[英]I can't figure out what's wrong with my NullPointerException or why it even exists
這些是什么？ 每當我嘗試將對象傳遞給數據庫助手時，我的應用程序都會崩潰。
變量名稱為“ e”。 我已經在Toast通知中將對象中的數據顯示出來，一切都很好，但是當我嘗試將其傳遞給數據庫助手時，我什么也沒得到。 我什至在每隔兩行中都添加了日志，但是由於該方法從未啟動，因此沒有任何結果通過。
我還嘗試將對象中的值添加到單獨的變量中並傳遞給它們（我重寫了helper方法），但仍然崩潰。
我非常接近將筆記本電腦從窗戶扔出去，請幫幫我。
我的占位符搜索類
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";
}
}
}
我的數據庫助手類
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;
}
}
我將兩者一起使用，如下所示：
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();
}
}
}
}
日志貓：
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
如果您查看控制台輸出的底部，則堆棧包含發生NullPointerException的行號：
...
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)
...
如上所示，在MainActivity類的第193行的onActivityResult()方法中，您正在對null變量進行調用。 由於我們看不到所發布代碼的行號，因此您必須在代碼中冒險到這一點，並確定此時哪些變量可以為null 。
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