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  • How to reference a cell in a external excel file based on a variable?

    - by Totty
    Hy I have a Excel File (a) and a cell into it that is equal to another cell in another file (b); The of the (b) excel file is "2010 something"; Now The cell (c) is ='[2010 something.xls]test'!$K$224 What I want is to make a variable that mantains the year and will be stored into a cell Then the cell (c) will change its reference based on the year; So in 2011 instead of looking for the 2010 something.xls will be looking for the 2011 something.xls How to do it? thanks

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  • why do we have to send the const " type " reference instead of just the types name to the constructo

    - by hamza
    i m trying to make a simple program ( & yes , it is a homework ) that can generate Dates , & like most of normal people : i made my Class attributes private , i tried to send the same type that i m working on to the constructor but the complier have not accept it , i did some research & i found out that in cases like that people generously send a const "type" reference to the constructor witch meant to me that have not understand OOP well so why do we have to send the const " type " reference instead of just the types name to the constructor ? & please give me some links or websites for beginners PS : sorry for my English

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  • XmlSerializer.Serialize doesn't save a file and doesn't throw an exception.

    - by Wodzu
    Hi guys. I am having problem with saving of my object. Take a look at this code: public void SerializeToXML(String FileName) { XmlSerializer fSerializer = new XmlSerializer(typeof(Configuration)); using (Stream fStream = new FileStream(FileName, FileMode.Create, FileAccess.Write, FileShare.None)) { fSerializer.Serialize(fStream, this); } } The problem is that when the user does not have rights to the location on hard disk, this function will not throw me any exception and do not save my file. For example saving to "C:\test.xml" act like nothing happened. And I would like to know if the file has not been saved and it would be good to know the reason why. I know that I could check if the file on given location exists and throw an exception manualy but shouldn't this be done by the XmlSerializer or FileStream itself? Thanks for your time

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  • How to reference individual cells in Excel to variable data from records in an external SQL table

    - by user273476
    I have a SQL table containing date oriented financial data eg. multiple daily records with fields for Date, Account code and Value. I want to set up dynamic links (formulas) from cells in an Excel speadsheet to this data so when the spreadsheet is loaded the data is fetched from all the relevant records. The spreadsheet has the Account codes on the x axis and Dates on the y. Each day the SQL table has new data in it for the new day and I want the spreadsheet to reference this new data for the column for the new day. Any ideas? I have seen how you can generally bring in data from a SQL table (in our case using ODBC as it is not MS SQL) but the data is not simply bringing in multiple records as you would a CVS file but specific records in the SQL table referencing to specific cells and columns in the spreadsheet.

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  • Is there a reason why a base class decorated with XmlInclude would still throw a type unknown exception when serialized?

    - by Tedford
    I will simplify the code to save space but what is presented does illustrate the core problem. I have a class which has a property that is a base type. There exist 3 dervived classes which could be assigned to that property. If I assign any of the derived classes to the container then the XmlSerializer throws dreaded "The type xxx was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically." exception when attempting to seralize the container. However my base class is already decorated with that attribute so I figure there must be an additional "hidden" requirement. The really odd part is that the default WCF serializer has no issues with this class hierarchy. The Container class [DataContract] [XmlRoot(ElementName = "TRANSACTION", Namespace = Constants.Namespace)] public class PaymentSummaryRequest : CommandRequest { /// <summary> /// Gets or sets the summary. /// </summary> /// <value>The summary.</value> /// <remarks></remarks> [DataMember] public PaymentSummary Summary { get; set; } /// <summary> /// Initializes a new instance of the <see cref="PaymentSummaryRequest"/> class. /// </summary> public PaymentSummaryRequest() { Mechanism = CommandMechanism.PaymentSummary; } } The base class [DataContract] [XmlInclude(typeof(xxxPaymentSummary))] [XmlInclude(typeof(yyyPaymentSummary))] [XmlInclude(typeof(zzzPaymentSummary))] [KnownType(typeof(xxxPaymentSummary))] [KnownType(typeof(xxxPaymentSummary))] [KnownType(typeof(zzzPaymentSummary))] public abstract class PaymentSummary { } One of the derived classes [DataContract] public class xxxPaymentSummary : PaymentSummary { } The serialization code var serializer = new XmlSerializer(typeof(PaymentSummaryRequest)); serializer.Serialize(Console.Out,new PaymentSummaryRequest{Summary = new xxxPaymentSummary{}}); The Exception System.InvalidOperationException: There was an error generating the XML document. --- System.InvalidOperationException: The type xxxPaymentSummary was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically. at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterPaymentSummaryRequest.Write13_PaymentSummary(String n, String ns, PaymentSummary o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterPaymentSummaryRequest.Write14_PaymentSummaryRequest(String n, String ns, PaymentSummaryRequest o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterPaymentSummaryRequest.Write15_TRANSACTION(Object o) --- End of inner exception stack trace --- at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id) at System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o, XmlSerializerNamespaces namespaces) at UserQuery.RunUserAuthoredQuery() in c:\Users\Tedford\AppData\Local\Temp\uqacncyo.0.cs:line 47

