從數據庫顯示列表視圖的錯誤

Question

即時嘗試從數據庫顯示列表視圖項目。但我的應用程序不斷崩潰。我用我過去的項目代碼來指導我，但仍然沒有運氣。

Module.java

@Override 
protected void onResume() { 
    super.onResume(); 
    ArrayList<String> labels = new ArrayList<String>(); 
    ListView lstDine = (ListView) this.findViewById(R.id.lst_module); 
    dbhelper.onCreate(null); 
    Cursor dinners = (Cursor) dbhelper.getAllLabels(); 
    dinners.close(); 
    lstDine.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, labels)); 
    lstDine.setOnItemClickListener(this); 

} 

DBHelper.java

public class DBHelper extends SQLiteOpenHelper { 
// Database Version 
private static final int DATABASE_VERSION = 1; 

// Database Name 
private static final String DATABASE_NAME = "spinnerExample"; 

// Labels table name 
private static final String TABLE_LABELS = "labels"; 

// Labels Table Columns names 
private static final String KEY_ID = "id"; 
private static final String KEY_NAME = "name"; 

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

// Creating Tables 
@Override 
public void onCreate(SQLiteDatabase db) { 
    // Category table create query 
    String CREATE_CATEGORIES_TABLE = "CREATE TABLE " + TABLE_LABELS + "(" 
      + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT)"; 
    db.execSQL(CREATE_CATEGORIES_TABLE); 
} 

// Upgrading database 
@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    // Drop older table if existed 
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_LABELS); 

    // Create tables again 
    onCreate(db); 
} 

/** 
* Inserting new lable into lables table 
* */ 
public void insertLabel(String label){ 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, label); 

    // Inserting Row 
    db.insert(TABLE_LABELS, null, values); 
    db.close(); // Closing database connection 
} 

/** 
* Removing label 
* */ 
public void removeLabel(String label){ 
SQLiteDatabase db = this.getWritableDatabase(); 

ContentValues values = new ContentValues(); 
values.put(KEY_NAME, label); 

// Removing Row 
db.delete(TABLE_LABELS, KEY_NAME + "=?", new String[] {label}); 
db.close(); // Closing database connection 
} 

/** 
* Getting all labels 
* returns list of labels 
* */ 
public List<String> getAllLabels(){ 
    List<String> labels = new ArrayList<String>(); 

    // Select All Query 
    String selectQuery = "SELECT * FROM " + TABLE_LABELS; 

    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 

    // looping through all rows and adding to list 
    if (cursor.moveToFirst()) { 
     do { 
      labels.add(cursor.getString(1)); 
     } while (cursor.moveToNext()); 
    } 

    // closing connection 
    cursor.close(); 
    db.close(); 

    // returning lables 
    return labels; 
} 
} 

錯誤日誌

07-25 08:36:37.007: D/dalvikvm(463): GC_EXTERNAL_ALLOC freed 600 objects/48072 bytes in 58ms 
07-25 08:36:40.347: D/dalvikvm(463): GC_EXTERNAL_ALLOC freed 321 objects/15992 bytes in 104ms 
07-25 08:36:42.907: D/AndroidRuntime(463): Shutting down VM 
07-25 08:36:42.907: W/dalvikvm(463): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 
07-25 08:36:42.937: E/AndroidRuntime(463): FATAL EXCEPTION: main 
07-25 08:36:42.937: E/AndroidRuntime(463): java.lang.RuntimeException: Unable to resume activity {sg.edu.tp.iit.mns/sg.edu.tp.iit.mns.Module}: java.lang.NullPointerException 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3128) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3143) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2684) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.os.Handler.dispatchMessage(Handler.java:99) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.os.Looper.loop(Looper.java:123) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread.main(ActivityThread.java:4627) 
07-25 08:36:42.937: E/AndroidRuntime(463): at java.lang.reflect.Method.invokeNative(Native Method) 
07-25 08:36:42.937: E/AndroidRuntime(463): at java.lang.reflect.Method.invoke(Method.java:521) 
07-25 08:36:42.937: E/AndroidRuntime(463): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
07-25 08:36:42.937: E/AndroidRuntime(463): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
07-25 08:36:42.937: E/AndroidRuntime(463): at dalvik.system.NativeStart.main(Native Method) 
07-25 08:36:42.937: E/AndroidRuntime(463): Caused by: java.lang.NullPointerException 
07-25 08:36:42.937: E/AndroidRuntime(463): at sg.edu.tp.iit.mns.DBHelper.onCreate(DBHelper.java:36) 
07-25 08:36:42.937: E/AndroidRuntime(463): at sg.edu.tp.iit.mns.Module.onResume(Module.java:50) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1149) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.Activity.performResume(Activity.java:3823) 
07-25 08:36:42.937: E/AndroidRuntime(463): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3118) 
07-25 08:36:42.937: E/AndroidRuntime(463): ... 12 more 

我不是河畔e哪部分出問題了。感謝您的幫助。如果您可以爲我編輯代碼，我們將非常感激。現在我已經開了很多次了。由於這個原因，我無法繼續下一部分。

Answer 1

dbhelper.onCreate(null); 

在上述線，要傳遞空引用，以便你正在 所致：

java.lang.NullPointerException 
07-25 08:36:42.937: E/AndroidRuntime(463): at sg.edu.tp.iit.mns.DBHelper.onCreate(DBHelper.java:36) 

可以傳遞DBHelper類對象

dbhelper.onCreate(dbhelper); 

Answer 2

首先，你應該打開數據庫 - 你會得到的數據形式的數據庫：

db=openOrCreateDatabase(DATABASE_NAME, MODE_WORLD_WRITEABLE, null);