SQLite使用方法

方法总结

方法	说明
getReadableDatabase()	SQLiteOpenHelper方法Create and/or open a database.
getWritableDatabase()	SQLiteOpenHelper方法Create and/or open a database that will be used for reading and writing.
onCreate(SQLiteDatabase db)	SQLiteOpenHelper方法Called when the database is created for the first time.
onOpen(SQLiteDatabase db)	SQLiteOpenHelper方法Called when the database has been opened.
onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)	SQLiteOpenHelper方法如果SQLiteOpenHelper创建时候输入的版本号和上一个不一致，将调用该方法例如(类SQLiteActivity.java) DatabaseHelper d = new DatabaseHelper(SQLiteActivity.this, "test_mars_db",2);SQLiteDatabase s = d.getReadableDatabase(); 如果上个版本号是1，而这次是2，执行该语句的时候，将会触发onUpgrade方法。DatabaseHelper类是自建类，继承SQLiteOpenHelper类Called when the database needs to be upgraded.
close()	SQLiteOpenHelper方法Close any open database object.

例子：
Strings.xml(/res/values)

<?xml version="1.0" encoding="utf-8"?>
<resources>
     <string name="hello">Hello World, SQLiteActivity!</string>
     <string name="app_name">SQLiteActivity</string>
     <string name="createTable">create table</string>
     <string name="upgrade">upgrade table</string>
     <string name="insert">insert</string>
     <string name="update">update</string>
     <string name="query">query</string>
</resources>

Main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<Button android:id="@+id/button1" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/createTable"></Button>
<Button android:id="@+id/button2" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/upgrade"></Button>
<Button android:id="@+id/button3" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/insert"></Button>
<Button android:id="@+id/button4" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/update"></Button>
<Button android:id="@+id/button5" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/query"></Button>
</LinearLayout>

DatabaseHelper.java

public class DatabaseHelper extends SQLiteOpenHelper {
	//DatabaseHelper作为一个助手类，提供两个功能
	//第一，getReadableDatabase()和getWritableDatabase()可以得到SQLiteDatabase
	//      如果第一次创建数据库，会调用SQLiteOpenHelper的onCreate方法
	//第二，提供onCreate()和onUpgrade()两个回调函数，允许创建和升级数据库
	private static final int VERSON = 1;
	public DatabaseHelper(Context context, String name, CursorFactory factory,
			int version) {
		super(context, name, factory, version);
	}
	public DatabaseHelper(Context context, String name) {
		this(context, name, VERSON);
	}
	public DatabaseHelper(Context context, String name, int version) {
		this(context, name, null, version);
	}
	//该函数在第一次创建数据库时执行，实际第一次得到SQLiteDatabase对象时执行
	@Override
	public void onCreate(SQLiteDatabase db) {
		System.out.println("create a Database");
		db.execSQL("create table user(id integer PRIMARY KEY autoincrement,name varchar(20))");
	}
	@Override
	 public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		System.out.println("update a database");
	 }
}

SQLiteActivity.java

public class SQLiteActivity extends Activity {
    /** Called when the activity is first created. */
      @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //该将创建库和表
        Button b1 = (Button)findViewById(R.id.button1);
        b1.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				DatabaseHelper d = new DatabaseHelper(SQLiteActivity.this, "test_mars_db");
				SQLiteDatabase s = d.getReadableDatabase();
			}
		});
        //该按钮测试版本不同触发的方法upgrade
        Button b2 = (Button)findViewById(R.id.button2);
        b2.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				DatabaseHelper d = new DatabaseHelper(SQLiteActivity.this, "test_mars_db",2);
				SQLiteDatabase s = d.getReadableDatabase();
			}
        });
        //该按钮做表数据插入操作
        Button b3 = (Button)findViewById(R.id.button3);
        b3.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				ContentValues cv = new ContentValues();
				cv.put("id", 1);
				cv.put("name", "zhangsan");
				DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_mars_db");
				SQLiteDatabase s = dbHelper.getWritableDatabase();
				s.insert("user", null, cv);
			}
        });
        //该按钮做表数据更新操作
        Button b4 = (Button)findViewById(R.id.button4);
        b4.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				ContentValues cv = new ContentValues();
				cv.put("id", 1);
				cv.put("name", "zhangsanfeng");
				DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_mars_db");
				SQLiteDatabase s = dbHelper.getWritableDatabase();
				s.update("user", cv, "id=?", new String[]{"1"});
			}
        });
        //该按钮做表数据查询操作
        Button b5 = (Button)findViewById(R.id.button5);
        b5.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_mars_db");
				SQLiteDatabase s = dbHelper.getWritableDatabase();
				Cursor c = s.query("user", new String[]{"id","name"}, "id=?", new String[]{"1"}, null, null, null);
				while(c.moveToNext()){
					String name = c.getString(c.getColumnIndex("name"));
					System.out.println("query-->"+name);
				}
			}
        });
      }
}

删除表语句!!

db.execSQL("DROP TABLE IF EXISTS "+FOOD_TABLE_NAME);