问题
In the code below, the getPieceTextFile() method takes an Activity context parameter, however when used, the context passed in appears to be null and leads to a NPE. Any suggestions why would be greatly appreciated.
The LogCat output and code listing are shown below.
LogCat
01-03 13:48:47.223: I/dalvikvm(571): threadid=3: reacting to signal 3
01-03 13:48:47.233: I/dalvikvm(571): Wrote stack traces to '/data/anr/traces.txt'
01-03 13:49:30.073: I/System.out(571): Asset Manager/IS not work.
01-03 13:49:30.073: W/System.err(571): java.io.FileNotFoundException: pieceText.txt
01-03 13:49:30.073: W/System.err(571): at android.content.res.AssetManager.openAsset(Native Method)
01-03 13:49:30.073: W/System.err(571): at android.content.res.AssetManager.open(AssetManager.java:315)
01-03 13:49:30.073: W/System.err(571): at android.content.res.AssetManager.open(AssetManager.java:289)
01-03 13:49:30.073: W/System.err(571): at com.lawson.englishlitrevision.ManipulateDatabase.getPieceTextFile(ManipulateDatabase.java:389)
01-03 13:49:30.073: W/System.err(571): at com.lawson.englishlitrevision.ManipulateDatabase.<init>(ManipulateDatabase.java:500)
01-03 13:49:30.082: W/System.err(571): at com.lawson.englishlitrevision.Novel.onCreate(Novel.java:22)
01-03 13:49:30.082: W/System.err(571): at android.app.Activity.performCreate(Activity.java:4465)
01-03 13:49:30.082: W/System.err(571): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-03 13:49:30.082: W/System.err(571): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-03 13:49:30.082: W/System.err(571): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-03 13:49:30.082: W/System.err(571): at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-03 13:49:30.082: W/System.err(571): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-03 13:49:30.092: W/System.err(571): at android.os.Handler.dispatchMessage(Handler.java:99)
01-03 13:49:30.092: W/System.err(571): at android.os.Looper.loop(Looper.java:137)
01-03 13:49:30.092: W/System.err(571): at android.app.ActivityThread.main(ActivityThread.java:4424)
01-03 13:49:30.092: W/System.err(571): at java.lang.reflect.Method.invokeNative(Native Method)
01-03 13:49:30.092: W/System.err(571): at java.lang.reflect.Method.invoke(Method.java:511)
01-03 13:49:30.092: W/System.err(571): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-03 13:49:30.092: W/System.err(571): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-03 13:49:30.102: W/System.err(571): at dalvik.system.NativeStart.main(Native Method)
01-03 13:49:30.102: W/dalvikvm(571): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
01-03 13:49:30.123: E/AndroidRuntime(571): FATAL EXCEPTION: main
01-03 13:49:30.123: E/AndroidRuntime(571): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lawson.englishlitrevision/com.lawson.englishlitrevision.Novel}: java.lang.NullPointerException
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.os.Handler.dispatchMessage(Handler.java:99)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.os.Looper.loop(Looper.java:137)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.ActivityThread.main(ActivityThread.java:4424)
01-03 13:49:30.123: E/AndroidRuntime(571): at java.lang.reflect.Method.invokeNative(Native Method)
01-03 13:49:30.123: E/AndroidRuntime(571): at java.lang.reflect.Method.invoke(Method.java:511)
01-03 13:49:30.123: E/AndroidRuntime(571): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-03 13:49:30.123: E/AndroidRuntime(571): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-03 13:49:30.123: E/AndroidRuntime(571): at dalvik.system.NativeStart.main(Native Method)
01-03 13:49:30.123: E/AndroidRuntime(571): Caused by: java.lang.NullPointerException
01-03 13:49:30.123: E/AndroidRuntime(571): at java.io.Reader.<init>(Reader.java:64)
01-03 13:49:30.123: E/AndroidRuntime(571): at java.io.InputStreamReader.<init>(InputStreamReader.java:79)
01-03 13:49:30.123: E/AndroidRuntime(571): at com.lawson.englishlitrevision.ManipulateDatabase.<init>(ManipulateDatabase.java:500)
01-03 13:49:30.123: E/AndroidRuntime(571): at com.lawson.englishlitrevision.Novel.onCreate(Novel.java:22)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.Activity.performCreate(Activity.java:4465)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-03 13:49:30.123: E/AndroidRuntime(571): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-03 13:49:30.123: E/AndroidRuntime(571): ... 11 more
01-03 13:49:30.553: I/dalvikvm(571): threadid=3: reacting to signal 3
01-03 13:49:30.563: I/dalvikvm(571): Wrote stack traces to '/data/anr/traces.txt'
01-03 13:49:30.683: I/dalvikvm(571): threadid=3: reacting to signal 3
01-03 13:49:30.693: I/dalvikvm(571): Wrote stack traces to '/data/anr/traces.txt'
Code
/**
* Contains SQL statements and manages connections
*
* @author Daniel Lawson
* @version 29/12/13
*/
package com.lawson.englishlitrevision;
import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.content.res.AssetManager;
import java.util.ArrayList;
import java.util.Scanner;
import java.io.File;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class ManipulateDatabase {
/** String representing the name of the database */
private static final String databaseName = "EnglishDatabase.db";
/** Int representing the current version of the database */
private static final int databaseVersion = 1;
// ----------------------------------------------------------------------------------
/**
* String representing the table that stores the name of the piece and
* whether it is a play or not.
