您必须检查要排序的选定列是否刚好在已排序的列的前面，如果是这样，还需要确定已经排序的列的排序方向(升序或降序)。

You must verify whether the column selected to be sorted is the immediately preceding column to have been sorted and, if it is, in which direction (ascending or descending) it was previously sorted.

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您可以通过从“Display Item Menu”列表中选择或撤销选定列，选择隐藏或显示指定的列，如图11中所示。

You can choose to hide or display specific columns by selecting or deselecting the column from "display Item Menu" list as shown in the Figure 11.

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我们做的第一件事是调用SelectionEvent的widget函数来确定选定了哪一列(清单3中的第24行)。

The first thing that we do is determine which of the columns is selected by calling the widget function of the SelectionEvent (line 24 in listing 3).

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