错误：无法找到符号类CopyDbActivity

Question

我一直在关注本教程在YouTube上关于

“如何包含在Android应用SQLite数据库”

这里是链接

https://www.youtube.com/watch?v=iE_bsPfB00w&t=2s

这是我的MainActivity的代码

import java.io.IOException; 
import android.database.Cursor; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.database.SQLException; 
import android.widget.Toast; 


public class MainActivity extends AppCompatActivity { 

Cursor c = null; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    ((Button) findViewById(R.id.button)).setOnClickListener(new 
    View.OnClickListener(){ 
     @Override 
     public void onClick(View v){ 
      DatabaseHelper myDbHelper = new 
      DatabaseHelper(CopyDbActivity.this); 
      try{ 
       myDbHelper.createDataBase(); 
      }catch (IOException ioe){ 
       throw new Error("Unable to create database"); 
      } 
      try{ 
       myDbHelper.openDataBase(); 
      }catch (SQLException sqle){ 
       throw sqle; 
      } 

    Toast.makeText(CopyDbActivity.this,"Success",Toast.LENGTH_SHORT).show(); 
    c= myDbHelper.query("penyakit_TABLE",null,null,null,null,null,null); 
      if(c.moveToFirst()){ 
       do{ 
Toast.makeText(CopyDbActivity.this,"simptom"+c.getString(1),Toast.LENGTH_LONG).show(); 

       }while(c.moveToNext()); 
      } 
     } 
    }); 
} 

}

我得到了这些错误。如何解决这个问题？

Error:(25, 64) error: cannot find symbol class CopyDbActivity 
Error:(36, 32) error: cannot find symbol class CopyDbActivity 
Error:(40, 40) error: cannot find symbol class CopyDbActivity 

Answer 1

只是MainActivity取代CopyDbActivity如下：

public class MainActivity extends AppCompatActivity { 

Cursor c = null; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    ((Button) findViewById(R.id.button)).setOnClickListener(new 
    View.OnClickListener(){ 
     @Override 
     public void onClick(View v){ 
      DatabaseHelper myDbHelper = new 
      DatabaseHelper(MainActivity.this); 
      try{ 
       myDbHelper.createDataBase(); 
      }catch (IOException ioe){ 
       throw new Error("Unable to create database"); 
      } 
      try{ 
       myDbHelper.openDataBase(); 
      }catch (SQLException sqle){ 
       throw sqle; 
      } 

    Toast.makeText(MainActivity.this,"Success",Toast.LENGTH_SHORT).show(); 
    c= myDbHelper.query("penyakit_TABLE",null,null,null,null,null,null); 
      if(c.moveToFirst()){ 
       do{ 
Toast.makeText(MainActivity.this,"simptom"+c.getString(1),Toast.LENGTH_LONG).show(); 

       }while(c.moveToNext()); 
      } 
     } 
    }); 
}