Android基础——数据持久化存储

数据持久化存储
文件存储
数据保存

数据读取

键值对存储
数据保存

数据读取

数据库存储
数据库创建

增加数据

更新数据

删除数据

查询数据

使用事物

升级数据库

内容来自于第一行代码中数据持久化存储这一章

数据持久化存储

文件存储

数据保存

Context.openFileOutput( )方法 用于文件输出

第一个参数：文件名 默认保存到 /data/data/包名/files/

第二个参数：文件操作方式 Context.MODE_PRIVATE(覆盖方式) Context.MODE_APPEND(附加方式，没有就创建文件)

Android4.2中废弃了MODE_WORLD_READABLE MODE_WORLD_WRITEABLE

public class MainActivity extends Activity {

private EditText edit;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
edit = (EditText) findViewById(R.id.edit);
}

@Override
protected void onDestroy() {
super.onDestroy();
String inputText = edit.getText().toString();
save(inputText);
}

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();
}
}
}
}

数据读取

Context.openFileInput( )方法 用于文件输入

public class MainActivity extends Activity {

private EditText edit;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
edit = (EditText) findViewById(R.id.edit);
String inputText = load();

if (!TextUtils.isEmpty(inputText)) {
edit.setText(inputText);
edit.setSelection(inputText.length());
Toast.makeText(this, "Restoring succeeded",
Toast.LENGTH_SHORT).show();

}
}

……

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();
}
}

注意：

1、TextUitls.isEmpty( )一次检查字符串两种空值 “”与null

2、StringBuffer与StringBuilder的区别

StringBuffer不是线程同步的，所以不是线程安全的，但比StringBuilder速度快

StringBuilder是线程同步的，所以是线程安全的

键值对存储

SharedPreferences使用键值对的方式来存储数据，当保存一条数据的时候，需要给这条数据提供一个对应的键，这样在读取数据的时候可以通过这个键把相应的值取出来。

Context类提供getSharedPreferences( )方法

文件存储在 /data/data/share_prefs/目录下

Context.getSharedPreferences( )

第一个参数：文件名

第二个参数：存储模式 Context.MODE_PRIVATE Context.MODE_MULTI_PROCESS

Android4.2版本中废弃了Context.MODE_WORLD_READABLE Context.MODE_WORLD_WIRTEABLE

Activity类提供getPreferences( )方法

只有一个参数，即操作模式。保存的文件名即Activity的类名

PreferenceManager类提供getDefaultSharedPreferences( )

只接收一个Context参数，静态方法，保存的文件名即应用程序的包名

数据保存

public class MainActivity extends Activity {

private Button saveData;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
saveData = (Button) findViewById(R.id.save_data);

saveData.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
SharedPreferences.Editor editor = getSharedPreferences("data",MODE_PRIVATE).edit();
editor.putString("name", "Tom");
editor.putInt("age", 28);
editor.putBoolean("married", false);
editor.commit();
}
});
}
}

数据读取

public class MainActivity extends Activity {

private Button saveData;
private Button restoreData;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
saveData = (Button) findViewById(R.id.save_data);
restoreData = (Button) findViewById(R.id.restore_data);

……

restoreData.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
SharedPreferences pref = getSharedPreferences("data",MODE_PRIVATE);
String name = pref.getString("name", "");
int age = pref.getInt("age", 0);
boolean married = pref.getBoolean("married", false);
Log.d("MainActivity", "name is " + name);
Log.d("MainActivity", "age is " + age);
Log.d("MainActivity", "married is " + married);
}
});
}
}

数据库存储

数据库创建

public class MyDatabaseHelper extends SQLiteOpenHelper {

public static final String CREATE_BOOK = "create table book ("
+ "id integer primary key autoincrement, "
+ "author text, "
+ "price real, "
+ "pages integer, "
+ "name text)";

private Context mContext;

public MyDatabaseHelper(Context context, String name, CursorFactory factory, int version) {
super(context, name, factory, version);
mContext = context;
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK);
Toast.makeText(mContext, "Create succeeded", Toast.LENGTH_SHORT).show();
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}
}

public class MainActivity extends Activity {

private MyDatabaseHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 1);
Button createDatabase = (Button) findViewById(R.id.create_database);

createDatabase.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
dbHelper.getWritableDatabase();
}
});
}
}

