访问数据库SQLiteopenHelper方法时，应用程序崩溃（nullpointerexception）

Question

I've got another problem with SQLite database. I am accessing to database with help of this class, and also, here I create database and pre-fill it.:

public class DatabaseHandler extends SQLiteOpenHelper {


    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

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

    // Table names
    private static final String TABLE_DEVICE = "device";
    private static final String TABLE_ICON = "icon";

    // Column names of device table
    private static final String ID_DEVICE = "idDevice";
    private static final String UNIT_NUMBER = "unitNumber";
    private static final String DEVICE_ID = "deviceId";
    private static final String FK_ICON = "kdIcon";

    // Column names of icon table
    private static final String ID_ICON = "idIcon";
    private static final String CATEGORY = "category";
    private static final String ON = "iconOn";
    private static final String OFF = "iconOff";
    private static final String ON_COOLING = "onCooling";
    private static final String ON_HEATING = "onHeating";
    private static final String ICON_0 = "icon0";
    private static final String ICON_10 = "icon10";
    private static final String ICON_20 = "icon20";
    private static final String ICON_25 = "icon25";
    private static final String ICON_30 = "icon30";
    private static final String ICON_40 = "icon40";
    private static final String ICON_50 = "icon50";
    private static final String ICON_60 = "icon60";
    private static final String ICON_75 = "icon75";
    private static final String ICON_80 = "icon80";
    private static final String ICON_90 = "icon90";
    private static final String ICON_100 = "icon100";

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


    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createDeviceTable = "CREATE  TABLE " + TABLE_DEVICE + " ("
                + ID_DEVICE + " INTEGER PRIMARY KEY NOT NULL  UNIQUE , "
                + UNIT_NUMBER + " INTEGER NOT NULL  UNIQUE , " + DEVICE_ID
                + " INTEGER NOT NULL  UNIQUE , " + FK_ICON + " INTEGER)";

        String createIconTable = "CREATE  TABLE " + TABLE_ICON + " (" + ID_ICON
                + " INTEGER PRIMARY KEY NOT NULL  UNIQUE , " + CATEGORY
                + " INTEGER NOT NULL , " + ON + " TEXT, " + OFF + " TEXT, "
                + ON_COOLING + " TEXT, " + ON_HEATING + " TEXT, " + ICON_0
                + " TEXT, " + ICON_10 + " TEXT, " + ICON_20 + " TEXT, "
                + ICON_25 + " TEXT, " + ICON_30 + " TEXT, " + ICON_40
                + " TEXT, " + ICON_50 + " TEXT, " + ICON_60 + " TEXT, "
                + ICON_75 + " TEXT, " + ICON_80 + " TEXT, " + ICON_90
                + " TEXT, " + ICON_100 + " TEXT)";

        db.execSQL(createDeviceTable);
        db.execSQL(createIconTable);

        ContentValues values = new ContentValues();
        values.put(ID_ICON, 1);
        values.put(CATEGORY, 3);
        values.put(ON, "lightbulb_0_v2");
        values.put(OFF, "lightbulb_100_v2");
        db.insert(TABLE_ICON, null, values);
        values.clear();

        values.put(ID_ICON, 2);
        values.put(CATEGORY, 3);
        values.put(ON, "lightbulb_0_v1");
        values.put(OFF, "lightbulb_max_v1");
        db.insert(TABLE_ICON, null, values);
        values.clear();

        values.put(ID_ICON, 3);
        values.put(CATEGORY, 3);
        values.put(ON, "electric_outlet_on");
        values.put(OFF, "electric_outlet_off");
        db.insert(TABLE_ICON, null, values);
        values.clear();

        values.put(ID_DEVICE, 1);
        values.put(UNIT_NUMBER, 35100191);
        values.put(DEVICE_ID, 116);
        values.put(FK_ICON, 2);
        db.insert(TABLE_DEVICE, null, values);
        values.clear();

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_DEVICE);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_ICON);

        // Create tables again
        onCreate(db);

    }

    // It is used to show all availabe icons of category.
    public List<String> getAllIconsOfOldCategory(int oldCategory) {
        List<String> iconsList = new ArrayList<String>();

        String SqlSelectIconsQuery = "";
        // if (oldCategory == 3)
        SqlSelectIconsQuery = "SELECT " + ON + " FROM " + TABLE_ICON;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(SqlSelectIconsQuery, null);
        if (cursor.moveToFirst()) {
            do {
                iconsList.add(cursor.getString(0));
                Log.v("BAZA", cursor.getString(0));
            } while (cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return iconsList;
        // return null;
    }

    public String getIcon(int deviceId, int unite_number, int status, int oldCategory) {
         SQLiteDatabase db = this.getReadableDatabase();
        // if (oldCategory == 3)
        String SqlFindIconId = "SELECT " + FK_ICON + " FROM " + TABLE_DEVICE
                + " WHERE " + UNIT_NUMBER + " = " + unite_number + " AND "
                + DEVICE_ID + " = " + deviceId;

        Cursor cursor = db.rawQuery(SqlFindIconId, null);
        if(cursor !=null){
            String icon;
            if(status == 0){
                icon = "SELECT "+ON+" FROM "+TABLE_ICON+ " WHERE "+ID_ICON +" = "+ cursor.getString(0);
            }else{
                icon = "SELECT "+OFF+" FROM "+TABLE_ICON+ " WHERE "+ID_ICON +" = "+ cursor.getString(0);
            }
            db.close();
            return db.rawQuery(SqlFindIconId, null).getString(0);
        }
        db.close();
        return null;
    }

}

Now, you can see the there are two methods. First, getAllIconsOfOldCategory(int oldCategory) and second getIcon(int deviceId, int unite_number, int status, int oldCategory) . In application, where I am using first metod, everything works....but when I try to use second method, application throws NullPointerException before getIcon() method start executing and application is Forced closed.