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  • How do I override a Spring bean definition yet still reference the overriden bean?

    - by Kevin
    I'm attempting to implement a delegate Service provider by overriding the bean definition for the original service with my delegate Service. However, as the name would imply, the delegate Service needs a reference to the original service to delegate calls to. I'm having trouble figuring out how to override the bean definition while using the original bean def without running into a circular reference issue. For example: <!-- Original service def in spring-context.xml --> <bean id="service" class="com.mycompany.Service"/> <!-- Overridden definition in spring-plugin-context.xml --> <bean id="service" class="com.mycompany.DelegatedService"/> <constructor-arg ref="service"/> </bean> Is this possible?

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  • Why pass by const reference instead of by value?

    - by Maulrus
    From what I understand: when you pass by value, the function makes a local copy of the passed argument and uses that; when the function ends, it goes out of scope. When you pass by const reference, the function uses a reference to the passed argument that can't be modified. I don't understand, however, why one would choose one over the other, except in a situation where an argument needs to be modified and returned. If you had a void function where nothing is getting returned, why choose one over the other?

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  • Avoiding repeated subqueries when 'WITH' is unavailable

    - by EloquentGeek
    MySQL v5.0.58. Tables, with foreign key constraints etc and other non-relevant details omitted for brevity: CREATE TABLE `fixture` ( `id` int(11) NOT NULL auto_increment, `competition_id` int(11) NOT NULL, `name` varchar(50) NOT NULL, `scheduled` datetime default NULL, `played` datetime default NULL, PRIMARY KEY (`id`) ); CREATE TABLE `result` ( `id` int(11) NOT NULL auto_increment, `fixture_id` int(11) NOT NULL, `team_id` int(11) NOT NULL, `score` int(11) NOT NULL, `place` int(11) NOT NULL, PRIMARY KEY (`id`) ); CREATE TABLE `team` ( `id` int(11) NOT NULL auto_increment, `name` varchar(50) NOT NULL, PRIMARY KEY (`id`) ); Where: A draw will set result.place to 0 result.place will otherwise contain an integer representing first place, second place, and so on The task is to return a string describing the most recently played result in a given competition for a given team. The format should be "def Team X,Team Y" if the given team was victorious, "lost to Team X" if the given team lost, and "drew with Team X" if there was a draw. And yes, in theory there could be more than two teams per fixture (though 1 v 1 will be the most common case). This works, but feels really inefficient: SELECT CONCAT( (SELECT CASE `result`.`place` WHEN 0 THEN "drew with" WHEN 1 THEN "def" ELSE "lost to" END FROM `result` WHERE `result`.`fixture_id` = (SELECT `fixture`.`id` FROM `fixture` LEFT JOIN `result` ON `result`.`fixture_id` = `fixture`.`id` WHERE `fixture`.`competition_id` = 2 AND `result`.`team_id` = 1 ORDER BY `fixture`.`played` DESC LIMIT 1) AND `result`.`team_id` = 1), ' ', (SELECT GROUP_CONCAT(`team`.`name`) FROM `fixture` LEFT JOIN `result` ON `result`.`fixture_id` = `fixture`.`id` LEFT JOIN `team` ON `result`.`team_id` = `team`.`id` WHERE `fixture`.`id` = (SELECT `fixture`.`id` FROM `fixture` LEFT JOIN `result` ON `result`.`fixture_id` = `fixture`.`id` WHERE `fixture`.`competition_id` = 2 AND `result`.`team_id` = 1 ORDER BY `fixture`.`played` DESC LIMIT 1) AND `team`.`id` != 1) ) Have I missed something really obvious, or should I simply not try to do this in one query? Or does the current difficulty reflect a poor table design?

