Android--数据储存
1.文件储存
文件储存数据
- 通过openFileOutput()方法创建一个FileOutputStream对象：
FileOutputStream out = null;
out = openFileOutput( "data", Context.MODE_PRIVATE );
- 借助FileOutputStream对象创建一个OutputStreamWriter对象
- 使用OutputStreamWriter对象创建一个BufferedWriter对象：
BufferedWriter writer = null;
writer = new BufferedWriter(new OutputStreamWriter(out));
- 通过BufferedWriter对象的write()方法写入数据：
writer.write(inputText);
- 关闭：
writer.close();
- eg：
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();
}
}
}
文件读取数据
- 通过openFileInput()方法创建一个FileInputStream对象：
FileInputStream in = null;
in = openFileInput( "data" );
- 借助FileInputStream对象创建一个InputStreamReader对象
- 通过InputStreamReader对象创建一个BufferedReader对象：
BufferedReader reader = null;
reader = new BufferedReader( new InputStreamReader(in) );
- 读取数据：
String line = "";
//将数据写入content对象
while ((line = reader.readLine()) != null){
content.append( line );
}
//将content对象return出去
return content.toString();
- 5.关闭：
reader.close();
- eg
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();
}
2. SharedPreferences储存
SharedPreferences储存数据
1.调用SharedPreferences对象的edit()方法创建一个SharedPreferences.Editor对象
SharedPreferences.Editor editor = getSharedPreferences( "data2",MODE_PRIVATE ).edit();
2.写入数据
editor.putString( "name","Sim" );
editor.putInt( "age",22 );
editor.putBoolean( "married",false );
3.提交
editor.commit();
eg
//button事件通过SharedPreferences方法储存数据到文件
saveData_button.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View view) {
SharedPreferences.Editor editor = getSharedPreferences( "data2",MODE_PRIVATE ).edit();
editor.putString( "name","Sim" );
editor.putInt( "age",22 );
editor.putBoolean( "married",false );
editor.commit();
Toast.makeText( MainActivity.this,"已通过SharedPreferences存储数据", Toast.LENGTH_SHORT ).show();
}
} );
SharedPreferences读取数据
1.调用SharedPreferences对象的edit()方法创建一个SharedPreferences.Editor对象
SharedPreferences pref = getSharedPreferences( "data2",MODE_PRIVATE );
2.读取数据
String name = pref.getString( "name","" );
int age = pref.getInt( "age",0 );
boolean married = pref.getBoolean( "married",false );
eg
//button事件通过SharedPreferences方法从文件读取数据
readData_button.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View view) {
SharedPreferences pref = getSharedPreferences( "data2",MODE_PRIVATE );
String name = pref.getString( "name","" );
int age = pref.getInt( "age",0 );
boolean married = pref.getBoolean( "married",false );
}
} );
3. SQLite数据库储存
创建数据库和建表操作
- 新建一个类继承SQLiteOpenHelper。里面编写创建、更新数据库的SQL语句
public class MyDatabaseHelper extends SQLiteOpenHelper {
//将SQL建表语句定义成一个常量
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,SQLiteDatabase.CursorFactory factory, int version) {
super( context, name, factory, version );
mcontext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
//建表
db.execSQL( CREATE_BOOK );
Toast.makeText( mcontext,"已创建数据库表",Toast.LENGTH_SHORT ).show();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//如果已经存在Book或Category表，则删除两张表，调用onCreate()方法重新建表
db.execSQL( "drop table if exists Book" );
onCreate( db );
}
}
- 构建这个类的对象调用构造方法创建数据库
//构建一个MyDatabaseHelper对象（数据库名为BookStoredb.db，版本号为1）
dbHelper = new MyDatabaseHelper( this,"BookStore.db",null,1 );
添加数据
- 获取SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getWritableDatabase();
- 实例化一个ContentValues用来装载待插入的数据
ContentValues values = new ContentValues( );
- 添加数据到ContentValues对象中
values.put( "name","Hello Sim" );
values.put( "author","Dan Brown" );
values.put( "pages",454 );
values.put( "price",16.96 );
- 调用insert()方法将ContentValues对象添加到表中
db.insert( "Book",null,values );
修改数据
- 获取SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getWritableDatabase();
- 实例化一个ContentValues用来装载待插入的数据
ContentValues values = new ContentValues( );
- 给ContentValues对象指定一组数据
values.put( "price",10.96 );
- 调用insert()方法将ContentValues对象添加到表中
db.update( "Book",values,"name=?",new String[]{"Hello Sim"} );
//将Book表里名字是Hello Sim的这本书价格改成10.96
删除数据
- 获取SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getWritableDatabase();
- 调用delete()方法删除数据
db.delete( "Book","pages>?",new String[]{"500"} );
//将Book表里pages值大于500的数据
查询数据
- 获取SQLiteDatabase对象
SQLiteDatabase db = dbHelper.getWritableDatabase();
- 调用query()方法查询数据
Cursor cursor = db.query( "Book",null,null,null,null,null,null );
if(cursor.moveToFirst()){
do{
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.e( "Query", "book name is"+name );
Log.e( "Query", "book author is"+author );
Log.e( "Query", "book pages is"+pages );
Log.e( "Query", "book price is"+price );
}while (cursor.moveToNext());
}
cursor.close();
4.内容提供器
自定义内容提供器
新建一个继承自 ContentProvider 的类，实现它的 6 个抽象方法：
onCreate()，getType()，insert()，delete()，update()，query()
