Only last task runs!

Question

I am in desperate to find a solution to my problem.

Following is the code which generates different task for each item in List

Answer 1

This might be a lambda scope problem.

Have you tried to assign the viewModel to a local variable before passing it to the StartNew method

...
Task validateMarked = Task.Factory.StartNew(() =>
{
    foreach (AccountContactViewModel viewModel in selectedDataList)
    {
        var localViewModel = viewModel;
        if (localViewModel != null)
        {
            Task validate = Task.Factory.StartNew(
                () => ValidateAccount(localViewModel),
                (TaskCreationOptions)TaskContinuationOptions.AttachedToParent);
        }
    }
});
...