Android编程中的5种数据存储方式

class viewocl implements view.onclicklistener{
    @override
    public void onclick(view v) {
      switch(v.getid()){
      case r.id.btnset:
        //步骤1：获取输入值
        string code = txtcode.gettext().tostring().trim();
        //步骤2-1：创建一个sharedpreferences.editor接口对象，lock表示要写入的xml文件名，mode_world_writeable写操作
        sharedpreferences.editor editor = getsharedpreferences("lock", mode_world_writeable).edit();
        //步骤2-2：将获取过来的值放入文件
        editor.putstring("code", code);
        //步骤3：提交
        editor.commit();
        toast.maketext(getapplicationcontext(), "口令设置成功", toast.length_long).show();
        break;
      case r.id.btnget:
        //步骤1：创建一个sharedpreferences接口对象
        sharedpreferences read = getsharedpreferences("lock", mode_world_readable);
        //步骤2：获取文件中的值
        string value = read.getstring("code", "");
        toast.maketext(getapplicationcontext(), "口令为："+value, toast.length_long).show();
        break;
      }
    }
}

public string read() {
    try {
      fileinputstream instream = this.openfileinput("message.txt");
      byte[] buffer = new byte[1024];
      int hasread = 0;
      stringbuilder sb = new stringbuilder();
      while ((hasread = instream.read(buffer)) != -1) {
        sb.append(new string(buffer, 0, hasread));
      }
      instream.close();
      return sb.tostring();
    } catch (exception e) {
      e.printstacktrace();
    } 
    return null;
  }
  public void write(string msg){
    // 步骤1：获取输入值
    if(msg == null) return;
    try {
      // 步骤2:创建一个fileoutputstream对象,mode_append追加模式
      fileoutputstream fos = openfileoutput("message.txt",
          mode_append);
      // 步骤3：将获取过来的值放入文件
      fos.write(msg.getbytes());
      // 步骤4：关闭数据流
      fos.close();
    } catch (exception e) {
      e.printstacktrace();
    }
}

<uses-permission android:name="android.permission.mount_unmount_filesystems"/>
<uses-permission android:name="android.permission.write_external_storage"/>

// 文件写操作函数
  private void write(string content) {
    if (environment.getexternalstoragestate().equals(
        environment.media_mounted)) { // 如果sdcard存在
      file file = new file(environment.getexternalstoragedirectory()
          .tostring()
          + file.separator
          + dir
          + file.separator
          + filename); // 定义file类对象
      if (!file.getparentfile().exists()) { // 父文件夹不存在
        file.getparentfile().mkdirs(); // 创建文件夹
      }
      printstream out = null; // 打印流对象用于输出
      try {
        out = new printstream(new fileoutputstream(file, true)); // 追加文件
        out.println(content);
      } catch (exception e) {
        e.printstacktrace();
      } finally {
        if (out != null) {
          out.close(); // 关闭打印流
        }
      }
    } else { // sdcard不存在，使用toast提示用户
      toast.maketext(this, "保存失败，sd卡不存在！", toast.length_long).show();
    }
  }
  // 文件读操作函数
  private string read() {
    if (environment.getexternalstoragestate().equals(
        environment.media_mounted)) { // 如果sdcard存在
      file file = new file(environment.getexternalstoragedirectory()
          .tostring()
          + file.separator
          + dir
          + file.separator
          + filename); // 定义file类对象
      if (!file.getparentfile().exists()) { // 父文件夹不存在
        file.getparentfile().mkdirs(); // 创建文件夹
      }
      scanner scan = null; // 扫描输入
      stringbuilder sb = new stringbuilder();
      try {
        scan = new scanner(new fileinputstream(file)); // 实例化scanner
        while (scan.hasnext()) { // 循环读取
          sb.append(scan.next() + "\n"); // 设置文本
        }
        return sb.tostring();
      } catch (exception e) {
        e.printstacktrace();
      } finally {
        if (scan != null) {
          scan.close(); // 关闭打印流
        }
      }
    } else { // sdcard不存在，使用toast提示用户
      toast.maketext(this, "读取失败，sd卡不存在！", toast.length_long).show();
    }
    return null;
}

db.executesql(string sql); 
db.executesql(string sql, object[] bindargs);
//sql语句中使用占位符，然后第二个参数是实际的参数集

db.insert(string table, string nullcolumnhack, contentvalues values); 
db.update(string table, contentvalues values, string whereclause, string whereargs); 
db.delete(string table, string whereclause, string whereargs);

