小弟这两天在写一个插件，需要获取当前选中的代码块，就照网上写了下边的代码
ISelectionService selectionService =Workbench.getInstance().getActiveWorkbenchWindow().getSelectionService();
ISelection selection = selectionService.getSelection();
TextSelection text = (TextSelection) selection;
可是运行就会报类型转换错误
org.eclipse.jface.text.TextSelection cannot be cast to org.eclipse.jface.text.TextSelection
这是什么原因，求大神帮我分析下