Returns the index of the first occurrence of an item with the specified key within the collection.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
If is called successively, the last returned index will be checked for a key match first, and if there is no match, the search starts at the beginning of the collection.
The key comparison is not case-sensitive. If the key parameter is null or an empty string, returns -1.
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.