Android SQLiteHelper问题

Question

我正在学习如何制作 Android 应用程序，而我正在开发的应用程序需要一个在启动时填充的数据库，然后只从中读取。

我在尝试获取 SQLiteDatabase 实例时在启动时遇到错误。

我的 DatabaseManager 构造函数:

public DatabaseManager(Context context)
{
    Log.d("Database Manager", "Database Manager Constructor");
    CustomSQLiteOpenHelper helper = new CustomSQLiteOpenHelper(context);
    db = helper.getReadableDatabase();
    Log.d("Database Manager", db.toString());
    Log.d("Database ", db.getPath());
}

错误出现在我尝试 getReadableDatabase() 方法的行中。

这是我的 SQLiteHelper 类的 stub ，如果它有用的话:

public class CustomSQLiteOpenHelper extends SQLiteOpenHelper
{
    public CustomSQLiteOpenHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        Log.d("Database Manager", "Helper Constructor");
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase db)
    {
        Log.v("Database Manager", "In onCreate Method");
        //deleteAllTables(db);
        initializeTables(db);
        fillMonstersTable(db);          
    }
}

出现错误时的 LogCat:

ERROR/AndroidRuntime(366): FATAL EXCEPTION: main
ERROR/AndroidRuntime(366): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{dk.thediabloman.descenthelper/dk.thediabloman.descenthelper.DescentApp}: java.lang.NullPointerException
ERROR/AndroidRuntime(366):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
ERROR/AndroidRuntime(366):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
ERROR/AndroidRuntime(366):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
ERROR/AndroidRuntime(366):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
ERROR/AndroidRuntime(366):     at android.os.Handler.dispatchMessage(Handler.java:99)
ERROR/AndroidRuntime(366):     at android.os.Looper.loop(Looper.java:123)
ERROR/AndroidRuntime(366):     at android.app.ActivityThread.main(ActivityThread.java:4627)
ERROR/AndroidRuntime(366):     at java.lang.reflect.Method.invokeNative(Native Method)
ERROR/AndroidRuntime(366):     at java.lang.reflect.Method.invoke(Method.java:521)
ERROR/AndroidRuntime(366):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
ERROR/AndroidRuntime(366):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
ERROR/AndroidRuntime(366):     at dalvik.system.NativeStart.main(Native Method)
ERROR/AndroidRuntime(366): Caused by: java.lang.NullPointerException
ERROR/AndroidRuntime(366):     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
ERROR/AndroidRuntime(366):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
ERROR/AndroidRuntime(366):     at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158)
ERROR/AndroidRuntime(366):     at dk.thediabloman.descenthelper.DatabaseManager.<init>(DatabaseManager.java:52)
ERROR/AndroidRuntime(366):     at dk.thediabloman.descenthelper.DescentApp.<init>(DescentApp.java:18)
ERROR/AndroidRuntime(366):     at java.lang.Class.newInstanceImpl(Native Method)
ERROR/AndroidRuntime(366):     at java.lang.Class.newInstance(Class.java:1429)
ERROR/AndroidRuntime(366):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
ERROR/AndroidRuntime(366):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)

感谢您的帮助!

Answer 1

这是我的主课

SmartDBHelper d=new SmartDBHelper(getApplicationContext()); d.open();

//这里的姓名、电话和邮箱已经从其他 Activity 中获取//所以不要盲目地把它放在下面的语句中

d.insertTitle(姓名、电话、邮箱); 游标 c=d.getAllTitles(); //c.getColumnName(0);

  for( int i=0;i<c.getCount();i++){
  if(c.moveToNext()){
      Log.e("c", ""+ c.getString(0) );    
      Log.e("d", ""+ c.getString(1) );
      Log.e("d4", ""+ c.getString(2) );   


  }
Log.e("r",""+c.getCount());

这是我的 sqllite 类

公共(public)类 SmartDBHelper 扩展 SQLiteOpenHelper {

private SQLiteDatabase dBH;
private static final String DATABASE_NAME = "yo.db";  
private static final int DATABASE_VERSION = 2;  
private static final String NOTIFY_TABLE_NAME = "user_notify_data"; 
private static final String HR_TABLE_NAME = "user_hr_data";  
private static final String NOTIFY_TABLE_CREATE =  
    "CREATE TABLE " + NOTIFY_TABLE_NAME + " (counter INTEGER PRIMARY KEY, " + 
    "userresponse TEXT, " + 
    "notifytime TEXT);";  


private static final String HR_TABLE_CREATE = 
    "CREATE TABLE " + HR_TABLE_NAME +  
    " (counter INTEGER PRIMARY KEY, " +   
    "hr TEXT, " + 
    "act TEXT, " + 
    "timestamp TEXT);";

public SmartDBHelper(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     
        Log.e("smartdbhelper", "before creation");    
        db.execSQL(NOTIFY_TABLE_CREATE);      
        Log.e("smartdbhelper", "middle creation"); 
        db.execSQL(HR_TABLE_CREATE);       
        Log.e("smartdbhelper", "after creation");  
        }   

    @Override   
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
        // TODO Auto-generated method stub     
        } 

    public SmartDBHelper open() throws SQLException 
    {
          dBH = getWritableDatabase(); 
         return this;
    }

    public long insertTitle(String isbn, String title, String publisher) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put("hr", isbn);
        initialValues.put("act", title);
        initialValues.put("timestamp", publisher);
        Log.e("insertes","i");

         dBH.insert(HR_TABLE_NAME, null, initialValues);

返回11111111；

    public Cursor getAllTitles() 
    {
        return dBH.query(HR_TABLE_NAME, new String[] {
                 "hr","act","timestamp"},null, 
                null, 
                null, 
                null, 
                null);
    }








    //---closes the database---    
    public void close() 
    {
        close();

}

这行得通。我已经试过了