.