33. Data storage. Preferences.

Lecture

In this lesson:

- data storage using Preferences

33. Data storage. Preferences. - video lesson version

Enough about Intent and Activity. Let's talk about data storage. There are several ways to store data in Android:

Preferences - as a analogy, you can bring Windows INI files

SQLite - database, tables

regular files - internal and external (on the SD card)

We will start with the simplest - Preferences . Values are saved as a pair: name , value . Just like for example extras in Intent.

Develop an application. It will have a text box and two buttons - Save and Load . By clicking on Save, we will save the value from the field, by clicking on Load - load .

Create a project:

Project name : P0331_SharedPreferences
Build Target : Android 2.3.3
Application name : SharedPreferences
Package name : ru.startandroid.develop.p0331sharedpreferences
Create Activity : MainActivity

Open main.xml and create such a screen:

  <? xml version = "1.0" encoding = "utf-8"?> 
  <LinearLayout 
  xmlns: android = "http://schemas.android.com/apk/res/android" 
  android: layout_width = "fill_parent" 
  android: layout_height = "fill_parent" 
  android: orientation = "vertical"> 
  <Edittext 
  android: id = "@ + id / etText" 
  android: layout_width = "match_parent" 
  android: layout_height = "wrap_content"> 
  <requestFocus> 
  </ requestFocus> 
  </ Edittext> 
  <LinearLayout 
  android: id = "@ + id / linearLayout1" 
  android: layout_width = "match_parent" 
  android: layout_height = "wrap_content" 
  android: orientation = "horizontal"> 
  <Button 
  android: id = "@ + id / btnSave" 
  android: layout_width = "wrap_content" 
  android: layout_height = "wrap_content" 
  android: text = "Save"> 
  </ Button> 
  <Button 
  android: id = "@ + id / btnLoad" 
  android: layout_width = "wrap_content" 
  android: layout_height = "wrap_content" 
  android: text = "Load"> 
  </ Button> 
  </ LinearLayout> 
  </ LinearLayout>

Input field and two buttons.

Now we write the code in MainActivity.java :

package ru.startandroid.develop.p0331sharedpreferences; 
 
 import android.app.Activity; 
 import android.content.SharedPreferences; 
 import android.content.SharedPreferences.Editor; 
 import android.os.Bundle; 
 import android.view.View; 
 import android.view.View.OnClickListener; 
 import android.widget.Button; 
 import android.widget.EditText; 
 import android.widget.Toast; 
 
 public class MainActivity extends Activity implements OnClickListener { 
 
 EditText etText; 
 Button btnSave, btnLoad; 
 
 SharedPreferences sPref; 
 
 final String SAVED_TEXT = "saved_text"; 
 
 
 /** Called when the activity is first created. */ 
 @Override 
 public void onCreate(Bundle savedInstanceState) { 
 super.onCreate(savedInstanceState); 
 setContentView(R.layout.main); 
 
 etText = (EditText) findViewById(R.id.etText); 
 
 btnSave = (Button) findViewById(R.id.btnSave); 
 btnSave.setOnClickListener(this); 
 
 btnLoad = (Button) findViewById(R.id.btnLoad); 
 btnLoad.setOnClickListener(this); 
 } 
 
 @Override 
 public void onClick(View v) { 
 switch (v.getId()) { 
 case R.id.btnSave: 
 saveText(); 
 break; 
 case R.id.btnLoad: 
 loadText(); 
 break; 
 default: 
 break; 
 } 
 } 
 
 void saveText() { 
 sPref = getPreferences(MODE_PRIVATE); 
 Editor ed = sPref.edit(); 
 ed.putString(SAVED_TEXT, etText.getText().toString()); 
 ed.commit(); 
 Toast.makeText(this, "Text saved", Toast.LENGTH_SHORT).show(); 
 } 
 
 void loadText() { 
 sPref = getPreferences(MODE_PRIVATE); 
 String savedText = sPref.getString(SAVED_TEXT, ""); 
 etText.setText(savedText); 
 Toast.makeText(this, "Text loaded", Toast.LENGTH_SHORT).show(); 
 } 
 }

Defining screen elements, assigning handlers and implementing onClick - everything is clear and as usual. We are interested in the methods we call in onClick

saveText - save data. First, using the getPreferences method, we get the sPref object of the SharedPreferences class, which allows you to work with data (read and write). The MODE_PRIVATE constant is used to configure access and means that after saving, data will only be visible to this application. Next, in order to edit the data, the Editor object is required - we get it from sPref. In the putString method, we specify the name of the variable - this is the constant SAVED_TEXT , and the value is the content of the etText field. To save the data, you need to commit. And for clarity, we display a message that the data is saved.

loadText - load data. Just like saveText, using the getPreferences method, we get an sPref object of the SharedPreferences class. MODE_PRIVATE is specified again, although it is used only when writing data. Here we do not use the Editor, because we are only interested in reading the data. We read with the help of the getString method - in the parameters we specify a constant - this is the name and the default value (empty string). Next, we write the value in the etText input field and display a message that the data has been read.

All save, run the application.

For a start, let's make sure that saving is basically necessary. Enter a thread text in the input field