1.定義:SQLite是一款輕量級的關係型數據庫,運行快,佔用資源少。
2.創建數據庫
*android爲方便管理數據庫,專門提供了SQLiteOpenHelper幫助類可以簡單地對數據庫進行創建和升級。
*SQLiteOpenHelper是一個抽象類,有兩個抽象方法,分別是onCreate()、onUpgrade()負責數據庫的創建和升級。
*SQLiteOpenHelper中還有兩個非常重要的實例方法:getReadableDatabase()和getWritableDatabase()。這兩個
方法都可以創建或打開一個現有的數據庫(如數據庫已存在則直接打開,否則創建一個新的數據庫),並返回一
個可對數據庫進行讀寫操作的對象。不同的是,當數據庫不可寫入時(如磁盤已滿),getReadableDatabase()
方法返回的對象將以只讀的方式打開數據庫,而getWritableDatabase()方法則將出現異常。
*SQLiteOpenHelper中有兩個構造方法可供重寫,一般使用參數少的構造方法即可。這個構造方法接收四個參數,
第一個參數是Context,第二個參數是數據庫名,第三個參數允許我們在查詢數據的時候返回一個自定義的Cursor,
一般都傳入null,第四個參數表示數據庫的版本號。數據庫文件存放在/data/data/<package name>/databases/目錄
下。
步驟:首先書寫創建語句,然後自定義一個類繼承SQLiteOpenHelper然後執行。
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<Button
android:id="@+id/create_database"
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="創建數據庫"/>
<Button
android:id="@+id/add_data"
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="添加數據"/>
<Button
android:id="@+id/update_data"
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="更新數據"/>
<Button
android:id="@+id/delete_data"
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="刪除數據"/>
<Button
android:id="@+id/query_data"
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="查詢數據"/>
</LinearLayout>
public class MyDatabaseHelper extends SQLiteOpenHelper {
//創建數據庫
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 sqLiteDatabase) {
//創建數據庫
sqLiteDatabase.execSQL(CREATE_BOOK);
Toast.makeText(mContext,"Created successed",Toast.LENGTH_SHORT).show();
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion)
{
}
}
public class MainActivity extends AppCompatActivity {
Button createDatabase;
Button addData;
Button updateData;
Button deleteData;
Button queryData;
private MyDatabaseHelper dbHelper;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
createDatabase=findViewById(R.id.create_database);
addData=findViewById(R.id.add_data);
updateData=findViewById(R.id.update_data);
deleteData=findViewById(R.id.delete_data);
queryData=findViewById(R.id.query_data);
//1創建數據庫
dbHelper=new MyDatabaseHelper(this,"BookStore.db",null,1);
createDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
dbHelper.getWritableDatabase();
}
});
}
}
3.升級數據庫
public class MyDatabaseHelper extends SQLiteOpenHelper {
//創建數據庫
public static final String CREATE_BOOK="create table Book("
+"id integer primary key autoincrement,"
+"author text,"
+"price real,"
+"pages integer,"
+"name text)";
//省級數據庫
public static final String CREATE_CATEGORY="create table Category("
+"id integer primary key autoincrement,"
+"category_name text,"
+"category_code integer)";
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 sqLiteDatabase) {
//創建數據庫
sqLiteDatabase.execSQL(CREATE_BOOK);
//升級數據庫
sqLiteDatabase.execSQL(CREATE_CATEGORY);
Toast.makeText(mContext,"Created successed",Toast.LENGTH_SHORT).show();
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
sqLiteDatabase.execSQL("drop table if exists Book");
sqLiteDatabase.execSQL("drop table if exists Category");
onCreate(sqLiteDatabase);
}
}
public class MainActivity extends AppCompatActivity {
Button createDatabase;
Button addData;
Button updateData;
Button deleteData;
Button queryData;
private MyDatabaseHelper dbHelper;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
createDatabase=findViewById(R.id.create_database);
addData=findViewById(R.id.add_data);
updateData=findViewById(R.id.update_data);
deleteData=findViewById(R.id.delete_data);
queryData=findViewById(R.id.query_data);
//1創建數據庫
// dbHelper=new MyDatabaseHelper(this,"BookStore.db",null,1);
//升級數據庫
dbHelper=new MyDatabaseHelper(this,"BookStore.db",
null,2);
}
}
4.添加數據
public class MainActivity extends AppCompatActivity {
Button createDatabase;
Button addData;
Button updateData;
Button deleteData;
Button queryData;
private MyDatabaseHelper dbHelper;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
createDatabase=findViewById(R.id.create_database);
addData=findViewById(R.id.add_data);
updateData=findViewById(R.id.update_data);
deleteData=findViewById(R.id.delete_data);
queryData=findViewById(R.id.query_data);
//1創建數據庫
// dbHelper=new MyDatabaseHelper(this,"BookStore.db",null,1);
//升級數據庫
dbHelper=new MyDatabaseHelper(this,"BookStore.db",
null,2);
createDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
dbHelper.getWritableDatabase();
}
});
//添加數據
addData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
SQLiteDatabase db=dbHelper.getWritableDatabase();
ContentValues values=new ContentValues();
values.put("name","The Da Vinci Code");
values.put("author","Dan Brown");
values.put("pages",454);
values.put("price",15.34);
//插入一條數據
db.insert("Book",null,values);
values.clear();
//開始第二組數據
values.put("name","The Lost Symbol");
values.put("author","Dan Brown");
values.put("pages",510);
values.put("price",23.43);
//插入第二條數據
db.insert("Book",null,values);
}
});
}
}
5.更新數據
//更新數據
updateData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
SQLiteDatabase db=dbHelper.getWritableDatabase();
ContentValues values=new ContentValues();
values.put("price",12.23);
db.update("Book",values,"name=?",new String[]{
"The Da Vinci Code"
});
}
});
6.刪除數據
//刪除數據
deleteData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
SQLiteDatabase db=dbHelper.getWritableDatabase();
db.delete("Book","pages>?",new String[]{"500"});
}
});
7.查詢數據
//查詢數據
queryData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
SQLiteDatabase db=dbHelper.getWritableDatabase();
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"));
}while (cursor.moveToNext());
}
cursor.close();
}
});