nullPointerException in Android vorbefüllten Datenbankprogramm

Question

Ich bastle mit einem Code, der auf eine vorbelegte Datenbank zugreift. Ich stoße auf einen NullPointerException-Fehler und ich kann nicht herausfinden, was los ist. Ich werde meinen Code veröffentlichen und wenn jemand helfen könnte, würde ich es sehr schätzen.

Aktivität:

public class Activity1c extends ListActivity { 


IngredientHelper mDbHelper=null; 
int char_property; 
int char_name; 
long a=1; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.act1c); 
    mDbHelper = new IngredientHelper(this); 

    Bundle extras = getIntent().getExtras(); 
    char_name = extras.getInt("char_name"); 
    char_property = extras.getInt("char_property"); 
    char_name+=1; 
    char_property+=1; 

    Toast.makeText(Activity1c.this, 
      "The char_name you picked was " + char_name + " and the property was "+char_property, 
      Toast.LENGTH_LONG).show(); 



    Cursor notesCursor = mDbHelper.fetchNote(a); 
    startManagingCursor(notesCursor); 

    // Create an array to specify the fields we want to display in the list (only TITLE) 
    String[] from = new String[]{IngredientHelper.COLUMN_TITLE,IngredientHelper.COLUMN_TITLE2}; 

    // and an array of the fields we want to bind those fields to (in this case just text1) 
    int[] to = new int[]{R.id.craft_type_display,R.id.spec_type_display}; 




    // Now create a simple cursor adapter and set it to display 
    SimpleCursorAdapter notes = 
     new SimpleCursorAdapter(this, R.layout.finalresult1, notesCursor, from, to); 
    setListAdapter(notes); 


}///end main 




    }///end class 

xml/act1c

 <?xml version="1.0" encoding="utf-8"?> 
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 


    android:layout_width="fill_parent" 
    android:layout_height="fill_parent"> 

<ListView android:id="@+id/android:list" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content"/> 
<TextView android:id="@+id/android:empty" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     /> 
    </LinearLayout> 

xml/finalresult1

<?xml version="1.0" encoding="utf-8"?> 
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:orientation="vertical" > 

    <TextView 
    android:id="@+id/craft_type_display" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" /> 

<TextView 
    android:id="@+id/spec_type_display" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" /> 

    </LinearLayout> 

Klasse/IngredientHelper

public class IngredientHelper extends SQLiteOpenHelper{ 

//we declare a bunch of useful constants 
//the should be pretty obvious what they are! 
private static final String DATABASE_PATH = "/data /data/com.android.Database_Practice_3_31_12/databases/"; 
private static final String DATABASE_NAME="infotest.sqlite"; 
private static final int SCHEMA_VERSION=1; 
public static final String TABLE_NAME = "info"; 
public static final String COLUMN_ID = "_id"; 
public static final String COLUMN_TITLE = "name"; 
public static final String COLUMN_TITLE2 = "phone"; 
public static final String COLUMN_TITLE3 = "fav_color"; 
public static final String COLUMN_TITLE4 = "home_city"; 

public SQLiteDatabase dbSqlite; 

private final Context myContext; 

public IngredientHelper(Context context) { 
    super(context, DATABASE_NAME, null, SCHEMA_VERSION); 
    this.myContext = context; 
    // check if exists and copy database from resource 
    //createDB(); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    // check if exists and copy database from resource 

} 

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

} 
public void createDatabase() { 
    createDB(); 
} 

private void createDB() { 

    boolean dbExist = DBExists(); 

    if (!dbExist) { 

     //By calling this method we create an empty database into the default system location 
     //We need this so we can overwrite that database with our database. 
     this.getReadableDatabase(); 
     //now we copy the database we included! 
     copyDBFromResource(); 

    } 

}  

private boolean DBExists() { 

    SQLiteDatabase db = null; 

    try { 
     String databasePath = DATABASE_PATH + DATABASE_NAME; 
     db = SQLiteDatabase.openDatabase(databasePath, null, 
       SQLiteDatabase.OPEN_READWRITE); 
     db.setLocale(Locale.getDefault()); 
     db.setLockingEnabled(true); 
     db.setVersion(1); 

    } catch (SQLiteException e) { 

     Log.e("SqlHelper", "database not found"); 

    } 

    if (db != null) { 

     db.close(); 

