foreach problem

Question

Hi all I initialized 6 datatables and I wish to make their columns identical. I use a foreach loop to do the work but I keep getting a cast error in the foreach line: Unable to cast object of type 'System.Windows.Forms.RadioButton' to type 'System.Data.DataTable'. Seems like although I specify in the loop the type DataTable the foreach loop tries to act on all controls even such that is not a DataTable and when it encounters another control it will issue an error. Am I doing something wrong or is this a bug? Can someone suggest a workaround? The code snippet: foreach (DataTable dataTable in Controls) { dataTable.Columns.Add(# typeof(int)); dataTable.Columns.Add(weekday typeof(decimal)); dataTable.Columns.Add(halfday typeof(decimal)); dataTable.Columns.Add(weekend typeof(decimal)); // // Add 24 DataRows first cell in first column is index (i) // for (int i = 0; i { dataTable.Rows.Add(i); } //Add the table to the dataSet MyDataSet.Tables.Add(dataTable); }

Vulpes · Answer

If you've created six DataTable objects already then what you need to do is to put them in an array or List . You can then use foreach to iterate through each DataTable in the array or List.

Sam · Answer

Thanks. I add up my tables into a dataset but I do it after I add properties. In any case as I wrote as you suggested a simple table array solved the problem. To add all tables to the dataset I anyhow need to itterate through the table thus the array solves it perfectly enabling me to do all I need in one foreach pass (set columns and rows and other properties add to dataset etc.).

Vulpes · Answer

Well IEnumerable is just a generic interface and so can't be instantiated itself. What you can do of course is to create a collection which implements IEnumerable - such as an array or list - and then assign a reference to the collection to a variable of the interface type. But this really brings us back to what we already have :) I don't know how you're currently instantiating the DataTables but what you could do is to add them to MyDataSet as you create them. You could then iterate through the MyDataSet.Tables collection using foreach and add columns and rows to each DataTable as you're doing now.

Sam · Answer

Thanks Vulpes for a good working idea. I defined a DataTable array that I can now itterate through. Nevertheless as this is more of a workaround I found out that the ultimate way is probably by: IEnumerable DataTable > Collection { get ; set ; } foreach( IEnumerable DataTable > t in Collection) {....... } But unfortunately it does not work for me. I can not get the Collection filled with my DataTables. Although you gave me a good working solution I still wonder if you know how to make my suggestion work.

Sam · Answer

Thanks Dapeng for nice idea. I have tried it but unfortunately it does not work and I get the error message that says that there are no DataTables in the Control list. The reason I found is that the Class Control represents only componenets with visual representation  while a DataTable is not a visual component. (This may also be the reason for my original error!) Do you know of another class (Instead of Control) that will also include DataTable? Thanks again.

dapeng zheng · Answer

Try to modify as : foreach (Control c in Controls) { if(c is Datatable) { Datatable datatable = (Datatable)c; dataTable.Columns.Add(# typeof(int)); dataTable.Columns.Add(weekday typeof(decimal)); dataTable.Columns.Add(halfday typeof(decimal)); dataTable.Columns.Add(weekend typeof(decimal)); // // Add 24 DataRows first cell in first column is index (i) // for (int i = 0; i { dataTable.Rows.Add(i); } //Add the table to the dataSet MyDataSet.Tables.Add(dataTable); } }