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This article mainly introduces some knowledge points in Android development. By reading this article, you will gain the following contents:
- Inheriting SQLiteOpenHelper to create databases and tables
- Insert database data
- Delete database data
- Query database data
- Modify database data
- Use case of database
Android provides a pair of SQLite Full support of the database. Any class in the application (excluding those outside the application) can access any database you create by name. If you want the database you create to be used by external applications, use ContentProvider to provide an interface. The use of SQLite lightweight database is as follows:
1. Inheriting SQLiteOpenHelper to create databases and tables
Create database tables
1. Grammar
The syntax for creating data tables is as follows:
2. Examples
Examples are as follows:
3. Inheriting SQLiteDBHelper to create databases and tables
The methods of creating database and data table are as follows:
4. Delete database tables
The method of deleting database tables is as follows:
DROP TABLE IF EXITS TABLE_NAME;
2. Insert database data
Method 1 for inserting data
- grammar
INSERT INTO TABLE_NAME [(column1, column2, column3,...columnN)] VALUES (value1, value2, value3,...valueN);
- Give an example
INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) VALUES (1, 'Paul', 32, 'California', 20000.00 );
Data insertion method 2
- grammar
INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);
- Give an example
INSERT INTO COMPANY VALUES (7, 'James', 24, 'Houston', 10000.00 );
Android encapsulation insert() insert data method 3
1. Grammar
insert(String table, String nullColumnHack, ContentValues values)
2. Examples
private SQLiteDatabase db; db.insert(SQLiteDBHelper.TABLE_NAME, null, values);
3. Delete database data
Method 1 for deleting database data
1. Grammar
DELETE FROM table_name WHERE [condition];
2. Examples
DELETE FROM COMPANY WHERE ID = 7;
2.Android encapsulation and deletion of database data method 2
1. Grammar
delete(String table, String whereClause, String[] whereArgs)
Give an example
private SQLiteDatabase db; db.delete(SQLiteDBHelper.TABLE_NAME, "name=?", new String[] { "Jack" });
4. Query database data
Query database method 1
1. Grammar
SELECT column1, column2, columnN FROM table_name;
Method of querying all data in a table
SELECT * FROM table_name;
2. Examples
//1. Query the specified column SELECT ID, NAME, SALARY FROM COMPANY; // 2. All contents in the query table SELECT * FROM COMPANY;
Android encapsulation query database method 2
1. Grammar
query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)
2. Examples
private SQLiteDatabase db; Cursor cursor = db.query(SQLiteDBHelper.TABLE_NAME, null, null, null, null, null, null);
5. Modify database data
Modifying database method 1
1. Grammar
UPDATE table_name SET column1 = value1, column2 = value2...., columnN = valueN WHERE [condition];
2. Examples
UPDATE COMPANY SET ADDRESS = 'Texas' WHERE ID = 6;
Android update encapsulation and modification of database method 2
1. Grammar
update(String table, ContentValues values, String whereClause, String[] whereArgs)
2. Examples
db.update(SQLiteDBHelper.TABLE_NAME, values, "nickname=?", new String[] { "J" });
6. Case study of database usage
- Achieving results
Create a database
The method of creating database is as follows:
public class SQLiteDBHelper extends SQLiteOpenHelper { public static String DB_NAME = "person.db"; // version must be greater than 1 public static int DB_VERSION = 1; public static String TABLE_NAME = "person"; public static String _ID = "_id"; public static String NAME = "name"; public static String NICK_NAME = "nickname"; public SQLiteDBHelper(Context context, String name, CursorFactory factory, int version) { super(context, name, factory, version); // TODO Auto-generated constructor stub } public SQLiteDBHelper(Context context) { super(context, DB_NAME, null, DB_VERSION); } @Override public void onCreate(SQLiteDatabase db) { // In SQLite databases, fields are typeless, except for primary keys, which must be integer. String sql = "CREATE TABLE " + TABLE_NAME + "(" + _ID + " INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL" + "," + NAME + " CHAR(10)," + NICK_NAME + " CHAR(10))"; db.execSQL(sql); } // Processing method of database upgrade, @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { if (newVersion > oldVersion) { // Delete old tables and create new ones String dropsql = "DROP TABLE IF EXITS " + TABLE_NAME; db.execSQL(dropsql); onCreate(db); } } }
Implementing the Method of Adding Data to Database
The implementation code of the method of adding data to the database is as follows:
// public void InsertSQL(View view) { InstertDB(); QueryDB(); } /** * Insertion Data Processing Method */ private void InstertDB() { ContentValues values = new ContentValues(); values.put("name", "Jack"); values.put("nickname", "J"); // Return value: the line number of the most recently inserted line long result = db.insert(SQLiteDBHelper.TABLE_NAME, null, values); if (result > 0) { Toast.makeText(getApplicationContext(), "Added Successfully", Toast.LENGTH_SHORT) .show(); } else { Toast.makeText(getApplicationContext(), "Failure to add", Toast.LENGTH_SHORT) .show(); } }
Implementation of Content Deletion Method in Database
The implementation code of the database deletion method is as follows:
/** * Delete data */ private void DeleteDb() { int result = db.delete(SQLiteDBHelper.TABLE_NAME, "name=?", new String[] { "Jack" }); if (result > 0) { Toast.makeText(getApplicationContext(), "Successful deletion", Toast.LENGTH_SHORT) .show(); } else { Toast.makeText(getApplicationContext(), "nothing Jack", Toast.LENGTH_SHORT) .show(); } }
Implementation of Content Modification Method in Database
The implementation code of database modification content method is as follows:
/** * Modify data */ private void UpdateDb() { // update person set name="Kitty" where nickname="J" ContentValues values = new ContentValues(); values.put("name", "Lucy"); int result = db.update(SQLiteDBHelper.TABLE_NAME, values, "nickname=?", new String[] { "J" }); if (result > 0) { QueryDB(); } }
Implementation of database query method
The implementation code of the database query method is as follows:
/** * Query Data Processing Method */ private void QueryDB() { // Select * from person where name= ? // db.rawQuery(s) // Cursor cursor - "result set" // When using SimpleCusorAdapter, cursor must contain "_id" in the record. // Cursor cursor = db.query(SQLiteDBHelper.TABLE_NAME, null, "name=?", // new String[] { "Jack" }, null, null, null); Cursor cursor = db.query(SQLiteDBHelper.TABLE_NAME, null, null, null, null, null, null); while (cursor.moveToNext()) { String name = cursor.getString(cursor.getColumnIndex("name")); String nickname = cursor.getString(cursor .getColumnIndex("nickname")); } // Exchange a new cusor with the original customer adapter.swapCursor(cursor); adapter.notifyDataSetChanged(); }
- The layout is as follows
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <Button android:id="@+id/insertdata" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="InsertSQL" android:text="Adding data" /> <Button android:id="@+id/deletedata" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="DeleteSQL" android:text="Delete data" /> <Button android:id="@+id/quarydata" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="QuarySQL" android:text="Query data" /> <Button android:id="@+id/modifydata" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="ModifySQL" android:text="Modify data" /> <ListView android:id="@+id/lv" android:layout_width="match_parent" android:layout_height="match_parent" /> </LinearLayout>
- The ListView item layout is as follows
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center_vertical" android:orientation="horizontal" android:padding="10dp" > <TextView android:id="@+id/name" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="name" /> <TextView android:id="@+id/nickname" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="nickname" /> </LinearLayout>
So far, this article is over. If there are any mistakes, you are welcome to make suggestions and corrections. At the same time look forward to your attention, thank you for reading, thank you!