增加数据

public class MainActivity extends Activity {

private MyDatabaseHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 2);
……

Button addData = (Button) findViewById(R.id.add_data);
addData.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
// 开始组装第一条数据
values.put("name", "The Da Vinci Code");
values.put("author", "Dan Brown");
values.put("pages", 454);
values.put("price", 16.96);
db.insert("Book", null, values); // 插入第一条数据
values.clear();
// 开始组装第二条数据
values.put("name", "The Lost Symbol");
values.put("author", "Dan Brown");
values.put("pages", 510);
values.put("price", 19.95);
db.insert("Book", null, values); // 插入第二条数据
}
});
}
}

更新数据

public class MainActivity extends Activity {

private MyDatabaseHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 2);
……
Button updateData = (Button) findViewById(R.id.update_data);

updateData.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("price", 10.99);
db.update("Book", values, "name = ?", new String[] { "The DaVinci Code" });
}
});
}
}

删除数据

public class MainActivity extends Activity {

private MyDatabaseHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 2);
……

Button deleteButton = (Button) findViewById(R.id.delete_data);

deleteButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
db.delete("Book", "pages > ?", new String[] { "500" });
}
});
}
}

查询数据

public class MainActivity extends Activity {

private MyDatabaseHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 2);
……
Button queryButton = (Button) findViewById(R.id.query_data);

queryButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
// 查询Book表中所有的数据
Cursor cursor = db.query("Book", null, null, null, null, null, null);
if (cursor.moveToFirst()) {
do {
// 遍历Cursor对象，取出数据并打印
String name = cursor.getString(cursor.
getColumnIndex("name"));
String author = cursor.getString(cursor.
getColumnIndex("author"));
int pages = cursor.getInt(cursor.getColumnIndex("pages"));
double price = cursor.getDouble(cursor.getColumnIndex("price"));
Log.d("MainActivity", "book name is " + name);
Log.d("MainActivity", "book author is " + author);
Log.d("MainActivity", "book pages is " + pages);
Log.d("MainActivity", "book price is " + price);
} while (cursor.moveToNext());
}
cursor.close();
}
});
}
}

使用事物

public class MainActivity extends Activity {

private MyDatabaseHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "BookStore.db", null, 2);
……
Button replaceData = (Button) findViewById(R.id.replace_data);

replaceData.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
db.beginTransaction(); // 开启事务
try {
db.delete("Book", null, null);
if (true) {
// 在这里手动抛出一个异常，让事务失败
throw new NullPointerException();
}
ContentValues values = new ContentValues();
values.put("name", "Game of Thrones");
values.put("author", "George Martin");
values.put("pages", 720);
values.put("price", 20.85);
db.insert("Book", null, values);
db.setTransactionSuccessful(); // 事务已经执行成功
} catch (Exception e) {
e.printStackTrace();
} finally {
db.endTransaction(); // 结束事务
}
}
});
}
}

升级数据库

public class MyDatabaseHelper extends SQLiteOpenHelper {

public static final String CREATE_BOOK = "create table Book ("
+ "id integer primary key autoincrement, "
+ "author text, "
+ "price real, "
+ "pages integer, "
+ "name text, "
+ "category_id integer)";

public static final String CREATE_CATEGORY = "create table Category ("
+ "id integer primary key autoincrement, "
+ "category_name text, "
+ "category_code integer)";

public MyDatabaseHelper(Context context, String name,CursorFactory factory, int version) {
super(context, name, factory, version);
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK);
db.execSQL(CREATE_CATEGORY);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
switch (oldVersion) {
case 1:
db.execSQL(CREATE_CATEGORY);
case 2:
db.execSQL("alter table Book add column category_id integer");
default:
}
}
}