Apr 15, 2024 -- Notes

IT 372 -- Apr 15, 2024

Specs for Projects

When you create your project, name it Proj1aSmith (replace 1a by the actual project number and Smith by your last name).

The package that you set when creating your project can be it372 so that the import statement at the top of your Java files will be
```
import it372.proj1asmith;
```
Change the title of your app in the strings.xml resource file. Display the title at the top of your app in a TextView widget.
Choose interesting colors and layouts for your projects. We will see how to display an image in an ImageView control today. For Project 1b or Project 2, you can improve your score for creativity by adding an image to your apps.
Extract colors and string constants to the resource files colors.xml and strings.xml.
Both the layout and activity files must have source code comments.

Both the layout and activity files must have headers that look like this:

In layout file:
<?xml version="1.0" encoding="utf-8"?>
<!-- Stan Smith
     Project 1a
     Apr 12, 2021 -->

In activity file:
// Stan Smith
// Project 1a
// Apr 12, 2021

Use Android Studio to create the zipfile of your project.

Practice Exercises

How does the Android app know which layout file to use?
Ans: It looks in the MainActivity.java file in the onCreate method:
```
setContentView(R.layout.activity_main);
```
This statement tells the activity that activity_main.xml is the layout file.
How do you start an Android app from the virtual device?
Ans: On the Galaxy Nexus API 22 virtual device, swipe up to view the installed apps. For some versions you click on this icon to show the installed apps:
.
Then scroll up or down to find the icon of the app you want to run and click it.
How do you uninstall apps from the Android virtual device? Ans: Click up to view the installed apps, then scroll to find the Settings Icon and click it. Scroll down to find Apps and click it. Scroll down to find Apps & notifications and click it. Click on SEE ALL 18 APPS, scroll to find the app you wish to uninstall, click on the App, click UNINSTALL.
Look at the complete Magic8Ball Example, complete with all 20 possible predictions.
If you have an Android phone, you may wish to install this app or other apps on your phone. To do this, turn on Developer options using these directions:
https://developer.android.com/studio/debug/dev-options
(You really must tap the Build Number option 7 times to enable Developer options). Then connect your phone to your PC with a USB cable and run the app in the Emulator. This will simultaneously install and run the app on your phone.
Look at the section Adding a ScrollView found below in these notes. Then display the following in a linear layout with a scrollview.
1. Display the numbers from 1 to 1000 in a textview control, one number per line. Add a ScrollView to allow the user to swipe up and down to view all the numbers.
  Answer: Here are the layout and activity files:
  activity_main.xml MainActivity.java
2. Start with some Lorem Ipsum text in a textview widget:
```
Lorem ipsum dolor sit amet, 
consectetur adipiscing elit. 
In nibh lectus, accumsan 
at ligula sagittis, bibendum 
suscipit enim.
```
  When the textview widget is clicked, concatenate 100 copies of this paragraph together and display the new repeated text in the textview. Add scrollbars so the user can see the entire textview.
  Answer: Here are the layout and activity files:
  activity_main.xml MainActivity.java

Android Event Handlers

Android event handlers can also be implemented with inner classes.
The details are in the TempConverter Example
Method 1 is to use an onClick attribute as we have been doing.
Method 2 is to use an inner class to implement the click event handler.
Method 3 is to use an anonymous inner class to implement the click event handler.
Method 4 (recommended method) is use the setEventListener method to add an anonymous event handler method defined with arrow notation. Unlike JavaScript that uses a fat arrow ( => ) to define a method defined with arrow notation, Java uses a thin arrow ( -> ).
The View.OnClickListener class is an inner class of the View class.

Using Images

Setting a background image:
- Copy the background image, for example, image1.jpg into the app/res/drawable folder.
- Add this attribute to the layout or widget:
```
android:background="@drawable/image1"
```
Use this Blackhole Image as the background image for an Android app.
You can also display an image in an ImageView widget.

Adding a ScrollView

If the height of a linear layout is too large to all be viewable on a device, add a ScrollView.
You can add a "ghost view" to pad the bottom of the layout if the bottom of the layout is cut off:
```
<View
    layout_width="match_parent"
    layout_height="25dp" />
```

Project 2

Look at Project 2.
What are some attributes to consider for LinearLayout, TextView, and EditText? Answer:
```
text  textSize  textColor  background  layout_margin  padding
```

BeerAdvisor Example

Look at the BeerAdvisor Example.

Array Adapters

Practice Problems
1. How to add items programatically to a Spinner widget? Use an ArrayAdapter object.
  Answer: Add a Spinner widget to the layout, with id set to spinner1. Then
  1. place the array of Integer objects to display in the spinner in an array list,
  2. set up an ArrayAdapter object that connects the spinner to the array list.
  Here is the Java code:
```
// Set up array list.
ArrayList<Integer> arrList = new ArrayList<Integer>( );
for(int n = 1001; n <= 1005; n++) {
    arrList.add(n);
}

// Set up array adapter.
ArrayAdapter<Integer> adapter = new ArrayAdapter<Integer>(
    this, android.R.layout.simple_list_item_1, arrList);
spinner1.setAdapter(adapter);
```
ChineseHoroscope Example:
1. Input a year of birth using a Spinner widget. Use an array adapter to load the years into the spinner.
2. Determine the Chinese horoscope animal corresponding to the year. The animal number can be obtained from year % 12.
3. Display the animal in a TextView widget.
Answer: The layout and activity files: activity_main.xml MainActivity.java