这是我的自定义提供商的代码，
大多是从SDK记事本项目中复制的
我不明白为什么我得到nullPointException，
为什么不创建提供程序实例？
package alon.beginner.registerform;
import android.database.SQLException;
import java.util.HashMap;
import alon.beginner.registerform.RegistrationFormMetaData.Users;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;
/**
* Provides access to the database of registered users.
* each user has a
* name, email , birthday date, a creation date and modification date
*/
public class RegistrationProvider extends ContentProvider {
private static final String TAG = "RegistrationProvider";
private static final String DATABASE_NAME = "register_yourself.db";
private static final int DATABASE_VERSION = 1;
private static final String USERS_TABLE_NAME = "users";
private static HashMap sUsersProjectionMap;
private static final int USERS = 1;
private static final int USER_ID = 2;
private static final UriMatcher sUriMatcher;
static {
sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
sUriMatcher.addURI(RegistrationFormMetaData.AUTHORITY, "users", USERS);
sUriMatcher.addURI(RegistrationFormMetaData.AUTHORITY, "users/#", USER_ID);
sUsersProjectionMap.put(Users._ID, Users._ID);
sUsersProjectionMap.put(Users.FULL_NAME, Users.FULL_NAME);
sUsersProjectionMap.put(Users.EMAIL, Users.EMAIL);
sUsersProjectionMap.put(Users.BIRTHDAY_DATE, Users.BIRTHDAY_DATE);
sUsersProjectionMap.put(Users.CREATED_DATE, Users.CREATED_DATE);
sUsersProjectionMap.put(Users.MODIFIED_DATE, Users.MODIFIED_DATE);
}
/**
* this class helps to create, open , and upgrade the database files
*/
private static class DatabaseHelper extends SQLiteOpenHelper{
DatabaseHelper(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db){
db.execSQL("CREATE TABLE " + USERS_TABLE_NAME + " ("
+ Users._ID + " INTEGER PRIMARY KEY, "
+ Users.FULL_NAME + " TEXT, "
+ Users.EMAIL + " TEXT, "
+ Users.BIRTHDAY_DATE + " TEXT, "
+ Users.CREATED_DATE + " INTEGER, "
+ Users.MODIFIED_DATE + " INTEGER"
+ ");" );
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS users");
onCreate(db);
}
}
private DatabaseHelper mOpenHelper;
@Override
public boolean onCreate() {
mOpenHelper = new DatabaseHelper(getContext());
return true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
qb.setTables(USERS_TABLE_NAME);
switch(sUriMatcher.match(uri)){
case USERS:
qb.setProjectionMap(sUsersProjectionMap);
break;
case USER_ID:
qb.setProjectionMap(sUsersProjectionMap);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
//if no sort order is specified use the default
String orderBy;
if (TextUtils.isEmpty(sortOrder)){
orderBy = Users.DEFAULT_SORT_ORDER;
} else {
orderBy = sortOrder;
}
//get the Database and run the query
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);
//Tell the cursor what uri to watch, so it knows when its source data changes
c.setNotificationUri(getContext().getContentResolver() , uri);
return c;
}//here i am
@Override
public String getType(Uri uri) {
switch(sUriMatcher.match(uri)){
case USERS:
return Users.CONTENT_TYPE;
case USER_ID:
return Users.CONTENT_ITEM_TYPE;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
}
@Override
public Uri insert(Uri uri, ContentValues initialValues) {
//Validate the requested uri
if (sUriMatcher.match(uri) != USERS )
throw new IllegalArgumentException("Unknown URI " + uri);
ContentValues values;
if (initialValues != null){
values = new ContentValues(initialValues);
} else {
values = new ContentValues();
}
Long now = Long.valueOf(System.currentTimeMillis());
//Make sure that the fields are all set
if(values.containsKey(Users.CREATED_DATE) == false )
values.put(Users.CREATED_DATE, now);
if(values.containsKey(Users.MODIFIED_DATE) == false )
values.put(Users.MODIFIED_DATE, now);
if(values.containsKey(Users.FULL_NAME) == false )
throw new IllegalArgumentException("Missing a full name field");
if(values.containsKey(Users.EMAIL) == false )
throw new IllegalArgumentException("Missing an Email field");
if(values.containsKey(Users.BIRTHDAY_DATE) == false)
throw new IllegalArgumentException("Missing a birthday date field");
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
long rowId = db.insert(USERS_TABLE_NAME,Users.FULL_NAME, values);
if (rowId > 0){
