Returns the number of columns contained in the receiver.
If no <code>TreeColumn</code>s were created by the programmer,
this value is zero, despite the fact that visually, one column
of items may be visible. This occurs when the programmer uses
the tree like a list, adding items but never creating a column.
@return the number of columns
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Returns the number of columns contained in the receiver. If no <code>TreeColumn</code>s were created by the programmer, this value is zero, despite the fact that visually, one column of items may be visible. This occurs when the programmer uses the tree like a list, adding items but never creating a column.
@return the number of columns
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>
@since 3.1