    } 

    return db != null ? true : false; 
} 

private void copyDBFromResource() { 

    InputStream inputStream = null; 
    OutputStream outStream = null; 
    String dbFilePath = DATABASE_PATH + DATABASE_NAME; 

    try { 

     inputStream = myContext.getAssets().open(DATABASE_NAME); 

     outStream = new FileOutputStream(dbFilePath); 

     byte[] buffer = new byte[1024]; 
     int length; 
     while ((length = inputStream.read(buffer)) > 0) { 
      outStream.write(buffer, 0, length); 
     } 

     outStream.flush(); 
     outStream.close(); 
     inputStream.close(); 

    } catch (IOException e) { 

     throw new Error("Problem copying database from resource file."); 

    } 

} 

public void openDataBase() throws SQLException { 

    String myPath = DATABASE_PATH + DATABASE_NAME; 
    dbSqlite = SQLiteDatabase.openDatabase(myPath, null, 
      SQLiteDatabase.OPEN_READWRITE); 

} 

@Override 
public synchronized void close() { 

    if (dbSqlite != null) 
    { 
     dbSqlite.close(); 
    } 
    super.close(); 

} 


public Cursor getCursor() { 

    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder(); 

    queryBuilder.setTables(TABLE_NAME); 

    String[] asColumnsToReturn = new String[] { COLUMN_ID,COLUMN_TITLE}; 

    //make sure you get your search by string pass correctly! 
    Cursor mCursor = queryBuilder.query(dbSqlite, asColumnsToReturn, null, 
      null, null, null, null); 

    return mCursor; 
} 

public String getName(Cursor c) { 
    return(c.getString(1)); 
} 

public Cursor fetchNote(long rowId) throws SQLException { 

    Cursor mCursor = 

     dbSqlite.query(true, TABLE_NAME, new String[] { 
       COLUMN_ID, COLUMN_TITLE,COLUMN_TITLE2,COLUMN_TITLE3,COLUMN_TITLE4}, COLUMN_ID + "=" + rowId, null, 
       null, null, null, null); 
    if (mCursor != null) { 
     mCursor.moveToFirst(); 
    } 
    return mCursor; 

} 

}

logcat

04-04 19:54:50.764: E/AndroidRuntime(454): Uncaught handler: thread main exiting due to uncaught exception 
04-04 19:54:50.774: E/AndroidRuntime(454): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.Database_Practice_3_31_12/com.android.Database_Practice_3_31_12.Activity1c}: java.lang.NullPointerException 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.app.ActivityThread.access$2200(ActivityThread.java:119) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.os.Handler.dispatchMessage(Handler.java:99) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.os.Looper.loop(Looper.java:123) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.app.ActivityThread.main(ActivityThread.java:4363) 
04-04 19:54:50.774: E/AndroidRuntime(454): at java.lang.reflect.Method.invokeNative(Native Method) 
04-04 19:54:50.774: E/AndroidRuntime(454): at java.lang.reflect.Method.invoke(Method.java:521) 
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
04-04 19:54:50.774: E/AndroidRuntime(454): at dalvik.system.NativeStart.main(Native Method) 
04-04 19:54:50.774: E/AndroidRuntime(454): Caused by: java.lang.NullPointerException 
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.Database_Practice_3_31_12.IngredientHelper.fetchNote(IngredientHelper.java:173) 
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.Database_Practice_3_31_12.Activity1c.onCreate(Activity1c.java:49) 
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
04-04 19:54:50.774: E/AndroidRuntime(454):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459) 

Answer 1

Ooof. Es ist schwer, all dem zu folgen.

Zuerst erhalten Sie den Fehler in fetchNote(). In der Stapelspur zeigt dies die fünfte Zeile von unten. Sie können die Zeilennummer am Ende verwenden, um in die Nähe von zu kommen, wo es passiert.

Meine Vermutung ist, dass die Abfrage fehlschlägt.

Meine weitere Vermutung ist, dass es ist, weil Sie versuchen, eine Datenbank "wiederherzustellen", indem Sie sie von einem anderen Ort byteweise kopieren. Ich bin nicht überzeugt, dass das funktionieren wird. Der beste Weg, um eine vorbereitete Datenbank in einer App bereitzustellen, besteht darin, ihre Daten in eine flache Datei zu schreiben und dann, wenn die App zum ersten Mal ausgeführt wird, die Datenbank zu erstellen und die Daten darin zu schreiben.

Im Entwicklerhandbuch enthält die Quelldatei DictionaryDatabase.java in der Beispielanwendung SearchableDictionary Beispielcode dafür.