contentvalues cv = new contentvalues();//实例化一个contentvalues用来装载待插入的数据
cv.put("title","you are beautiful");//添加title
cv.put("weather","sun"); //添加weather
cv.put("context","xxxx"); //添加context
string publish = new simpledateformat("yyyy-mm-dd hh:mm:ss")
            .format(new date());
cv.put("publish ",publish); //添加publish
db.insert("diary",null,cv);//执行插入操作

string sql = "insert into user(username,password) values ('jack johnson','ilovepopmuisc');//插入操作的sql语句
db.execsql(sql);//执行sql语句

string whereclause = "username=?";//删除的条件
string[] whereargs = {"jack johnson"};//删除的条件参数
db.delete("user",whereclause,whereargs);//执行删除

string sql = "delete from user where username='jack johnson'";//删除操作的sql语句
db.execsql(sql);//执行删除操作

contentvalues cv = new contentvalues();//实例化contentvalues
cv.put("password","ihatepopmusic");//添加要更改的字段及内容
string whereclause = "username=?";//修改条件
string[] whereargs = {"jack johnson"};//修改条件的参数
db.update("user",cv,whereclause,whereargs);//执行修改

string sql = "update user set password = 'ihatepopmusic' where username='jack johnson'";//修改的sql语句
db.execsql(sql);//执行修改

db.rawquery(string sql, string[] selectionargs);
db.query(string table, string[] columns, string selection, string[] selectionargs, string groupby, string having, string orderby);
db.query(string table, string[] columns, string selection, string[] selectionargs, string groupby, string having, string orderby, string limit);
db.query(string distinct, string table, string[] columns, string selection, string[] selectionargs, string groupby, string having, string orderby, string limit);

c.move(int offset); //以当前位置为参考,移动到指定行 
c.movetofirst();  //移动到第一行 
c.movetolast();   //移动到最后一行 
c.movetoposition(int position); //移动到指定行 
c.movetoprevious(); //移动到前一行 
c.movetonext();   //移动到下一行 
c.isfirst();    //是否指向第一条 
c.islast();   //是否指向最后一条 
c.isbeforefirst(); //是否指向第一条之前 
c.isafterlast();  //是否指向最后一条之后 
c.isnull(int columnindex); //指定列是否为空(列基数为0) 
c.isclosed();    //游标是否已关闭 
c.getcount();    //总数据项数 
c.getposition();  //返回当前游标所指向的行数 
c.getcolumnindex(string columnname);//返回某列名对应的列索引值 
c.getstring(int columnindex);  //返回当前行指定列的值 

string[] params = {12345,123456};
cursor cursor = db.query("user",columns,"id=?",params,null,null,null);//查询并获得游标
if(cursor.movetofirst()){//判断游标是否为空
  for(int i=0;i<cursor.getcount();i++){
    cursor.move(i);//移动到指定记录
    string username = cursor.getstring(cursor.getcolumnindex("username");
    string password = cursor.getstring(cursor.getcolumnindex("password"));
  }
}

cursor result=db.rawquery("select id, name, inventory from mytable");
//cursor c = db.rawquery("s name, inventory from mytable where id=?",new stirng[]{"123456"});   
result.movetofirst(); 
while (!result.isafterlast()) { 
  int id=result.getint(0); 
  string name=result.getstring(1); 
  int inventory=result.getint(2); 
  // do something useful with these 
  result.movetonext(); 
 } 
 result.close();

import android.content.context;
import android.database.sqlite.sqlitedatabase;
import android.database.sqlite.sqlitedatabase.cursorfactory;
import android.database.sqlite.sqliteopenhelper;
public class sqlitedbhelper extends sqliteopenhelper {
  // 步骤1：设置常数参量
  private static final string database_name = "diary_db";
  private static final int version = 1;
  private static final string table_name = "diary";
  // 步骤2：重载构造方法
  public sqlitedbhelper(context context) {
    super(context, database_name, null, version);
  }
  /*
   * 参数介绍：context 程序上下文环境 即：xxxactivity.this 
   * name 数据库名字 
   * factory 接收数据，一般情况为null
   * version 数据库版本号
   */
  public sqlitedbhelper(context context, string name, cursorfactory factory,
      int version) {
    super(context, name, factory, version);
  }
  //数据库第一次被创建时，oncreate()会被调用
  @override
  public void oncreate(sqlitedatabase db) {
    // 步骤3：数据库表的创建
    string strsql = "create table "
        + table_name
        + "(tid integer primary key autoincrement,title varchar(20),weather varchar(10),context text,publish date)";
    //步骤4：使用参数db,创建对象
    db.execsql(strsql);
  }
  //数据库版本变化时，会调用onupgrade()
  @override
  public void onupgrade(sqlitedatabase arg0, int arg1, int arg2) {
  }
}

