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Thank you. solved.
When I keep the last column in DataGridView null, compiler give the following error in line
System.NullReferenceException: 'Object reference not set to an instance of an object.'
System.NullReferenceException: 'Object reference not set to an instance of an object.'
I have check marked null properties for this column in SQL server.
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Quote:
dataGridView1.Rows[i].Cells[10].Value.ToString()
If the cell's Value is null, what do you think the result of calling the ToString method on the value will be? 
Remove those .ToString() calls, and pass the cell values directly to the parameters.
myCommand.Parameters.AddWithValue("@Number", dataGridView1.Rows[i].Cells[0].Value);
myCommand.Parameters.AddWithValue("@CostCenter", dataGridView1.Rows[i].Cells[1].Value);
myCommand.Parameters.AddWithValue("@pType", dataGridView1.Rows[i].Cells[2].Value);
myCommand.Parameters.AddWithValue("@ServiceType", dataGridView1.Rows[i].Cells[3].Value);
myCommand.Parameters.AddWithValue("@Receiver", dataGridView1.Rows[i].Cells[4].Value);
myCommand.Parameters.AddWithValue("@WorkCenter", dataGridView1.Rows[i].Cells[5].Value);
myCommand.Parameters.AddWithValue("@Start", dataGridView1.Rows[i].Cells[6].Value);
myCommand.Parameters.AddWithValue("@End", dataGridView1.Rows[i].Cells[7].Value);
myCommand.Parameters.AddWithValue("@Remaining", dataGridView1.Rows[i].Cells[8].Value);
myCommand.Parameters.AddWithValue("@Status", dataGridView1.Rows[i].Cells[9].Value);
myCommand.Parameters.AddWithValue("@ReceiveDate", dataGridView1.Rows[i].Cells[10].Value);
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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That's not an SQL error - that's a C# error:
myCommand.Parameters.AddWithValue("@ReceiveDate", dataGridView1.Rows[i].Cells[10].Value.ToString());
If the cell value is null, you can't call ToString (or any other property / method) on it.
You could try
myCommand.Parameters.AddWithValue("@ReceiveDate", dataGridView1.Rows[i].Cells[10].Value?.ToString());Depending on your C# version.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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private void btnSave_Click(object sender, EventArgs e)
{
update.PerformClick();
SqlCeConnection connection = new SqlCeConnection();
connection.ConnectionString = @"Data Source=C:\Users\Dell\Desktop\DataGridView\PMinfo.sdf";
SqlCeCommand myCommand = new SqlCeCommand();
myCommand.Connection = connection;
connection.Open();
myCommand.CommandText = "DELETE FROM PMinfo";
connection.Close();
myCommand.CommandText = @"INSERT into [PMinfo] (Number, CostCenter, pType, ServiceType, Receiver, WorkCenter, Start, [End], Remaining, Status, ReceiveDate) values(@Number, @CostCenter, @pType, @ServiceType, @Receiver, @WorkCenter, @Start, @End, @Remaining, @Status, @ReceiveDate)";
connection.Open();
for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
myCommand.Parameters.AddWithValue("@Number", dataGridView1.Rows[i].Cells[0].Value);
myCommand.Parameters.AddWithValue("@CostCenter", dataGridView1.Rows[i].Cells[1].Value);
myCommand.Parameters.AddWithValue("@pType", dataGridView1.Rows[i].Cells[2].Value);
myCommand.Parameters.AddWithValue("@ServiceType", dataGridView1.Rows[i].Cells[3].Value);
myCommand.Parameters.AddWithValue("@Receiver", dataGridView1.Rows[i].Cells[4].Value);
myCommand.Parameters.AddWithValue("@WorkCenter", dataGridView1.Rows[i].Cells[5].Value);
myCommand.Parameters.AddWithValue("@Start", dataGridView1.Rows[i].Cells[6].Value);
myCommand.Parameters.AddWithValue("@End", dataGridView1.Rows[i].Cells[7].Value);
myCommand.Parameters.AddWithValue("@Remaining", dataGridView1.Rows[i].Cells[8].Value);
myCommand.Parameters.AddWithValue("@Status", dataGridView1.Rows[i].Cells[9].Value);
myCommand.Parameters.AddWithValue("@ReceiveDate", dataGridView1.Rows[i].Cells[10].Value);
myCommand.ExecuteNonQuery();
}
connection.Close();
}
1- Clearing table doesn't work.
