我在Android中使用SQLite直接，直接的SQL运气很好，但这是我第一次在ContentProvider中包装数据库。调用getWritableDatabase()或getReadableDatabase()时，我一直收到空指针异常。这只是我在代码中初始化时犯的一个愚蠢的错误，还是存在更大问题？
public class DatabaseProvider extends ContentProvider {
...
private DatabaseHelper databaseHelper;
private SQLiteDatabase db;
...
@Override
public boolean onCreate() {
databaseHelper = new DatabaseProvider.DatabaseHelper(getContext());
return (databaseHelper == null) ? false : true;
}
...
@Override
public Uri insert(Uri uri, ContentValues values) {
db = databaseHelper.getWritableDatabase(); // NULL POINTER EXCEPTION HERE
...
}
private static class DatabaseHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "cogsurv.db";
public static final int DATABASE_VERSION = 1;
public static final String[] TABLES = {
"people",
"travel_logs",
"travel_fixes",
"landmarks",
"landmark_visits",
"direction_distance_estimates"
};
// people._id does not AUTOINCREMENT, because it's set based on server's people.id
public static final String[] CREATE_TABLE_SQL = {
"CREATE TABLE people (_id INTEGER PRIMARY KEY," +
"server_id INTEGER," +
"name VARCHAR(255)," +
"email_address VARCHAR(255))",
"CREATE TABLE travel_logs (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"server_id INTEGER," +
"person_local_id INTEGER," +
"person_server_id INTEGER," +
"start DATE," +
"stop DATE," +
"type VARCHAR(15)," +
"uploaded VARCHAR(1))",
"CREATE TABLE travel_fixes (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"datetime DATE, " +
"latitude DOUBLE, " +
"longitude DOUBLE, " +
"altitude DOUBLE," +
"speed DOUBLE," +
"accuracy DOUBLE," +
"travel_mode VARCHAR(50), " +
"person_local_id INTEGER," +
"person_server_id INTEGER," +
"travel_log_local_id INTEGER," +
"travel_log_server_id INTEGER," +
"uploaded VARCHAR(1))",
"CREATE TABLE landmarks (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"server_id INTEGER," +
"name VARCHAR(150)," +
"latitude DOUBLE," +
"longitude DOUBLE," +
"person_local_id INTEGER," +
"person_server_id INTEGER," +
"uploaded VARCHAR(1))",
"CREATE TABLE landmark_visits (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"server_id INTEGER," +
"person_local_id INTEGER," +
"person_server_id INTEGER," +
"landmark_local_id INTEGER," +
"landmark_server_id INTEGER," +
"travel_log_local_id INTEGER," +
"travel_log_server_id INTEGER," +
"datetime DATE," +
"number_of_questions_asked INTEGER," +
"uploaded VARCHAR(1))",
"CREATE TABLE direction_distance_estimates (_id INTEGER PRIMARY KEY AUTOINCREMENT," +
"server_id INTEGER," +
"person_local_id INTEGER," +
"person_server_id INTEGER," +
"travel_log_local_id INTEGER," +
"travel_log_server_id INTEGER," +
"landmark_visit_local_id INTEGER," +
"landmark_visit_server_id INTEGER," +
"start_landmark_local_id INTEGER," +
"start_landmark_server_id INTEGER," +
"target_landmark_local_id INTEGER," +
"target_landmark_server_id INTEGER," +
"datetime DATE," +
"direction_estimate DOUBLE," +
"distance_estimate DOUBLE," +
"uploaded VARCHAR(1))"
};
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
Log.v(Constants.TAG, "DatabaseHelper()");
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.v(Constants.TAG, "DatabaseHelper.onCreate() starting");
// create the tables
int length = CREATE_TABLE_SQL.length;
for (int i = 0; i < length; i++) {
db.execSQL(CREATE_TABLE_SQL[i]);
}
Log.v(Constants.TAG, "DatabaseHelper.onCreate() finished");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
for (String tableName : TABLES) {
db.execSQL("DROP TABLE IF EXISTS" + tableName);
}
onCreate(db);
}
}
}
一如既往，感谢您的帮助！
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不确定此详细信息是否有帮助，但此处的LogCat显示异常：
删除了死亡的ImageShack链接
答案 0 :(得分：6)
而不是：
databaseHelper = new DatabaseProvider.DatabaseHelper(getContext());
尝试：
databaseHelper = new DatabaseProvider.DatabaseHelper(this);
看看是否有帮助。
如果没有，您可以发布NullPointerException堆栈跟踪吗？
答案 1 :(得分：2)
这个错误几乎可以肯定是因为传入了无效的上下文：
super(context, DATABASE_NAME, null, DATABASE_VERSION);
答案 2 :(得分：2)
我在非活动中遇到了SQLite nullpointerexception的问题，问题是它有一个无效的上下文。
我的修复是在onCreate而不是构造函数中传递上下文。尝试从其他地方查找上下文以进行getApplicationContext()。
答案 3 :(得分：1)
在初始帮助程序后的一段时间内尝试使用getWritableDatabase()
你得到NullPointerException因为数据库没有完全准备好
并且不要在ui线程中执行此操作，否则可能会导致ANR
答案 4 :(得分：1)
我刚遇到这个问题并意识到它有点像红鲱鱼。
我的问题源于我使用ContentProvider的方式。
我实际上是直接访问ContentProvider而不是通过ContentResolver。如果您的新用户使用ContentProviders，它本质上是一种简单的方法。
希望有所帮助：）
答案 5 :(得分：0)
确保在创建AVD时，请指定一定量的SD卡空间。我有同样的问题，这解决了它。如果这没有帮助，您还可以尝试使用-wipe-data选项启动模拟器。
答案 6 :(得分：0)
当在query（）中调用getReadableDatabase（）时，我得到了同样的NullPointerException错误，因为我不正确地查询了我的内容提供者。我看不出构建数据库的方式有什么问题。 getContext（）应该为您提供适当的上下文对象。但是，我会关注您如何向内容提供商发出查询。您应该确保对内容解析器有一个有效的引用（即通过调用getContentResolver（）。query（..））并使用它来执行查询。