import android.content.context;
import android.database.cursor;
import android.database.sqlite.sqlitedatabase;
import com.chinasoft.dbhelper.sqlitedbhelper;
public class diarydao {
  private sqlitedbhelper sqlitedbhelper;
  private sqlitedatabase db;
  // 重写构造方法
  public diarydao(context context) {
    this.sqlitedbhelper = new sqlitedbhelper(context);
    db = sqlitedbhelper.getwritabledatabase();
  }
  // 读操作
  public string execquery(final string strsql) {
    try {
      system.out.println("strsql>" + strsql);
      // cursor相当于jdbc中的resultset
      cursor cursor = db.rawquery(strsql, null);
      // 始终让cursor指向数据库表的第1行记录
      cursor.movetofirst();
      // 定义一个stringbuffer的对象，用于动态拼接字符串
      stringbuffer sb = new stringbuffer();
      // 循环游标，如果不是最后一项记录
      while (!cursor.isafterlast()) {
        sb.append(cursor.getint(0) + "/" + cursor.getstring(1) + "/"
            + cursor.getstring(2) + "/" + cursor.getstring(3) + "/"
            + cursor.getstring(4)+"#");
        //cursor游标移动
        cursor.movetonext();
      }
      db.close();
      return sb.deletecharat(sb.length()-1).tostring();
    } catch (runtimeexception e) {
      e.printstacktrace();
      return null;
    }
  }
  // 写操作
  public boolean execother(final string strsql) {
    db.begintransaction(); //开始事务
    try {
      system.out.println("strsql" + strsql);
      db.execsql(strsql);
      db.settransactionsuccessful(); //设置事务成功完成 
      db.close();
      return true;
    } catch (runtimeexception e) {
      e.printstacktrace();
      return false;
    }finally { 
      db.endtransaction();  //结束事务 
    } 
  }
}

public synchronized sqlitedatabase getreadabledatabase() { 
  if (mdatabase != null && mdatabase.isopen()) { 
    // 如果发现mdatabase不为空并且已经打开则直接返回 
    return mdatabase; 
  } 
  if (misinitializing) { 
    // 如果正在初始化则抛出异常 
    throw new illegalstateexception("getreadabledatabase called recursively"); 
  } 
  // 开始实例化数据库mdatabase 
  try { 
    // 注意这里是调用了getwritabledatabase()方法 
    return getwritabledatabase(); 
  } catch (sqliteexception e) { 
    if (mname == null) 
      throw e; // can't open a temp database read-only! 
    log.e(tag, "couldn't open " + mname + " for writing (will try read-only):", e); 
  } 
  // 如果无法以可读写模式打开数据库 则以只读方式打开 
  sqlitedatabase db = null; 
  try { 
    misinitializing = true; 
    string path = mcontext.getdatabasepath(mname).getpath();// 获取数据库路径 
    // 以只读方式打开数据库 
    db = sqlitedatabase.opendatabase(path, mfactory, sqlitedatabase.open_readonly); 
    if (db.getversion() != mnewversion) { 
      throw new sqliteexception("can't upgrade read-only database from version " + db.getversion() + " to " 
          + mnewversion + ": " + path); 
    } 
    onopen(db); 
    log.w(tag, "opened " + mname + " in read-only mode"); 
    mdatabase = db;// 为mdatabase指定新打开的数据库 
    return mdatabase;// 返回打开的数据库 
  } finally { 
    misinitializing = false; 
    if (db != null && db != mdatabase) 
      db.close(); 
  } 
}

