运行时错误，当我试图连接到数据库表

Question

我的应用程序使用SQLiteOpenHelper。 表已成功创建，但SQL精简版管理器显示空表。

public class DBHelper extends SQLiteOpenHelper { 
    public static final String DATABASE_NAME = "MyBD.db"; 
    public static final int DATABASE_VERSION = 1; 

    public final String SMS_TABLE = "sms_table"; 

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

@Override 
public void onCreate(SQLiteDatabase db) { 
try 
{ 
    String request; 
    request ="create table " + SMS_TABLE + "(" 
      + "id INTEGER primary key autoincrement," 
      + "sender text," 
      + "date text," 
      + "read text," 
      + "message text" + ");";   
    db.execSQL(request); 
} 
catch(SQLException ex) 
{ 
    Log.d("DBCreator", "onCreate exception " +ex.getMessage()); 
} 
} 
@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 

} 
} 

使用它...

public class SecureMessagesActivity extends Activity 
{ 
DBHelper dbHelper; 
public void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    SQLiteDatabase db = dbHelper.getWritableDatabase(); 

    db.close(); 
} 

结果看起来很伤心......（logcat的）

08-02 09:25:42.976: D/AndroidRuntime(29643): Shutting down VM 
08-02 09:25:42.976: W/dalvikvm(29643): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
08-02 09:25:42.996: E/AndroidRuntime(29643): FATAL EXCEPTION: main 
08-02 09:25:42.996: E/AndroidRuntime(29643): java.lang.RuntimeException: Unable to start activity ComponentInfo{org.secure.sms/org.secure.sms.SecureMessagesActivity}: java.lang.NullPointerException 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.os.Handler.dispatchMessage(Handler.java:99) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.os.Looper.loop(Looper.java:123) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.ActivityThread.main(ActivityThread.java:3683) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at java.lang.reflect.Method.invokeNative(Native Method) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at java.lang.reflect.Method.invoke(Method.java:507) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at dalvik.system.NativeStart.main(Native Method) 
08-02 09:25:42.996: E/AndroidRuntime(29643): Caused by: java.lang.NullPointerException 
08-02 09:25:42.996: E/AndroidRuntime(29643): at org.secure.sms.SecureMessagesActivity.onCreate(SecureMessagesActivity.java:40) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-02 09:25:42.996: E/AndroidRuntime(29643): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
08-02 09:25:42.996: E/AndroidRuntime(29643): ... 11 more 
08-02 09:25:43.027: W/ActivityManager(70): Force finishing activity org.secure.sms/.SecureMessagesActivity 
08-02 09:25:43.547: W/ActivityManager(70): Activity pause timeout for HistoryRecord{40727540 org.secure.sms/.SecureMessagesActivity} 
08-02 09:25:45.227: W/InputManagerService(70): Window already focused, ignoring focus gain of: com.android.internal.view.IInputMethodClient$Stub$Proxy@40606e60 
08-02 09:25:45.267: I/Process(29643): Sending signal. PID: 29643 SIG: 9 
08-02 09:25:45.297: I/ActivityManager(70): Process org.secure.sms (pid 29643) has died. 
08-02 09:25:50.508: D/dalvikvm(280): GC_EXPLICIT freed 15K, 55% free 2599K/5703K, external 716K/1038K, paused 71ms 
08-02 09:25:53.987: W/ActivityManager(70): Activity destroy timeout for HistoryRecord{40727540 org.secure.sms/.SecureMessagesActivity} 
08-02 09:25:55.607: D/dalvikvm(315): GC_EXPLICIT freed 4K, 54% free 2539K/5511K, external 716K/1038K, paused 95ms 

Answer 1

你在哪里实例dbHelper？您dbHelper是null

SQLiteDatabase db = dbHelper.getWritableDatabase(); 

Answer 2

java.lang.NullPointerException 

您DBHelper dbHelper;是null在SecureMessagesActivity

所以使用

public class SecureMessagesActivity extends Activity 
{ 
DBHelper dbHelper; 
public void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    dbHelper=new DBHelper(this);// pass context 
    SQLiteDatabase db = dbHelper.getWritableDatabase(); 

    db.close(); 
} 

Answer 3

您尚未初始化databaseHelper：

public class SecureMessagesActivity extends Activity 
    { 
DBHelper dbHelper; //<-- no init 
    public void onCreate(Bundle savedInstanceState) 
    { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.main); 

dbHelper = new DBHelper(this); //<-- do this 

SQLiteDatabase db = dbHelper.getWritableDatabase(); 

db.close(); 
    } 

Answer 4

/查询创建配置文件和步骤表 私人静态最终字符串CREATE_PROFILE_TABLE =“创建表配置文件（_id整数不空null主键自动增量，配置文件空，状态文本非空）”;

private static final String CREATE_STEP_TABLE = "create table step (_id integer not null primary key autoincrement,value integer not null,delay integer not null,profile_id integer default 0, FOREIGN KEY (profile_id) REFERENCES profile(id))"; 


//constructor 
public EcConferenceOpenHelper(Context context, String name, 
     CursorFactory factory, int version) { 
    super(context, name, factory, version); 
    // TODO Auto-generated constructor stub 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    // TODO Auto-generated method stub 

    db.execSQL(CREATE_PROFILE_TABLE); 
    db.execSQL(CREATE_STEP_TABLE); 

} 

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

    onCreate(db); 
}