/// <summary>
/// Initializes a new instance of the <see cref="PageNumberAndItemNumbers"/> struct.
/// </summary>
/// <param name="pageNumber">
/// Initial value for the <see cref="PageNumber"/> field.
/// </param>
/// <param name="pageSize">
/// The <see cref="PageNumberAndSize.Size"/>
/// of each page in a "paged" collection.
/// </param>
/// <param name="totalItems">
/// The total number of items in a "paged" collection.
/// </param>
/// <param name="isLastPage">
/// Optional signal for setting the <see cref="LastItemNumber"/>
/// value, whether to calculate if <paramref name="pageNumber"/>
/// is the last page or to use this value.
/// </param>
internal PageNumberAndItemNumbers(
int pageNumber, byte pageSize, int totalItems, bool?isLastPage = null)
{
Contract.Requires <ArgumentOutOfRangeException>(
pageNumber >= PageNumberAndSize.FirstPageNumber,
"An ordinal page number is not a zero-based index. The number must be at least one.");
Contract.Requires <ArgumentOutOfRangeException>(
totalItems >= 0, "The number of items in the list must not be negative!");
if (pageSize >= PageNumberAndSize.MinimumPageSize && (totalItems > 0))
{
// A page of fixed size which has items.
this.PageNumber = pageNumber;
this.LastItemNumber = pageNumber * pageSize;
this.FirstItemNumber = this.LastItemNumber - pageSize + 1;
// Determine whether this is the last page,
// either by a parameter value or by calculation.
if ((isLastPage.HasValue && isLastPage.Value) ||
(PagingInfoCalculator.CalculateTotalPages(pageSize, totalItems) == this.PageNumber))
{
// If is the last page, replace the
// calculated LastItemNumber with
// the totalItems value.
this.LastItemNumber = totalItems;
}
}
else
{
// An unbounded or empty page.
this.PageNumber = PageNumberAndSize.FirstPageNumber;
this.FirstItemNumber = totalItems > 0 ? 1 : 0;
this.LastItemNumber = totalItems;
}
}
public void CalculatesCorrectTotalPages()
{
Assert.Throws <ArgumentOutOfRangeException>(
() => PagingInfoCalculator.CalculateTotalPages(10, 0));
Assert.Throws <ArgumentOutOfRangeException>(
() => PagingInfoCalculator.CalculateTotalPages(0, 1138));
Assert.AreEqual(1, PagingInfoCalculator.CalculateTotalPages(10, 1));
Assert.AreEqual(1, PagingInfoCalculator.CalculateTotalPages(10, 10));
Assert.AreEqual(2, PagingInfoCalculator.CalculateTotalPages(10, 11));
Assert.AreEqual(2, PagingInfoCalculator.CalculateTotalPages(10, 20));
}