*/
private static final String pieceTable = "pieceTable";
/**
* String representing the table that stores the name of the point made,
* which piece it belongs to, and which element it pertains to.
*/
private static final String specificTable = "specificTable";
/**
* String representing the table that stores the element, the piece it
* belongs to, and whether or not it is a character.
*/
private static final String elementTable = "elementTable";
/**
* String representing the table that stores the quote and the point it
* links to.
*/
private static final String quoteTable = "quoteTable";
/**
* String representing the table that stores the piece and the
* correct/incorrect responses on various dates
*/
private static final String statsTable = "statsTable";
// ----------------------------------------------------------------------------------
/** String representing the piece field of the piece table */
private static final String pieceField = "piece";
/** String representing the type field of the piece table */
private static final String typeField = "isPlay";
/** String representing the point field of the specific table */
private static final String pointField = "point";
/** String representing the element field of the element table */
private static final String elementField = "element";
/** String representing the elType field of the element table */
private static final String elTypeField = "isCharacter";
/** String representing the quote field of the quote table */
private static final String quoteField = "quote";
/** String representing the ID field of the stats table */
private static final String idField = "statId";
/** String representing the correct field of the stats table */
private static final String correctField = "correct";
/** String representing the incorrect field of the stats table */
private static final String incorrectField = "incorrect";
/** String representing the date field of the stats table */
private static final String dateField = "date";
// ----------------------------------------------------------------------------------
/** String array representing all the fields of the piece table */
private static final String[] pieceTableFields = { pieceField, typeField };
/** String array representing all the fields of the specific table */
private static final String[] specificTableFields = { pointField,
pieceField, elementField };
/** String array representing all the fields of the quote table */
private static final String[] quoteTableFields = { quoteField, pointField };
/** String array representing all the fields of the element table */
private static final String[] elementTableFields = { elementField,
pieceField, elTypeField };
/** String array representing all the fields of the stats table */
private static final String[] statsTableFields = { idField, pieceField,
correctField, incorrectField, dateField };
// ----------------------------------------------------------------------------------
/** SQL statement to create the piece table. */
private static final String createPieceTable = "CREATE TABLE " + pieceTable
+ " (" + pieceField + " TEXT NOT NULL PRIMARY KEY, " + typeField
+ " INTEGER);";
/** SQL statement to create the specific table. */
private static final String createSpecificTable = "CREATE TABLE "
+ specificTable + "(" + pointField + " TEXT NOT NULL PRIMARY KEY,"
+ pieceField + " TEXT NOT NULL," + elementField + " TEXT NOT NULL)";
/** SQL statement to create the quotes table. */
private static final String createQuoteTable = "CREATE TABLE " + quoteTable
+ "(" + quoteField + " TEXT NOT NULL PRIMARY KEY," + pointField
+ " TEXT NOT NULL PRIMARY KEY)";
/** SQL statement to create the element table. */
private static final String createElementTable = "CREATE TABLE "
+ elementTable + "(" + elementField + " TEXT NOT NULL PRIMARY KEY,"
+ pieceField + " TEXT NOT NULL," + elTypeField + " INTEGER)";
/** SQL statement to create the stats table. */
private static final String createStatsTable = "CREATE TABLE " + statsTable
+ "(" + idField + " INTEGER PRIMARY KEY," + pieceField
+ " TEXT NOT NULL," + correctField + " INTEGER," + incorrectField
+ " INTEGER," + dateField + " DATE)";
// ----------------------------------------------------------------------------------
/**
* SQL statement to search the piece table - replace [columnName] and
* [value] with field to be searched and what value to look for.