2- When I can more than 1 rowsin DataGridView, compliler gives following error:
System.ArgumentException: 'The SqlCeParameter with this name is already contained by this SqlCeParameterCollection.'
I reviewed the loop but I couldn't find out the reason.
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Alex Dunlop wrote: I reviewed the loop but I couldn't find out the reason
Hint: What do you suppose the "Add" part of "AddWithValue" might mean?
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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It adds a value to the end of the SqlParameterCollection.
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And the error message is telling you "The SqlCeParameter with this name is already contained by this SqlCeParameterCollection"
Put the two together, and ...
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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I think I need to put open and close parameters of sql inside the loop so in each iteration I open the sql write a row into sql table and close it and open it again and loop....
Am I right? Maybe I'd give it a try tomorrow.
modified 23-Nov-20 14:54pm.
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See Dave's reply[^] below.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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I solved it by adding
<pre lang="c#">myCommand.Parametes.Clear();
The final code:
private void btnSave_Click(object sender, EventArgs e)
{
update.PerformClick();
SqlCeConnection connection = new SqlCeConnection();
connection.ConnectionString = @"Data Source=C:\Users\Dell\Desktop\DataGridView\PMinfo.sdf";
SqlCeCommand myCommand = new SqlCeCommand();
myCommand.Connection = connection;
connection.Open();
myCommand.CommandText = "Delete From PMinfo";
myCommand.ExecuteNonQuery();
connection.Close();
myCommand.CommandText = @"INSERT into [PMinfo] (Number, CostCenter, pType, ServiceType, Receiver, WorkCenter, Start, [End], Remaining, Status, ReceiveDate) values(@Number, @CostCenter, @pType, @ServiceType, @Receiver, @WorkCenter, @Start, @End, @Remaining, @Status, @ReceiveDate)";
connection.Open();
for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
myCommand.Parameters.Clear();
myCommand.Parameters.AddWithValue("@Number", dataGridView1.Rows[i].Cells[0].Value);
myCommand.Parameters.AddWithValue("@CostCenter", dataGridView1.Rows[i].Cells[1].Value);
myCommand.Parameters.AddWithValue("@pType", dataGridView1.Rows[i].Cells[2].Value);
myCommand.Parameters.AddWithValue("@ServiceType", dataGridView1.Rows[i].Cells[3].Value);
myCommand.Parameters.AddWithValue("@Receiver", dataGridView1.Rows[i].Cells[4].Value);
myCommand.Parameters.AddWithValue("@WorkCenter", dataGridView1.Rows[i].Cells[5].Value);
myCommand.Parameters.AddWithValue("@Start", dataGridView1.Rows[i].Cells[6].Value);
myCommand.Parameters.AddWithValue("@End", dataGridView1.Rows[i].Cells[7].Value);
myCommand.Parameters.AddWithValue("@Remaining", dataGridView1.Rows[i].Cells[8].Value);
myCommand.Parameters.AddWithValue("@Status", dataGridView1.Rows[i].Cells[9].Value);
myCommand.Parameters.AddWithValue("@ReceiveDate", dataGridView1.Rows[i].Cells[10].Value);
myCommand.ExecuteNonQuery();
}
connection.Close();
}
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That's one way to do it, but it's the least performant and increases heap fragmentation.
Creating one set of parameter objects and reusing them is a much better method.
modified 25-Nov-20 0:59am.
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You're not reusing parameters, you're creating new ones on every iteration of the loop. On the first iteration of the loop, your Parameters collection will have 11 parameters. On the second, 22 parameters. On the 3rd, 33 parameters...
Create the parameters OUTSIDE the loop, then just set the values inside.
