Returns an array of <code>TreeColumn</code>s which are the
columns in the receiver. Columns are returned in the order
that they were created. If no <code>TreeColumn</code>s were
created by the programmer, the array is empty, 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.
<p>
Note: This is not the actual structure used by the receiver
to maintain its list of items, so modifying the array will
not affect the receiver.
</p>
@return the items in the receiver
@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 an array of <code>TreeColumn</code>s which are the columns in the receiver. Columns are returned in the order that they were created. If no <code>TreeColumn</code>s were created by the programmer, the array is empty, 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. <p> Note: This is not the actual structure used by the receiver to maintain its list of items, so modifying the array will not affect the receiver. </p>
@return the items in the receiver
@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>
@see Tree#getColumnOrder() @see Tree#setColumnOrder(int[]) @see TreeColumn#getMoveable() @see TreeColumn#setMoveable(bool) @see SWT#Move
@since 3.1