May 13, 2019 -- Notes

IT 372 -- May 13, 2019

Which classes/objects are used when working with Sqlite databases in an Android app?
Ans: SQLiteOpenHelper, derived class StudentsDBHelper, SQLiteDatabase, ContentValues, Cursor
How do you add strings to a spinner, both in the XML layout file and dynamically in the Java activity file?
Ans: In the layout, set up an array in strings.xml that contains the strings to go into the spinner. Then set the entries property to connect this array to the spinner. In the activity code, use an ArrayAdapter object to connect an ArrayList collection to the spinner.
Write a simple Android app that tests a RatingBar widget. (On the takehome final, you will be asked to test a widget that we have not covered in class.)
What techniques do you use for debugging your Android apps?
Ans: (a) Write lines to the Logcat window with Log.i or to the Run window with System.out.println.
(b) Comment out lines and add them back in one by one to locate the line that causes the app to crash.
(c)Use the Android Debugger: put breakpoints in your code, which show up as maroon disks in the gray area to the left of the editor lines. Use the Debug 'app' button in the toolbar to the right to start the debugger. Step Over, Step Into, and Step Out buttons above the Debug Window at the bottom of Android Studio. Check the values of variables in the Variable Window. Here are, respectively, the Android Studio Debug 'app', Step Over, Step Into, and Step Out buttons:

Look at this .Net Example, which is similar to Project 4. Here are screen dumps of the main window, which shows a map of the rivers and houses, and the listing dialog, which shows listing information for a house that is clicked.

Create an app that displays twelve month buttons using the month icons in this zip file: month-icons.zip
Place a LinearLayout in a ScrollView to allow scrolling.
Modify the MonthButtons Example (MonthButtons1) to add the buttons to the layout dynamically (MonthButtons2).
Look at the MonthButtons1 Example.
Look at the MonthButtons2 Example that creates the buttons dynamically and adds them to the layout in a for loop.

To draw in a view, create a subclass class derived from View, which overrides the onDraw method.
This is similar to Swing, where you create a subclass of Panel and override the onDraw method.

Here is a simple onDraw method:

@Override
public void onDraw(Canvas c) {
    Paint p = new Paint( );
    p.setColor(Color.RED);
    c.drawCircle(100, 120, 30, p);
}

The MyView class should also have this constructor:

public MyView(Context context) {
    super(context);
}

Finally, a MyView object must be instantiated and added to the layout in the Java activity code:

 MyView mv = new MyView(this);
LinearLayout ll = (LinearLayout) findViewById(R.id.layout);
ll.addView(mv);

The touch events that we will discuss come in three forms:
1. A finger not in contact with a view comes in contact with the view (ACTION_DOWN).
2. A finger in contact with a view moves to a different location on the view without losing contact (ACTION_MOVE).
3. A finger in with a view raises and loses contact with the view (ACTION_UP).
Use the setOnTouchListener to add a touch event handler to a view.
Look at the TouchEvent1 Example.