*/
private static final String searchPieceTable = "SELECT * FROM "
+ pieceTable + " WHERE [columnName] = '[value]';";
/**
* SQL statement to search the specific table - replace [columnName] and
* [value] with field to be searched and what value to look for.
*/
private static final String searchSpecificTable = "SELECT * FROM "
+ specificTable + " WHERE [columnName] = '[value]'";
/**
* SQL statement to search the quote table - replace [columnName] and
* [value] with field to be searched and what value to look for.
*/
private static final String searchQuoteTable = "SELECT * FROM "
+ quoteTable + " WHERE [columnName] = '[value]'";
/**
* SQL statement to search the element table - replace [columnName] and
* [value] with field to be searched and what value to look for.
*/
private static final String searchElementTable = "SELECT * FROM "
+ elementTable + " WHERE [columnName] = '[value]'";
/**
* SQL statement to search the stats table - replace [columnName] and
* [value] with field to be searched and what value to look for.
*/
private static final String searchStatsTable = "SELECT * FROM "
+ statsTable + " WHERE [columnName] = '[value]'";
// ----------------------------------------------------------------------------------
/**
* SQL statement to update the piece table - replace [assignValues] and
* [condition] with items to be altered + their new values and the condition
* where if true, this change should be applied.
*/
private static final String updatePieceTable = "UPDATE " + pieceTable
+ " SET [assignValues] WHERE [condition]";
/**
* SQL statement to update the specific table - replace [assignValues] and
* [condition] with items to be altered + their new values and the condition
* where if true, this change should be applied.
*/
private static final String updateSpecificTable = "UPDATE " + specificTable
+ " SET [assignValues] WHERE [condition]";
/**
* SQL statement to update the quote table - replace [assignValues] and
* [condition] with items to be altered + their new values and the condition
* where if true, this change should be applied.
*/
private static final String updateQuoteTable = "UPDATE " + quoteTable
+ " SET [assignValues] WHERE [condition]";
/**
* SQL statement to update the element table - replace [assignValues] and
* [condition] with items to be altered + their new values and the condition
* where if true, this change should be applied.
*/
private static final String updateElementTable = "UPDATE " + elementTable
+ " SET [assignValues] WHERE [condition]";
/**
* SQL statement to update the stats table - replace [assignValues] and
* [condition] with items to be altered + their new values and the condition
* where if true, this change should be applied.
*/
private static final String updateStatsTable = "UPDATE " + statsTable
+ " SET [assignValues] WHERE [condition]";
// ----------------------------------------------------------------------------------
/**
* SQL statement to delete from the piece table - replace [condition] the
* condition where if true, this deletion should be applied.
*/
private static final String deleteFromPieceTable = "DELETE FROM "
+ pieceTable + " WHERE [condition]";
/**
* SQL statement to delete from the specific table - replace [condition] the
* condition where if true, this deletion should be applied.
*/
private static final String deleteFromSpecificTable = "DELETE FROM "
+ specificTable + " WHERE [condition]";
/**
* SQL statement to delete from the quote table - replace [condition] the
* condition where if true, this deletion should be applied.
*/
private static final String deleteFromQuoteTable = "DELETE FROM "
+ quoteTable + " WHERE [condition]";
/**
* SQL statement to delete from the element table - replace [condition] the
* condition where if true, this deletion should be applied.
*/
private static final String deleteFromElementTable = "DELETE FROM "
+ elementTable + " WHERE [condition]";
/**
* SQL statement to delete from the stats table - replace [condition] the
* condition where if true, this deletion should be applied.