SqlCeConnection connection = new SqlCeConnection();
connection.ConnectionString = @"Data Source=C:\Users\Dell\Desktop\DataGridView\PMinfo.sdf";
SqlCeCommand myCommand = new SqlCeCommand(@"INSERT into [PMinfo] (Number, CostCenter, pType, ServiceType, Receiver, WorkCenter, Start, End, Remaining, Status, ReceiveDate) values(@Number, @CostCenter, @pType, @ServiceType, @Receiver, @WorkCenter, @Start, @End, @Remaining, @Status, @ReceiveDate)");
myCommand.Connection = connection;
myCommand.Parameters.Add("@Number", SqlDbType.NVarChar);
myCommand.Parameters.Add("@CostCenter", ...);
myCommand.Parameters.Add("@pType", ...);
myCommand.Parameters.Add("@ServiceType", ...);
myCommand.Parameters.Add("@Receiver", ...);
myCommand.Parameters.Add("@WorkCenter", ...);
myCommand.Parameters.Add("@Start", ...);
myCommand.Parameters.Add("@End", ...);
myCommand.Parameters.Add("@Remaining", ...);
myCommand.Parameters.Add("@Status", ...);
myCommand.Parameters.Add("@ReceiveDate", ...);
connection.Open();
for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
myCommand.Parameters["@Name"] = dataGridView1.Rows[i].Cells[0].Value.ToString();
myCommand.Parameters["@CostCenter"] = ...
...
myCommand.ExecuteNonQuery();
}
connection.Close();
DO NOT STORE DATES AS STRINGS IN THE DATABASE! Store them as the appropriate DateTime type.
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SortedSet implements:
[System.Serializable]
public class SortedSet<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.Generic.ISet<T>, System.Collections.ICollection, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable There are numerous examples of using ElementAt on SortedSets on the web, like this [^], however, I find using it on a SortedSet<KeyValuePair<string, string>>
if (SortedNames != null)
{
for (int i = 0; i < SortedNames.Count; i++)
{
KeyValuePair<string, string> item = SortedNames.ElementAt[i];
Console.WriteLine(item);
}
}
creates a compile error: "CS0021 Cannot apply indexing with [] to an expression of type 'method group" ... I can't locate any matching error report for this and SortedSet.
fyi: I am using a custom IComparer<KeyValuePair<string, string>> for sorting, but, that's working as expected.
Hypothesis: something about using KeyValuePair results in this error.
Ideas ?
thanks, Bill
«One day it will have to be officially admitted that what we have christened reality is an even greater illusion than the world of dreams.» Salvador Dali
modified 23-Nov-20 1:47am.
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Hey Bill!
For using KeyValuePair in SortedSet, you need to define IComparable for it. Until it's not there, SortedSet would not be able to work on the datatype (as inherently it is supposed to sort)
To see what I say, comment your ElementAt line and run the code. You will get a runtime error as "At least one object must implement IComparable."
UPDATE: Below sample works fine with ElementAt. Where is the gap?
Once we have a defined sorted data, we can access with ElementAt. I put up a quick example:
class SortedSetDemo
{
static void Main(string[] args)
{
var words = new string[]
{"the", "quick", "brown", "fox", "jumps",
"over", "the", "lazy", "dog"};
var wordSet2 = new SortedSet<KeyValuePair<int, string>>(new KVPKeyComparer<int, string>());
int x = 0;
foreach (string word in words)
{
x++;
wordSet2.Add(new KeyValuePair<int, string>(x, word));
}
Console.WriteLine("Set items in sorted order:");
for (int j = 0; j < wordSet2.Count; j++)
{
var item = wordSet2.ElementAt(j);
Console.WriteLine(item);
}
}
public class KVPKeyComparer<TKey, TValue> : IComparer<KeyValuePair<TKey, TValue>> where TKey : IComparable
{
public int Compare(KeyValuePair<TKey, TValue> x, KeyValuePair<TKey, TValue> y)
{
if(x.Key == null)
{
if(y.Key == null)
return 0;
return -1;
}
if(y.Key == null)
return 1;
return x.Key.CompareTo(y.Key);
}
}
}
Outputs:
[1, the]
[2, quick]
[3, brown]
[4, fox]
[5, jumps]
[6, over]
[7, the]
[8, lazy]
[9, dog]
modified 23-Nov-20 4:44am.