Uri userUri = ContentUris.withAppendedId(Users.CONTENT_URI, rowId);
getContext().getContentResolver().notifyChange(userUri, null);
return userUri;
}
throw new SQLException("Failed to insert row into " + uri);
}
@Override
public int delete(Uri uri, String where, String[] whereArgs) {
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
int count;
switch (sUriMatcher.match(uri)){
case USERS:
count = db.delete(USERS_TABLE_NAME, where, whereArgs);
break;
case USER_ID:
String userId = uri.getPathSegments().get(1);
count = db.delete(USERS_TABLE_NAME,
Users._ID + "=" + userId +
(!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""),
whereArgs);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
@Override
public int update(Uri uri, ContentValues values, String where,
String[] whereArgs) {
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
int count;
switch (sUriMatcher.match(uri)){
case USERS:
count = db.update(USERS_TABLE_NAME, values, where, whereArgs);
break;
case USER_ID:
String userId = uri.getPathSegments().get(1);
count = db.update(USERS_TABLE_NAME, values,
Users._ID + "=" + userId + (!TextUtils.isEmpty(where) ? " AND (" + where + ')' : ""),
whereArgs);
break;
default:
throw new IllegalArgumentException("Unkown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
}
10-03 14:25:14.476: INFO/ActivityManager(63): Start proc alon.beginner.registerform for activity alon.beginner.registerform/.RegisterForm: pid=287 uid=10041 gids={}
10-03 14:25:14.488: INFO/AndroidRuntime(281): NOTE: attach of thread 'Binder Thread #3' failed
10-03 14:25:15.388: INFO/ARMAssembler(63): generated scanline__00000077:03545404_00000004_00000000 [ 47 ipp] (67 ins) at [0x34e7d0:0x34e8dc] in 893200 ns
10-03 14:25:15.545: INFO/ActivityThread(287): Publishing provider alon.beginner.registerform.RegistrationFormMetaData: alon.beginner.registerform.RegistrationProvider
10-03 14:25:15.623: WARN/dalvikvm(287): Exception Ljava/lang/NullPointerException; thrown during Lalon/beginner/registerform/RegistrationProvider;.
10-03 14:25:15.634: WARN/dalvikvm(287): Class init failed in newInstance call (Lalon/beginner/registerform/RegistrationProvider;)
10-03 14:25:15.634: DEBUG/AndroidRuntime(287): Shutting down VM
10-03 14:25:15.634: WARN/dalvikvm(287): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): FATAL EXCEPTION: main
10-03 14:25:15.660: ERROR/AndroidRuntime(287): java.lang.ExceptionInInitializerError
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at java.lang.Class.newInstanceImpl(Native Method)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at java.lang.Class.newInstance(Class.java:1429)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.app.ActivityThread.installProvider(ActivityThread.java:4494)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.app.ActivityThread.installContentProviders(ActivityThread.java:4281)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4237)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.app.ActivityThread.access$3000(ActivityThread.java:125)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2071)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.os.Handler.dispatchMessage(Handler.java:99)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.os.Looper.loop(Looper.java:123)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at android.app.ActivityThread.main(ActivityThread.java:4627)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at java.lang.reflect.Method.invokeNative(Native Method)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at java.lang.reflect.Method.invoke(Method.java:521)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at dalvik.system.NativeStart.main(Native Method)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): Caused by: java.lang.NullPointerException
10-03 14:25:15.660: ERROR/AndroidRuntime(287): at alon.beginner.registerform.RegistrationProvider.(RegistrationProvider.java:45)
10-03 14:25:15.660: ERROR/AndroidRuntime(287): ... 15 more
答案 0 :(得分：1)
您尚未初始化sUsersProjectionMap数据成员，因此它是null，因此当您尝试使用时会引发NullPointerException。
变化：
private static HashMap sUsersProjectionMap;
为：
private static HashMap sUsersProjectionMap=new HashMap();
更好的方法是使用泛型，因此在上面两行中出现HashMap而不是HashMap<String, String>。