android - DBHelper 无法解析为变量

Question

我正在开发一个简单的注册登录系统。在每个类中，每个 DbHelper 事件都有许多相同的错误。错误是 DBHelper 无法解析为变量。我的资源文件没有错误。我在这里发布类代码之一

这是我的代码

package my.DataBase;

import my.DataBase.R;

import android.app.Activity;

import android.content.ContentValues;

import android.content.Intent;

import android.database.sqlite.SQLiteDatabase;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.AdapterView;

import android.widget.AdapterView.OnItemSelectedListener;

import android.widget.ArrayAdapter;
import android.widget.Button;

import android.widget.EditText;

import android.widget.Spinner;

import android.widget.Toast;


public class Registration extends Activity implements OnClickListener, OnItemSelectedListener


{
 // Variable Declaration should be in onCreate()
 private Button mSubmit;
 private Button mCancel;

 private EditText mFname;
 private EditText mLname;
 private EditText mUsername;
 private EditText mPassword;
 private EditText mEmail;
 private Spinner mGender;
 private String Gen;

 protected DBHelper DB = new DBHelper(Registration.this); 

 @Override
 protected void onCreate(Bundle savedInstanceState) {


  super.onCreate(savedInstanceState);
  setContentView(R.layout.register);

  //Assignment of UI fields to the variables
  mSubmit = (Button)findViewById(R.id.submit);
  mSubmit.setOnClickListener(this);

  mCancel = (Button)findViewById(R.id.cancel);
  mCancel.setOnClickListener(this);

  mFname = (EditText)findViewById(R.id.efname);
  mLname = (EditText)findViewById(R.id.elname);

  mUsername = (EditText)findViewById(R.id.reuname);
  mPassword = (EditText)findViewById(R.id.repass);
  mEmail = (EditText)findViewById(R.id.eemail);


  mGender = (Spinner)findViewById(R.id.spinner1);

  // Spinner method to read the on selected value
  ArrayAdapter<State> spinnerArrayAdapter = new ArrayAdapter<State>(this,
               android.R.layout.simple_spinner_item, new State[] { 
            new State("Male"), 
            new State("Female")});
  mGender.setAdapter(spinnerArrayAdapter);
  mGender.setOnItemSelectedListener(this); 
 }



 public void onClick(View v) 
 {

  switch(v.getId()){

  case R.id.cancel:
   Intent i = new Intent(getBaseContext(), LoginActivity.class);
   startActivity(i);
   //finish();
   break;

  case R.id.submit:


   String fname = mFname.getText().toString();
   String lname = mLname.getText().toString();

   String uname = mUsername.getText().toString();
   String pass = mPassword.getText().toString();
   String email = mEmail.getText().toString();


   boolean invalid = false;

   if(fname.equals(""))
   {
    invalid = true;
    Toast.makeText(getApplicationContext(), "Enter your Firstname", Toast.LENGTH_SHORT).show();
   }
   else

   if(lname.equals(""))
   {
    invalid = true;
    Toast.makeText(getApplicationContext(), "Please enter your Lastname", Toast.LENGTH_SHORT).show();
   }
   else

    if(uname.equals(""))
    {
     invalid = true;
     Toast.makeText(getApplicationContext(), "Please enter your Username", Toast.LENGTH_SHORT).show();
    }
    else


      if(pass.equals(""))
     {
      invalid = true;
      Toast.makeText(getApplicationContext(), "Please enter your Password", Toast.LENGTH_SHORT).show();

   }
     else 
      if(email.equals(""))
   {
    invalid = true;
    Toast.makeText(getApplicationContext(), "Please enter your Email ID", Toast.LENGTH_SHORT).show();
   }
     else
      if(invalid == false)
      {
       addEntry(fname, lname, Gen, uname, pass, email);
       Intent i_register = new Intent(Registration.this, LoginActivity.class);
       startActivity(i_register);
       //finish();
      }

      break;
      }
    }





 public void onDestroy()
 {
  super.onDestroy();
  DB.close();
 }



 private void addEntry(String fname, String lname, String Gen, String uname, String pass, String email) 
 {

  SQLiteDatabase db = DB.getWritableDatabase();

  ContentValues values = new ContentValues();
  values.put("firstname", fname);
  values.put("lastname", lname);
  values.put("gender", Gen);
  values.put("username", uname);
  values.put("password", pass);
  values.put("email", email);

  try
  {
   db.insert(DBHelper.DATABASE_TABLE_NAME, null, values);

   Toast.makeText(getApplicationContext(), "your details submitted Successfully...", Toast.LENGTH_SHORT).show();
  }
  catch(Exception e)
  {
   e.printStackTrace();
  }
 }


  public void onItemSelected(AdapterView<?> parent, View view, int position, long id) 
     {
      // Get the currently selected State object from the spinner
      State st = (State)mGender.getSelectedItem();

      // Show it via a toast
      toastState( "onItemSelected", st );
     } 


 public void toastState(String name, State st) 
 {
  if ( st != null )
     {
   Gen = st.name;
  //Toast.makeText(getBaseContext(), Gen, Toast.LENGTH_SHORT).show();

     }

 }


 public void onNothingSelected(AdapterView<?> arg0) {
  // TODO Auto-generated method stub

 }

}

Answer 1

在这里:

protected DBHelper DB = new DBHelper(Registration.this); 

将 DB 的初始化移动到一个方法中，而不是在类级别初始化:

protected DBHelper DB;  //<<< declare here
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.register);

  DB = new DBHelper(Registration.this);  //<<<< initialize here..
   .....