college/Summer-2024/CS-3443/Slides/txt/18_Android App Development - Rowdy Quiz File IO.txt

Application
Programming
Hend Alkittawi

Android Development
Building An Application That
Utilizes Data

ROWDY QUIZ APP
-

We created the Rowdy Quiz app, with hard-coded questions

-

Now, it is time to load the questions from a data file

-

We will also add a logo to our screen

WORKING WITH DATA
Reader

Writer

InputStream

OutputStream

InputStreamReader

PrintWriter

FileInputStream

FileOutputStream

FileReader

OutputStreamWriter

ObjectInputStream

ObjectOutputStream

FileWriter

PrintStream

WORKING WITH DATA
-

Classes utilized for reading and writing data in Android
-

Activity

-

AssetManager

-

InputStream

-

OutputStream

READING DATA FROM A FILE
-

To read data from a file:
-

place the file in the Assets folder
- app > New > Folder > Assets Folder (do not change the folder
location)

READING DATA FROM A FILE
-

Under the model package, modify QuizBank.java
-

Modify the loadQuestions() method to create the questions from a data
(*.csv) file
-

the method uses the Activity, AssetManger and InputStream classes to read
the data from the file
public void loadQuestions(MainActivity activity){
AssetManager manager = activity.getAssets();
Scanner scan = null;
String filename = "test.csv";
try {
InputStream file = manager.open(filename);
scan = new Scanner(file);
// do something with the file data
}
catch (IOException e) { // handle exception }
}

READING DATA FROM A FILE
-

For the controller, modify MainActivity.java
-

onCreate() calls the createQuizBank() method to load the questions
in the quiz bank

-

createQuizBank() calls the loadQuestions() method which requires

an AssetManager to load the data from the *.csv file in the
Assets folder
-

Get an AssetManager object from MainActivity using
activity.getAssets()
private void createQuizBank(){
quizBank = new QuizBank();
quizBank.loadQuestions(this);
}

READING DATA FROM A FILE
-

In QuizBank.java
public void loadQuestions(MainActivity activity){
AssetManager manager = activity.getAssets();
Scanner scan = null;
try {
InputStream file = manager.open("test.csv");
scan = new Scanner(file);
// do something with the file data
}
catch (IOException e) {
// handle exception
}
}

-

In MainActivity.java
private void createQuizBank(){
quizBank = new QuizBank();
quizBank.loadQuestions(this);
}

ROWDY QUIZ APP UML

WRITING DATA TO A FILE
-

The Assets folder is read-only, we cannot write data to the
files in the Assets folder

-

To write data to a file, create a file in the AVD memory.

-

Once created, the file can be located in the AVD memory by
navigating to View > Tool Windows > Device Explorer then data
> user > 0 > edu.utsa.cs3443.projectName > files

WRITING DATA TO A FILE
-

Under the model package, modify QuizBank.java
-

add the saveData() method to save data to a (*.txt) file
-

the method uses the Activity and OutputStream classes to read the data
from the file

public void saveData(MainActivity activity){
try {
OutputStream out = activity.openFileOutput(filename, Context.MODE_PRIVATE );
out.write("test writing to a file".getBytes(StandardCharsets.UTF_8));
out.close();
} catch (IOException e) {
System.out.println("Failed to write data");
}
}

WRITING DATA TO A FILE
-

For the controller, modify MainActivity.java
-

onCreate() calls the createQuizBank() method to load the questions
in the quiz bank

-

saveData() method requires an Activity to access the AVD
memory
quizBank.loadQuestions(this);
quizBank.saveData(this); // call it wherever your code needs to save data

READING DATA FROM A FILE
-

In QuizBank.java
public void saveData(MainActivity activity){
try {
OutputStream out = activity.openFileOutput(filename, Context.MODE_PRIVATE );
out.write("test writing to a file".getBytes(StandardCharsets.UTF_8));
out.close();
} catch (IOException e) {
System.out.println("Failed to write data");
}
}

-

In MainActivity.java
quizBank.saveData(this);

WORKING WITH DATA
-

What if we would like to update data in a file from the Assets
folder?
-

The Assets folder is read-only, we cannot write data to the
files in the Assets folder

-

A work around this is to create a copy of the file from the
Assets to the AVD memory, then use the “copy file” for reading
and writing data.

ADDING IMAGEVIEWS TO THE LAYOUT
-

Use an ImageView in the layout file to display an
image on the screen

-

ImageViews can display images from the drawable
folder
-

-

Place the image file under res > drawable

The ImageView’s src attribute specifies the image
that the ImageView will display
<ImageView
android:layout_width ="wrap_content"
android:layout_height ="wrap_content"
android:src="@drawable/rowdylogo"/>

CODE DEMO
-

Walk through the
Android App in Android
Studio

DO YOU HAVE ANY
QUESTIONS?

THANK
YOU!

@

hend.alkittawi@utsa.edu

By Appointment
Online