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  • slow mysql count because of subselect

    - by frgt10
    how to make this select statement more faster? the first left join with the subselect is making it slower... mysql> SELECT COUNT(DISTINCT w1.id) AS AMOUNT FROM tblWerbemittel w1 JOIN tblVorgang v1 ON w1.object_group = v1.werbemittel_id INNER JOIN ( SELECT wmax.object_group, MAX( wmax.object_revision ) wmaxobjrev FROM tblWerbemittel wmax GROUP BY wmax.object_group ) AS wmaxselect ON w1.object_group = wmaxselect.object_group AND w1.object_revision = wmaxselect.wmaxobjrev LEFT JOIN ( SELECT vmax.object_group, MAX( vmax.object_revision ) vmaxobjrev FROM tblVorgang vmax GROUP BY vmax.object_group ) AS vmaxselect ON v1.object_group = vmaxselect.object_group AND v1.object_revision = vmaxselect.vmaxobjrev LEFT JOIN tblWerbemittel_has_tblAngebot wha ON wha.werbemittel_id = w1.object_group LEFT JOIN tblAngebot ta ON ta.id = wha.angebot_id LEFT JOIN tblLieferanten tl ON tl.id = ta.lieferant_id AND wha.zuschlag = (SELECT MAX(zuschlag) FROM tblWerbemittel_has_tblAngebot WHERE werbemittel_id = w1.object_group) WHERE w1.flags =0 AND v1.flags=0; +--------+ | AMOUNT | +--------+ | 1982 | +--------+ 1 row in set (1.30 sec) Some indexes has been already set and as EXPLAIN shows they were used. +----+--------------------+-------------------------------+--------+----------------------------------------+----------------------+---------+-----------------------------------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+--------------------+-------------------------------+--------+----------------------------------------+----------------------+---------+-----------------------------------------------+------+----------------------------------------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 2072 | | | 1 | PRIMARY | v1 | ref | werbemittel_group,werbemittel_id_index | werbemittel_group | 4 | wmaxselect.object_group | 2 | Using where | | 1 | PRIMARY | <derived3> | ALL | NULL | NULL | NULL | NULL | 3376 | | | 1 | PRIMARY | w1 | eq_ref | object_revision,or_og_index | object_revision | 8 | wmaxselect.wmaxobjrev,wmaxselect.object_group | 1 | Using where | | 1 | PRIMARY | wha | ref | PRIMARY,werbemittel_id_index | werbemittel_id_index | 4 | dpd.w1.object_group | 1 | | | 1 | PRIMARY | ta | eq_ref | PRIMARY | PRIMARY | 4 | dpd.wha.angebot_id | 1 | | | 1 | PRIMARY | tl | eq_ref | PRIMARY | PRIMARY | 4 | dpd.ta.lieferant_id | 1 | Using index | | 4 | DEPENDENT SUBQUERY | tblWerbemittel_has_tblAngebot | ref | PRIMARY,werbemittel_id_index | werbemittel_id_index | 4 | dpd.w1.object_group | 1 | | | 3 | DERIVED | vmax | index | NULL | object_revision_uq | 8 | NULL | 4668 | Using index; Using temporary; Using filesort | | 2 | DERIVED | wmax | range | NULL | or_og_index | 4 | NULL | 2168 | Using index for group-by | +----+--------------------+-------------------------------+--------+----------------------------------------+----------------------+---------+-----------------------------------------------+------+----------------------------------------------+ 10 rows in set (0.01 sec) The main problem while the statement above takes about 2 seconds seems to be the subselect where no index can be used. How to write the statement even more faster? Thanks for help. MT

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  • iOS Development: Why isn't my try block catching the exception?