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Hi Sandeep,
Did you not see my statement: Quote: fyi: I am using a custom IComparer<keyvaluepair<string, string="">> for sorting, but, that's working as expected.
«One day it will have to be officially admitted that what we have christened reality is an even greater illusion than the world of dreams.» Salvador Dali
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Sure I missed it. Apologies.
Now, If you are using, you should not get the error. Sample I shared above is working fine for ElementAt, to which your query was related to. Is that of some help?
UPDATE:
Chuck it. It's the square and circular brackets difference between yours and my code. You already got that, so 
modified 23-Nov-20 4:47am.
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Hi Sandeep-ji, कोई बात नहीं
See Richard Deeming's post for the correct diagnosis.
thanks, Bill
«One day it will have to be officially admitted that what we have christened reality is an even greater illusion than the world of dreams.» Salvador Dali
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SortedSet<T>[^] doesn't have a property called ElementAt.
The ElementAt[^] method is an extension method defined for all IEnumerable<T> instances. You'll need round parentheses to call it, rather than square brackets, and you'll need a using System.Linq; declaration at the top of your code file.
But in your example, it would be better to simply use a foreach loop instead. The ElementAt method has to create an enumerator and enumerate i elements of the set for each iteration of your for loop, whereas a foreach loop would only create a single enumerator and enumerate the set once.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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There's some basic performance data in the Microsoft docs for a few collection types:
Collections and Data Structures | Microsoft Docs[^]
Sorted Collection Types | Microsoft Docs[^]
But there are so many different collection classes available these days, even if you restrict yourself to the BCL, that it would be difficult to find a source to compare the performance of all of them.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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I need some guidance and advice to build a questionnaire system similar to Google forms that include two parts,
the first part is a desktop system with vb.net or c# and separate SQL server database (it must be a desktop system because it will be part of a vb.net old system, The new project will be called from within the main interface of the old project )
and the second part is a web system, and the two systems are linked to one SQL server database through a local network and a local server
the desktop system builds multiple questionnaires forms and each questionnaire is associated with a specific user to answer these questions through the web system via the username that will be assigned to him by the desktop system... Here, I would like to note that each user has a different questionnaire from the other...
The desktop system will also use the answers to build a dashboard has charts and report based on the analysis of the answers
My questions ...
1- What is the best way to design (questionnaire builder) if I want it to work and similar to Google Forms method and user interface of building questions if each user has its own questionnaire that contains an unlimited set of questions, the new question is added through the Add button and each question is specified by the admin It determines the nature of the answer and the answer and contains a tool to choose a specific classification from a group of classifications that are added to the system, and each question contains in addition to the answers a field of notes and evaluation from 1 to 5, and after building this questionnaire for a specific user it is permanently saved and linked with this user and there is a possibility to edit these questions on This questionnaire for the future.
Is the User Control method the best way to build a question-building interface, or is there a better way and how?
2- What are your tips and directions that help me to build a better design for such a system?
Greetings
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Hi all,
I'm dipping my toes into the world of Docker and thought as part of my learning curve I'd try and containerize a recent net core api project. I've written a Dockerfile which seems to build the image ok but fails when I try running it with a file not found error. Any ideas guys ? This is only the beginning as the API makes calls to a postgresql database but the Docker way seems to be layered so I thought I'd start with the API first - am I correct doing it this way ?
Docker file
FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build-env
WORKDIR /app
COPY . ./
RUN dotnet publish -c Release -o out
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
COPY --from=build-env /app/out .
ENTRYPOINT ["dotnet", "MyAPI.dll"]
"I didn't mention the bats - he'd see them soon enough" - Hunter S Thompson - RIP
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