zeliboba_fett zeliboba_fett - 1 month ago 9
Android Question

How do I retrieve data from database using cursor? (Android, SQLite)

I am stuck. I can't find out what I do wrong, so please help anybody.
Though it's quite simple task, I don't understand how actually database looks like.

Here's the code I use to insert data into table in database:

EditText title = (EditText)findViewById(R.id.Title);
String Title = title.getText().toString();

EditText d = (EditText)findViewById(R.id.director);
String Director = d.getText().toString();

SQLiteDatabase db = openOrCreateDatabase("Films", MODE_PRIVATE, null);
db.execSQL("CREATE TABLE IF NOT EXISTS MyFilms (idFilm INTEGER PRIMARY KEY AUTOINCREMENT, Title VARCHAR, Director VARCHAR, Year INTEGER, Rating INTEGER);");
db.execSQL("INSERT INTO MyFilms (Title) VALUES('" + Title + "');");
db.execSQL("INSERT INTO MyFilms (Director) VALUES('" + Director + "');");
db.close();


Does this code gives me a table with columns
idfilm
,
Title
,
Director
,
Year
,
Rating
?
If it's so, there's still a problem when I try to retrieve all the titles from
Title
column using this code:

SQLiteDatabase db = openOrCreateDatabase("Films", MODE_PRIVATE, null);
Cursor c = db.rawQuery("SELECT * FROM MyFilms",null);
c.moveToFirst();

while (c.isAfterLast() == false) {
String Title = c.getString(c.getColumnIndex("Director"));
stringList.add(Title); //This I use to create listlayout dynamically and show all the Titles in it
c.moveToNext();
}


The error log:

05-21 17:50:14.666: E/AndroidRuntime(27045): FATAL EXCEPTION: main
05-21 17:50:14.666: E/AndroidRuntime(27045): java.lang.NullPointerException
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:355)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.ArrayAdapter.getView(ArrayAdapter.java:323)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.AbsListView.obtainView(AbsListView.java:1409)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.ListView.measureHeightOfChildren(ListView.java:1216)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.ListView.onMeasure(ListView.java:1127)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.View.measure(View.java:8313)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.RelativeLayout.measureChild(RelativeLayout.java:566)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:381)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.View.measure(View.java:8313)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.View.measure(View.java:8313)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.LinearLayout.measureVertical(LinearLayout.java:531)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.View.measure(View.java:8313)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.View.measure(View.java:8313)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.ViewRoot.performTraversals(ViewRoot.java:839)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.view.ViewRoot.handleMessage(ViewRoot.java:1859)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.os.Handler.dispatchMessage(Handler.java:99)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.os.Looper.loop(Looper.java:123)
05-21 17:50:14.666: E/AndroidRuntime(27045): at android.app.ActivityThread.main(ActivityThread.java:3683)
05-21 17:50:14.666: E/AndroidRuntime(27045): at java.lang.reflect.Method.invokeNative(Native Method)
05-21 17:50:14.666: E/AndroidRuntime(27045): at java.lang.reflect.Method.invoke(Method.java:507)
05-21 17:50:14.666: E/AndroidRuntime(27045): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-21 17:50:14.666: E/AndroidRuntime(27045): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-21 17:50:14.666: E/AndroidRuntime(27045): at dalvik.system.NativeStart.main(Native Method)


Why does DDMS throw NullPointerException? How should I get the data from "Title"? I tried to use c.getString(), but when I ask for c.getString(1) there's still NullPointerException though it returns "Director" when I set c.getString(2). Please, help!

Answer

Your problem happens when you populate the database (your first code segment).

You need to combine the INSERT statements:

db.execSQL("INSERT INTO MyFilms (Title, Director, Year) VALUES('" 
    + title + "','" + director + "'," + year + ");");

Otherwise, you wind up with rows that contain a null value for Title or Director.

(Note: Don't use the SQL notation above, because it may leave you vulnerable to SQL injection. I only wrote it this way for the sake of simplicity. In production code, you should use parameters or sanitize your values. Don't become a victim of Little Bobby Tables).

EDIT

Here are some threads regarding prepared statements:

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