我无法弄清楚我的NullPointerException有什么问题或者为什么它甚至存在

Question

What are they? My application keeps crashing whenever I try to pass an object over to my database helper.

The variable name is "e". I've had the data in the object display in a toast notification and everything is fine but when i try to pass it to the database helper I get nothing. I've even added Logs to every second line but nothing gets passed as the method never starts.

I also tried adding the values from the object into separate variables and passing them through (I rewrote the helper method) but it still crashes.

I'm very close to throwing my laptop through the window, please help me.

My placeholder search class

package com.typhoon2099.mediacatalogue;

//This class is used to query the details of the barcode scanned or entered
//This in done in lieu of an open online database
//If an online database is found this class can be replaced to utilise it
public class SearchForBarcode{
//Initialise Variables
public String barcode;
public String mediatype;
public String title;
public String author;

//Set variables based on the input barcode
public SearchForBarcode(String inputBarcode){        
    barcode = inputBarcode;
    //An if statement is used because switch case cannot be used for anything other than int
    //And a 13 digit barcode is too big to fit in an int variable.
    //(JDK 1.7 supports string based cases but Android does not support it)
    if (barcode.equals("5014503113629")){
        mediatype = "DVD";
        title = "The Young Ones Series One";
        author = "Rik Mayall, Ade Edmondson, Nigel Planer, Christopher Ryan, Alexei Sayle";
    }
    else if (barcode.equals("5014503151423")){
        mediatype = "DVD";
        title = "The Office: Complete Series One & Two";
        author = "Ricky Gervais, Martin Freeman, Mackenzie Crook, Lucy Davis";
    }
    else if (barcode.equals("5050582261103")){
        mediatype = "DVD";
        title = "Shaun of the Dead";
        author = "Simon Pegg, Nick Frost, Lucy davis, Kate Ashfield, Dylan Moran, Bill Nighy, Penelope Wilton";
    }
    else if (barcode.equals("5021290037243")){
        mediatype = "Game";
        title = "Batman: Arkham Asylum (PS3)";
        author = "Warner Brothers";
    }
    else if (barcode.equals("5026555402323")){
        mediatype = "Game";
        title = "Bioshock 2 (PS3)";
        author = "2K Games";
    }
    else if (barcode.equals("5021290046573")){
        mediatype = "Game";
        title = "Tomb Raider Trilogy HD (PS3)";
        author = "Crystal Dynamics";
    }
    else if (barcode.equals("6025273901261")){
        mediatype = "CD";
        title = "Flesh Tone";
        author = "Kelis";
    }
    else if (barcode.equals("724358480924")){
        mediatype = "CD";
        title = "Duran Duran";
        author = "Duran Duran";
    }
    else if (barcode.equals("5099969605529")){
        mediatype = "CD";
        title = "Sounds of the Universe";
        author = "Depeche Mode";
    }
    else if (barcode.equals("9781427802118")){
        mediatype = "Book";
        title = "Sgt Frog Vol. 13";
        author = "Mine Yoshizaki";
    }
    else if (barcode.equals("978009940953")){
        mediatype = "Book";
        title = "Star Wars - The New Jedi Order: Vector Prime";
        author = "R. A. Salvatore";
    }
    else{
        mediatype = "Not Found";
        title = "Not Found";
        author = "Not Found";
    }
}
}

My Database Helper class

package com.typhoon2099.mediacatalogue;

import java.util.ArrayList;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DatabaseHelper {
    private static final String DATABASE_NAME = "mediaDatabase";
private static final int DATABASE_VERSION = 2;
private static final String TABLE_NAME = "table";

private OpenHelper mDbHelper;
private SQLiteDatabase mDb;
private SQLiteDatabase mDbr;
private final Context mCtx;

private static final String TAG = "UserDbAdapter";

private static class OpenHelper extends SQLiteOpenHelper{
    OpenHelper(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table "+TABLE_NAME+"" +
                " (_id integer primary key," +
                " mediatype text not null," +
                " title text not null" +
                " author text not null" +
                " wishlist integer" +
                ");");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }

}
public DatabaseHelper(Context ctx) {
    this.mCtx = ctx;
}
 //This method is called from the controlling class when the open() call is used
//it creates an instance of openHelper (detailed above) and sets up appropriate   
//connections to the database.
public DatabaseHelper open() throws SQLException {
    mDbHelper = new OpenHelper(mCtx);
    mDb = mDbHelper.getWritableDatabase();
    mDbr = mDbHelper.getReadableDatabase();
    return this;
}
//used to close db connections
public void close() {
    mDbHelper.close();
}
//When we wish to insert a record we can call this method, passing   
//in the appropriate parameters.  The method then binds the   
//parameters to the insert command and then executes it
//against the appropriate table in the mDB database instance
public long addMedia(SearchForBarcode result) {
    Log.d(TAG,"Line 1");        
    ContentValues initialValues = new ContentValues();
    Log.d(TAG,"Line 2");        
    initialValues.put("_id", result.barcode);
    Log.d(TAG,"Line 3");        
    initialValues.put("mediatype", result.mediatype);
    Log.d(TAG,"Line 4");        
    initialValues.put("title", result.title);
    Log.d(TAG,"Line 5");        
    initialValues.put("author", result.author);
    Log.d(TAG,"Line 6");        
    initialValues.put("wishlist", 0);
    Log.d(TAG,"Line 7");        

