Android應用程序在調用Cursor方法後崩潰

Question

我在我的兩個按鈕中，一個用於插入，另一個用於顯示。插入工作正常，但點擊顯示按鈕後，我的應用程序崩潰，N I得到以下錯誤

02-15 00:36:28.207: E/AndroidRuntime(25942): FATAL EXCEPTION: main 
02-15 00:36:28.207: E/AndroidRuntime(25942): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.indianrailwaybooking/com.example.indianrailwaybooking.SQLView}: java.lang.NullPointerException 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.os.Looper.loop(Looper.java:123) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.ActivityThread.main(ActivityThread.java:3683) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at java.lang.reflect.Method.invokeNative(Native Method) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at java.lang.reflect.Method.invoke(Method.java:507) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at dalvik.system.NativeStart.main(Native Method) 
02-15 00:36:28.207: E/AndroidRuntime(25942): Caused by: java.lang.NullPointerException 
02-15 00:36:28.207: E/AndroidRuntime(25942): at com.example.indianrailwaybooking.Reservation.getData(Reservation.java:96) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at com.example.indianrailwaybooking.SQLView.onCreate(SQLView.java:36) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
02-15 00:36:28.207: E/AndroidRuntime(25942): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
02-15 00:36:28.207: E/AndroidRuntime(25942): ... 11 more 

這裏是我的光標方法

public String getData() { 
    // TODO Auto-generated method stub 
    ourDatabase = ourHelper.getWritableDatabase(); 
    String [] columns = new String[]{KEY_BOOKING, KEY_PERSON1, KEY_PERSON2, KEY_PERSON3, KEY_PERSON4}; 
    Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null ,null); 
    String result = ""; 
    ourDatabase.close(); 

    int iBooking = c.getColumnIndex("KEY_BOOKING"); 
    int iPerson1 = c.getColumnIndex("KEY_PERSON1"); 
    int iPerson2 = c.getColumnIndex("KEY_PERSON2"); 
    int iPerson3 = c.getColumnIndex("KEY_PERSON3"); 
    int iPerson4 = c.getColumnIndex("KEY_PERSON4"); 

    for(c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){ 
     result = result + c.getString(iBooking) + " " + " " + c.getString(iPerson1) + " " + c.getString(iPerson2) + " " + c.getString(iPerson3) + " " + c.getString(iPerson4) + "\n"; 
    } 

    Toast.makeText(context, result, Toast.LENGTH_LONG).show(); 

    return result; 
} 

這是從哪兒GetData方法被調用的類。

public class SQLView extends Activity { 

    private DBHelper obj; 
    AlertDialog alert; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.sqlview); 
     Reservation resv = new Reservation(this); 
     String result = resv.getData(); 
     EditText et = (EditText) findViewById(R.id.tvSQLinfo); 
     et.setText(result); 
    } 

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

} 

Answer 1

硬，沒有看到更多的代碼的說，我想嘗試通過ourHelper.getReadableDatabase();更換ourHelper.getWritableDatabase();並刪除ourDatabase.close();

嘗試：

public String getData() { 
    // TODO Auto-generated method stub 
    ourDatabase = ourHelper.getReadableDatabase(); 
    String [] columns = new String[]{KEY_BOOKING, KEY_PERSON1, KEY_PERSON2, KEY_PERSON3, KEY_PERSON4}; 
    Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null ,null); 
    String result = ""; 

    int iBooking = c.getColumnIndex("KEY_BOOKING"); 
    int iPerson1 = c.getColumnIndex("KEY_PERSON1"); 
    int iPerson2 = c.getColumnIndex("KEY_PERSON2"); 
    int iPerson3 = c.getColumnIndex("KEY_PERSON3"); 
    int iPerson4 = c.getColumnIndex("KEY_PERSON4"); 

    for(c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){ 
     result = result + c.getString(iBooking) + " " + " " + c.getString(iPerson1) + " " + c.getString(iPerson2) + " " + c.getString(iPerson3) + " " + c.getString(iPerson4) + "\n"; 
    } 

    Toast.makeText(context, result, Toast.LENGTH_LONG).show(); 

    return result; 
}