    - by BeachRunnerJoe
    Hi. I have an exception being thrown in my code, but when I wrap it in an try/catch block, it doesn't get caught. The NSLog statement is never called in the catch block. Here's the code... NSInteger quoteLength; [data getBytes:(void *)&quoteLength range:NSMakeRange(sizeof(messageType), sizeof(quoteLength))]; @try { //Debugger stack trace shows an NSException being thrown on this statement NSData *stringData = [data subdataWithRange:NSMakeRange(sizeof(messageType) + sizeof(quoteLength), [data length])]; NSString *quote = [[NSString alloc] initWithData:stringData encoding:NSUTF8StringEncoding]; NSLog(@"received quote: %@",quote); [quote release]; } @catch (NSException * e) { NSLog(@"Exception Raised: %@", [e reason]); } Why doesn't it get caught? Thanks so much!

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  • Can I use a string variable to reference a class variable?

    - by rson
    Here's the scenario: I have an external swf file with x number of movieclips in its library that I load into a containing swf. Each MC in the external swf is linked with a class name and referenced on frame 1 as such var unique1:lineSequence1 = new lineSequence1(); the unique1 variable name will match a string variable I create in the containing swf: function initLines():void{ lineLoader = new Loader(); lineLoader.load(new URLRequest("theLines.swf")); //load external swf lineLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, linesLoaded); } function linesLoaded(e:Event):void{ var loadedswf:MovieClip = e.target.content as MovieClip; var initialLines = projects[0].pageid; //projects is an xmllist trace("initialLines: "+initialLines); //returns "initialLines: unique1" lines_holder_mc.addChild(loadedswf.[initialLines]); } I would like to use the initialLines variable as the reference to unique1 instead of hardcoding unique1 into loadedswf.unique1 to reference said variable in the loaded swf.

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  • Databinding in combo box