    return mDb.insert(TABLE_NAME, null, initialValues);
}  
//This function is used to delete an item from the database by passing through the barcode for the item.
public void deleteMedia(String barcode) {
    String args = "_id = "+barcode;
    mDb.delete(TABLE_NAME, args, null);
}

public void UpdateWishlist(String barcode, String addOrRemove){
    ContentValues args = new ContentValues();
    if(addOrRemove.equals("add")){
        args.put("wishlist", "1");
    }
    else{
        args.put("wishlist","0");
    }
    mDb.update(TABLE_NAME, args, "barcode = ?", new String[]{barcode});
}

//This function is used to select all the madia of a particular type for displaying in the tabs
public ArrayList<String[]> selectMedia(String mediatype) {
    ArrayList<String[]> results = new ArrayList<String[]>();
    int counter = 0;
    Cursor cursor = this.mDbr.query(TABLE_NAME, new String[]{"_id", "title", "author", "rating"}, "mediatype = "+"?",new String[]{mediatype}, null, null, "title asc");
    if (cursor.moveToFirst()) {
        do {
            results.add(new String[3]);
            results.get(counter)[0] = cursor.getString(0).toString();
            results.get(counter)[1] = cursor.getString(1).toString();
            results.get(counter)[2] = cursor.getString(2).toString();
            results.get(counter)[3] = cursor.getString(3).toString();
            counter++;
        } while (cursor.moveToNext());
    }
    if (cursor != null && !cursor.isClosed()) {
        cursor.close();
    }
    return results;
}
}

I use the two together like so:

public void onActivityResult(int requestCode, int resultCode, Intent intent) {
    IntentResult scanResult = IntentIntegrator.parseActivityResult(requestCode, resultCode, intent);
    if (scanResult != null) {
        if (resultCode == 0){
            //If the user cancels the scan
            Toast.makeText(getApplicationContext(),"You cancelled the scan", 3).show();
        }
        else{
            String contents = intent.getStringExtra("SCAN_RESULT");
            String format = intent.getStringExtra("SCAN_RESULT_FORMAT");
            if (format.equals("EAN_13") || format.equals("UPC_A")){
                //If the barcode scanned is of the correct type then pass the barcode into the search method to get the product details
                SearchForBarcode result = new SearchForBarcode(contents);
                Log.d(TAG,"Got from Database");        
                if(result.title.equals("Not Found")){
                    Toast.makeText(getApplicationContext(), "Details Not Found", 5).show();
                }
                else{
                    if(database.addMedia(result)>=0){
                        Toast.makeText(getApplicationContext(),result.title+" added to catalogue", 5).show();                    
                    }
                    else{
                        Toast.makeText(getApplicationContext(), "The product is already in the database", 5).show();
                    }
                }
            }
            else{
                //If the barcode is not of the correct type then display a notification
                Toast.makeText(getApplicationContext(),contents+" "+format, 3).show();
            }
        }
    }
}

Log cat:

 12-08 16:28:20.525: I/System.out(6862): Sending WAIT chunk 12-08 16:28:20.525: W/ActivityThread(6862): Application com.typhoon2099.mediacatalogue is waiting for the debugger on port 8100... 12-08 16:28:20.626: I/dalvikvm(6862): Debugger is active 12-08 16:28:20.726: I/System.out(6862): Debugger has connected 12-08 16:28:20.726: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:20.926: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:21.126: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:21.326: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:21.526: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:21.737: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:21.937: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:22.137: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:22.337: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:22.537: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:22.738: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:22.938: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:23.138: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:23.338: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:23.538: I/System.out(6862): waiting for debugger to settle... 12-08 16:28:23.739: I/System.out(6862): debugger has settled (1439) 12-08 16:28:24.089: D/dalvikvm(6862): GC_EXTERNAL_ALLOC freed 53K, 50% free 2726K/5379K, external 0K/0K, paused 31ms 12-08 16:28:28.784: W/KeyCharacterMap(6862): Can't open keycharmap file 12-08 16:28:28.784: W/KeyCharacterMap(6862): Error loading keycharmap file '/system/usr/keychars/atmel-touchscreen.kcm.bin'. hw.keyboards.131074.devname='atmel-touchscreen' 12-08 16:28:28.784: I/KeyCharacterMap(6862): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 12-08 16:28:31.636: D/PhoneWindow(6862): couldn't save which view has focus because the focused view com.android.internal.policy.impl.PhoneWindow$DecorView@40515630 has no id. 12-08 16:28:33.718: W/IInputConnectionWrapper(6862): showStatusIcon on inactive InputConnection 12-08 16:28:33.748: W/IInputConnectionWrapper(6862): InputConnection = android.view.inputmethod.BaseInputConnection@4052b0b8, active client = false 12-08 16:28:38.553: D/MainActivity(6862): Got from Database 12-08 16:29:12.206: W/ActivityThread(7049): Application com.typhoon2099.mediacatalogue is waiting for the debugger on port 8100... 12-08 16:29:12.216: I/System.out(7049): Sending WAIT chunk 12-08 16:29:12.226: I/dalvikvm(7049): Debugger is active 12-08 16:29:12.416: I/System.out(7049): Debugger has connected 12-08 16:29:12.416: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:12.616: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:12.817: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:13.017: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:13.217: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:13.427: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:13.627: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:13.817: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:14.028: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:14.228: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:14.428: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:14.628: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:14.828: I/System.out(7049): waiting for debugger to settle... 12-08 16:29:15.029: I/System.out(7049): debugger has settled (1343) 12-08 16:29:15.269: D/dalvikvm(7049): GC_EXTERNAL_ALLOC freed 58K, 50% free 2726K/5379K, external 0K/0K, paused 30ms 12-08 16:29:16.650: W/KeyCharacterMap(7049): Can't open keycharmap file 12-08 16:29:16.650: W/KeyCharacterMap(7049): Error loading keycharmap file '/system/usr/keychars/atmel-touchscreen.kcm.bin'. hw.keyboards.131074.devname='atmel-touchscreen' 12-08 16:29:16.650: I/KeyCharacterMap(7049): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 12-08 16:29:18.973: D/PhoneWindow(7049): couldn't save which view has focus because the focused view com.android.internal.policy.impl.PhoneWindow$DecorView@405132f8 has no id. 12-08 16:29:20.044: W/IInputConnectionWrapper(7049): showStatusIcon on inactive InputConnection 12-08 16:29:20.044: W/IInputConnectionWrapper(7049): InputConnection = android.view.inputmethod.BaseInputConnection@4052b0a8, active client = false 12-08 16:29:25.249: D/MainActivity(7049): Got from Database 12-08 16:29:31.895: D/AndroidRuntime(7049): Shutting down VM 12-08 16:29:31.895: W/dalvikvm(7049): threadid=1: thread exiting with uncaught exception (group=0x4001d5a0) 12-08 16:29:31.965: E/AndroidRuntime(7049): FATAL EXCEPTION: main 12-08 16:29:31.965: E/AndroidRuntime(7049): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=195543262, result=-1, data=Intent { act=com.google.zxing.client.android.SCAN flg=0x80000 (has extras) }} to activity {com.typhoon2099.mediacatalogue/com.typhoon2099.mediacatalogue.MainActivity}: java.lang.NullPointerException 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityThread.deliverResults(ActivityThread.java:2883) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityThread.handleSendResult(ActivityThread.java:2925) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityThread.access$2000(ActivityThread.java:132) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1063) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.os.Handler.dispatchMessage(Handler.java:99) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.os.Looper.loop(Looper.java:143) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityThread.main(ActivityThread.java:4196) 12-08 16:29:31.965: E/AndroidRuntime(7049): at java.lang.reflect.Method.invokeNative(Native Method) 12-08 16:29:31.965: E/AndroidRuntime(7049): at java.lang.reflect.Method.invoke(Method.java:507) 12-08 16:29:31.965: E/AndroidRuntime(7049): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 12-08 16:29:31.965: E/AndroidRuntime(7049): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 12-08 16:29:31.965: E/AndroidRuntime(7049): at dalvik.system.NativeStart.main(Native Method) 12-08 16:29:31.965: E/AndroidRuntime(7049): Caused by: java.lang.NullPointerException 12-08 16:29:31.965: E/AndroidRuntime(7049): at com.typhoon2099.mediacatalogue.MainActivity.onActivityResult(MainActivity.java:193) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.Activity.dispatchActivityResult(Activity.java:4010) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityGroup.dispatchActivityResult(ActivityGroup.java:123) 12-08 16:29:31.965: E/AndroidRuntime(7049): at android.app.ActivityThread.deliverResults(ActivityThread.java:2879) 12-08 16:29:31.965: E/AndroidRuntime(7049): ... 11 more 12-08 16:29:33.467: I/Process(7049): Sending signal. PID: 7049 SIG: 9 

Answer 1

If you look towards the bottom of your console output, the stack contains the line number where the NullPointerException occurs:

...
12-08 16:29:31.965: E/AndroidRuntime(7049): Caused by: java.lang.NullPointerException
12-08 16:29:31.965: E/AndroidRuntime(7049):     at com.typhoon2099.mediacatalogue.MainActivity.onActivityResult(MainActivity.java:193)
12-08 16:29:31.965: E/AndroidRuntime(7049):     at android.app.Activity.dispatchActivityResult(Activity.java:4010)
12-08 16:29:31.965: E/AndroidRuntime(7049):     at android.app.ActivityGroup.dispatchActivityResult(ActivityGroup.java:123)
...

As you can see above, on line 193 of the MainActivity class, in the onActivityResult() method, you're calling a method on a variable that is null . Since we can't see the line numbers for the code posted, you'll have to venture to this point in your code and determine which variable(s) can be/are null at this point.