public synchronized sqlitedatabase getwritabledatabase() { 
  if (mdatabase != null && mdatabase.isopen() && !mdatabase.isreadonly()) { 
    // 如果mdatabase不为空已打开并且不是只读模式 则返回该实例 
    return mdatabase; 
  } 
  if (misinitializing) { 
    throw new illegalstateexception("getwritabledatabase called recursively"); 
  } 
  // if we have a read-only database open, someone could be using it 
  // (though they shouldn't), which would cause a lock to be held on 
  // the file, and our attempts to open the database read-write would 
  // fail waiting for the file lock. to prevent that, we acquire the 
  // lock on the read-only database, which shuts out other users. 
  boolean success = false; 
  sqlitedatabase db = null; 
  // 如果mdatabase不为空则加锁 阻止其他的操作 
  if (mdatabase != null) 
    mdatabase.lock(); 
  try { 
    misinitializing = true; 
    if (mname == null) { 
      db = sqlitedatabase.create(null); 
    } else { 
      // 打开或创建数据库 
      db = mcontext.openorcreatedatabase(mname, 0, mfactory); 
    } 
    // 获取数据库版本(如果刚创建的数据库,版本为0) 
    int version = db.getversion(); 
    // 比较版本(我们代码中的版本mnewversion为1) 
    if (version != mnewversion) { 
      db.begintransaction();// 开始事务 
      try { 
        if (version == 0) { 
          // 执行我们的oncreate方法 
          oncreate(db); 
        } else { 
          // 如果我们应用升级了mnewversion为2,而原版本为1则执行onupgrade方法 
          onupgrade(db, version, mnewversion); 
        } 
        db.setversion(mnewversion);// 设置最新版本 
        db.settransactionsuccessful();// 设置事务成功 
      } finally { 
        db.endtransaction();// 结束事务 
      } 
    } 
    onopen(db); 
    success = true; 
    return db;// 返回可读写模式的数据库实例 
  } finally { 
    misinitializing = false; 
    if (success) { 
      // 打开成功 
      if (mdatabase != null) { 
        // 如果mdatabase有值则先关闭 
        try { 
          mdatabase.close(); 
        } catch (exception e) { 
        } 
        mdatabase.unlock();// 解锁 
      } 
      mdatabase = db;// 赋值给mdatabase 
    } else { 
      // 打开失败的情况：解锁、关闭 
      if (mdatabase != null) 
        mdatabase.unlock(); 
      if (db != null) 
        db.close(); 
    } 
  } 
}

public class sqliteactivity extends activity {
  public diarydao diarydao;
  //因为getwritabledatabase内部调用了mcontext.openorcreatedatabase(mname, 0, mfactory); 
  //所以要确保context已初始化,我们可以把实例化dao的步骤放在activity的oncreate里
  @override
  protected void oncreate(bundle savedinstancestate) {
    diarydao = new diarydao(sqliteactivity.this);
    initdatabase();
  }
  class viewocl implements view.onclicklistener {
    @override
    public void onclick(view v) {
      string strsql;
      boolean flag;
      string message;
      switch (v.getid()) {
      case r.id.btnadd:
        string title = txttitle.gettext().tostring().trim();
        string weather = txtweather.gettext().tostring().trim();;
        string context = txtcontext.gettext().tostring().trim();;
        string publish = new simpledateformat("yyyy-mm-dd hh:mm:ss")
            .format(new date());
        // 动态组件sql语句
        strsql = "insert into diary values(null,'" + title + "','"
            + weather + "','" + context + "','" + publish + "')";
        flag = diarydao.execother(strsql);
        //返回信息
        message = flag?"添加成功":"添加失败";
        toast.maketext(getapplicationcontext(), message, toast.length_long).show();
        break;
      case r.id.btndelete:
        strsql = "delete from diary where tid = 1";
        flag = diarydao.execother(strsql);
        //返回信息
        message = flag?"删除成功":"删除失败";
        toast.maketext(getapplicationcontext(), message, toast.length_long).show();
        break;
      case r.id.btnquery:
        strsql = "select * from diary order by publish desc";
        string data = diarydao.execquery(strsql);
        toast.maketext(getapplicationcontext(), data, toast.length_long).show();
        break;
      case r.id.btnupdate:
        strsql = "update diary set title = '测试标题1-1' where tid = 1";
        flag = diarydao.execother(strsql);
        //返回信息
        message = flag?"更新成功":"更新失败";
        toast.maketext(getapplicationcontext(), message, toast.length_long).show();
        break;
      }
    }
  }
  private void initdatabase() {
    // 创建数据库对象
    sqlitedbhelper sqlitedbhelper = new sqlitedbhelper(sqliteactivity.this);
    sqlitedbhelper.getwritabledatabase();
    system.out.println("数据库创建成功");
  }
}