SQLite数据库存储

MainActivity

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
private Button mButtonCreateDB;
    private Button mButtonInsert;
    private  SQLiteDatabase db;
    private Button mButtonUpdate;
    private Button mButtonDelete;
    private Button mButtonSelect;
    private EditText mEditTextUsername;
    private EditText mEditTextPassword;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SQLiteOpenHelper helper=new SQLiteOpenHelper(getApplicationContext(),"My_First_DB1.db");
        db=helper.getWritableDatabase();
        mButtonCreateDB= (Button) findViewById(R.id.button_db);
        mButtonCreateDB.setOnClickListener(this);
        mButtonInsert= (Button) findViewById(R.id.button_insert);
        mButtonInsert.setOnClickListener(this);
        mButtonUpdate= (Button) findViewById(R.id.button_update);
        mButtonUpdate.setOnClickListener(this);
        mButtonDelete= (Button) findViewById(R.id.button_delete);
        mButtonDelete.setOnClickListener(this);
        mButtonSelect= (Button) findViewById(R.id.button_select);
        mButtonSelect.setOnClickListener(this);
        mEditTextUsername= (EditText) findViewById(R.id.edittext_username);
        mEditTextUsername.setOnClickListener(this);
        mEditTextPassword= (EditText) findViewById(R.id.edittext_password);
        mEditTextPassword.setOnClickListener(this);
    }


    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.button_db:

       //必须调用getWritableDatabase()方法，为了调用到TestSQLiteOpenHelper里面的方法

                Toast.makeText(MainActivity.this,Toast.LENGTH_SHORT).show();
                break;
            case R.id.button_insert:
// ContentValues value=new ContentValues();
// value.put("name","zhangsan");
// value.put("password","123456");
// db.insert("user",value);
                ContentValues value=new ContentValues();
       //得到从屏幕上输入的数据; 
             value.put("name",mEditTextUsername.getText().toString());
                value.put("password",mEditTextPassword.getText().toString());
                db.insert("user",value);
                break;
            case R.id.button_update:
                ContentValues values=new ContentValues();
                values.put("password","abcdef");
                db.update("user",new String []{"zhangsan"});
                break;
            case R.id.button_delete:
                db.delete("user",Toast.LENGTH_SHORT).show();
                break;
            case R.id.button_select:
                Cursor cursor=db.query("user",4");//4是用来分页显示的(倒序的时候出去前四个)
// Cursor cursor=db.rawQuery("select * from user","用户名"+name+"密码"+password);
                    cursor.moveToNext();

                }
                break;
            default:
                break;

        }
    }
}

activity_main.xml

<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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <EditText
        android:id="@+id/edittext_username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入用户名"/>
    <EditText
        android:id="@+id/edittext_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入密码"/>

    <Button
        android:id="@+id/button_db"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="创建数据库"/>
    <Button
        android:id="@+id/button_insert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="插入数据"/>
    <Button
        android:id="@+id/button_update"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="修改数据"/>
    <Button
        android:id="@+id/button_delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="删除数据"/>
    <Button
        android:id="@+id/button_select"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="查询数据"/>




</LinearLayout>

（编辑：李大同）

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public class MainActivity extends AppCompatActivity implements View.OnClickListener{
private Button mButtonCreateDB;
    private Button mButtonInsert;
    private  SQLiteDatabase db;//创建SQLiteDatabase对象
     @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //对SQLiteOpenHelper进行实例化以后，在调用它的getReadableDatabase()或getWritableDatabase()方法来创建数据库
        SQLiteOpenHelper helper=new SQLiteOpenHelper(getApplicationContext(),"My_First_DB1.db");//创建的My_First_DB1.db数据库文件会存放在/data/data/《packsge name》/database/目录下
        db=helper.getWritableDatabase();
        mButtonCreateDB= (Button) findViewById(R.id.button_db);
        mButtonCreateDB.setOnClickListener(this);
         @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.button_db:
          Toast.makeText(MainActivity.this,"创建了数据库",Toast.LENGTH_SHORT).show();
                break; 
                 default:
                break;

        }
    }
}

public class SQLiteOpenHelper extends android.database.sqlite.SQLiteOpenHelper {
//参数Context必须要有它才能对数据库进行操作，第二个参数是数据库名，创建数据库时使用的就是这里指定的名称，第三个参数允许我们在查询数据的时候返回一个自定义的Cursor，一般都是传入null，第四个参数表示当前数据库的版本号，可用于对数据库进行升级操作。
    public SQLiteOpenHelper(Context context,String name,SQLiteDatabase.CursorFactory factory,int version) {
        super(context,name,factory,version);
    }
    public SQLiteOpenHelper(Context context,String name){
        this(context,null,1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table if not exists user(id integer not null primary key autoincrement,name varchar(20),password varchar(20))");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion) {

    }
}

<Button
        android:id="@+id/button_db"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="创建数据库"/>

case R.id.button_insert:
  ContentValues value=new ContentValues();
               value.put("name","zhangsan");
                value.put("password","123456");
                db.insert("user",value);
                //如果要插入多条数据，在插入第一条数据完成后，需要用到value.clear();然后在组装第二条要插入的数据。
                // value.put("name","lisi");
                // value.put("password","123");
                //db.insert("user",null,value);
                break;

case R.id.button_update:
                ContentValues values=new ContentValues();
                values.put("password","abcdef");
                //第三个参数对应的是SQL语句的where部分，表示去更新所有name等于？的行，而？是一个占位符，可以通过第四个参数提供的一个字符串数组为第三个参数中的每个占位符指定相应的内容。
                //将名字是zhangsan的密码改为acdef
                db.update("user",values,"name=?",new String []{"zhangsan"});
                break;

case R.id.button_delete:
 //删除名为zhangsan的这一条数据
                db.delete("user",new String []{"zhangsan"});
                Toast.makeText(MainActivity.this,"删除了名称是张三的数据",Toast.LENGTH_SHORT).show();
                break;

case R.id.button_select:

                Cursor cursor=db.query("user","id desc","3,4");//4是用来分页显示的(倒序的时候除去前四个)
// Cursor cursor=db.rawQuery("select * from user",null);
                cursor.moveToFirst();
                while(!cursor.isAfterLast()){
                    String name=cursor.getString(cursor.getColumnIndex("name"));
                    String password=cursor.getString(cursor.getColumnIndex("password"));
                 Log.d("cursor","用户名"+name+"密码"+password);
                    cursor.moveToNext();

                }
                break;