編輯:關於android開發
public class MyDatabaseHelper extends SQLiteOpenHelper { private static final String db_name = "SQLite_db.db";//數據文件的名字 private static int NUMBER = 1;//當前數據庫版本,用於升級 private static final String table_name = "students";//表名 private static String sql = null;//sql語句 public MyDatabaseHelper(Context context) { super(context, db_name, null, NUMBER);//數據庫文件保存在當前應用所在包名:<包>/database/ } @Override public void onCreate(SQLiteDatabase db) { sql = "CREATE TABLE " + table_name + " (" + "id INTEGER PRIMARY KEY ," + "name VARCHAR(50) NOT NULL)";//創建數據庫的SQL語句 db.execSQL(sql);//執行SQL語句 } /** * 當數據庫進行升級是調用,這裡通過NUMBER值來進行判斷,數據庫是否升級 */ public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { //第一種寫法 sql = "ALTER TABLE " + table_name + " ADD sex VARCHAR(2) NULL"; Log.i("sql", sql); db.execSQL(sql); //第二種寫法 //db.execSQL("ALTER TABLE students ADD sex VARCHAR(10) NULL"); } }
下面我們在主Activity中創建這個類,然後進行數據的生成:
public class Activityone extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_one); //創建SqlLite數據庫 SQLiteOpenHelper helper = new MyDatabaseHelper(this); helper.getWritableDatabase(); } }
到這裡我們關於SQLite的創建就為大家分享完畢,需要提示的就是onUpgrade()方法,這個方法一般不執行,當我們的數據庫版本發生變化時,才會被執行。
下面我們來一起學習一下如何在Android中來使用SQLite數據庫,來完成對數據的增、刪、改、查、統計。
我們通過創建一個管理學生信息的數據庫來完成對SQLite功能的介紹展示,首先為了方便對學生類進行管理,我們先創建一個學生類:
public class tab_students { public Integer id;//學生Id public String name;//學生姓名 public String password;//學生密碼 public String school;//學生學校 public tab_students(){ } public tab_students(int _id,String _name,String _password){ id=_id; name=_name; password=_password; } public Integer getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String _name) { name = _name; } public String getPassword() { return password; } public void setPassword(String _password) { password = _password; } public String getSchool() { return school; } public void setSchool(String _school) { school = _school; } @Override public String toString() { return "id:"+this.getId()+" name:"+this.getName()+" password:"+this.getPassword(); } }
有了學生類,下面我們創建數據庫配置文件:
public class MyTabOpen extends SQLiteOpenHelper{ private static final String db_sql = "SQLiter.db"; private static int NUMBER = 1; private static final String tab_name = "students"; private static String sql = null; public MyTabOpen(Context context) { super(context, db_sql, null, NUMBER); } @Override public void onCreate(SQLiteDatabase db) { sql = "CREATE TABLE " + tab_name + " (" + "id INTEGER PRIMARY KEY ," + "name VARCHAR(20) NOT NULL ," + "password VARCHAR(20) NOT NULL)"; db.execSQL(sql); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { //在更新數據庫時,因原先數據庫表中已有數據,所以新增加的列屬性只能設置為“可以為空” db.execSQL("ALTER TABLE students ADD school VARCHAR(10) NULL"); } }
對於這個文件,大家有什麼疑問請看上面的SQLite數據庫創建講解。
這裡我們的主Activity的代碼如下,對於主Activity的布局文件,就不在粘代碼了,布局文件全是Button按鈕:
public class Activityone extends Activity { private static tab_students stu = null; private static tab_service ser = null; private static int conn = 1; private TextView mytext = null; private Button mybutton1 = null;//添加數據 private Button mybutton2 = null;//刪除數據 private Button mybutton3 = null;//修改數據 private Button mybutton4 = null;//查詢數據 private Button mybutton5 = null;//分頁獲取數據 private Button mybutton6 = null;//獲取數據總數 private Button mybutton7 = null;//普通頁面跳轉 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_one); mytext = (TextView)findViewById(R.id.textview); mytext.setText("增刪改查序"+"("+"sql語句"+")"); mybutton1 = (Button)findViewById(R.id.button1); mybutton2 = (Button)findViewById(R.id.button2); mybutton3 = (Button)findViewById(R.id.button3); mybutton4 = (Button)findViewById(R.id.button4); mybutton5 = (Button)findViewById(R.id.button5); mybutton6 = (Button)findViewById(R.id.button6); mybutton7 = (Button)findViewById(R.id.button7); mybutton1.setOnClickListener(new mybuttonlistener()); mybutton2.setOnClickListener(new mybuttonlistener()); mybutton3.setOnClickListener(new mybuttonlistener()); mybutton4.setOnClickListener(new mybuttonlistener()); mybutton5.setOnClickListener(new mybuttonlistener()); mybutton6.setOnClickListener(new mybuttonlistener()); mybutton7.setOnClickListener(new mybuttonlistener()); } class mybuttonlistener implements OnClickListener{ @Override public void onClick(View v) { switch (v.getId()) { case R.id.button1://添加數據 ser =new tab_service(getApplicationContext()); stu = new tab_students(conn++,"小米","abc123"); ser.save(stu); break; case R.id.button2://刪除數據 ser =new tab_service(getApplicationContext()); ser.del(1); break; case R.id.button3://修改數據 ser =new tab_service(getApplicationContext()); stu = new tab_students(1,"HTC","acm123"); ser.update(stu); break; case R.id.button4://查詢數據 ser =new tab_service(getApplicationContext()); stu=ser.find(1); System.out.println(stu.toString()); break; case R.id.button5://分頁獲取數據 ser =new tab_service(getApplicationContext()); List<tab_students> list = ser.getScrollDate(0,5); for(tab_students stu : list){ System.out.println(stu.toString()); } break; case R.id.button6://獲取數據總數 long number = 0; ser =new tab_service(getApplicationContext()); number=ser.gettab(); System.out.println("數據庫中共有:"+number+"條記錄."); break; default: Activityone.this.startActivity(new Intent(Activityone.this,Activitytwo.class));//普通跳轉 break; } } } }
大家可能已經看到了,這裡我們對SQLite的操作,都是通過tab_service.java類完成了,下面就為大家揭曉如何對SQLite進行操作:
public class tab_service { private MyTabOpen mytabopen = null; private static SQLiteDatabase db = null; private static String sql = null; private static final String tab_name = "students"; public tab_service(Context context) { this.mytabopen = new MyTabOpen(context);//獲得數據庫操作實例 } //添加數據 public void save(tab_students students){ db = mytabopen.getWritableDatabase(); sql = "insert into "+tab_name+"(id,name,password) values(?,?,?)"; db.execSQL(sql, new Object[]{students.getId(),students.getName(),students.getPassword()}); db.close(); //為了提高性能sqliter數據庫可以不關閉 } //刪除數據 public void del(Integer id){ db = mytabopen.getWritableDatabase(); sql = "delete from "+tab_name+" where id = ?"; db.execSQL(sql, new Object[]{id}); db.close(); } //更新數據 public void update(tab_students students){ db = mytabopen.getWritableDatabase(); sql = "update "+tab_name+" set name=?,password=? where id=?"; db.execSQL(sql, new Object[]{students.getName(), students.getPassword(), students.getId()}); db.close(); } //查詢數據 public tab_students find(Integer id){ //getReadableDatabase()與getWritableDatabase()通過查看源代碼知道,getReadableDatabase()方法在磁盤空間滿的時候,仍能返回數據庫操作實例,不過此時的實例只能用於讀不能寫 db = mytabopen.getReadableDatabase(); sql = "select * from "+tab_name+ " where id=?"; Cursor cur = db.rawQuery(sql, new String[]{id.toString()}); if(cur.moveToFirst()){ String name = cur.getString(cur.getColumnIndex("name")); String password = cur.getString(cur.getColumnIndex("password")); return new tab_students(id,name,password); } cur.close(); db.close(); return null; } //分頁獲取數據 public List<tab_students> getScrollDate(int again,int last){ List<tab_students> list = new ArrayList<tab_students>(); db = mytabopen.getReadableDatabase(); sql = "select * from "+tab_name+ "limit ?,? order by id asc";//根據查詢結果的id對數據進行升序排列 //sql = "select * from " +tab_name+ " limit ?,?"; Cursor cur = db.rawQuery(sql, new String[]{String.valueOf(again), String.valueOf(last)}); while (cur.moveToNext()) { int id = cur.getInt(cur.getColumnIndex("id")); String name = cur.getString(cur.getColumnIndex("name")); String password = cur.getString(cur.getColumnIndex("password")); tab_students stu = new tab_students(id, name, password); list.add(stu); } cur.close(); db.close(); return list; } //獲取數據總數目 public long gettab(){ db = mytabopen.getReadableDatabase(); sql = "select count(*) from "+tab_name; Cursor cur = db.rawQuery(sql, null); cur.moveToFirst(); long result = cur.getLong(0); return result; } }
是不是感覺和我們的SQL數據庫操作一樣,sql語句沒有什麼區別,是的,他們完全一致。沒學過數據庫的小朋友是不是已經抓狂啦,不要擔心,Android工程師想到了你們,Android為我們封裝好了一套對SQLite數據庫進行操作的規范,下面我們就一起來學習一下,如何通過Android提供的規范晚場上面的操作。
這裡我們只需要修改一下,我們上面對數據庫操作的類:
public class tab_service_two { private MyTabOpen mytabopen = null; private static SQLiteDatabase db = null; private static final String tab_name = "students"; public tab_service_two(Context context) { this.mytabopen = new MyTabOpen(context);//獲得數據庫操作實例 } //添加數據 public void save(tab_students students){ db = mytabopen.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("id", students.getId()); values.put("name", students.getName()); values.put("password", students.getPassword()); db.insert(tab_name, null, values); db.close(); } //刪除數據 public void del(Integer id){ db = mytabopen.getWritableDatabase(); db.delete(tab_name, "id=?", new String[]{id.toString()}); db.close(); } //修改數據 public void update(tab_students students){ db = mytabopen.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("name", students.getName()); values.put("password", students.getPassword()); db.update(tab_name, values, "id=?", new String[]{students.getId().toString()}); db.close(); } //查詢數據 public tab_students find(Integer id){ //getReadableDatabase()與getWritableDatabase()通過查看源代碼知道,getReadableDatabase()方法在磁盤空間滿的時候,仍能返回數據庫操作實例,不過此時的實例只能用於讀不能寫 db = mytabopen.getReadableDatabase(); //當要查詢數據庫表中的所以信息時,第二個參數可以使用設置為空來代替數組 Cursor cur = db.query(tab_name, new String[]{"name","password"}, "id=?", new String[]{id.toString()}, null, null, null); if(cur.moveToFirst()){ String name = cur.getString(cur.getColumnIndex("name")); String password = cur.getString(cur.getColumnIndex("password")); return new tab_students(id,name,password); } cur.close(); db.close(); return null; } //分頁獲取數據 public List<tab_students> getScrollDate(int again,int last){ List<tab_students> list = new ArrayList<tab_students>(); db = mytabopen.getReadableDatabase(); Cursor cur = db.query(tab_name, null, null, null, null, null, "id asc", again+","+last); while (cur.moveToNext()) { int id = cur.getInt(cur.getColumnIndex("id")); String name = cur.getString(cur.getColumnIndex("name")); String password = cur.getString(cur.getColumnIndex("password")); tab_students stu = new tab_students(id, name, password); list.add(stu); } cur.close(); db.close(); return list; } //獲取數據總數 public long gettab(){ db = mytabopen.getReadableDatabase(); Cursor cur = db.query(tab_name, new String[]{"count(*)"}, null, null, null, null, null); cur.moveToFirst(); long result = cur.getLong(0); return result; } }
好了關於SQLite在Android平台的使用,就為大家介紹完畢,內容很簡單,沒有太大的難度,相信小伙伴一定能理解。新手學習,高手交流。
上次講的Android上的SQLite分頁讀取,只用文本框顯示數據而已,這次就講得更加深入些,實現
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