*/
private static final String deleteFromStatsTable = "DELETE FROM "
+ statsTable + " WHERE [condition]";
// ----------------------------------------------------------------------------------
/**
* SQL statement to insert into the piece table - replace [values] with the
* values to be inserted.
*/
private static final String insertIntoPieceTable = "INSERT INTO "
+ pieceTable + " VALUES ([values])";
/**
* SQL statement to insert into the specific table - replace [values] with
* the values to be inserted.
*/
private static final String insertIntoSpecificTable = "INSERT INTO "
+ specificTable + " VALUES ([values])";
/**
* SQL statement to insert into the quote table - replace [values] with the
* values to be inserted.
*/
private static final String insertIntoQuoteTable = "INSERT INTO "
+ quoteTable + " VALUES ([values])";
/**
* SQL statement to insert into the element table - replace [values] with
* the values to be inserted.
*/
private static final String insertIntoElementTable = "INSERT INTO "
+ elementTable + " VALUES ([values])";
/**
* SQL statement to insert into the quote table - replace [values] with the
* values to be inserted.
*/
private static final String insertIntoStatsTable = "INSERT INTO "
+ statsTable + " VALUES ([values])";
// ----------------------------------------------------------------------------------
/**
* SQLiteDatabase representing the English database
*/
private SQLiteDatabase dataBase;
/**
* Instance of DatabaseHelper class utilised to 'access' database
*/
private DatabaseHelper baseHelper;
/**
* Content of the Database Manipulator (ManipulateDatabase class)
*/
private Activity context;
/**
* Boolean to store whether or not this is the first time this base/version
* has been launched
*/
private boolean initialLaunch = false;
/**
* File for the BufferedReader to read into Database
*/
private File pieceList;
/**
* Method to get pieceText file from assets for BufferedReader to use
*
* @param ctx
* @throws IOException
*/
private InputStream getPieceTextFile(Activity ctx) throws IOException {
try {
AssetManager manager = ctx.getAssets();
InputStream is = manager.open("pieceText.txt");
return is;
} catch (Exception e) {
System.out.println("Asset Manager/IS not work.");
e.printStackTrace();
return null;
}
}
/*
* private File specificList = new File("specificList.txt");
*
* private BufferedReader specificScan = new BufferedReader(new FileReader(
* "specificList.txt"));
*
* private File elementList = new File("elementList.txt");
*
* private BufferedReader elementScan = new BufferedReader(new FileReader(
* "elementList.txt"));
*
* private File quoteList = new File("quoteList.txt");
*
* private BufferedReader quoteScan = new BufferedReader(new FileReader(
* "quoteList.txt"));
*/
/**
* Method to open the database
*/
private void openSesame() {
try {
dataBase = baseHelper.getWritableDatabase();
} catch (SQLiteException e) {
System.out.println("Database couldn't be opened");
e.printStackTrace();
}
}
/**
* Method to close the database
*/
private void closeSesame() {
baseHelper.close();
}
public ArrayList<String> getPieces(String typePiece) {
try {
openSesame();
ArrayList<String> pieces = new ArrayList<String>();
String command = searchPieceTable
.replace("[columnName]", typeField);
command = command.replace("[value]", typePiece);
Cursor cursor = dataBase.rawQuery(command, null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
pieces.add(cursor.getString(cursor.getColumnIndex(pieceField)));
cursor.moveToNext();
}
closeSesame();
return pieces;
} catch (SQLiteException e) {
e.printStackTrace();
System.out.println("SQL Problem");
ArrayList<String> defaultReturn = new ArrayList<String>();
defaultReturn.add("There is is default item.");
defaultReturn.add("Because the proper ArrayList");
defaultReturn.add("Wasn't filled properly");
return defaultReturn;
}
}
public ArrayList<String> getAllPieces() {
try {
openSesame();
ArrayList<String> allPieces = new ArrayList<String>();
String instruction = "SELECT * FROM pieceTable";
Cursor cursor = dataBase.rawQuery(instruction, null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
