運行時創建數據庫異常

Question

我正在開發一個數據庫應用程序來輸入它的註釋。但是當我在模擬器上運行此應用程序時，它立即停止說Unfortunately!Notepad2 has stopped working。請幫助我正確地工作。 有兩個文件。 一個MainActivity.java：

package com.example.notepad2; 

import android.os.Bundle; 
import android.app.Activity; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 

public class MainActivity extends Activity implements OnClickListener { 
    EditText title,body; 
    Button btn; 
    NotepadDb notepad; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     title=(EditText)findViewById(R.id.title); 
     body=(EditText)findViewById(R.id.body); 
     btn=(Button)findViewById(R.id.btn); 
     btn.setOnClickListener(this); 
     notepad=new NotepadDb(this); 
     notepad=notepad.open(); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 

     notepad.insert(title.getText().toString(), body.getText().toString()); 
     notepad.close(); 
    } 

} 

，另一個是NotepadDb.java

package com.example.notepad2; 

import android.app.Activity; 
import android.content.Context; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteDatabase.CursorFactory; 
import android.database.sqlite.SQLiteOpenHelper; 

public class NotepadDb extends Activity { 
private static final String DATABASE_NAME="Notepad"; 
private static final String TABLE_NAME="note"; 
private final int DATABASE_VERSION=1; 
private static final String KEY_TITLE="title"; 
private static final String KEY_BODY="body"; 
private static final String ID="_id"; 
private static final String Query="create table note(_id integer auto_increment primary key,title text not null,body text not null);"; 
DatabaseHelper dbHelper; 
SQLiteDatabase mydb; 
private Context cntxt; 
public class DatabaseHelper extends SQLiteOpenHelper{ 

    public DatabaseHelper(Context context) { 
     super(context, DATABASE_NAME,null, DATABASE_VERSION); 
     // TODO Auto-generated constructor stub 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     // TODO Auto-generated method stub 
     db.execSQL(Query); 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     // TODO Auto-generated method stub 
     db.execSQL("drop table note"); 
     onCreate(db); 
    } 

} 
public NotepadDb(Context context){ 
    cntxt=context; 
} 
public NotepadDb open() throws SQLException{ 
    dbHelper=new DatabaseHelper(cntxt); 
    mydb=dbHelper.getReadableDatabase(); 
    return this; 
} 
public void insert(String title,String body){ 
    mydb.execSQL("insert into note values(null,"+title+","+body+");"); 

} 
public void close(){ 
    dbHelper.close(); 
} 

} 

Answer 1

你DatabaseHelper不應該在一個Activity類包裹。擺脫NotepadDb的構造函數和方法，並將所需的所有內容移到DatabaseHelper類中。

MainActivity

public class MainActivity extends Activity implements OnClickListener 
{ 
EditText title,body; 
Button btn; 
DatabaseHelper dbh; 

@Override 
protected void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    title = (EditText)findViewById(R.id.title); 
    body = (EditText)findViewById(R.id.body); 
    btn = (Button)findViewById(R.id.btn); 
    btn.setOnClickListener(this); 
    dbh = new DatabaseHelper(this); 
    dbh.open(); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) 
{ 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 

@Override 
public void onClick(View v) 
{ 
    dbh.insert(title.getText().toString(), body.getText().toString()); 
    dbh.close(); 
} 
} 

DatabaseHelper

public class DatabaseHelper extends SQLiteOpenHelper 
{ 
private static final String DATABASE_NAME="Notepad"; 
private static final String TABLE_NAME="note"; 
private static final int DATABASE_VERSION=1; 
private static final String KEY_TITLE="title"; 
private static final String KEY_BODY="body"; 
private static final String ID="_id"; 
private static final String Query="create table note(_id integer auto_increment primary key,title text not null,body text not null);"; 
SQLiteDatabase mydb; 

public DatabaseHelper(Context context) 
{ 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

@Override 
public void onCreate(SQLiteDatabase db) 
{ 
    db.execSQL(Query); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
{ 
    db.execSQL("drop table note"); 
    onCreate(db); 
} 

public void open() throws SQLException 
{ 
    mydb = this.getWritableDatabase(); 
} 

public void insert(String title, String body) 
{ 
    mydb.execSQL("insert into note (title, body) values (\"" + title + "\",\"" + body + "\");"); 
} 

public void close() 
{ 
    mydb.close(); 
} 
}