    - by muralekarthick
    Hi I have two forms, and a class, queries return in Stored procedure. Stored Procedure: ALTER PROCEDURE [dbo].[Payment_Join] @reference nvarchar(20) AS BEGIN -- SET NOCOUNT ON added to prevent extra result sets from -- interfering with SELECT statements. SET NOCOUNT ON; -- Insert statements for procedure here SELECT p.iPaymentID,p.nvReference,pt.nvPaymentType,p.iAmount,m.nvMethod,u.nvUsers,p.tUpdateTime FROM Payment p, tblPaymentType pt, tblPaymentMethod m, tblUsers u WHERE p.nvReference = @reference and p.iPaymentTypeID = pt.iPaymentTypeID and p.iMethodID = m.iMethodID and p.iUsersID = u.iUsersID END payment.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Data; using System.Data.SqlClient; using System.Windows.Forms; namespace Finance { class payment { string connection = global::Finance.Properties.Settings.Default.PaymentConnectionString; #region Fields int _paymentid = 0; string _reference = string.Empty; string _paymenttype; double _amount = 0; string _paymentmethod; string _employeename; DateTime _updatetime = DateTime.Now; #endregion #region Properties public int paymentid { get { return _paymentid; } set { _paymentid = value; } } public string reference { get { return _reference; } set { _reference = value; } } public string paymenttype { get { return _paymenttype; } set { _paymenttype = value; } } public string paymentmethod { get { return _paymentmethod; } set { _paymentmethod = value; } } public double amount { get { return _amount;} set { _amount = value; } } public string employeename { get { return _employeename; } set { _employeename = value; } } public DateTime updatetime { get { return _updatetime; } set { _updatetime = value; } } #endregion #region Constructor public payment() { } public payment(string refer) { reference = refer; } public payment(int paymentID, string Reference, string Paymenttype, double Amount, string Paymentmethod, string Employeename, DateTime Time) { paymentid = paymentID; reference = Reference; paymenttype = Paymenttype; amount = Amount; paymentmethod = Paymentmethod; employeename = Employeename; updatetime = Time; } #endregion #region Methods public void Save() { try { SqlConnection connect = new SqlConnection(connection); SqlCommand command = new SqlCommand("payment_create", connect); command.CommandType = CommandType.StoredProcedure; command.Parameters.Add(new SqlParameter("@reference", reference)); command.Parameters.Add(new SqlParameter("@paymenttype", paymenttype)); command.Parameters.Add(new SqlParameter("@amount", amount)); command.Parameters.Add(new SqlParameter("@paymentmethod", paymentmethod)); command.Parameters.Add(new SqlParameter("@employeename", employeename)); command.Parameters.Add(new SqlParameter("@updatetime", updatetime)); connect.Open(); command.ExecuteScalar(); connect.Close(); } catch { } } public void Load(string reference) { try { SqlConnection connect = new SqlConnection(connection); SqlCommand command = new SqlCommand("Payment_Join", connect); command.CommandType = CommandType.StoredProcedure; command.Parameters.Add(new SqlParameter("@Reference", reference)); //MessageBox.Show("ref = " + reference); connect.Open(); SqlDataReader reader = command.ExecuteReader(); while (reader.Read()) { this.reference = Convert.ToString(reader["nvReference"]); // MessageBox.Show(reference); // MessageBox.Show("here"); // MessageBox.Show("payment type id = " + reader["nvPaymentType"]); // MessageBox.Show("here1"); this.paymenttype = Convert.ToString(reader["nvPaymentType"]); // MessageBox.Show(paymenttype.ToString()); this.amount = Convert.ToDouble(reader["iAmount"]); this.paymentmethod = Convert.ToString(reader["nvMethod"]); this.employeename = Convert.ToString(reader["nvUsers"]); this.updatetime = Convert.ToDateTime(reader["tUpdateTime"]); } reader.Close(); } catch (Exception ex) { MessageBox.Show("Check it again" + ex); } } #endregion } } i have already binded the combo box items through designer, When i run the application i just get the reference populated in form 2 and combo box just populated not the particular value which is fetched. New to c# so help me to get familiar

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  • Why timed lock doesnt throws a timeout exception in C++0x?

    - by Vicente Botet Escriba
    C++0x allows to lock on a mutex until a given time is reached, and return a boolean stating if the mutex has been locked or not. template <class Clock, class Duration> bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time); In some contexts, I consider an exceptional situation that the locking fails because of timeout. In this case an exception should be more appropriated. To make the difference a function lock_until could be used to get a timeout exception when the time is reached before locking. template <class Clock, class Duration> void lock_until(const chrono::time_point<Clock, Duration>& abs_time); Do you think that lock_until should be more adequate in some contexts? if yes, on which ones? If no, why try_lock_until will always be a better choice?

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  • Is it possible to have a mysql table accept a null value for a primary_key column referencing a diff

    - by Dr.Dredel
    I have a table that has a column which holds the id of a row in another table. However, when table A is being populated, table B may or may not have a row ready for table A. My question is, is it possible to have mysql prevent an invalid value from being entered but be ok with a NULL? or does a foreign key necessitate a valid related value? So... what I'm looking for (in pseudo code) is this: Table "person" id | name Table "people" id | group_name | person_id (foreign key id from table person) insert into person (1, 'joe'); insert into people (1, 'foo', 1)//kosher insert into people (1, 'foo', NULL)//also kosher insert into people(1, 'foo', 7)// should fail since there is no id 7 in the person table. The reason I need this is that I'm having a chicken and egg issue where it makes perfect sense for the rows in the people table to be created before hand (in this example, I'm creating the groups and would like them to pre-exist the people who join them). And I realize that THIS example is silly and I would just put the group id in the person table rather than vice-versa, but in my real-world problem that is not workable. Just curious if I need to allow any and all values in order to make this work, or if there's some way to allow for null.

