数据存储之SQLite

茅屋为秋风

　　dbHelper.java
　　


package com.terry;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.util.Log;
public class dbHelper extends SQLiteOpenHelper {
private final static String DATABASE_NAME="sec_db";
private final static int DATABASE_VERSION=1;
private final static String TABLE_NAME="sec_pwd";
public final static String FIELD_ID="_id";
public final static String FIELD_TITLE="sec_Title";

public dbHelper(Context context)
{   
/**
* 通过构造函数来创建数据库,如果进入此函数，不存在此数据库则创建，如果存在此数据库则打开连接，
* 只要进入此方法就可以用打开的连接获得getWritableDatabase()或getReadableDatabase()这两个方法。
*/
super(context, DATABASE_NAME,null, DATABASE_VERSION);
}

/**
* 一个数据库中可以包含多个表，每一条数据都存在指定的表中，要创建可以通过 execSQL 方法来执行一条 SQL 语句。
*/
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
//创建了表名为“sec_pwd” 的数据表，表内存在一个 integer 类型的主键和一个 text 类型的字段，并执行创建该表。
String sql="Create table "+TABLE_NAME+"("+FIELD_ID+" integer primary key autoincrement,"
+FIELD_TITLE+" text );";
db.execSQL(sql);

}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
String sql=" DROP TABLE IF EXISTS "+TABLE_NAME;
db.execSQL(sql);
onCreate(db);
}
/**
* 查询数据
* @return
*/
public Cursor select()
{
SQLiteDatabase db=this.getReadableDatabase();
Cursor cursor=db.query(TABLE_NAME, null, null, null, null, null,  " _id desc");
return cursor;
}
/**
* 添加数据
* @param Title
* @return
*/
public long insert(String Title)
{   
/**
* 封装了一个使用SQLite 的 insert 方法，向表中添加数据，但是insert 方法要求把数据都打包到 ContentValues 中，
*  ContentValue 其实可就是一个 HashTable，Key值是字段名称，Value 值是字段的值。
* 通过 ContentValues 的put 方法就可以把数据库放到 ContentValue 对象中，然后插入到表中去。
*/
SQLiteDatabase db=this.getWritableDatabase();
ContentValues cv=new ContentValues();
cv.put(FIELD_TITLE, Title);
long row=db.insert(TABLE_NAME, null, cv);
return row;
}
/**
* 删除数据
* @param id
*/
public void delete(int id)
{
SQLiteDatabase db=this.getWritableDatabase();
String where=FIELD_ID+"=?";
String[] whereValue={Integer.toString(id)};
db.delete(TABLE_NAME, where, whereValue);
}
/**
* 修改数据
* @param id
* @param Title
*/
public void update(int id,String Title)
{
SQLiteDatabase db=this.getWritableDatabase();
String where=FIELD_ID+"=?";
String[] whereValue={Integer.toString(id)};
ContentValues cv=new ContentValues();
cv.put(FIELD_TITLE, Title);
db.update(TABLE_NAME, cv, where, whereValue);
}


}

　　这里用到了Menu做功能按钮，实例代码如下：
　　package com.terry;


import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteCursor;
import android.os.Bundle;
import android.view.Menu;  
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;

public class testDbActivity extends Activity {
private dbHelper db;
private Cursor myCursor;
private ListView myListView;
private EditText myEditText;
private int _id;
protected final static int MENU_ADD=Menu.FIRST;
protected final static int MENU_EDIT=Menu.FIRST+1;
protected final static int MENU_DELETE=Menu.FIRST+2;
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// TODO Auto-generated method stub
super.onCreateOptionsMenu(menu);
menu.add(Menu.NONE, MENU_ADD, 0, R.string.ADD);
menu.add(Menu.NONE, MENU_EDIT, 0,R.string.EDIT);
menu.add(Menu.NONE, MENU_DELETE, 0,R.string.DELETE);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// TODO Auto-generated method stub
super.onOptionsItemSelected(item);
switch (item.getItemId()) {
case MENU_ADD:
operation("add");
break;
case MENU_EDIT:
operation("edit");
break;
case MENU_DELETE:
operation("delete");
break;
default:
break;
}
return true;
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myEditText=(EditText)findViewById(R.id.EditText1);
myListView=(ListView)findViewById(R.id.ListView1);
db=new dbHelper(testDbActivity.this);
myCursor=db.select();
SimpleCursorAdapter adpater=new SimpleCursorAdapter(this
, R.layout.test, myCursor,
new String[]{dbHelper.FIELD_TITLE},
new int[]{R.id.topTextView});
myListView.setAdapter(adpater);
myListView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// TODO Auto-generated method stub
myCursor.moveToPosition(arg2);
_id=myCursor.getInt(0);
myEditText.setText(myCursor.getString(1));
}
});

myListView.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
// TODO Auto-generated method stub
SQLiteCursor sc=(SQLiteCursor)arg0.getSelectedItem();
_id=sc.getInt(0);
myEditText.setText(sc.getString(1));
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
});
}
private void operation(String cmd)
{
if(myEditText.getText().toString().equals(""))
return;
if(cmd=="add")
db.insert( myEditText.getText().toString());
if(cmd=="edit")
db.update(_id,  myEditText.getText().toString());
if(cmd=="delete")
db.delete(_id);
myCursor.requery();
myListView.invalidateViews();
myEditText.setText("");
_id=0;
}




}