Apr 10, 2024 -- Notes

IT 372 -- Apr 10, 2024

What does the Android R class do?
Answer: It manages the resources in an Android app, for example: ids, colors in the colors.xml file and strings in the strings.xml file. You can use the id to create a Java object like this:
```
TextView tv = findViewById(R.id.txt_temp);
```

Show how display a string dynamically from the strings.xml resource file. Answer:

TextView tv = findViewById(R.id.txt_name);
tv.setText(getString(R.string.first_name));

Show how to change a color dynamically from the colors.xml resource file. Answer:

LinearLayout layout = findViewById(R.id.main);
layout.setBackgroundColor(getColor(R.color.purple));
// or
layout.setBackgroundColor(0xFFFF00FF);

An inner class is a class that is defined completely within another class.
If an inner class is only used by the containing class, the accessibility of the inner class is defined as private.
Look at the InnerClass Example.
Android event handlers can also be implemented with inner classes.
The MyFrame class in the InnerClass Example shows how a Swing event handler is implemented.

This example shows how to define and use a simple interface. On your computer, create a folder with files ManageOutput.java, A.java, and Main.java. Then, from a Command Line (Windows) or Terminal (Mac) window, compile and run this project:
```
> javac *.java
> java Main
```

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 an anonymous event handler method.
The View.OnClickListener class is an inner class of the View class.