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  • Excel - Dynamic reference based on the row I paste into?

    - by michaelmichael
    I have a simple, oft-used formula that I paste into spreadsheets I receive. It looks like this: =IF(AND(D8="COMPLETE",E8=""),A8,"") It looks in D8 for the word "COMPLETE" and checks that E8 is blank. If both conditions are fulfilled it grabs the contents of A8. It works fine. The only problem with this is that I don't always paste it into row 8. Every spreadsheet is different. I usually end up spending a few seconds making the formula fit the current spreadsheet I'm working on by dragging the cell references to the appropriate row. Hence, my question: Is there a way to make an absolute row reference based on whatever row I paste into? For example, if I paste the above formula into a cell in row 25, the formula would automatically look like this: =IF(AND(D25="COMPLETE", E25=""), A25, "")

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  • In Java, how do I set a return type if an exception occurs?

    - by beagleguy
    hey all, I'm new to Java and was wondering if I define a method to return a database object like import java.sql.*; public class DbConn { public Connection getConn() { Connection conn; try { Class.forName("com.mysql.jdbc.Driver").newInstance(); if(System.getenv("MY_ENVIRONMENT") == "development") { String hostname = "localhost"; String username = "root"; String password = "root"; } conn = DriverManager.getConnection("jdbc:mysql:///mydb", username, password); return conn; } catch(Exception e) { throw new Exception(e.getMessage()); } } } if the connection fails when I try to create it what should I return? eclipse is telling me I have to return a Connection object but if it fails I'm not sure what to do. thanks!

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  • Why does my SQL database not work in Android?

    - by user1426967
    In my app a click on an image button brings you to the gallery. After clicking on an image I want to call onActivityResult to store the image path. But it does not work. In my LogCat it always tells me that it crashes when it tries to save the image path. Can you find the problem? My onActivityResult method: mImageRowId = savedInstanceState != null ? savedInstanceState.getLong(ImageAdapter.KEY_ROWID) : null; @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { if(requestCode == PICK_FROM_FILE && data != null && data.getData() != null) { Uri uri = data.getData(); if(uri != null) { Cursor cursor = getContentResolver().query(uri, new String[] { android.provider.MediaStore.Images.ImageColumns.DATA}, null, null, null); cursor.moveToFirst(); String image = cursor.getString(0); cursor.close(); if(image != null) { // HERE IS WHERE I WANT TO SAVE THE IMAGE. HERE MUST BE THE ERROR! if (mImageRowId == null) { long id = mImageHelper.createImage(image); if (id > 0) { mImageRowId = id; } } // Set the image and display it in the edit activity Bitmap bitmap = BitmapFactory.decodeFile(image); mImageButton.setImageBitmap(bitmap); } } } } This is my onSaveInstanceState method: private static final Long DEF_ROW_ID = 0L; @Override protected void onSaveInstanceState(Bundle outState) { outState.putLong(ImageAdapter.KEY_ROWID, mImageRowId != null ? mImageRowId : DEF_ROW_ID); super.onSaveInstanceState(outState); } This is a part from my DbAdapter: public long createImage(String image) { ContentValues cv = new ContentValues(); cv.put(KEY_IMAGE, image); return mImageDb.insert(DATABASE_TABLE, null, cv); }

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  • How to generate links to the android Classes' reference in javadoc ?

    - by Kaillash
    Hi, When I generate Javadoc for my android project in eclipse, there are lots of warnings like cannot find symbol symbol : class TextView and warning - Tag @see: reference not found: android.app.Dialog I also tried -link http://developer.android.com/reference/ -link http://java.sun.com/j2se/1.4.2/docs/api/ in Extra javadoc options tab in Configure Javadoc Arguments dialog of eclipse-Export Javadoc. But only -link http://java.sun.com/j2se/1.4.2/docs/api/ is working i.e for String class link http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html?is-external=true is generated. but for android.app.Dialog , no link is generated. Please help !!

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  • Is throwing an exception a healthy way to exit?

