Gets or sets the format string used to create group headers for each GroupDescription. The GroupHeaderFormat contains placeholders for the group name, current value, and item count. The placeholders are enclosed in curly brackets. For example, the default value for the GroupHeaderFormat property is: "{name}: {value} ({count} items)"

'宣言
 
Public Property GroupHeaderFormat As System.String

public System.string GroupHeaderFormat {get; set;}