So, below I will provide the class, where I use this Databashandler class and its methods. Here is, lets call it classA.java. So, classA (this extends to another class)is used to render listView and every individual line of listView. ([ImageView][Text][SwitchButton]-->this is one line in listView). Here I've got onCreate() method: I think it's nothing wrong with this method, because it doesn't show any error and it works when I press on imageView(you will see more explanation below).

private DatabaseHandler db;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    db = new DatabaseHandler(classA.this
            .getParent());

}

So, in this class, there is methos renderDevice() which is used to render all lines in listview, and it return view. And my goal is, to check, if there is image in database, show this one, and if there is not, than show pre defined one. But, it doesn't work... It's all right till the line, where I call db.getIcon() method. Then it show the error. And the method don't even start executing.

ImageView device_status_image = (ImageView) lightView
                .findViewById(R.id.device_status_image);
        Settings settings = Settings.getInstance();  
        String icon = db.getIcon(light.id, settings.getLastPkAccessPoint(), status, light.oldCategory);

        if ( icon != null) {
            int resId = getResources().getIdentifier(icon, "drawable",
                    getPackageName());
            device_status_image.setImageResource(resId);
        } else
            device_status_image.setImageResource(R.drawable.normal_icon); 

        }

But, moreover, I've got onClickListener on device_status_image . And here works everything... So, it open up a dialog. That means that ClassA.this.getParent() is good and it works. And you can see, I call db.getAllIconsOfOldCategory() where I set new adapter.

device_status_image.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            final Dialog dialog = new Dialog(ClassA.this
                    .getParent());
            dialog.setContentView(R.layout.list_view_icon);
            listView = (ListView) dialog.findViewById(R.id.list_view);

            IconAdapter adapter = new IconAdapter(inflater, light.id,
                    light.oldCategory, light.name, db
                            .getAllIconsOfOldCategory(light.oldCategory));    

            listView.setAdapter(adapter);
            dialog.show();

            Button bCancel = (Button) dialog.findViewById(R.id.bCancel);
            bCancel.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {
                    dialog.dismiss();

                }
            });

        }
    });

So, I tried to add String icon = db.getIcon(light.id, settings.getLastPkAccessPoint(), status, light.oldCategory); into OnClickListener, just to check if here the method execute (I check this with debugging) and it worked, the method getIcon() executed... But, when I put it back to the place where it need to be. Surprise, surprise, it don't work any more..

And, here is log file, if it will help you. Thanks! It is very long.

09-16 01:35:59.167: E/AndroidRuntime(28019): FATAL EXCEPTION: main
09-16 01:35:59.167: E/AndroidRuntime(28019): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mysite.android/com.mysite.mobile.LightsActivity}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mysite.android/com.mysite.mobile.classA}: java.lang.NullPointerException
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.startActivityNow(ActivityThread.java:1991)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:703)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabHost.setCurrentTab(TabHost.java:350)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:154)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:540)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.view.View.performClick(View.java:3549)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.view.View$PerformClick.run(View.java:14393)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.os.Handler.handleCallback(Handler.java:605)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.os.Handler.dispatchMessage(Handler.java:92)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.os.Looper.loop(Looper.java:154)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.main(ActivityThread.java:4945)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at java.lang.reflect.Method.invokeNative(Native Method)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at java.lang.reflect.Method.invoke(Method.java:511)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at dalvik.system.NativeStart.main(Native Method)
09-16 01:35:59.167: E/AndroidRuntime(28019): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mysite.android/com.mysite.mobile.classA}: java.lang.NullPointerException
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.startActivityNow(ActivityThread.java:1991)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:703)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabHost.setCurrentTab(TabHost.java:350)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.widget.TabHost.addTab(TabHost.java:240)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.mysite.mobile.LightsActivity.changeDeviceTabs(LightsActivity.java:34)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.mysite.mobile.LightsActivity.onCreate(LightsActivity.java:19)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.Activity.performCreate(Activity.java:4531)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)
09-16 01:35:59.167: E/AndroidRuntime(28019):    ... 18 more
09-16 01:35:59.167: E/AndroidRuntime(28019): Caused by: java.lang.NullPointerException
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.mysite.mobile.classA.renderDevice(classA.java:89)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.mysite.mobile.MyViewDeviceActivity.renderDevices(MyViewDeviceActivity.java:58)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.mysite.mobile.MyViewDeviceActivity.onCreate(MyViewDeviceActivity.java:30)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at com.mysite.mobile.classA.onCreate(classA.java:38)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.Activity.performCreate(Activity.java:4531)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
09-16 01:35:59.167: E/AndroidRuntime(28019):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)
09-16 01:35:59.167: E/AndroidRuntime(28019):    ... 29 more

Answer 1

From what I can tell in your logs, you should check that 'light' and Settings.getInstance() aren't null. The reason why it would work in your onClickListener and not in that method is probably because they get instantiated somewhere before you click the image but not before renderDevice() is called.

Try doing something like this in your renderDevice() method:

ImageView device_status_image = (ImageView) lightView
            .findViewById(R.id.device_status_image);
    Settings settings = Settings.getInstance();

    if( light == null)
    {
       /* instantiate your light variable */
    }

    if ( settings == null )
    {
      /* write the necessary code to make sure your singleton gets created */
    }  
    String icon = db.getIcon(light.id, settings.getLastPkAccessPoint(), status, light.oldCategory);

    if ( icon != null) {
        int resId = getResources().getIdentifier(icon, "drawable",
                getPackageName());
        device_status_image.setImageResource(resId);
    } else
        device_status_image.setImageResource(R.drawable.normal_icon); 

    }