Persistence Technology

Android has 3 ways to persist data:

1.SharedPreferences

2. File reading

3. Database

 

SharedPreferences

Code example:

// save the data in the Editor
SharedPreferences.Editor editor= getSharedPreferences("data",MODE_PRIVATE).edit();
editor.putString("name","Tom");
editor.apply();

//fetch data
SharedPreferences sharedPreferences=getSharedPreferences("data",MODE_PRIVATE);
Log.d("testData",sharedPreferences.getString("name",""));

 

 

 

Store data to file

public void save(String inputText) {
    FileOutputStream out = null;
    BufferedWriter writer = null;
    try {
        out = openFileOutput("data", Context.MODE_PRIVATE);
        writer = new BufferedWriter(new OutputStreamWriter(out));
        writer.write(inputText);
    } catch (IOException e) {
        e.printStackTrace ();
    } finally {
        try {
            if (writer != null) {
                writer.close();
            }
        } catch (IOException e) {
            e.printStackTrace ();
        }
    

 

read data from file

public String load() {
    FileInputStream in = null;
    BufferedReader reader = null;
    StringBuilder content = new StringBuilder();
    try {
        in = openFileInput("data");
        reader = new BufferedReader(new InputStreamReader(in));
        String line = "";
        while ((line = reader.readLine()) != null) {
            content.append(line);
        }
    } catch (IOException e) {
        e.printStackTrace ();
    } finally {
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException e) {
                e.printStackTrace ();
            }
        }
    }
    return content.toString();
}

 

 

SQLite database, operate with LitePal

1. Add a line of code to the Application tag of AndroidManifest.xml:

   

android:name="org.litepal.LitePalApplication"

 

2. Create the assets directory and add a litepal.xml file

    The content in <list> is the path of the mapping object, fill in according to the actual situation

<?xml version="1.0" encoding="utf-8"?>
<litepal>
    <dbname value="BookStore" ></dbname>

    <version value="2" ></version>

    <list>
        <mapping class="com.example.litepaltest.Book"></mapping>
    </list>
</litepal>

 

3. Create a javabean class, pay attention to extends DataSupport

public class Book extends DataSupport {
 //Add properties, and add setter(), getter() methods  
   private int id ;
     private String author ;
     private double price ;
     public int getId() {
         return id ;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

 

4. Create the database

  

Connector.getDatabase();

 

5. Add data

Book book = new Book();
book.setAuthor("1");
book.setPrice(1);
book.save();

 

6. Update the data with id=1

Book book = new Book();
book.setAuthor("2");
book.setPrice(1);
book.update(1);

 

7. Deletion of data

DataSupport . deleteAll (Book. class , "price < ?" , "15" ); //Delete the data in the Book table whose price is less than 15

  

DataSupport. deleteAll (Book. class ); // delete the entire table

 

8. Query data

List<Book> books = DataSupport.findAll(Book.class);
for (Book book: books) {
    Log.d("MainActivity", "book ID is " + book.getId());
    Log.d("MainActivity", "book author is " + book.getAuthor());
    Log.d("MainActivity", "book price is " + book.getPrice());
}