Question

I have a list of objects in C# that have a property called ‘Sequence’. This list is then bound to a DataGridView, ordering by this Sequence.

The user is able to drag and drop rows – so if we have something like the following:

Name,Sequence 
Test1,1 
Test2,2
Test3,3 
Test4,4 
Test5,5

Dragging ‘Test1’ to between ‘Test3’ and ‘Test4’ should modify the sequence of anything effected to be the following:

Name,Sequence 
Test2,1 
Test3,2
Test1,3 
Test4,4 
Test5,5

I can’t quite figure out the algorithm to use to update the list when they drag and drop a row. A simple way would be to loop through all the rows in the grid and and update the sequence to be the row index + 1, but I think this will add some overhead.

Answer 1

See if you can avoid storing Sequence with the object, otherwise a possibility of it getting out of sequence will always remain. You can pair up an object with its sequence for downstream consumption when enumerating through the container:

class MyData {
    string Name {get; set;}
}
class DataWithSequence {
    MyData Data {get;set;}
    int Sequence{get;set;}
}
...
IList<MyData> list = new List<MyData>();
IEnumerable<DataWithSequence> GetData() {
    return list.Select((d,i)=> new DataWithSequence {Data=d, Sequence=i+1});
}