cursor index out of bound exception 0 android

Question

I have developed an android application which has content of a little book.. the application have an option of " continue reading" which used when " onback pressed" and " on pause" it stores the page and other info on shared preferences and retrieve them when pressing continue reading... however it shows" cursor index out of bounds exception" index 0 requested with size of 0 when using this option and force closes the app. i want it to remain for a while at least... the codes are working fine in other application but here it shows exception

here is what happens to clarify the problem:

1 : normally install the apk file on device and open a text to read.

2: user press back button and goes to other parts of the application like setting or....

3: user press " continue reading" BEFORE CLOSING THE APP" app can retrieve what ever he was reading.

4: user closes the app.

5: opens it again and press "continue reading"

6:app cant retrieve the text and force closes.

or:

1:run the app from eclipse in emulator .

2:it does everything ok as long as the code is opene and run from eclipse.

3:shutdown the emulator or disconnect from eclips.

4:run the emulator.

5:open the app and press "continue reading".

6:force close.

here is my "TextShow" class:

protected void onCreate(Bundle savedInstanceState) {
load(book,name,Page2);
}
private void load(String sea,String Name,int page3){
db.open();
titr.setText(Name);
matn.setText(db.main_display("content", sea, Name, page3));
page.setText("page"+ Page2 + "from"+ Page1);
db.close();
}

public void onBackPressed() {

SharedPreferences sp=getApplicationContext().getSharedPreferences("cont",        0);
Editor ed=sp.edit();
ed.clear();
ed.putString("book", book);
ed.putString("name", name);
ed.putInt("page",Page1);
ed.commit();
finish();

}
@Override
protected void onPause() {
SharedPreference sp=getApplicationContext().getSharedPreferences("cont", 0);
Editor ed=sp.edit();
ed.clear();
ed.putString("book", book);
ed.putString("name", name);
ed.putInt("page",Page1);
ed.commit();
super.onPause();
}

here is my Main class:

ImageView cont=(ImageView) findViewById(R.id.cont);
cont.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {
sp=getApplicationContext().getSharedPreferences("cont", 0);
    if(sp.getString("name", "*")!="*"){
        Intent i=new Intent(Main.this,TextShown.class);
        i.putExtra("book",sp.getString("book", "*"));
        i.putExtra("name",sp.getString("name", "*"));
        i.putExtra("page",sp.getInt("page", 0)+"");
        startActivity(i);
        overridePendingTransition(R.anim.in, R.anim.out);

            }else{
                Toast.makeText(getApplicationContext(), "there is no ending point", Toast.LENGTH_LONG).show();
            }


        }

    });

here is my database class...method for retrieving the text :

public String main_display(String table,String sea,String name,int page){
    Cursor cu=mydb.rawQuery("select * from "+table+" where BookName='"+sea+"' and StoryName='"+name+"' and Page="+page, null);
    cu.moveToFirst();
    String s=cu.getString(4);
    return s;

}

Answer 1

The exception says, that the data at index 4 could not be found, because it is not a valid index. Please note, that indexes starts from 0.

Here are some general improvements to avoid suche mistakes:

1.) You should not use hard coded indexes when retrieving data from cursor, because you can easily messed up them. Instead of that you should create a class, which simply holds the column names as string constants. Then you can define your table as follows:

private static final String CREATE_TABLE_LOGIN = "CREATE TABLE IF NOT EXISTS "
    + LoginColumns.TABLE_NAME + "(" + LoginColumns._ID + " INTEGER PRIMARY KEY autoincrement, "
    + LoginColumns.KEY_LOGIN_ABCOCOE + " VARCHAR(100) NOT NULL, "
    + LoginColumns.KEY_LOGIN_VALID + " INTEGER NOT NULL);";

2.) You should always add a check to see if the cursor has items and use the column names instead of the plain index.

public String main_display(String table,String sea,String name,int page){
    Cursor cu=mydb.rawQuery("select * from "+table+" where                               BookName='"+sea+"' and StoryName='"+name+"' and Page="+page, null);
    if (cu.moveToFirst()){
        // just an example
        String s=cu.getString(cursor.getColumnIndex(LoginColumns.KEY_LOGIN_ABCOCOE)
        return s;
    }
    return null;
}

If this does not fix your problem, please provide some more information such as stacktrace etc.

Answer 2

Add a check to see if cursor has items:

if (cu.moveToFirst()) {
    String s=cu.getString(4);
} else {
    Log.e("TAG", "Cursor empty!");
}