allPieces.add(cursor.getString(cursor
.getColumnIndex(pieceField)));
cursor.moveToNext();
}
closeSesame();
return allPieces;
} catch (Exception e) {
e.printStackTrace();
ArrayList<String> defaultList = new ArrayList<String>();
defaultList.add("Catch default");
return defaultList;
}
}
/**
* Constructor
*
* @param contextIn
* Context of the MainpuxlateDatabase class
* @throws IOException
*/
public ManipulateDatabase(Activity contextIn) throws IOException {
baseHelper = new DatabaseHelper(contextIn);
context = contextIn;
BufferedReader pieceScan = new BufferedReader(new InputStreamReader(
getPieceTextFile(context), "UTF-8"));
openSesame();
String line;
String x;
String pieceName;
String isDrama;
String point;
String element;
String quote;
String isCharacter;
int commaPoint;
int commaPoint2;
if (true) {
while ((x = pieceScan.readLine()) != null) {
line = pieceScan.readLine();
System.out.println(line);
commaPoint = line.indexOf(",");
pieceName = line.substring(0, commaPoint);
isDrama = line.substring(commaPoint + 1, line.length() - 1);
ContentValues pv = new ContentValues();
pv.put(pieceField, pieceName);
pv.put(typeField, isDrama);
dataBase.insert(pieceTable, null, pv);
System.out.println("DAMN YOU MORONIC CRETIN!!");
}
/*
* while ((x = specificScan.readLine()) != null) { line =
* specificScan.readLine(); System.out.println(line); commaPoint =
* line.indexOf(","); point = line.substring(0, commaPoint);
* commaPoint2 = (line .substring(commaPoint + 1, line.length() - 1)
* .indexOf(",")); pieceName = line.substring(commaPoint + 1,
* commaPoint2); element = line.substring(commaPoint2 + 1,
* line.length() - 1);
*
* ContentValues sv = new ContentValues(); sv.put(pointField,
* point); sv.put(pieceField, pieceName); sv.put(elementField,
* element); dataBase.insert(specificTable, null, sv); } while ((x =
* elementScan.readLine()) != null) { line = elementScan.readLine();
* System.out.println(line); commaPoint = line.indexOf(","); element
* = line.substring(0, commaPoint); commaPoint2 = (line
* .substring(commaPoint + 1, line.length() - 1) .indexOf(","));
* pieceName = line.substring(commaPoint + 1, commaPoint2);
* isCharacter = line .substring(commaPoint2 + 1, line.length() -
* 1);
*
* ContentValues ev = new ContentValues(); ev.put(elementField,
* element); ev.put(pieceField, pieceName); ev.put(elTypeField,
* isCharacter); dataBase.insert(elementTable, null, ev);
*
* } while ((x = quoteScan.readLine()) != null) { line =
* quoteScan.readLine(); System.out.println(line); commaPoint =
* line.indexOf(","); quote = line.substring(0, commaPoint); point =
* line.substring(commaPoint + 1, line.length() - 1);
*
* ContentValues qv = new ContentValues(); qv.put(quoteField,
* quote); qv.put(pointField, point); dataBase.insert(quoteTable,
* null, qv); }
*/
}
}
// ----------------------------------------------------------------------------------
/**
* Database helper - Three basic methods - required database tasks
*
* @author Daniel Lawson
* @version 30/12/13
*/
private class DatabaseHelper extends SQLiteOpenHelper {
private DatabaseHelper(Context theContext) {
super(theContext, databaseName, null, databaseVersion);
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(createPieceTable);
/*
* db.execSQL(createSpecificTable);
* db.execSQL(createQuoteTable); db.execSQL(createElementTable);
* db.execSQL(createStatsTable);
*/
initialLaunch = true;
} catch (SQLiteException e) {
System.out.println("Failed to create table(s)");
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + pieceTable);
db.execSQL("DROP TABLE IF EXISTS " + specificTable);
db.execSQL("DROP TABLE IF EXISTS " + quoteTable);
db.execSQL("DROP TABLE IF EXISTS " + elementTable);
db.execSQL("DROP TABLE IF EXISTS " + statsTable);
onCreate(db);
}
}
}
回答1:
It is not because your context is null.
getPieceTextFile returned null(Might have returned from exception part) and BufferReaderCreation also failed at line number 500.
Ensure that you have pieceText.txt file in assets folder
来源：https://stackoverflow.com/questions/20905405/context-being-passed-into-method-for-getassets-is-null