安卓我无法创建SQLite数据库。错误:java。lang.NullPointerException
以下是我的课程:
statobjectid。java
public class StatsObjectId extends Activity {
DBClass db;
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
db = new DBClass(this);
}
public void addObjId(String objid){
Log.e("objectid","This is the object id going to store: "+objid);
db.addObjectId(objid); //This is the line# 105
if(getObjId()){
Log.e("objectid","Successfully stored!");
}else{
Log.e("objectid","Error in storing object id!");
}
}
public boolean getObjId(){
boolean result;
try{
c = db.getObjectId();
c.moveToFirst();
String str = c.getString(c.getColumnIndex("objectid"));
Log.e("objectid","Object id returned form DB: "+str);
result = true;
}catch(CursorIndexOutOfBoundsException e){
Log.e("objectid","Cursor index out of bound");
result = false;
e.printStackTrace();
}catch(Exception e){
Log.e("objectid","Some Another Exception");
result = false;
e.printStackTrace();
}
return result;
}
ParseComServerAccessor。java
public class ParseComServerAccessor {
//I am skipping some irrelevant code
public void putStats(String authtoken, String userId, Tas statsToAdd) throws Exception {
//Again skip some code
//Here I got some HttpResponse and I need to extract an object id and save it to database
HttpResponse response = httpClient.execute(httpPost);
String responseString = EntityUtils.toString(response.getEntity());
JSONObject json = new JSONObject(responseString);
Log.e("objectid","Now Object Id is: "+json.getString("objectId") );
StatsObjectId ob = new StatsObjectId();
ob.addObjId(json.getString("objectId")); // This is the line#156
//skip some code
}
}
TasSyncAdapter。java
public class TasSyncAdapter extends AbstractThreadedSyncAdapter {
//skipped Constructor code
public void onPerformSync(Account account, Bundle extras, String authority,
ContentProviderClient provider, SyncResult syncResult) {
//skipped some code
ParseComServerAccessor parseComService = new ParseComServerAccessor();
//skipped some code again
parseComService.putStats(authToken, userObjectId, remoteTas); //This is the line# 134
//skip some code
}
}
现在,当我运行我的应用程序时。。。这是下面的日志
Tag Text
objectid This is the object id going to store: 9AFysqffz7
System.err java.lang.NullPointerException
System.err at com.myapp.ds_app.StatsObjectId.addObjId(StatsObjectId.java:105)
System.err at com.myapp.ds_app.syncadapter.ParseComServerAccessor.putStats(ParseComServerAccessor.java:156)
System.err at com.myapp.ds_app.syncadapter.TasSyncAdapter.onPerformSync(TasSyncAdapter.java:134)
System.err at 安卓.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:254)
DBClass。java
public class DBClass extends SQLiteOpenHelper {
private static final String DATABASE_NAME="myapp.db";
public DBClass(Context cxt){
super(cxt, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase mydatabase) {
mydatabase.execSQL("CREATE TABLE IF NOT EXISTS temp (objectid STRING)");
}
public Cursor getObjectId(){
Cursor cursor = getReadableDatabase().rawQuery("SELECT objectid FROM temp", null);
return cursor;
}
public void addObjectId(String objid){
try{
ContentValues cv = new ContentValues(1);
Log.e("objectid","In DBClass and object id: "+objid);
cv.put("objectid", objid);
Log.e("objectid","Content value contains: "+cv.toString());
getWritableDatabase().insert("temp", "objectid", cv);
}catch(NullPointerException e){
e.printStackTrace();
}
}
}
现在,我在这一点上被绊倒了! 到目前为止,我只需要保存一个值。我试图创建一个文件,而不是在数据库中保存一个值。但ContextWrapper也有一些例外
我目前有兴趣处理数据库
如果你们需要任何其他信息,请告诉我
如果有人能解释这件事,我将不胜感激。我是安卓新手,很想了解这个问题。提前谢谢
# 1 楼答案
您正在实例化一个活动类。你不允许那样做。(当你这样做的时候,Android中应该有一些东西告诉你)基本上,上下文没有初始化,因为Android需要这样做才能有一个功能性的活动
另外,Android(在创建活动时)使用适当的上下文调用onCreate方法。您没有(也不能),因此您的db为空
在AbstractThreadedSyncAdapter中,您有一个
getContext
方法来获取适当的上下文。使用此选项初始化数据库并在其中插入数据,而不是将其传递给Activity对象