1. Field Trip #32 Digital Alarm Clock By Keith Lynn

2. Views A View is the basic building block for a GUI component Almost every component we add to an application is a View Some views are simple Some are complex Some view allow us to contain other views

3. RelativeLayout RelativeLayout is a View that contains other views The RelativeLayout makes use of the id of a View When we place a component on the RelativeLayout, we create an instance of a RelativeLayout.LayoutParams We can use this to specify the width and height of a component

4. RelativeLayout.LayoutParams In addition to specifying the width and height of a component, we can also specify where the component will be placed relative to other components We do this by adding a rule to the layout params There are several constants we can use: RelativeLayout.BELOW, RelativeLayout.ABOVE, etc.

5. LinearLayout LinearLayout is another View that contains other Views It lays them out next to each other We can also create a LinearLayout.LayoutParams

6. EditText An EditText is a View which allows the user to enter data The EditText like all other views is created as part of a context We can retrieve the text in an EditText by using the method getText()

7. Button A Button is a simple component Typically the button is a gray rectangle We are not required to place a label in the Button A Button like an EditText is created in a Context When we want to detect and act on a button click, we attach an OnClickListener to it

8. Spinners Another component we can use is the Spinner The Spinner places text in a list and we can scroll through the list We can determine which item was selected with the method getSelectedItem()

9. Events Clicking a Button generates an OnClick event We can detect and act on a button click by creating an instance of an OnClickListener OnClickListener is an inner class of View It contains the method onClick(View v) When the button is clicked and an OnClickListener is attached to it, its onClick method is called and a reference to the source is sent to it

10. Threads A thread is a single line of execution in a program When we start an app, a thread is created that handles the app It will detect events and call call the listeners that are listening for them If we want time consuming work to be performed, then we cannot place that work in the main thread of the app It would cause the app to freeze

11. Threads, cont'd In order to do time consuming work, we create a parallel thread Thread implements the Runnable interface Typically we create a Runnable class and then use this Runnable class to create the Thread The method run determines what the thread does We do not call the run method directly We allow the system to start the Thread (and call the run method) by calling start()

12. Threads, cont'd We control the thread by using a special variable We should never call the stop method on a thread Instead of placing an infinite loop in a thread, we create a loop controlled by a variable When we want the thread to stop, we change the variable

13. ImageView In order to place images on a View, we create an ImageView We place an image in the ImageView by creating an instance of a Drawable object and then place that in the ImageView with the method setImageDrawable In order to create the Drawable object, we drag the image into one of the drawable folders This generates an id in R.java We then use this id to create the Drawable

14. Image The image itself is a stadard image Typically we use a gif, jpg, or png When we drag the image into a drawable folder, an id is created in R.java Typically the id is R.drawable.imagename Notes that the extension is not included in the id

15. Sound In order to add sound to an app, we create the folder raw under res We then drag the sound file into raw This will create an id in R.java The id will be be R.raw.soundfilename We play the sound by creating an instance of a MediaPlayer using the id We start the sound playing by using the start method

16. Obtaining System Time In order to obtain the system time, we use the Calendar class We can create an instance of a Calendar with the method Calendar.getInstance() We then use the get method to specify what information we want We can send the constants Calendar.HOUR_OF_DAY, Calendar.MINUTE, and Calendar.SECOND

17. Creating an Alarm In order to create the alarm, we will place EditTexts and a Spinner on the app to allow the user to specify what time the alarm is for We then create a Thread which will obtain the system time and display it After we set the alarm and we reach that time, an alarm goes off