    - by ramaseshan
    I have a setup that looks like this. class Checker { // member data Results m_results; // see below public: bool Check(); private: bool Check1(); bool Check2(); // .. so on }; Checker is a class that performs lengthy check computations for engineering analysis. Each type of check has a resultant double that the checker stores. (see below) bool Checker::Check() { // initilisations etc. Check1(); Check2(); // ... so on } A typical Check function would look like this: bool Checker::Check1() { double result; // lots of code m_results.SetCheck1Result(result); } And the results class looks something like this: class Results { double m_check1Result; double m_check2Result; // ... public: void SetCheck1Result(double d); double GetOverallResult() { return max(m_check1Result, m_check2Result, ...); } }; Note: all code is oversimplified. The Checker and Result classes were initially written to perform all checks and return an overall double result. There is now a new requirement where I only need to know if any of the results exceeds 1. If it does, subsequent checks need not be carried out(it's an optimisation). To achieve this, I could either: Modify every CheckN function to keep check for result and return. The parent Check function would keep checking m_results. OR In the Results::SetCheckNResults(), throw an exception if the value exceeds 1 and catch it at the end of Checker::Check(). The first is tedious, error prone and sub-optimal because every CheckN function further branches out into sub-checks etc. The second is non-intrusive and quick. One disadvantage is I can think of is that the Checker code may not necessarily be exception-safe(although there is no other exception being thrown anywhere else). Is there anything else that's obvious that I'm overlooking? What about the cost of throwing exceptions and stack unwinding? Is there a better 3rd option?

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  • Class Template Instantiation: any way round this circular reference?

    - by TimYorke34
    I have two classes that I'm using to represent some hardware: A Button and an InputPin class which represent a button that will change the value of an IC's input pin when it's pressed down. A simple example of them is: template <int pinNumber> class InputPin { static bool IsHigh() { return ( (*portAddress) & (1<<pinNumber) ); } }; template <typename InputPin> class Button { static bool IsPressed() { return !InputPin::IsHigh(); } }; This works beautifully and by using class templates, the condition below will compile as tightly as if I'd handwritten it in assembly (a single instruction). Button < InputPin<1> > powerButton; if (powerButton.IsPressed()) ........; However, I am extending it to deal with interrupts and have got a problem with circular references. Compared to the original InputPin, a new InputPinIRQ class has an extra static member function that will be called automatically by the hardware when the pin value changes. I'd like it to be able to notify the Button class of this, so that the Button class can then notify the main application that it has been pressed/released. I am currently doing this with function pointers to callbacks. In order for the callback code to be inlined by the compiler, I need to pass the function pointers as template parameters. So now, both of the new classes have an extra template parameter that is a pointer to a callback function. Unfortunately this gives me a circular reference because to instantiate a ButtonIRQ class I now have to do something like this: ButtonIRQ< InputPinIRQ< A1, ButtonIRQ<....>::OnPinChange, OnButtonChange > pB; where the <...... represents the circular reference. Does anyone know how I can avoid this circular reference? I am new to templates, so might be missing something really simple. It's important that the compiler knows exactly what code will be run when the interrupt occurs as it then does some very useful optimisation - it is able to inline the callback function and literally inserts the callback function's code at the exact address that is called on a h/w interrupt.

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  • Why does the assignment operator return a value and not a reference?

    - by Nick Lowman
    I saw the example below explained on this site and thought both answers would be 20 and not the 10 that is returned. He wrote that both the comma and assignment returns a value, not a reference. I don't quite understand what that means. I understand it in relation to passing variables into functions or methods i.e primitive types are passed in by value and objects by reference but I'm not sure how it applies in this case. I also understand about context and the value of 'this' (after help from stackoverflow) but I thought in both cases I would still be invoking it as a method, foo.bar() which would mean foo is the context but it seems both result in a function call bar(). Why is that and what does it all mean? var x = 10; var foo = { x: 20, bar: function () {return this.x;} }; (foo.bar = foo.bar)();//returns 10 (foo.bar, foo.bar)();//returns 10

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