我不知道我的 NullPointerException 有什么问题，或者它为什么存在 [英] I can't figure out what's wrong with my NullPointerException or why it even exists
本文介绍了我不知道我的 NullPointerException 有什么问题，或者它为什么存在的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
它们是什么?每当我尝试将对象传递给我的数据库助手时，我的应用程序都会崩溃.
What are they? My application keeps crashing whenever I try to pass an object over to my database helper.
变量名是e".我已经在 toast 通知中显示了对象中的数据，一切都很好，但是当我尝试将它传递给数据库助手时，我什么也没得到.我什至每两行都添加了 Logs，但由于该方法从未启动，因此没有传递任何内容.
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.
我还尝试将对象中的值添加到单独的变量中并传递它们(我重写了辅助方法)，但它仍然崩溃.
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.
我差点把笔记本电脑扔到窗外，请帮帮我.
I'm very close to throwing my laptop through the window, please help me.
我的占位符搜索类
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";
}
}
}
我的数据库助手类
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;
}
}
我像这样同时使用两者:
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();
}
}
}
}
日志猫:<代码>
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
推荐答案
如果您看向控制台输出的底部，堆栈包含发生 NullPointerException 的行号:
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)
...
正如你在上面看到的，在 MainActivity 类的第 193 行，在 onActivityResult() 方法中，你正在调用一个变量的方法，它是 <代码>空.由于我们无法看到已发布代码的行号，因此您必须冒险到代码中的这一点，并确定此时哪些变量可以是/是 null.
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.
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